Rein A. Roos The Forgotten Pollution The Increasing pace of Industrialization throughout the world has brought with It a serious, and ever Increasing threat from air pollution. It Is true that this threat Is being taken seriously, and that many responsible research workers, government advisors and others are working towards Its reduction. But air pollution seems to have something of the nature of a hydra-headed monster: tackle one problem and another immediately grows to take its place. Actions taken sometimes have results that are far from what was envisioned, sometimes even seeming to make the problem worse. In "The Forgotten Pollution", Roos shows clearly and In an often entertaining way, how many of the "unexpected" side effects of pollution by waste gases and particles can be explained by paying attention to the electrical activity of the atmosphere and the earth. Using an Instrument, which he has developed the Electrostatic Charged Aerosol Monitor (ECAM), together with other instruments and reference to the literature, much of it dating back to the early days of science, when electrostatics was appreciated as a science more than It Is today, Roos has succeeded In explaining many hitherto "puzzling" phenomena in a clear, simple and intellectually satisfying way. 1SBN 0-7923-3917-7 Kluwer Academic Publishers I 9 780792 339175 Kluwer Academic Publishers ! A C.I.P. Catalogue record for this book is available from the Library of Congress The Forg~tten Pollution Rein A. Roos ISBN 0-7923-3917-7 Published by Kluwer Academic Publishers, P.O. Box 17,3300 AA Dordrecht, The Netherlands. Kluwer Academic Publishers incorporates the publishing programmes of D. Reidel, Martinus Nijhoff, Or W. Junk and MTP Press. Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers, 101 Philip Drive, Norwell, MA 02061, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers Group, P.O. Box 322, 3300 AH Dordrecht, The Netherlands. Book cover design and layout: Juvi Torres Printed on acid-free paper All Rights Reserved © 1996 A. A. RooslKluwer Academic Publishers No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without writlen permissi n from the copyright owner. Printed in the Netherlands KLUWER ACADEMIC PUBLISHERS DORDRECHT I BOSTO I LO DO voor mijn Arjen -Jean The Forgotten Pollution [1.3. E[ectricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11.3.1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. lIJ.2. Di tribution .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. lIJJ. Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. IlJ.4. Some remarks on comfort IUS Electrical heating. . . . . . . . . . . . . . . . . . . . . . . . .. Il.4. Electrical field 11.4.1. Introduction 11.4.2. Open fire. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. II.4J. The TV set 11.4.4. Uphol tery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. lIS Electro tatic air cleaner and ionizers . . . . . . . . . . . . . . .. 11.5.1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Il.5.2. What do they have in common? 11.5J. What is the differenc~ 11.6. Health effect 11.6.1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11.6.2. Air conditioning and climate control. . . . . . . . . .. 11.6J. Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11.6.4. Charged particles and health . . . . . . . . . . . . . . . .. 11.7. Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 100 100 100 102 105 109 114 114 114 119 126 132 132 133 139 141 141 142 148 152 161 The atmosphere is not what it is popularly believed to be t 63 IlU. Introduction 1II.2. Particles in the atmo phere . . . . . . . . . . . . . . . . . . . . . .. IlI.2.1. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1II.2.2. Partjcle and albedo .. III.2J. Condensation nuclei. . . . . . . . . . . . . . . . . . . . . .. IlU. Pollution sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Il1.3.1. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. IIIJ.2. Forest fire IIIJ.2. Car emission I1I.3.3. The electrostatic precipitator . . . . . . . . . . . . . . .. IlIA. Transport and sinks. . . . . . . . . . . . . . . . . . . . . . . . . . . .. IlI.4.1. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. IlI.4.2. Dust . . . . . . . . . . . . . . . . . .. IlI.4.3. Selective deposition IlI.4A. Visibility, ozone layer, and nitrates . . . . . . . . . . .. IlI.4.5. Torrential rains. . . . . . . . . . . . . . . . . . . . . . . . . .. Contents 8 163 166 166 167 167 170 170 171 177 184 193 193 194 199 206 209 IlI.4A. Visibility, ozone layer, and nitrates. . . . . . . . . . .. IlI.4.5. Torrential rains. . . . . . . . . . . . . . . . . . . . . . . . . .. IllS Interesting atmospheric phenomena. . . . . . . . . . . . . . .. IlI.5.1. Self-sustained electrical storms. . . . . . . . . . . . . .. III.5.2. Fair weather lighming . . . . . . . . . . . . . . . . . . . . .. III.5J. Aircraft accidents IlI.5A. Earthquakes III.5.5. The dino climate. . . . . . . . . . . . . . . . . . . . . . . . .. rv. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 206 209 212 212 222 225 229 232 235 Section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Vertical potential gradients and electric fields 239 1.1. History 1.2. Definition '.' . . . . . . . . . . . . . . . . . . . .. 1.3. Earth's Vertical Potential Gradient. . . . . . . . . . . . . . . . .. 1.3.1. The electro phere . . . . . . . . . . . . . . . . . . . . . . . . .. 1.3.2. Fair weather variations. . . . . . . . . . . . . . . . . . . . .. 1.3.3. Thunderstorm variations 1.304. ormal weather variations. . . . . . . . . . . . . . . . . .. lA. Consequences of high electric fields 1.5. T riboelectricity .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1.6. Space charges 1.7. Field-free space 1.8. High voltage lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1.9. Outdoor and indoor fields. . . . . . . . . . . . . . . . . . . . . . . .. 1.9.1 In general a house resemble a Faraday Cage. . . . .. 1.10. Other indoor fields 1.11. Field variations through motion 1.12. Electrical field measurements 1.13. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Gas and electricity 239 242 244 244 244 245 246 248 250 254 256 259 261 261 263 267 269 275 279 2.1. Ionization 2.2. Cosmic rays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2.3. Radioactivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 204. Electrical gas discharges 2.4.1. Collection of atmospheric charges 2.4.2. The Townsend regime 279 284 286 290 290 290 Contents 9 ,. The Forgotten Pollution 2.5. Photoioni:ation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2.6. loni:ation by combustion 2.7. Various effects ofioni:ation ................•...... 2.7.1. The Lenard effect ..........••••••••••...... 2.7.2. Zeleny's observations 2.7.3. The Wilson's observations ............•...... 2.7.4. Miihleisen's observations ....•.•.•••......... 2.7.5. Possible coherence 2.8. Measuring Methods. . . . . . . . . . . . . . . . . • . . • . . . . . . . .. 2.8.1. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2.8.2. The ion counter. . . . . . . . . . . . . . . . . . . . . . . . . .. 2.8.3. The ion counter and a ctJmbu tion space charge .. 2.9. References The electric field, mixture of ions and airborne particles 3.1. Introduction 3.1.1. What' in a name? 3.1.2. Definitions 3.1.3. Particle izes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3.1.4. Particle modification and activation 3.2. Electrical activation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3.2.1. Extra particle activation. . . . . . . . . . . . . . . . . . . .. 3.2.2. Electrostatic forces. . . . . . . . . . . . . . . . . . . . . . . .. 3.2.3. Mobility 3.2.4. Particle Charging 3.3. Natural extra activation of airborne particles 3.3.1. Energy rich particles 3.3.2. The Boltzmann charge equilibrium 3.3.3. Gaseous discharges. . . . . . . . . . . . . . . . . . . . . • . .. 3.3.4. Vegetation .........................•••... 3.3.5. Photoactivity .......................••.... 3.4. Artificial extra activation of airborne particles ...•..... 3.4.1. Electrostatic precipitation 3.4.2. Diffusion charging 3.4.3. Field or bombardment charging 3.4.4. Back discharge 3.4.5. Conversion and selective deposition. . . . . . . . . . .. 3.4.6. Electrode behaviour. . . . . . . . . . . . . . . . . . . . . . .. Contents 10 299 301 309 309 309 312 313 314 315 315 317 318 320 3.5. Measuring methods 3.5.1. General 3.5.2. Measuring capacitor 3.5.3. The filter method 3.5.4. The induction method 3.5.5. The discharge variation method 3.6. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. INDEX 374 374 374 376 377 377 379 18 t 121 323 323 324 325 327 328 328 331 332 334 335 335 338 342 343 347 348 348 349 350 358 361 364 Contents I I The Forgotten PoUution • • ···r • • -'... Vegetation ...L • • --.J•.. •• III 1.1. Introduction By using platinum needles, partly connected to the bark and the wood of a living tree, Becquerel observed different electric current flows, revealing that the earth obtairts continuous positive charges and that the parenchyma transmits negative charges to the air by means of water vapour. Becquerel went so far that he declared, in a memorandum of 1850, that the earth's vegetation is one of the principle origins of atmospheric electricity. This Becquerel was himself the grandfather of the Becquerel who received the Noble prize and whose name is related to the disintegration rate of radioactive material. It is strange that, although still cited by Dary in 1900, this remarkable conclusion has since been neglected. Recent studies on the currents through a tree during a thunderstorm or during a point discharge event make no mention Becquerel's remarks. It is a pleasure on one hand, and a pity on the other, that the current situation of the earth's lower atmosphere indicates that Becquerel was probably right and that he will not so easily be forgotten rhis time. Vegetation Section 1 The Forgotten Pollution 1.2. The Electrostatic Charged Aerosol Monitor (ECAM) Figure 1.2.1 The ECAM as manufactured by Lapsor - F78270 Oavent The ECAM is a device capable of measuring in real time the sum of the charge carried by po itively and negatively charged airborne particles. This is al 0 called space charge. This aspect, together with a remarkable sensitivity, made it po sible to create a new instrument, the Electrostatic Charged Aerosol Monitor (ECAM). It was this instrument that gave me a sort of extra eye, capable of seeing things which are invisible to other. It will be clear that thi i;like a dream for a curious person like me, but let me first of all explain where this eye came from. Research aimed at removing the radioactive source which i currently used in a great number of smoke detectors showed that this could be done by means of low current gas discharges. The sensor based on this principle proved to have an excellent sensitivity and was capable of detecting a great number of burning substances, even the invisible alcohol fire. Particles produced by a combustion process often carry electrical charges and, becau e their minute size means that their settli,{g velocity is very low, this causes the smoke to behave as a space charge. In order to investigate the probability that other space charges, either man-made or of natural origin, could effect the reliability of this detector, long term recordings were carried out in a semi urban area near the Seine valley. When the result showed that the detector was capable of signalling the radioactive clouds of the damaged Chernobyl reactor (an accident which was initially denied) as they drifted over Lower Normandy, the idea arose that the unit could be used to observe atmospheric space charges out of doors. However, in the simple form of the detector this was of course impossible, due to its open structure. For this reason a more suitable unit was constructed, in which the high voltage section and the sensitive current amplifier section are effectively - Principle schematic of the ECAM Clean air out Aowmeter • Chapter 1 Vegetation Section 1 The Forgotten Pollution separated from the measuring chamber. The charged particle flow can be controlled by a pump. However it was assumed that even this was not good enough for outdoor atmospheric mea urements, so a special filter section was added, providing particle-free air around a core that contains air with particles; a so-called laminar flow arrangement. This was done to prevent contamination and condensation on the walls of the measuring chamber. This, together with other refinements, allowed t.he bUilding of an original, new instrument, the ECAM, which is shown in Figure I.2.1. Because no reliable real time date were available on the levels of space charge in Western Europe, it was decided to obtain the background level by measuring the outdoor atmosphere in a rural area, with no major industrial activities. This area lay in the vicinity of a small village, oce, 588 inhabitants, situated in the sparsely populated Le Perche region of the Department de l'Orne, and it was here that the first measurements started. Figure!.3.1 1.3. The Atmospheric Aerosol Observatory (AAO) at Noce The geographical situation of the ob ervatory is shown in Figure 1.3.1 . The site is urrounded by a mixture of agricultural land and forests. Once installed, the new instrument produced an unexpected response in this area which was considered to be Paris space charge free. Repeated observations showed that there was a peak which appeared regularly about two hours after sunrise. However, this could not be confirmed by a clear Noce • Observatory modification in the visibility, when it Chapter 1 occurred. In order to locate the peak clearly in the solar cycle, the ob ervatory was equipped with a photocell as well as a differential temperature measuring system, at a height of 0.50 and 4.50 m. Because of the influence of space charges on the electric field, it was decided to add another instrument to the observatory, in order to measure the earth's electric field or vertical potential gradient (VPG) as it is referred to by atmospheric electricity re earcher . This instrument, together with my "eye", formed a good team and made it possible to unravel a part of the electrical behaviour of the atmosphere close to th~ ground. Figure 1.3.2 shows the details of the instrumentation. It is important to know that the earth carries a negative charge and that the electro phere, some 50 km overhead, carries a positive charge. This means that lots of particles coming from the _ earth, and thus carrying a negative charge, are drawn into the atmosphere rather than falling back to the earth as is generally believed, thus influencing the Vertical Potential Gradient. A typical recording obtained at the beginning of our ob ervations is shown in Figure 1.3.3. The presence of the morning peak remained unexplained for quite a time. Eminent aero 01 and atmospheric chemistry scientists were contacted, but none could give a sati factory answer. It was finally an article by Miihleisen (1958), which made clear that it was probably caused by evaporation of the vegetation, which in turn confirmed the observation of Becquerel on this point. So, indeed, vegetation does seem to be quite active and it could thus be of great interest to observe whether larger aerobiological particles, like spores and pollen, also take part in this morning activity. This was fully understood by the Pasteur Institute of Paris, who made it pos ible to add a so called pollen trap, or pollen sampler, to the instrumentation of the observatory: Figure 1.3.4. The instrument works on the following principle. Air is drawn in with a rate of IO litres/min, and directed towards a rotating drum covered with adhesive tape. Vegetation Section 1 The Forgotten Pollution Figure 1.3.2 Part of the Point discharge current Noc~ ! C.. + - Temperature---..n: 7 Solar activity Vertical potential--+ gradient 11II Small airborne particles will follow the gas streamlines and are not intercepted, but the long stopping distance of the pollen and the spores means that they cannot follow the streamlines, and they will be intercepted by the adhesive tape. Once a week the drum was sent to the Pasteur Institute and its contents were analyzed. • When the recording capacity was increased thanks to some help from the Centre National de Recherche Scientifique (CNRS), other, more classical meteorological observations, like humidity, air pressure, wind direction, and wind speed, could be added, making the observatory well ectuipped meteorologically, electrically and biologically. observatory ! , l Figure 1.3.3 Typical behavior of the vertical potential gradient (F - Field) and the charged particle content (I) (ECAM) in rural air at the atmospheric aerosol observatory at Noc~ (61) m=noon F (V/m) -l _.- 1-. ...__•' . -~~ .1-: _.j... ---I ~~:.~~. +100 Field !~~. o -~:- ~ f:ft_ ~- .. : -100 -f- . ECAM/ . . ' 20 . ".'0 ... 10 ,.' '~~'~. m l Chapter t o t (2h/DI\? Vegetation - Section 1 The Forgotten Pollution Figure 1.3.4 Typical pollen and spores trap , ".r- ... counter, show that the particles (aerosols) are negatively charged, and are thus drawn upwards in the direction of the positive electrosphcre surrounding the earth. This situation is illustrated in Figure 1.4.1. In fair weather, the water content of the airborne particles will gradually decrease through the increa ing influence of the sunlight. The powerful ultra-violet radiation spectrum of the sunlight cause the top of the exchange layer to behave like a chemical reactor and it is believed that this causes the terpene content of the updrift to polymerize, which sometimes gives rise tq the bluish shade that hangs over forests in the summer afternoon. But the negative charge can also be removed from the particles and so neutral or positively charged particle will drift back in the afternoon, where they are observed in the vertical potential gradient, which varies randomly; but they cannot be observed by the ECAM because their size has become so small that they cannot be detected by this instrument. A might be expected, the fluctuations in the VPG signal end immediately when the sun sets and the atmospheric reactor ceases to operate. Thus the combination of a new and a classical instrument made it possible to obtain a better view of what happens in the lower atmosphere under so-called fair weather conditions. - Tape is sent once a week to Pasteur Institute for visual analysis and pollen spores count - - air (1 0 l/min) . .;L Chapter 1 ~... 1.4. The updrift-downdrift cycle 1.5. The acid rain problem Let us return to the observation of an important peak in pace charge just after sunri e and the variation of the vertical potential gradient at the same time, and the fact that this ends near noon. As explained, this behaviour seems to be related to the activity of vegetation; an opinion which i trengthened by other, independent observations. It does indeed seem to be an emission of water and terpenes. The classic space chargeobservations and those carried out by ourselves using a Gerdien ion An excellent opportunity to test this improved view under circumstances other than fine weather came when an invitation was received to participate for some days in the prestigious DEFORPA progran1 at a site in the French Vosges called Donon. Regular observation campaigns had been undertaken at this site in order to look for a correlation between acidification and rainfall. When this seemed to be non-existent, some years of observations were carried out on the role of snow in this Vegetation The Forgotten Pollution Sec:tion t process. However. this, too, proved to be inconclusive, so the attention of the atmospheric chemists finally zoomed in on the hydrogen peroxide hypothesis. This assumes that acidification takes place according the following reaction (Renard. 1992): 50 2 + H20 + H20 2 -. H2 50 4 + H20 Figure 1.4.1 ·····D"~·······.. fII~ ._ ,._,,-,,- Photoionization Top of ex,:::ch~a:::n~ge=-------t~~ "-;>T---' III .. .. . ..... . .. -.. .. :.+:;..: . :~ Molecular / :•• • partides •• Sun rise Noon + Vertical potential gradient Charged aereosol (ECAM) Chapter t 111111111111111 I According to this concept the SO, produced by human activiry should indeed produce sufphuric acid and be responsible for the tree starvation taking place in the Vosges region. However, because this effect appeared quite suddenly, the quantiry of sulphur compound in the atmosphere must have increased a great deal in recent year. The nece sary hydrogen peroxide, H20 2, is believed to be produced by two H02 radicals. The e radicals are produced in clean air through the photolysis of ozone, and in a polluted atmosphere through photochemical reactions.- involving volatile organic compounds. All these reactions are likely to produce the same amount of H02 radicals in the air in the Vosges, which is still of "good" qualiry; or the amount might be slightly reduced by the falling penetration depth of the sun's rays due to the increa ing turbidiry in the __ atmosphere. However, emissions of sulphur oxides from ~ the main sources has been subject to rigorous legislation and control in Western Europe, and i thus more likely to remain stable, or even to fall slightly, than to increase. A potential source which is often overlooked is natural gas, which contains ome 10 mg of sulphur per rd, but its gradually increasing use still makes it difficult to explain the sudden tree starvation that initiated the DEFORPA program. Hydrogen peroxide. H,O" in the atmosphere was observed by the French te~ ~f the Universiry of Paris VI who i ued the invitation for our participation and a German team of the institute fur Spektrochemie of the Universiry of Dortmund. Both were situated on a meadow at some 2 km from the Donon tower. The atmospheric electriciry equipment was copied from the equipment used at the Atmospheric Aerosol Observatory (AAO), and was set up close to the Donon Observatory tower for electrical power considerations. The tower is staffed and maintained by ASPA people. who were of great help during the observation period. The installed equipment consisted of: 1. Vertical potential gradient (VPG) meter to observe the earth's electric field. similar to the one used at AAO. Vegetation The Forgotten Pollution Section t height 1 m (VPG 1) 2. Same as point 1, height 7 m (VPG 2). 3. Electrostatic charged aerosol monitor (ECAM), metal suction tube, height 1.5 m. 4. Experimental space charge filter, similar to the one described by Obolensky (1925). 5. Four-channel analogue recorder. During the 30-h measuring period when the AAO team was present at the Donon site, two events occurred causing important variations in the observed vertical potent~l gradient. These periods were: - a fog period; - a thunderstorm. Both events will be treated hereafter in greater detail. • Figure 1.5.1 Vertical potential gradient (VPC) and charged aerosol (ECAM) observations at the Donon station (Vosges) F = Fog, T - Thunderstorm 1.5.1. The fog period This period lasted from 17.00 h to 22.00 h local time on 17 October 1990 (Figure 1.5.1F). When the equipment was installed at about 16.00 LT in the fading daylight of the end of October, photochemistry due to the sun's rays should be quite scarce. The vertical potential gradient (VPG) observed by the VPG-2 mast was only some 10 Vfm, a value rarely observed at the AAO station. Inspection of the site in the early evening during a period of dense fog revealed that the channel recording the VPG-2 signal had been saturated. For reproduction reasons the ensitivity etting of the recorder was not altered, but a control by means of a multimeter showed that the value observed had to be more than 500 Vfm. Furthermore, the ECAM signals showed saturation on _ _ the recorder when confronted with the fog particles. ~ 1.5.2. The thunderstorm period T F(V/m) This event occurred berween 0.00 hand 1.30 h local time on the 18th October 1990, and was heard at the hotel some three kilometres away (Figure I.5.1T). The next morning the vertical potential gradient (VPG) showed the alternating VPG variations so typical of thunderstorms in this part of Europe. The ECAM signal faded away, but it came back some hours after the thunderstorm had disappeared. The only time the experimental Obolensky-type space charge filter gave a signal was during the thunderstorm event. 80 60 40 20 o..f--+--------=.+--+!jj!h,+t---f'lIi-l(pA) 40 THE DONON TOWER, some characteristics: 17 18 19 20 21 22 17 October 23 24 02 03 04 05 06 18 October H(Ll) Chapter 1 Geographical The tation is situated in the Grandfontaine community, at about 2 km from the Donon col in a forest parcel belonging to the Office National des Forets (ON F) . The Vegetation Section 1 The Forgotten Pollution site is at 750m altitude and sllTrounded by fir and pine trees, more or less affected by starvation, Figure 1. When we compare them with the electrical activity figures, we notice that the concentration of hydrogen peroxide clearly increases with atmo pheric electrical activity, in spite of the fact that the sun cannot be responsible for reactions. It is interesting to see that the SO, signal shows a retarded maximum during the fog period, while the NO, increases with fog, but decreases during the thunderstorm. So let us see if our extended view, added to the atmospheric chemistty observations, means that we are able to figure out what happened here. Structural See also Figure 2 for a drawing of the tower. Height of the tower 47m, about 12m, higher than the surrounding vegetation. The tower has fOllT measuring platforms, connected by an elevator. Management Association de Surveillance de la Pollution Atmospherique en Alsace (ASPA) Equipment round the clock observatiqn of the following parameters: Height above canopy +7m +16m +30m wind dir/speed El +44m x Figure 1 Figure 2 Station de Mesure de la Pollution Almospherique en Zone Forestiere (col du Donon - Vosgues) temperature X X X X Geographical Situation of the Donon Observatory humidity X x X X Tower pressure X radiation x S02 x x x X nitrogen oxides X x X X X 03 X X X x CO 2 X X X X aerosol X X X X ~rl ~/TDonon ~ ~ 1.5.3. The chemical signals As mentioned before, these signals were derived from two s urces: the hydrogen peroxide observation came from the meadow some 2 km from the site and was observed by the French and the German team. The other chemical signals came from the nearby Donon Tower which registered them at 44 m above the forest canopy. The different values for the gases measured are shown in FigllTe 1.5.2. Chapter 1 Platform 44m FRANCE Platform 30m Platform 16m AGENCE POUR lA QUAlIT! DE l'A1R Colmar ArtMede :1.-). R1ZZOTI Entreprise:P.·Lt\oWTIU: Local technique Vegetation III Section 1 The Forgotten Pollution 1.5.4. Analysis Figure 1.5.2 Values for different air pollutants during the fog (F) and thunderstorm (l) period - ASPA Data. HO 2 2 (pp b) 30 30 ! 20 20 10 10 ,. 1< 19 21 o El 17 r- 01 • • 40 23 03 rr o 05 hrs. 21 23 01 • ~ C1'(pm) 03 ~ 25 r- 30 20 I,: 1/ 20 .\ 15 I. 10 10 0 I , 17 • 19 21 ~ 23 n 01 03 ++ T 0 05 hrs. I 17 • 19 21 ~ 23 01 03 ++ T 05 hrs. First of all, the very low vertical potential gradient initially observed under the trees is an indication that there is a good conductivity. The low level of pollution in this area, assisted by the filtering effect of the canopy are probably the main reason behind this observation. causing ga eou ions to remain "alive" for much longer times than in an industrial atmosphere. As mentioned, the vertical potential gradient increa ed dramatically during the fog periods. The observed value, in excess of 500 V/m, will cause potential of the order of 20 000 Vat the tops of the e high pine trees. Fine branches and pointed needles increase the electric field locally, and it will come as no surprise that faint gas discharges will occur under these circumstances. The reason behind thi sudden increase in vertical potential gradient during this period is thought to be the fact that negative gaseous ions are preferred condensation sites for water molecules at high humidity levels. These negatively charged droplet will be drawn towards the positively charged electrosphere and, on the other hand, through gravidity back to earth, giving them a very good stability. This will then create an almost impenetrable layer for charge carriers entraining the conductivity below the trees. So when the electrical field line can no longer terminate on the ground due to this effect, they will do so at the extremities of the trees. In case of the thunderstorm, the electric field involved are of such a magnitude that gaseous discharges occur from all pointed objects. These discharges are known to produce a number of gaseous ions. In the case of positively charged tips, these are H+, 0+, NO,; in case of negative points, which is of course far more common due to the positive electrosphere, we find COj - • 0,-, 1-, NO,-. Hydration of the nitric oxide produces nitric acid, HN0J' so it seems quite logical that fogs often contain droplets with very low pH values. ° Chapter 1 Vegetation III Section 1 The Forgotten Pollution As mentioned, the negative discharge will be favoured naturally, the ozone produced in this way will substiture that formed by the sun in the reactions shown in the chemical box. The q signal is very interesting. As mentioned, NO, is formed in the discharges of both polarities. In ca e of a negative discharge it reacts with the ozone produced, 0" according to the following reaction: This is a reaction which competes with the formation of hydrogen peroxide, H 20" but it is still produced during the fog period. During the thunderstorm, on the other hand, positive ions are also produced, disfavouring the formation of NO, and favouring the production of hydrogen peroxide. El Figure 1.5.3 Current through a metal point during a thunderstorm (after Chalmers. 1962) 1(uA) +2 ./ 10 -2 ! 1(uA) I. 5.5. Selective deposition Chalmers (1962) has observed two phenomena in respect ro trees in full leaf; namely that the current through the tree can be of opposite of sign than the one flowing through a nearby metal point. This is illustrated in Figure 1.5.3 where we see that a positive current leaves the tree during three lighming strokes, while a nearby metallic point a well nearby field mills, show that the fir t two impacts where indeed positive, but that the third was negative. So there is a clear difference between a tree in full leaf and a metal point. Thi is also illustrated when we compare the observations made between the current levels through a tree and those through a nearby metal point as a function of the e timated applied voltage (Milner, 1961). The results are shown in Figure 1.5.4. Here we ee that current starts ro flow at much higher voltage levels for a tree in full leaf than for a metal point. The behaviour of a tree without leaves is almost similar to that of a metal point according ro the same author. Chapter 1 ! ! I !: III Flash I Current through a nearby Iree during the same thunderstorm +5 t~('\ ~ .. , ~\ ~/?II 0..L--------r-----------, 10 o I Minutes ~ So the difference has to have its origin in the leaves. How can that be explained? Quite simply: these leaves are covered by a natural wax layer. Such a layer is known ro retain electric charges for quite a while. If we take the example of camauba wax, electric charges can be retained for over one year. This type of behaviour is called an electret, which means that such charged leaves Vegetation Section 1 The Forgotten Pollution start to act as a 'magnet' for oppositely electrically charged airborne particles and ions, thus causing elective deposition of air pollutants. Charge retention means that the tree will act like a capacitor and will exhibit a different behaviour than a metal point or a tree without leaves. The different observations of Chalmers and Milner are in agreement with this view, so let us continue. Figure 1.5.4 Currents observed at various occasions against the vertical potential gradient (after Milner et al., 1961) 10 Ell •• < c: 3 ~ • •• • • a <:: '0 c. 11 "]j '" ~ , 0 0 1000 2000 Vertical poteneial gradient (V/m) 3000 Current through a nearby tree at various occasions against the vertical potential gradient 10 < 3 iii a'= Cl) Cl) ,.= 0 , 0 Chapter 1 • 1000 2000 Vertical poteneial gradient (V/m) 3000 Figure 1.5.5, plates 1 - 6 show a schematic of the selective deposition in the case of a fog period. Plate 1 shows the distribution of lines of force in fair weather. Plate 2 shows the distortion of the line of force due to the lack of conductivity in the fog layer. If the field strength near the tip of the tree becomes sufficiently high, the atmospheric air will become decomposed with the emission of negative ions, Plate 3. However, ions are produced in pairs; repelled by the fair weather field, they will return towards the tree, Plate 4. This will charge the tree and reduce the elc;.ctric field ensed by the tip of the tree. Once the fog di ipates, the initial field line will be rein tated, together with those produced by the charging of the leaves, Plate 5. However, the charges can be retained for quite some time, which means that the tree will still attract pollutants, even after the fog has disappeared, Plate 6. This model explains the ob ervation that a tree in full leaf needs vety high field values before a good, mea urable current starts to flow. It also suggests that the leaves act as temporary accumulators for certain products initiated by the gas discharge. The removal of these products will occur in different way. One can think of: - the products being repelled to the ground through electrostatic forces between the leaves and the ground; - the products may fall to the ground in a liquid form, scavenged by rain or conden ation drops; - the imilarity of sign between the leaves and the products should encourage re uspension through the action of the wind. In any case, the electric action of charged leaves will repel qne type of air pollution and attract another. As we know, gas discharges themselves are also effective producers of nitrogen oxides. Like the god Janus, nitrogen oxide are two faced: they have a good face because they make a readily assimilated type of fertilizer but, on the other hand, they produce nitric acid, which acidifies the soil, and nitrates which pollute our water resources. With respect to the magnitude of this Vegetation III Section 1 The Forgotten Pollution Figure 1.5.5 + + • + + Electrosphere , Earth ... + A+ + + I Chapter 1 + Negative pollution: sulphur. chlorine are attracted Earth effect, it is interesting to know that observations on nitrates have been carried out in Great Britain for over 150 year. The results show that for a hectare of land where no fertilizer at all has ever been used, some 40 kg of nitrates still leaches out of it, without the farmers being responsible for it. To return to our starving trees in the Vo ges forest, which often carry a po itive charge, thus selectively attracting negatively charged pollutants: this very simply explains the delayed arrival of SO: in Figure 1.5.2, but it also makes clear why if ha been ob erved that forests tend to attract a lot more of these pollutants than the nearby fields. However, as we have stated above: although the increase in sulphur in the atmosphere of the Vosges seems likely, as does its selective deposition, it is still not clear why this starvation effect is so sudden. But, as we have seen, the chemical reaction that produces hydrogen peroxide and, later on sulphuric acid, is also related to electrical gas discharges, so the more gas discharges there are, the more acid is produced. Gas discharges not only produce ions but also a great number of very fine particle which are known to act as effective condensation nuclei. One of the reasons for gas discharge i the presence of a great quantity of water in the form of fog. When condensation nuclei enter such a region even more droplets will occur, making the fog even more dense and thus the gas discharge more powerful and thus more particles, etc. In other words, an infernal circle arises. The high electric fields that cause the e discharges are known to force trees to send out their sap through a phenomenon called electra-evaporation. This behaviour not only intensifies the fog, it also dries out the tree. This will become highly dangerous for trees, especially during a dry period. The fact that, for several years, few rain measurements were made during the DEFORPA campaigns emphasize that it was obviously a dry period. Vegetation Section I The Forgotten Pollution From laboratory te ts it is clear that gas discharges start earlier and are more intense in the pre ence of traces of certain active gases. The CFCs used a propellant in aerosol spray cans are electronegative. The u e of these chemicals was quite extensive at the start of the DEFORPA program and increased during its execution, until they became banned towards the end of the campaign. Let us now summarize our arguments concerning the cause of this tree starvation: -1 selective attract~on of pollutants by the trees; -2 increased transformation of sulphur into sulphuric acid; -3 the infernal circle of fog formation; -4 e1ectro-evaporation makes trees dry up; -5 increasing use of CFCs accentuates all the effects mentioned in this list. It i fascinating to see that, in this case, too, the extended view affords explanations where classical approaches break down. Whether this should mean that electrical effects in air pollution have to be considered as an extra forgotten dimension is not yet clear: let us wait and see. l1li 1.6. Pesticide spraying When I a ked my son's paediatrician, who lives quite near the Atmospheric Aerosol Laboratory of oce, his opinion about the occurrence of pulmonary problems in this group of the population, the answer was that they were in general low, except in case when pesticide spraying started in the area; especially when this was done by means of helicopters and aeroplanes. Pesticides are coming under increased scrutiny for a variety of reasons. However, if we limit ourselves to their airborne behaviour and see whether our broadened view of pollution can be of help in analyzing this problem, then we are first of all confronted with the resuspension Chapter I in the air through evaporation of the pesticides from the soil and plant leaves. It has been shown that this an important dissipation mechanism for these substance. For certain rype of pesticides up to 90% of the product disappeared in this way within 24 h. This could explain the rather high concentrations of pesticides that have been reported in rainwater and fog. But it seems that it is not this mechanism that triggered off the pulmonary problems among the children living near the observatory, because these are exclu ively linked to airborne spraying, and not to the more general method of application 6y means of spray arms connected to a tractor. So what is so special about the airborne application? The emitted cloud leaving the aircraft will act like an artificial fog. This means that gaseous ions will be intercepted by it, thus substantially reducing the electrical conductiviry near the ground. Thi means that the electric field lines are prevented from reaching the ground, cau ing an increase in the vertical potential gradient. The combustion motors used in aircraft will release mainly positively charged exhaust gases, often leaving the aucraft negatively charged. ow, if we compare the aircraft and the emitted particles with Lord Kelvin's water dropper, then the particle should carry negative charges with them, thus reducing the final charge on the aircraft. However, as soon as such a particle becomes exposed to the fair weather field, which will generally exist because it is under such meteorological conditions that spraying is often done, it will sense an upwardly directed electrostatic force, which will help it to remain airborne for a longer time. This means that the spray fog becomes more persistent. The increased vertical potential gradient will concentrate field lines near pointed objects which penetrate the layer and, analogous to natural fog conditions, gaseous discharges will then become very likely, see figure 1.6.1. Vegetation Section 1 The Forgotten Pollution Figure 1.6.1 breaking up large molecular structures. If, for example, we consider the chemical composition of the organopho phate pesticide parathion: and we compare it with that of tabun, a nerve gas used in warfare: Concentration because of pesticide fog El It is clear that this manner of deposition is far from ideal, because the slightest wind will produce deposition on unwanted targets. For this reason a great number of experiments have been carried out, aimed at modifying the process into a real e1ectro tatic spray. Here different meth~ds are used to charge in such a way that droplets will be drawn towards the vegetation. This process does indeed increase the deposition of the pesticide on the target crop and thus, similar to electrostatic precipitation, charges will build up there. The wax-like layer covering the leaves will retain the deposited charges and, when a certain charge level is exceeded, gas discharges (so-called back discharges) of the corona type take place from the pesticide-covered vegetation. Gaseous discharges are known to produce pernicious gases, such as 0, and N02• The latter damages the cilia, even at levels of 4 molecules in 10 000 000 air molecules. The cilia play a crucial role in the nose and airways: they wave backwards and forward , carrying mucus and foreign bodies ou t of the body through the nostrils or mouth. But this is not all. Gas discharges of the corona type are highly energetic and are known to be capable of Chapter 1 then we see that some'molecular shake-up by this gas discharge mechanism could cause the transformation of one substance into the other. So an electrical dimension does indeed remove a great deal of obscurity from a question posed by Bartle ~ (1991) "Every year people in Britain are made ill by ~ exposure to organophosphate pesticides. Why do they find it so difficult to get anyone to take them seriously?" What should be taken seriously is the capability of the electrically orientated view of pollution to come up with logical and comprehensible response where the simplified explanations fail completely. 1.7. Vegetation under very high electric stress It was during the night of 8-9 August 1992 that a very special storm passed over the Atmospheric Aerosol Ob ervatory at Noce (61) in the region called the Perche. Figure l. 7.1. shows the record as observed by the station. As can be seen, the vertical potential gradient had already shown important fluctuations during the day; however it was just after 16.00 LT that some point discharges were observed. A clear increase came at 21.00 LT and preceded the storm by almost one hour. The windspeed suddenly increased to hurricane levels, while the temperature dropped from 20"C to 13 QC in a Vegetation Section 1 The Forgotten Pollution Figure 1.7.1 few minutes. The only remarkable ob ervation, however, was the fact that the ky wa howing an almost uniform blui h-white glow and no thunderbolts were seen or heard, in spite of the high electrical activity recorded at the observatory. However the next morning it became clear that this was not a normal storm. As is shown in Figure I. 7.2, a great number of trees (mainly poplars) lost their crowns, leaving only some 6 m of bare trunk tanding. Another type of tree damage is shown in Figure 1.7.3. Here the tree is bent and remairred so, even in the absence of wind. A quick trip through the region made it clear that Current and vertical potential gradient through a metal point o - - I Storm -----. - Figure 1.7.2 -0.5 , " " Beheaded polla", • 8 August 1992 L 1000 o )1 ~---Vertical potential gradient -1000 6.00 16.00 12.00 24.00 Local time (h) Chapter 1 Vegetation Section t The Forgotten Pollution the damage occurred only in the lower parts of the landscape valleys, forest clearing, etc. The damage done to these trees, however, is fundamentally different from that caused by lighming, as shown in Figure 1.7.4. Inspection of the fallen crowns revealed that a major part was covered with leaves having a strange silvery-grey appearance. However, other branches on the same crown had kept the normal green colour that they should have had at this time of the year. Figure 1.7.4 Trunk splits up into board like segments (Hermant, 1993) Figure 1.7.3 Even without wind the trees remain bent III A laboratory test was carried out on the estrange grey leaves and the healthy green ones. A sample of 140 of each type of leaf was collected and weighed. The leaves were then dried in the environmental test chamber of the Laboratory for Aeroactivity (LA) at Longny (61). Once dried, both amples were weighed Chapter t Vegetation The Forgotten Pollution Section 1 Figure 1.7.5 again, and a correction factor established to make them comparable, see the table below. Twig stilt green Weight (g) Type of leaves initial dry normal poplar leaves 360 240 330 220 110 grey poplar leaves 260 220 260 220 40 initial corrected dry corrected difference This means that the grey leaves had suffered an extra weight loss of 110 -40 = 70 g during the storm. The lost material is likely to be water and volatile organic compounds (VOCs). Assuming a specific gravity of I, then each leaf had lost about 0.5 g of this material during the weather event. Assuming some 100 000 leaves affected per crown, this means that some 50 I (50 kg) of liquid had been ejected. But the leaves still attached to less affected trees also showed a strange appearance, as illustrated in Figure 1.7.5. They hung in an odd way and were carbon black, as if they had been burned. Similar observation were made when the tops of the fallen crowns were investigated. Here the leaves were roo carbonized to remain connected to the twigs and had often fallen to the ground as ash. Inspection of the point were the crown had left the trunk taught us that there was a kind of torsion mechanism involved. Some of the crowns which had not been fully disconnected showed the clear characteristic of twisting at the interface point, as is illustrated in Figure 1.7.6. Inspection of the beheaded trees sll.owed that the extremity looked as if the wood had been cooked for some time, creating a bunch of independent fibres, as illustrated in Figure 1.7.7. Another observa tion was the strange change of colour of the sapwood where the bark had been removed. The normal transparent aspect was often changed into bright orange. The removal of the bark from some parts of the trees revealed a strange pattern of lines (Fig I. 7.8), 1:1 Chapter 1 Affected poplar tree branch I Figure 1.7.7 Figure 1.7.8 Cooked wood Electrical current traces under the bark Vegetation Section 1 The Forgotten Pollution Figure 1.7.6 with some similarities to the so-called Lichtenberg (1744-1799) figures, which are produced when a discharge hits a surface. The fact that no damage was done to the sapwood excludes causation of the patterns by insects. They are probably caused by an electric current circulating in the tree. Twisted tree 1.7.1. The crown removal mechanism If we now combine the different observations we can arrive at the following model (see also Figure 1.7.9). The Figure 1.7.9 • - Continued on following page Ordinary forest / Typical production arrangement as found in the Perche for poplar trees - highly affected by the storm + Let's assume a high level of atmospheric electricity Chapter 1 + + + + + Lines of force concentrate Vegetation Section t The Forgotten Pollution figure shows the rypical form of the poplar tree as found in the Perche region. For silvicultural reasons the lower branches of the trunk are repeatedly removed. Assuming a high electric field overhead, then gas di charges will occur at the extremities of the tree, and gas ions will be emitted towards the ky. During their ascent they collide with neutral gas molecules, imparting an upward momentum to them, too. This effect is called the electric wind and was reported by Hauksbee in 1709. For a long time it had been considered to be a laboratory curiosity, until more recent scierttific investigations have been carried out on this "wind". Even at low di charge current Figure 1.709 El ,-.,-. I---r the electric wind velocity easily reaches values in excess of 40 km/h. The phenomenon i now being investigated in connection with the extingui hing of fires. So if we assume that this takes place near the top of the tree, then a depression will be created in the crown, see Figure I. 7.10. The current needed for the discharge will pass mainly through the sapwood and will thu gradually heat up the tree through the Joule effect. This will also cau e electrochemical reactions in the sap. The power dissipation will be concentrated in that part of the tree that has the highest electrical resistance which, in case of the poplar tree 'cleared of the lower branches, as is the case in the Perche region, i just under the crown. So ,_1 C_on_ti_on_u_e,d,from Prrev-,-io_u_s_p_ag_e r --'r ~-,~0 ,::- --,- ~ ~ V ~ Electrical discharges take place ,L .J, , I ...- ... The ions transfer momentum to neutral @ gas partides which start to move in the same direction ~ i Electric wind >40 km/h This is called the -electric- wind; described by ~ ~ ~ Continued on following page + + + + ~ A ... j ,- - Figure 1.7.10 ----,,----, .J.. -=Y£-~- Electrical discharges at the top means that a current passes trough the tree ~ 1 Electric wind Storm 30 - 160 krn/h _..........o::~=--""".~~~..; : Cbapter t Vegetation Section 1 The Forgotten PoUution when the main wind reaches such a tree, it will sense a chimney effect caused by the electric wind produced by the gas discharges. While swirling upwards, the wind will cause a torsion on the crown. The wood just under it has been made fragile through the cooking effect of the gas discharge current, so it is no wonder that after some repeated twists, as has been reported by an eye witness of such an event, the crown is separated from the trunk in some seconds. Instantaneously the field lines will move towards another nearby tree and the same scenario takes pace. Plantations of some 300 poplars were beheaded within 10 minutes during this storm. In case of younger trees with thinner crowns, the twisting wilt be less and Figure 1.7.10 Continued from previous page ~ Electric t 'I ~;."<) ~. Cooked wood /1-~'c:: ------...Current traces under bark Result: the crown is removed in less than a minute: leaves burned and empty --~ \ Storm . .:. Young ;~~~...... Bent tree Chapter 1 )Bending '., b storm .~:." ........._/ y the tree will bend in the direction of the wind. However, the Joule effect of the discharge will steam the inside, making it impossible for the tree to retain its initial position after the storm. 1.7.2. The Leaves As mentioned before, a great part of leave in the fallen crowns were almost completely emptied of their sap and showed a strange grey colour, while others on the same crown remained green. The most plau ible explanation for this behaviour is that it was produced by the so-called electro-evaporation effect. This was de cribed for the first time by Gilbert in 1600, who reported that a drop, when submitted to a piece of charged amber, changed its form from a rounded one into a pointed one, a cone. Later ..investigations showed that in doing so the drop emitted a ~ myriad number of fine droplets, thus causing it to evaporate quite rapidly, so-called electro-evaporation (Figure 1.7.11). Similar to the electric wind this effect has also been viewed as a laboratory curiosity and it is only recently that attempts have been made to understand the phenomenon. The theoretical work by Taylor has caused effect to also be referred to as the T aylor cone. It is quite likely that the measured 0.5 g of liquid loss per leaf is caused by this phenomenon. Spray rates of 1 g/min have been reported for Taylor cones. It is interesting to notice that it was only the leaves that were emptied. The twigs to which they were connected still showed a healthy green aspect, so it seems that the refilling of the leaves by the sap of the tree could not cope with the speed of the electro-evaporation. Other leaves affected by this electro-evaporation, but situated near the extremities of the crown, were also submitted to the conduction current of the gas discharges as well as the toxic, decomposed air products that are produced by this phenomenon. It is probably the combination of these effects that caused these leaves to become carbonized, while still hanging on the twigs. Vegetation Section I The forgotten Pollution Figure 1.7.11 Figure 1.7.11 Continued on following page Continued irom previous page + '"~ ++ + body + + + ~ Amber Water drop --, r 0- El - "r A cone instead of a Sphere...... also called Tayior Cone . .:L O--.J drop 8'" 1\ ... ... / - - ':r A mist of very fine water droplets - , ... 00 0 0 0 0 0 0 0 0 0 0 000 00 00 0 0 . .:L /\ ..- ... ~... Tayior cone, also called electro- Hydrocarbon + water mist P ..: L// L...:.. / L- : 0 o ..I:... ...:L -'--J L1._--L'----- ~ 00 °0 ~_1JaA:::ation~ J o Chemical analysis of the leaves collected from various parts of the crown showed that those situated near the top had a higher oxygen/carbon ratio (Borra, personal communication) than those leaves picked from lower parts. At first sight this seems strange because the top le~ves were transformed into ash. However, gas discharges of the corona type are known to be powerful oxidizers, which seem to imply that no corona-like discharges occurred on the other lower leaves, and that the singular aspect of the upper leaves should come from a combination of electric current, electro-evaporation and chemistry. The rapid drying of the leaves should force the tree to draw up water as quickly as possible Chapter I "r 0 0 ... 0 ..- ... ~__' from the soil. It is still unclear if it is this reaction, or a possible e1ectrochemical modification of the sap that caused the strange red-orange decoloration of the sapwood after exposure to ambient air for a while. I 1.4.3. Pisciculture White water It was only several days after the storm hit the region that reports arrived concerning surface water. In the Longny area some 20 km north of the observatory the Vegetation III The Forgotten Pollution Section 1 Figure 1.7.12 water had become white. This also happened in the Le Mans area some 60 km to the south in the ame period. Water sample were taken there and sent away for laboratory analysis. However no pollution could be detected. A imilar event happened some weeks before at Bretoncelles at some 10 km from Noce. Here, too, there wa white water but no sign of pollution. However, on the 22th of July, when it happened in Bretoncelles, as well as on the 8th of August, when the phenomenon occurred again, the Atmospheric Aerosol Observatory noted important level of point discharge. When di cussing the matter with the personnel of the Direction Departemental de Agriculture (DDA) they mentioned that similar effects occur when they do what they call electrical fishing, which involve two electrodes being placed in the water. Upon applying an electric source to the electrodes an electrical field is created and a current flow. This immobilizes the fish, which can be removed efficiently in this way from a pond, for example. So probably, in the case of white water, we are dealing with the electrolysis of water. This can be done in the laborarory by means of a simple instrument consisting of a reservoir filled with slightly conducting water and two platinum electrodes connected to an electrical battery. As soon as a current flows through the water oxygen will be released from the positive electrode and hydrogen from the negative one. So we split the water up according to the following reaction: - 2 Hp (I) -+ 2 H2 (g) + 02 (g) l=liquid phase, g=gas phase. The upwelling gases form small bubbles in the water, modifying its refractive index and giving the whitish impre sion, which disappears when it is allowed to rest after the current has been removed. That this reaction is quite likely to occur in case of point discharge events is illustrated in Figure 1.7.12. Here the tree forms the positive electrode, while the earth is the negative one. + + + + Oxygen Bubbles give the waler its while look i 00 The current flowing through the water will produce electrolysis and the gases formed will give it its white aspect. As mentioned before, fish are affected by this process and it is not impossible that their death is somel~ow related to this electrical water pollution that, apart from decomposition, also produces ozone. It will be interesting to follow the performance of the two oxygen wells recently installed in the River Seine, intended to breathe life back into this polluted river in case of thunderstorms. Polluted water I It was at the fish farm at Preaux, only 2 km from Noce, that the lethal activity of the water produced by the storm was mentioned for the first time. The farm is quite a small one, producing mainly rainbow trout and a small quantity of the fario variant. The farm is situated on the small Erre river, which accumulates its water from the region around Noce, see Figure I. 7.13. In case of Vegetation Chapter 1 The Forgotten Pollution Section 1 important rainfall, a wave of water tends to reach the farm some 7-8 h after the start. This was also the case after the storm of 8 August 1992. However, according to eyewimes e , although it had a normal appearance, the water was differenr. The trout behaved as if they wanred to escape from it, and within 2 h 500 kg of rainbow trout had died, together with 50 kg of H-+-1 fario trout. A water sample taken o 1 2 3 km at the beginning of the event wa unfortunately thrown away during the hour the farmer was busy removing the killed fish from his ponds. The financial blow of the event and the feeling of impotence meant that all reminders had been removed, unfortunately leaving only an eye-wimess report. On the same Erre river, ome kilometers downstream, there is another, larger fish farm near the village of St. Hilaire sur Erre. When the fish farmer was asked if he had, problems after the storm he related that he had lost some 30 kg, not much different from the quantity he loses during problem periods. When told about the loss of his colleague at Preaux, he suggested that this was caused by suffocation, a problem he prevented by not feeding his fish when he learned about the possibility of thunderstorm activity. This reduces the fishes need for oxygen. He also performed some measurements on the oxygen level in the Erre water and that of the Chevre river that flows into it just before arriving at his farm. The levels (4mg/! and 3mg/!, respectively) were below the normal level of some 8-12 mg/!, but not so low that it could explain the mass killing at his colleague's fish farm. It was finally extra evidence obtained from the Brochard pond, some 20 km further to the north, close to Longny where the white water reports came from, which threw a clarifying light on the matter. These ponds, unconnected to the Erre water system but also Figure 1.7.13 Chapter 1 affected by the storm, obtain urface water from the surrounding Reno forest. Some well water is also received and, when mixed with water from the pond, is fed to a partly covered shed, where cultivated trout of the rainbow varianr are kept. Another smaller trout stock i housed in two pools near the pond. These are directly connected to the water in the pond. This is not a fish farm: all the fish are bought and released into the ponds for angling purposes. At this site the quantity of fish that was lost was 500 kg. The problems started some hours after the storm in the pools. The eyes of the fish swelled up and finally di appeared, leaving the fi h blind. Blisters on the skin also appeared. Here, too, the fish disliked the water and death arrived within hours. Inspection of the shed during the night seemed to indicate that everything was till all well here. However, upon returning in the ~ morning it became clear that here too, almost the whole ~ trout population had been eliminated by the evenr. Inspection of the remaining trout revealed that visible damage was done to them, either blindness and or strange white stripes on the normal black back of the trout. Discussion Let us see whether we are able to understand what could have caused the death of these fishes, taking into account what we know about electrical activity in nature. First of all the delay in the death of the fish and the storm event excludes direct electrical phenomena. In that case it is likely that the transport mechanism involved is the water. This is underlined by the fact that the trout partly supplied with water from a well lived longer than those exposed to surface water. 0 it seems that we are dealing with highly polluted surface water. The chemical analysis, done during the far les violent fog period, showed that it is very likely that the following products were formed during the storm period: Vegetation The Forgotten Pollution Section 1 - volatile organic compounds from the vegetation; - nitrogen oxides from the air; - ozone from the air; - water and salts from the vegetation. As we have seen from the fog period, hydrogen peroxides is likely to be formed. The nitrogen oxides are also likely to produce nitric acid. Recenrly Borra, when submitting tree tips to electrical discharges, obtained results that indicate that the salts are likely to produce bleach water (NaCIO) under these circumstances. As mentioned, the most affected trees during the storm event were popla1" . The branches, twigs and leaves of this tree can be effectively used as a mordant for the dying of various materials, so the volatile organic compounds released should also be taken into account. Now when we add a likely oxygen depletion and ozone production due to electrolysis, then our polluted water will be formed by a succession of waves containing: - nitric acid, mordant; - hydrogen peroxide, bleach water; - reduced oxygen content; covered by: - a layer of organic material blocking the oxygen exchange with the air. According to toxicologists, such a compo ition could explain the rapid death of the fish, the blindness, as well as the decoloration. However, what, then, was the miracle that saved the fish farm at St. Hilaire from the fate that hits its colleagues? The solution probably comes from the small Chevre river that flows into the Erre just upstream of the farm. The water of the Chevre is collected around the village of Verrieres. Here, however, there were major soil engineering operations being conducted in connection with the re-allotment of a part of the agricultural domains. The soil in the Perche region is very basic so it is probably the water from the Chevre that neutralized the acids in the Erre river to such an extent that the trout in the St. Hilaire fish farm could survive without El Chapter 1 too much loss. This water related aspect of the storm was quite astonishing, and if we look at the ecological and economic consequences involved, research into the problem can easily be justified. A validation of the suggestion on neutralization of the acid comes from the Le Perche]oumal of 18 March 1993, when an accident caused several thousand litres of nitric acid to be released into the Erre, causing even larger losses of fish at the first fish farm, whilst the second was spared again when the wa ter from the Chevre ,en tered the stream just before the farm, where it was once again neutralized as shown by the analysis performed by the authorities after the accident. 1.7.4. Types of trees involved During the storm in the Perche, it is remarkable to notice that almost no air to ground discharges were recorded for the forest of St. Reno, but that 15 000 metric tons of the finest oak wood was brought down. Indeec\, some sites seem to be more affected than others by this type of special storm. For example, according to De Koning (1922) the forest near the Hague in the Netherlands was severely hit in the years 1853, 1858, 1860, 1881, and 1911. Investigations into the frequency of this type of storm in the Perche revealed that they also occur quite regularly, but that they are less localized. In fact the region affected stretched from the Bordeaux area to Poitiers, the Loir Valley, the Perche, and to the Somm area. Similar torm damage was also observed in the Vosges, Belgium and the south of the Netherlands. Returning to the observation of de Koning, concerning the trees susceptible to damage by electric phenomena, he presents the following list: Vegetation Section 1 Poplars Oaks The Forgouen Pollution 284 (36,4%) Walnuts 10 (1,3%) (1,3%) 169 (21,6%) Cherry 10 Willows 89 (11,4%) 8eech 8 (1,0%) Elm trees 63 (8,1%) Apple 8 (1,0%) Pear trees 35 (4,5%) Chestnuts 7 (0,9%) Conifers 33 (4,2%) Alders 6 (0,7%) Ash trees 31 (3,9%) Birch 2 (1,3%) lime trees 20 (2,5%) Others 5 (rest) These trees were struck in The Netherlands near the beginning of the 20th century. He explains the fact that poplars and oaks are high on the list by the fact that both trees have a low fat and a high starch level. Fatcontaining trees are bad conductors and thus less susceptible to being struck than the well conducting, starch-containing trees. The fact that conductivity plays an important role could also be deduced from the fact that, during the storm in the Perche, the trees containing mi detoe, which consumes part of the sap of the tree, were le affected than those without. So there is obviously a clear difference in the electrical behaviour of the different tree specIes. And if we look at the list given by de Koning, then the German saying "Eichen soli man weichen, Buchen soli man suchen" which means, roughly, "Do not hide under an oak in case of a thunderstorm but look for a beech", seems fully appropriate and less of an old wive's tale, as is often assumed. Chapter 1 1.8. Vegetation under natural electric stress [n case of fair weather the earth's vertical potential gradient has values between 100 V/m and 200 V/m. [n case of thunderstorms the value increases rapidly to values in excess of 5000 V/m. But we do not always have fair weather, nor thunderstorms. We are often confronted with situations producing intermediate values. These situations can be caused by various mechanism, such as: -fog; -air pollution; -lack of vegetation; -snow layer; -pollen emission. _ The consequence i that the extremities of high objects • are expo ed to high-field conditions, which can cause: in case of tree in full leaf: water emission; ap emission; selective deposition; ozone/nitrogen oxides production; gas ions; and, in case of a metal point or a tree without leaves: ozone/nitrogen oxides production; gas ions. The reason behind this is the presence of a gas discharge current, when the field strength near the extremity reaches a certain critical value of the order of 3 MV/m. At that moment the discharge starts to become what is called self-sustaining, and a corona discharge regime is initiated. However, far below the critical value, nonsustained discharges rake place in the T ownsend regime. Here the current is impulsive, with high peak values but a low mean value, which means that it is often ignored, a sumed to be of no importance. However investigations into the consequences of these low currents have made it clear that they are as active as their self-sustained Vegetation The Forgotten Pollution Section 1 I. 8. 1. Forests counterparts, but that it takes more time to arrive at the same results. So it may be assumed that when vegetation, and of course trees in particular, is submitted to field conditions which are not high enough to cause corona discharges, the effects will become similar to those caused by high field conditions when the time of exposure is increased. However this also gives the tree time to adapt it elf to this situation by, for example, a better control of its sap emi sion or the adoption of a shape which is less affected by the high field. Let us now take a look at different situations were trees are under a form of electric tress. Most of these situations are induced by human activity. If we take an homogeneous forest then the electrical field lines will be uniformly distributed over the canopy. The trees in this forest will adapt their shape and metabolism to this situation. But suppose we cut a clearing in this forest, see Figure 1.8.1. Now the ground will receive a number of field lines and so will the canopy. However, when it come to the trees near the edge of the clearing, they will suddenly be confronted with an important increase of electrical stJ;tss, not only because of their location but also because their shape is not adapted to field lines coming in from the side. If trees are already fully grown, the adaptation of their metabolism will take Figure 1.8.1 Figure 1.8.1 Continued on following page ,----------------, + + I I + + + r----------, + Field lines Gearing , Colder. so often fog / ~ ) ~V~~h':h:~ Chapter 1 They put leaves under electric stress ···:r ~---------.---, ::': :,.. r-;-------------,--, )~... ,L~~~..,L f! J. : /~.;~. . Electra evaporation loss of nutrients ... ...-... Field lines concentrate on edge "':r Continued from previous page I r J?:: )))~J» \.. r &! .I. Fieldlll1es , :•• concentrate on new ~/ edge losses will kill the tree .{;', ~.. Vegetation - Section 1 The forgotten Pollution too long and the tree will suffer and probably die under these conditions. The fact that clearings are deprived of the insulating layer of the canopy means that the temperature there will often be lower than in the forest, making fog formation more likely. This will block the field lines going to the ground in the clearing, diverting them to the trees at the edge of the forest, increasing the electric stress on them even further. According to de Koning (1922), the right way to make a clearing (see Figure 1.8.2) is to cut a 20 m-\vide slot through the forest. Over the course of several years this space should be filled up with gradually smaller trees. Once they are sufficiently high, then the clearing can be cut without risk. His explanation is that these new trees protect the new edge against the influence of the wind. However, when we look at the field line distribution obtained with this method, we see that the harmful field line concentration at the edge has also disappeared. • Figure 1.8.2 Continued from previous page After a few years .. slot too small for high field line concentration III Figure 1.8.2 Contirued on following page -Grownup trees Now the projected cut Final cut Rounded edges prevent unwanted field line concentration Chapter 1 Vegetation The Forgotten Pollution Section I The electrical tress mechanism also easily explains observations made by Brazilian and American researchers who were trying to discover what caused the huge cloud of ozone which had been detected in the troposphere over central Brazil. The ozone appears to come from the fore t in Amazonia, which does not in fact seem too strange if we realise that there are clearings cut on a very large scale, without any precaution being taken to protect the forest edge. The trees in tropical forests easily reach 30 m in height, so even low vertical potential gradient value will give important voltage values near the top of the trees, but probably the worst thing that happens is the fact that the branches are burned in the clearance. This type of air pollution is capable of creating high fields by intercepting gas ions and in this way reducing the near-ground conductivity of the clearing. Then the situation becomes similar to the fog event and the typical products of gas discharges like, ozone and nitrogen oxides, are likely to occur. Because this clearance activity takes place on a very large scale, the presence of an ozone cloud over Brazil becomes less puzzling when electrical stress, and thus the extra dimension, i taken into account. Figure 1.8.3 The forest Ill) Q{ I~ ~ ~ I 1.8.2. Deserts If we continue to cut clearings, then the general humidity level will gradually drop, making the region increasingly arid. More clearings mean that the ratio between edge trees and forest trees increases, so an increa ing number of trees will come under stress under worsening circumstances. This is a situation in which a self-sustained destruction mechanism is likely to occur. This means that when deforestation has surpassed a critical level, then nature will give a helping hand by producing a desert, see Figure 1.8.3. Once this situation is reached, there will be no extremities left that can moderate the vertical potential gradient and the Chapter I 11- 1 .I. . .n.1I .... LJ , © I Thedese_rt_ _ Vegetation The Forgotten PoUotion Section 1 situation becomes similar to that of the polar region, where values of 5000 VIm are no exception (Benninghoff, 1985). This will mean that only vegetation of a limited height can survive under the condition that it grows in a hape that limits the concentration of field lines. This means that, in such areas in Western Europe, only low level brushwood is often found, with a more-orless spherical shape. Reforestation of such area shows that even species resistant to these harsh electric stress conditions have difficulty in surviving. Their shoots are short, a are their needles, which stand very close together. And, of course, the tree tends to grow more horizontally than vertically. The change in root pattern under these conditions i also interesting. The roots often remain quite close to the surface, see Figure 1.8.4. It is unclear whether this behaviour is linked to the need of the tree to dissipate the electric charges it easily receives through the tribo-electric action of the wind. - Figure 1.8.4 >--Aj-'rr-oo-tsys-te-m-- Chapter 1 ~ 1.8.3. Hedges In the Perche region of France where the Atmospheric Aerosol Observatory is situated, the meadows and fields have been urrounded by hedges for centuries. Although the region is quite unfit for the large scale production of meat or cereals due to its lack of drainage, the multitude of soil types and its hilly character, the agricultural policy of the European Union has forced the farms to increase the cale of their exploitation. This makes re-allotment necessary, during which process a great number of hedges get 10 t. It will be clear that such an important change in the landscape is not appreciated by everyone and several societies for the protection of nature are trying to bring the process to a halt. Their arguments for the _. preservation of the hedges takes a multiple form: - hedges break the wind, thus reducing soil erosion; - they also retain water, thus creating a better micro climate and also preventing soil loss towards the rivers. - the hedges erve as a natural habitat for birds and small animals; - the landscape 10 es its attractive character for tourists Unfortunately none of these arguments carry financial weight, which interests the small-scale farmer in the region. And it is only with another subvention from the European Union that some of the hedges become replanted. However, it is once again the extended view that is capable of proposing an argument that interests the farmer. In order to understand it we have to go back to rural France in the time that fertilizers were not so commonplace as they are nowadays. According to Dary (1900) it was Father Paulin, sometime around 1850, who, as director of the agricultural institute of Beauvais, used his 'geomagnetifere' to obtain excellent growth re ults with the surrounding cultures. This was certified by several agricultural commis ions and at shows. The apparatus which Father Paulin christened Vegetation Section t The Forgotten Pollution with the complicated name of geomagnetifere, and which is shown in Figure 1.8.5, is in fact nothing other than a simple multiple lightning conductor supported by a wooden pole connected to the ground by a complex network of metallic wires. The results obtained mean tha t it looks as if we are dealing with another form of fertilization. The natural process is as follows: all organic material decays more or less as it lies on the ground or when it is dug into it (leaves, branches, roots, etc.). This is caused by bacteria producing some free nitrogen, N2, but also ammonia, NHJ' This ammonia, however, is not liberated, but transformed into nitrous acid, HN02, and later on into nitric acid HNq. This is also caused by bacteria: the nitrate bacteria which produce the nitrous acid, and the nitrate bacteria which produce the nitric acids. The modification of ammonia to nitric acid is called the nitrification process. The nitric acid and its salts, called nitrates, can be assimilated by the plant. The common natural fertilizer, Chili saltpeter, has the chemical composition NaNq. Now the operation of the geomagnetifere becomes much clearer. As the observation at the Atmospheric Aerosol Observatory at Noce.have made clear, atmospheric conditions are regularly present which induce point discharges and thus nitrogen containing products at the tip of a mast, having a lot in common with the one used by Father Paulin. Similar observations have been made in Scandinavia, where it was found that this was the case for several hundreds of hours per year (Aurela, 1992); results which were confirmed by the observations at the Atmospheric Aerosol Observatory at Noce. The Scandinavian ob ervations showed that at that time there was a marked increase in the gaseous N ~ con tent of the air. As mentioned before, this process cau es a part of the 40 kg of nitrates per hectare observed in the United Kingdom. Nitric acid, HNOJ , particles are also a part of the discharge process, and when they fall onto the soil nearby they will contribute to natural fertilization proces es and will thus stimulate plant growth. So if we 1&1 Chapter t want to increase the beneficial effect that the geomagnetifere has on the yield of a crop, we should have a row of them. However, that suddenly begins to look like hedges, because, as we know, trees do behave like metal points, especially when they have no leaves. So there i an economic argument against the removal of the hedges: they are their own producers of fertilizers, extracting them free from the surrounding air and distributing them onto the nearby fields. Ffgure 1.8.5 The Geomagnetifere of Father Paulin III ...... .... ..",-.- CC.,__ ..... 0": Vegetation Section I The Forgotten Pollution Another point in favour of the hedges, one already mentioned in respect to the geomagnetilhe, is the fact that they will intercept the electrical field lines under low atmospheric conductivity condition, thus protecting the nearby plants from electrical stress. Both effects are illustrated in Figure 1.8.6. So everything concerning electrical stress to vegetation is not so negative as at first sight. It may be assumed that when studied in greater detail, its application can be of help in the fight against increased desertification around the world and the disastrous effects of overfertilization currently observed in Western Europe. • Figure 1.8.6 r----;;;;:---=-------- r---------,---------,--------, Hedges .J:.. o 0 Gas discharges starts in this part, producing nitric oxides in the form of gas and partides Providing a protective dome for field lines ~·v j ".~ ~ "b-~I •.. \\.·= ... Hedges: free fertilizer and crop protection ~Th'.''''';"' . . _~"'" ~:; ~i.:~~:::/ ~::-.;,-'/~-;:~~ similarity with the geomagnetiferere of fatherPaulin // Chapter I Vegetation -- The Forgotten Pollution Section I 1.9. The world of pollen and spores I. 9. 1. Introduction By applying our electric dimension to the world of pollen and spores we obtain results which reveal a surprising and fascinating aspect of nature, making it the most pleasant of my observation . In order to reproduce plants produce pollen and spores, which are often transported through the air. The size of such particles differs between the various species of plants, ranging from·6 to 60/Lm for spores and 10 to 100/Lm for pollen grains. These sizes, however, mean that long distance dispersion of pollen and spores is quite unlikely, because gravity will interfere and cause them to fall back to the earth, as shown in the table below for different particle sizes. assuming unit density. III particle diameter (pm) settling velocity (cm/s) settling height per minute (m) settling height per hour (m) settling height per day (m) 6 0.196 0.117 7 168 10 0.305 0.183 11 263 20 1.21 0.72 43 1036 40 4.82 2.89 173 4164 60 10.3 6.18 370 8899 100 24.8 14.88 893 21427 So almost all spores and pollen should return to the earth within one day even when launched at the top of the exchange layer. One way by which they could arrive at the top of the exchange layer could be participation in the previously described updrift-downdrift cycle. I discussed this possibility at the International Conference Chapter 1 on Aerobiology in Stockholm. It became clear that a pollen-spore trap had to be added to the instrumentation already available at the Atmospheric Aerosol Observatory at Noce and it was the Pasteur Institute of Paris which made thi possible. It organized a specially modified method to determine the number and origin of the species intercepted by the trap, Figure 1.9.1 (Surra, 1991). I. 9.2. Observations The results were viewe"d with great interest. because the trap at the Atmospheric Aerosol Observatory was the only one in the Pasteur pollen detection network that was not installed in or near a large city. The relative closeness of Paris to the observatory (some 100 km in a • srraight line) made the comparison between a large city and an "unpolluted" countryside an interesting item. The results for a period of some 25 weeks are shown in Figure 1.9.2. Although some pollen data could not be obtained from the observatory for a period of about four weeks, due to technical problems, the figure shows that numbers increase considerably at both sites when grasses start to pollinate. One remarkable observation i that at the beginning of the season the amount of pollen in Paris is much higher than in the countryside. This is thought to be caused by the fact that the city temperature tends to be some degrees higher than that of the countryside, making an earlier pollination likely. A second period of almost two months revealed important activity in the countryside, while practically no pollen was observed in Paris, although the dominant wind dIrection at the observatory is often directed towards Paris. This indicates that the frequently made assumption that the countryside should be considered as the generator of the pollen found in the city is not valid in this case. The screening off of the city from the countryside pollen could have been caused by the inversion layer that often covers Paris. Vegetation The Forgotten Pollution Section 1 Figure 1.9,1 Figure 1.9,2 PARIS 2000 ~" ~I ~ ~r., ~,l~, 1: I. ~~ ~ +,I~ T · :~~~ h ~ ~ '" ...!.,. :-1 H :-1 :1 :-. 0:,," ~I" 11- ~. ::.. ~ ~I, .'" .., .- .. ~I';j I I '" " ~ t:~:~~~' '" -"'r-=-- j '--1 '1 '-f- ~ ~ :f'Pl: f-: ~ ··~ :-1 H:-1 H:- < r-- ~'-j~~~~:~' · . l:l:'~ f-: I - -P'~H ~~ ~'--1 ~'- '~" · N '" • , I-- '" 15 20 25 ,. 14 :l. ~ ,:~' :~r:-1 :--1 -' -=- '~~8 ~ ~ ~, ,..:.~ ~ f2>1':-1 ~ ~ :-. '" I~ = 'f-:'~ ·· -' '~, :-.j', ~~, f-'H,rI~ :. <f~ • ::! ~ -¥ ~ ~ 0 ~ 0 ~ ~ ~ '-1 :-1 '-1 rl '- 'P'P'8 Hiro.",,.."." .... , . . . ~'h sl~ ~l~ H '- , ' < < 2~ I! ,! " .• :! ~s 1991 Crass pollen present .1 ~ N '" ~ ~ <C 2000 l~~~~~< ~ rl. ":1 H:1 H:-" -' t-=V' ~~~~:C ~: f- : .. .. ~ I~ li: I - S ; 0 Noce f-- F F' " ~d ~ Correspondance ~ adfesser ~ le a>nteneu pollinique de I'air - Ahobiologie· Institut Pasteur· 28 rue du D' Roux - 75724 Paris cedex , 5 . (1) 45 68 82 29 et 33 Chapter 1 # ~ "'c ~ ~ ~ , C V' ~ r-. :~ ~ ~ ~ ~: :-1 :- .. - "'~p ~:-1 H ~ f-: ~,. "'~ HH~ ~~ . -. "'P ~ H~ f-" ... '~':,:r~ :1 :- . et2- ... ~ '" ~ Week ;-... .! ::i~ ;-- S~ Hi · "8 , ~:(~ ':~ :-.j ~·,..::.. 'Pl:l~ f-: ~ , ~' w 40 ;. ~ "Q 35 I-- N ~ 30 .. .. 0 15 20 25 30 35 40 Week # 1991 ~ - No count due to technical problems Vegetation Section 1 The Forgotten Pollution Another interesting observation was the way the pollen was deposited on the collecting tape inside the pollen trap. In Paris pollen and soot particles are generally intercepted more or less independen tly of each other, as illustrated in plate A of Figure 1.9.3. In colder periods, when a wood fire was used for heating the observatory, the pollen was sometimes found in groups together, partly covered with a black substance thought to be soot from the chimney, see plate B. By comparing the number of pollen grains and the current obtained by measuring the charged aerosols averaged over a day I noticed a clear phase shift between the two signals. This, however, was not the <;3se for the days when point discharge currents were observed, caused by thunderstorm and other related atmo pheric activities. Under such conditions both signals were in phase. So it seems that there is some interdependence between pollen and charged airborne particles. A closer look at this phenomenon is given in Figure 1.9.4, which shows the period of 19-24 June in detail. The same figure Ell Figure 1.9.3 Figure I .9.4 Observations made at the Atmospheric Aerosol Observatory atNoc~ (61) France +200 Vertical potential gradient (V/m) - -200 50 o Pollen (Number per mJI 50 Charged Aerosol Level (pA) o Clado-Sporium Spores (Number per mJI I A. .. '. B A l:i. Chapter 1 Pollen .soot 50 o 19-6-'91 Vegetation The Forgotten Pollution Section I also shows the behaviour of the vertical potential gradient (VPG) or electric field during this period. Indeed, during this period there is a clear interdependence between the number of pollen grains and the quantity of airborne particles. In fact, when there are lots of particles there are almost no pollen grain present. However, when there are many pollen grains then the charged airborne particles are ab ent and simultaneously there is also an important increase in the vertical potential gradient. Such a behaviour of the vertical potential gradient ha also been ebserved during the fog period in the French Vosges and is caused by the reduction in conductivity in the lower part of atmo phere. The installation of an almost stationary layer of fog particles intercepting smaller charged particles insulates the electro phere from the earth's surface, causing it to concentrate its field lines near higher objects and thus raising the potential gradient there. Because the field increase was indeed observed at an extremity (7 m high pole), this indicated that pollen and fog seemed to behave in a very similar way. However pollen grains are far larger than fog droplets, so they need an extra mecha,nism to give them lift. - Figure 1.9.5 + + + '~ J ,1 hI"J,,f,"":' , -,11".,,, ";r 0 0 ,.:L 01 .' ""If ""01Y!,,/J.1tVi / 00 0 0 0 0 0 0 0 1'" .J:.. Negativel y charged aerosol vegetationaJ origin Chapter I Pollen 9 , .. .,@>:i:~. 0 Pollen 0 '9 01 t O",~ 9° 0 0 90 00 0 / 0 pposite movements "'r: ++:-i" @ Electrostatic o 0 o~ I. 9.3. Particle charging Let us look at Figure 1.9.5, which assumes that pollen, neutral and charged particles are released simultaneously up to a certain height. Then the fine airborne particles will continue to follow the flow lines of the air, while the pollen becomes stationary under the influence of gravitation. This is a situation almost identical to that of a filter, where the fibres are replaced by pollen as dust removers. 0 the finer particles will be intercepted, but so also will their electrical charge. Because these fine particles are emitted from the earth they will carry a negative charge and, when intercepted, they will provide the pollen with a charge of such a sign that it will sense a ''';r + Pollen act like fibers of a filter f!) o G . ra"tation ~.. The interce ted negative charges cause the North sea 4" pOlle~'7spores Clouds The sun controls altitude by removing charges with UVlight Vegetation - The Forgotten PoUution Section 1 force drawing it upwards in the direction of the electrosphere. This force will be increased even more, as was discu sed earlier, by the conductivity reduction cau ed by the interception of charge carriers. It is thu this mechanism that allows pollen and pores to remain aloft for a very long time and be transported over very long distances totally incompatible with their weight. But this mechanism of charge increase and field increase can make it po sible for pollen to reach considerable heights, which could interfere with their mission, namely fecundation. Although potentially dangerous, it is the UV part of the solar spectrum that will limit this height, by removing one or more electrons from the pollen grain by photoionization. The grains will become less charged and continue their voyage at a lower and safer level. Now Gregory's (1971) narrative of aircraft pollen and spore sampling, told in the van Leeuwenhoek lecture to the Royal Society of London, becomes clear: One flight took ample between Yorkshire and the Skagerrak, around midday with the wind between south and west in July 1964. The flight first encountered the expec ed day-time Cladosporium and pollen cloud coming off the land; this again, as expected, decreased in concentration oon after leaving the coast. But rather unexpectedly concentrations increased again to a maximum at 400 to 500 km out. Furthermore, in between, at lOO to ZOO km, and again further out still at 400 to 500 km, they found maxima of the moist air spore types, such a Sporobolomcyes and the hyaline ascospores, which had almost certainly been liberated into the air that night. Evidently the aircraft, starting in that day's spore cloud, next flew into the previous night's cloud, on into the previous day' cloud and finally near the Danish coast, into that of its preceding night. Instead of falling into the North Sea, as one would expect some 48 h after their release, these spores and pollen clouds remained aloft due to the very remarkable electrical mechanism described above. - Chapter 1 1.9.4. Pollen as aircIeaner The behaviour of pollen when confronted with other particle has been studied by groups in France and Sweden. This work has made it clear that the urface of the pollen becomes completely modified when transported through a high pollution region, and in such a way that one could consider the pollen as an effective indicator of the state of the atmosphere. Figure 1.9.6 shows the elements observed on the surface of two unpolluted pollen grains and six others, captured near a paper mill (Cerceau-Larrival, et. al. 1991). As can be een, their surface composition has completely changed Figure 1.9.6 III Chemical signature of the surfaces of: Polluted pollen unpolluted pollen (After MT Cerceau et al.. 1991) through their capability to intercept fine airborne particles. But their interception capability is not only limited to these, as is shown in Figure 1.9.7, where we see large silica particles in intimate contact with a Betula Verrncosa pollen grain. All these observations underline the particle interception theory as principal transport mechanism for pollen. This charging, of course, also has its limits under fair weather conditions because, once charged, the pollen will increasingly repel charges of the Vegetation The Forgotten Pollution Section 1 Figure 1.9.7 Intercepted particles on the surface of a Betula Vel71Jcosa pollen (after M.T Cerceau et al.. 1991) o• Chapter 1 • 0t I. 9.5. Pollen sampling A mentioned before, the classic method of pollen and spore sampling is by means of a trap, a device that sucks in air and deposits the particles on a slowly rotating, sticky drum. For the purposes of analysis one desires to collect a great number of grains. A straightforward approach is to suck them over a much greater area. However the results proved in general to be unsatisfactory. Fundamental light has been thrown on this problem by Benninghoff (1982) during a measurement campaign at the South Pole. Here two simple sedimentation pollen traps were used. Each trap could be connected to or disconnected from the earth in a very simple way. From observations it became clear that the deposition of matter in the traps depends on the electric field present and their electrical relationship with the earth. Weight differences between the two collectors could be as high as a factor six. Only during fine weather conditions, with low electric fields, did both traps receive similar amounts of matter. This effect can be simply explained if we see how equipotentiallines are affected when an obstacle like a building is encountered, the so-called exposure factor, Figure 1.9.8. Traps too will have an exposure factor, deviating or concentrating the material transported along these equipotential lines and so influencing their sampling. - Figure 1.9.8 same sign. However, by means of so-called bombardment or field charging, much higher charge level can be obtained. This is often the case with thunderstorm activity and it comes as no surprise that complaints greatly increase at that moment from the ufferers of pulmonary problems when confronted with pollen or spores which carry such a quantity of charge that, upon landing in the respiratory system, electroevaporation occurs and a mist of fine allergenic material is released. .. +100V Trajectories of: o small. mobile charged pollen _large. less mobile pollen Fundamental research into the charge on pollen continues. The experimental set up is shown in Figure 1.9.9. When a charged particle passes the rings, the oscilloscope will produce a pulse indicating the charge level and polarity of the charge on the particle. The separation between the two pulses depends on the aerodynamic diameter of the particle and the pulse obtained at the target, its capacity for charge transfer. Future tests will include charged aerosols in order to understand the ability of pollen to collect surrounding charges and application of cellular structures or mucus to the target in order to see how this reacts to the interception of large charged particles like pollen. Vegetation - Section 1 Figure 1.9.9 Contact free charge measurement (after P.H.W. Vercoulen et aI., 1992) Metal ring ~;;;;;;;;j;;;f;;";'" Metal ring a:;;;:;;;f;;;:;;;;;;;;;:., Metal target - Oscilloscope 1.10. Conclusion This amazing world of pollen and spores brings the chapter on vegetation to an end. It has to be said that Becquerel was entirely right in his 1850 memorandum on the relationship he observed between our planetary biology and electricity. Numerous observations carried out recently have shown this; however, they also proved that 8ecquerel was in fact too modest and that electrical effects are playing such a fundamental role in the biosphere that, if they are left out (as was the case with the DEFORPA program), only a skeleton of reality remains and no coherent action can be taken when our world suffers under the aggres ion of air pollution. It is electrical effects that run like a connecting link through all air pollution effects, giving them an extra dimension and thus revealing the synergy that exists between air pollution and vegetation. If this is the case with vegetation, leading to such farreaching conclusions, what will be the consequences of this 'forgotten' dimension when we apply it to other aspects of life with which we are all confronted daily, namely our habitat and the climate? This is done in the next two chapters of this book. Chapter 1 The Forgotten Pollution -, The habitat" puzzle • • ••• 11.1. Historical It may be assumed that once mankind started to live in close spaces like caves, they increasingly became exposed to airborne particles different in nature than those encountered in the open air. Radioactive gases welling up from the earth mixed with particles emitted from the human bodies and the clothes they were wearing. Another powerful particle generator was the open fire used during darkne s and in cold weather. Pests varying from lice to mice added to proliferate illnesses. It i widely assumed that this unhygienic lifestyle was one of the main reasons why these people died at an early age. For centuries the picture remained almost static, even after the invention of the broom and the duster; however some mysterious facts were observed in the Middle Ages during great epidemics. Their proliferation is assumed to be related in general with rat and a parasite exchange between them and people. However, those persons rich enough to bum candles around them during these period were miraculously spared, indicating a possible connection with airborne particles. It is since the 19th century that things started to change, when Pasteur showed that microorganisms are The habitat puzzle -- Section 1 The Forgotten Pollution not spontaneously generated but that they are transported by the surrounding air. Important changes n lifestyle occurred, the vacuum cleaner was invented, electric lamps were used instead of candles and gas lamps. The open fire started to be replaced by closed stoves or central heating. High voltage screens as used for TV sets and computer, together with ionizers, air cleaners, air conditioners, 020nizers and microwave ovens are the most recent invaders of our habitat. Last but not least we have to mention the increasing number of modem highly static materials that are used a carpets, wall cladding and upholstery and which are found in those spaces where we spend an average of 80 % of our time, our habitat. Although most of these items are promoted as being good for our well being, or at least as inoffensive, this does not mean that this is necessarily so: truth and elastic seem to have something in common in this respect. Another fundamental modification came in the seventies when, under the influence of an a sumed energy crisis, building had to become energy efficient, resulting in increased insulation and reduced ventilation. Complaints of inhabitants about the quality of indoor climate resulted in the invention of a new term 'sick building yndrome' but not much more. Its existence is strongly defended by its sufferers and just as strongly denied by a great number of specialists; but, all polemic aside, a question does arise: is there something wrong with our habitat? Thi is indeed the case when you become infected by streptococcus by merely visiting the administrative part of one of those modern hospitals with highly sophisticated air treatment systems, as happened in my case, or when you take a shower and you get legionnaire's disease. In fact you may ask whether we are back in the cave and, if so, why? It will be clear that if there was a simple answer to this question, the problem would already have been solved a long time ago, so let's see if, once again, a dimension has not been left out, as was the ca e with vegetation. - Chapter 2 Although complex, it is possible to isolate a number of facts, each playing its part in what I like to call our habitat puzzle. Let u take a look at them in the following paragraphs. 11.2. The clean air syndrome 11.2.1. Introduction Well being in our time has become related to a bright, clean, and thus du t-free environment. If you are not convinced, take a look at the TV ads on thi ubject. The invention of the vacuum cleaner ha been hailed as one of the greatest steps in the progress of mankind and its use has become probably one of the most institutionalized rituals of our time How is thi po sible? Probably through this very simple philosophy: Situation Appreciation dust layers unhealthy, unhygienic dusty, smoky atmosphere unhealthy, unhygienic clean air good for health However, this clean air still contains a great number of particles of different nature, most of them too small to be detected by the eye. Although everybody knows that even when certain things are not visible to the eye, like radioactivity, for example, you still have to take account of it. This point of view has not reached the general public when it comes to clean air. There is, however, a mall group of people who are convinced of the hidden danger of these invisible particles and they tend to use almost every air cleaning method to remove these invisible particles and, with them, their anxiety. This group is considered by the majority to be somewhat eccentric. However, as we will The habitat puzzle Section 1 The Forgotten PoUutlon ee, both groups have one thing in common: the clean air syndrome. 11.2.2. The respiratory system Figure 11.2.1 , . r- El •.. Sac . .,L ~•.. lung Trachea 100% C QI 'u ~ c o .., .;;; o Cl. - QI o I 0.01 0.1 Chapter 2 1.0 10 lOO 0.01 I I 0.1 1.0 10 lOO 0.01 Aerodynamic diameter (micrometers) 0.1 1.0 10 lOO From the standpoint of panicle deposition, the human respiratory system can be divided into three regions: - the head region, where the inhaled air is warmed and humidified; - the lung region with its 2<XXl km of capillaries and its gas exchange area of 30 m'; - the tracheobronchial region, a tubular ection interconnecting the head region with the lung region. A great number of particles are present in the 10 <XXl to 20000 litres of air an adult uses each day. A number of these particle will become deposited via different mechanisms. Once deposited in the head and tracheobronchial regions they will be moved upwards to the mouth and the nose by the continuous movement of the cilia found in the mucus lining these regions. This cleaning process is effective and in general these regions are cleared in a matter of a few hour. When particle can also deposit in the lung region then this clearing is almost nonexistent. For insoluble particles it can take several months before they reappear in the head region, while sol uble particles pass through the thin alveolar membrane before entering the bloodstream. The depo ition of the particles is size dependent. This is illustrated in Figure 11.2.1, which schematically shows the fraction of particles that will deposit in the various regions of the respiratory system. From the figure it can be seen that larger visible particles (over 1 tLm) are deposed mainly in the head region and that fine invisible panicles (less than 0.1 tLm) are deposed mainly in the lung region. The amount actually deposited in the tracheobronchial regions is low for most almost all particle sizes. The increased retention of the invisible particles in the lung region has to be seriously considered if we take into account the impossibility of our body to clean this region effectively. The habitat puzzle - Section t The Forgotten Pollution 11.2.3. The coexistence between particles If we produce a great number of invisible particle in a closed room, then after some time we will observe visible particles. How is this po sible? This is caused by a process called coagulation which was described at the beginning of this century by 5moluchov ki. It is the perpetual movement of fine particles through thermal and aerodynamic effects, also called Brownian motion, that causes this effect. When we look at their weight we see that it is so small that t-hey remain airborne for a very long time. An invisible, 0.1 pm diameter, unit density particle will settle less than 10 cm per day. But their perpetual movement causes encounters and once the particles touch, they stick together and form particles which steadily increase in size and visibility. It also makes them less mobile, further increasing their capability to intercept finer particles. However, their settling velocity al 0 increases. A visible, I pm particle descends more than 3 m per 24 h, although the fine particles that go to make it up descend only some centimeters in the same time. This process of coagulation is effectively illustrated by a smouldering cigarette, see Figure 11.2.2. When you look just above the combustion region, you don't see any moke at all. The particles produced are so small that they are completely invisible. However, slightly further away, their size has increased through coagulation to such a level that the blue part of the visible light is efiectively scattered by them, producing a faint blue haze. On top of this region the coagulation causes the particles to become so large and visible that they are able to obscure our vision: cigarette smoke. It will be clear that, due to thermal effects, the coagulation of cigarette smoke is extremely rapid compared with that occurring in our closed room. So what is the fundamental lesson that can be learned from this? Large particles (visible) are effective removers of small (invisible) particles. III Chapter 2 Armed with this information let us take a closer look at the behaviour of the vacuum cleaner. Figure 11.2.2 . . , L <.t.~~.l.",J, L ....• r I'; r§goo~ ~ iijg§ .•~~~:~:~:. coagulation ' ',oe\ « "..e Blue smoke ::lJ":':' Rapid Invisible smoke .,~ _, _at .. 00000 ...... 0 0 0 White smoke I L..:::.JOOOO ';r ~;... Blue smoke partide' \ .. ::" The different partide sizes involved in micrometers: ~.,/ . "e~ ~,~~ ~. InVISible moke. ~ particle .••: L ."- Tarlike substance Invisible .J :•.. I 0.001 I 0.01 Blue I 0.1 White i 1.0 Tbe habitat puzzle Section I The Forgotten Pollution 11.2.4. The vacuum cleaner Figure IU,) schematically shows the principle of the vacuum cleaner. At 1 the particle-laden air is sucked into the mouthpiece and flows through tube 2 and hose 3 to the dust deposition region 4, made of a paper or tissue filter bag. The air movement is caused by a powerful turbine, 5, driven by an electric motor 6. For cooling purposes air is drawn through it and, before reentering the room, it is sometimes filtered by a filter, 7. Vacuum cleaners are considered to efficiently remove large particles, 0 motor power and thus air flow i an important selling argument. But this also ensures that when these particles impact in the dust deposition region, particles will easily disintegrate into maller, invisible particles. These will join the violent airstream, S, that flows through the dust pack, D. Together with the air stream these particles pass through the highly turbulent turbine area, T. When entering the motor, M, the particle passes through a region with a high level of chemically and electrically active species, such as radicals and ions, created in the air by means of the high-temperature arc surrounding collector C. These 'treated' fine particles will leave the vacuum cleaner together with the airstream. Only a limited number of particles will be intercepted by the output filter, F, the cleaning efficiency of which is rarely taken seriously. So the daily cleaning ritual of a vacuum cleaner looks like thi : 1. large visible dust particle are sucked up; 2. impaction with dust pack produces a lot of fine particles; 3. particles are small enough to follow the air stream lines; 4. particles are "treated", thus modified in the motor region; 5. a cloud of invisible particles will fill the room after the cleaning procedure. During daytime and at night: - Chapter 2 6. coagulation will ensure that these particles become increasingly vi ible; 7. the e large particles will settle and form a dust layer; 8. vacuum cleaner is needed to remove the dust; 9. return to 1. Figure 11.2.3 continued on following page L .••: ~~ large visible partide Impacted dust ~ Coarse dust partide breaks up at Y--' Impact dust layer The habitat puzzle Section 1 The Forgotten Pollution So a more appropriate name for the classic vacuum cleaner is "du t recycler". Figure 11.2.3 continued form previous page r-:-----~--~ Fib'Ure 11.2.4 ':11: 6 ~: •.. Electrical arcs on the collector treats the very fine ust partides 11.2.5. The particle-free habitat Let us now take a look what happens if we are able to obtain the ideal of the clean air syndrome people -a particle-free space. Fortunately a lot of work on this subject has been carried out, mainly by the electronics industry. The increasing complexity of integrated circuits has made it necessary that the distance between the different components of which they are composed is so small that even an invisible particle is capable of causing Chapter 2 a short circuit, thus rendering the integrated circuit useless. This meant that in dusty surroundings the productivity of the electronics industry became almost zero. For thi reason special rooms were created in order to minimize the number of dust particles in the air, the so-called clean rooms. In these rooms special ceilings containing very large, high efficiency filters which, in combination with laminar air flow, arc capable of removing a great number of unwanted particles. Their capability to do 0 is expressed in so-called classes. A room of class 1000 according to the Federal Standard 2090 contain less that! 1000 particles with a size of DJ iLm or more per cubic foot (27 litre). This is some 0.37 particles per cubic centimetre, a very low value compared with the number of particles with a similar size found in urban areas, which are often a factor ~ 1000 to 10 000 higher. ~ From the beginning it became clear that the filtering was only a part of the olution to obtaining a genuine clean room. The instruments and equipment used inside proved to be powerful generators of particles; so too were the gases used in the integrated circuit production process. But all this was nothing compared with the large t contamination source, the people working in the clean room. The numerous particles produced by their breath, skin and clothing made it necessary to virtually isolate them from the clean room. This was done by surrounding them with very special suits, covering the hand with gloves and filtering the air exhausted by them before it was relea ed into the clean room. An example of the person-on-the-moon costume the currently in use in these environments is shown in Figure II.Z.4. The limit for the classic clean room under influence of technological need has been pushed by various means down to class 10 or 100. However this is still not good enough for the electronics industry of tomorrow. So the only solution is to remove the people completely from the room and make a closed space in which only equipment and integrated circuits are present. The habitat puule Section 1 The Forgotten Pollution Concerning people and a particle-free space, it will be clear that this is in fact imaginary, because people are a very efficient producer of particles. This mean that the drive for clean air, the clean air syndrome, should be taken with a large grain of salt, otherwise it could easily end up in a clean air phobia. lI.l. Electricity 11.3.1. Introduction III A very fundamental change in the habitat came with the availability of electricity. In particular, the use of the electric lamps fundamentally modified the behaviour of people after sunset. This change can still be felt when you go back to this pre-electric time during a camping vacation using oil or gas lamps as light sources. Other important changes caused by electricity were the use of motors as a substitute for muscular force. A good example is once again the vacuum cleaner. Its capability to be used as a heat source must also be mentioned. Let us take a look at the possible impliqtions for the indoor climate cau ed by the use of electricity. 11.3.2. Distribution Electricity is distributed by means of conductive wires covered by an insulator. As soon as they are connected to the power supply, an electric field is created around those wj.res, which are generally located in the walls and the ceiling. When an electric load in the form of a lamp, motor or heater is connected to the electrical distribution system, a magnetic field is also created around these wires. Both fields used to be screened off in the time that metal tubing was u ed to guide the wires. The modem plastic tubes, on the other hand, allow the electric and magnetic fields to en ter our indoor space. How far this affects the habitat is difficult to say. The amplitude of the electric field in the viciniry of the wires is in the same order of magnitude as that of the earth's electric field. The magnetic field depends on the amount of current flowing through the wires. There is, however, one fundamental difference between these fields and the natural ones, namely the indoor fields vary in direction from 50 to 60 times per econd, while they are almost stationary in nature. The existence of these fields can easily be measured, remember the hum in your gramophone pick-up; that's perhaps how it got its name: it not only picks up music but also electromagnetic interference and it i by this type of electrical pollution that electrical circuits in walling and ceilings are detected. When it comes to the interaction with the inhabitants, the influence of these fields is les clear. Although it is generally assumed that they are harmless, some sufferers of certain troubles claim to be influenced by these electromagnetic fields, which they consider to be electrical smog. Some of them have in tailed special devices capable of removing the high electric field from the distribution system at moments when no electric power is required. Special twisted cables are also available, intended to reduce the magnetic field generated. Data on these effects are often anecdotal and waved aside by non-sufferers as fairy tales. This, however, does not mean that these effects are non-existent and, instead of tea ing, scientists would better employed looking for ways to extract more useful data. This because it is known that certain people and animals are sensitive to electric fields and their variations. This is also the case with magnetic fields. Also, it is known that very feeble fields can be u ed to fundamentally modify the behaviour of substances which are soluble in a liquid, like the transformation of calcite into aragonite in the case of hard water. - Chapter 2 The habitat puzzle Section 1 The Forgotten Pollution But neither can we exclude the possibility that these fields are changing the behaviour of water molecules and/or airborne particles, thus causing an influence in a more indirect way. The best protection, until we really know about the influence of our electricity distribution system, is the return to the pre-war solution of an entirely hielded system. 11.3.3. Lighting The electric Ii~ht bulp In spite of its simple appearance, it took quite a while before the electric light bulb as we know it now was created more than a century ago. What was remarkable was that its light was very similar to the yellow-white light prod uced by the gas powered lamps used on a large scale, thus simplifying economic comparison. Both lamps proved to be inefficient in terms of power consumption, and they produced a lot of heat, but it was probably the fact that the gas powered lamp affected the habitat with their combustion products, while the electric lamp did not, due to the fact that its filament was housed in a hermetically closed glass envelope, which finally, after years of struggle, meant that, latter finally became the winner. Figure Il.3.1 shows the three different types of lamps generally found in our indoor environment. The breakthrough came with the invention of fluorescent lamps. Here the ga inside the tube produces a bluish light which extends into the ultraviolet, making the lamp unacceptable for indoor purpo es. However, by coating the inside of the tube with a fluorescent powder, the wavelength of the light emitted by the gas discharge can be converted into one acceptable for lightning. Depending on the type of coating, lamps can be made producing light ranging from the yellow produced by the early light bulbs to the striking white produced by the sun. The glass used for'"the tubes of these lamps effectively filters out the ultraviolet light produced in the Figure 11.3.1 The Edison type light bulb The fluorescent lamp Fluorescent li~htnin~ It has een known for a long time that low-pressure, gasfilled tubes are able to produce light when an adequate voltage is applied to the electrodes inside the tube. However, the colour of the light depends upon the type of gas used. Neon, for example, produces an orange-red glow which makes it very attractive for publicity purposes but less useful as source of indoor lightning. Chapter 2 The Edison packed halogen lamp The Halogen lamp The habitat puzzle The Forgotten Pollution Seccion t di charge. Recent arguments, like its high efficiency in transforming electrical energy into light and its long life, have not been powerful enough to cause it to replace the classic light bulb. One of the main handicaps is the fact that the fluorescent lamp needs a complex system to start and maintain the light emission. This not only adds extra cost but also weight, making its application les flexible than the light bulb. On the other hand, the light bulb has experienced a remarkable renaissance in recent times, as we shall ee. The haloeen lamp . Even during the conception of the electric light bulb it became clear that if the voltage to the lamp was increased, the light became brighter and whiter and thus better suited for general purpo es. However, the life of the glowing filament decreased drastically under these circumstances, although the materials used for it were capable of withstanding the very high temperatures involved. The reason for this short life behaviour was the sputtering of the filament, causing its diameter to decrease and thus leading to the failure of the lamp. Quite recently it has been shown that when halogens like iodine are added to the atmosphere urrounding the filament, this sputtering process can be halted. This type of lamp is called a halogen lamp. In order to produce this effect it is necessary that the filament temperature is high enough that the whole ultraviolet spectrum ranging from UVA, UVB to UVC, is emitted by these lamps. As is well known, UVB emis ion is harmful to the skin and eyes and an unprotected halogen lamp not too far away from your night table would give you a nice dose, one you would normally expect from a brief holiday in the mountains. The effects ofUVC, which is even more energetic than UVB, on health are little known because this radiation normally does not arrive at the earth's surface. - Chapter 2 This emission can be easily observed by using the schematic shown in Figure 11.3.2, which shows a simple but effective UVC detector. When pointed towards an unprotected halogen lamp the detector circuit produces a high signal level. What is the influence of such a powerful ultraviolet light source on the habitat, apart from the already mentioned health hazards? The answer is that the energy of the emitted light is such that neutral airborne particles are likely to become ionized. This is photoionization, a process in which an electron is removed, leaving the remaining particle with a positive charge. Thi process is in fact quite similar to what happens during combustion. Here too a great number of mainly positive particles are produced. So from this point of view the new born halogen lamp looks much like the predecessor of the light bulb, namely the gas lamp. ..... It continues to do 0 even if a protective glass screen _ is placed in front of the halogen lamp in order to cut UV emissions. This becau e the high level of dissipation makes it necessary that a flow of air passes the envelope, so the dust contained in this air will still become ionized. Only the very recent way of packaging these halogen lamps, by adding a hermetic secondary envelope, has ensured that they become compatible with their ancestors when it come to indoor climate. 11.3.4. Some remarks on comfort Evaporation I Condensation If we want to understand the influence which different mode of heating have on our habitat, then we should have some understanding of the behaviour of water molecules, among other things. Let us return to the end of the 18th century when it became clear that the space charge surrounding the lower part of the earth's atmosphere was predominantly positive. It was Volta who explained this phenomenon as The habitat puzzle Section I The Forgotten Pollution Figure 11.3.2 Unprotected halogens: your personal hole in the ozone layer effect .··s········· .....".'".. : Sun ~ Halogen lamp : Light spot = 1.0 Pulse output when looking into the sun Output when looking into a 20 W Halogen I~~I Pulse output when looking at the reflection of a halogen lamp Sensitivity of R. 1490 tube Vb + The more light flashes the higher the concentration of LNC 350V Vb 0.5 0.1 being caused by the evaporation of the water in the oceans, releasing positively charged water vapour and so leaving the earth negative. This opinion was lost in the beginning of the 20th century when the positive space charge was attributed to the photoionization of the airborne particles in the lower atmosphere. It was R. Miihleisen who, in 1958, brought back the old evaporation theory by means of a simple test, the results of which are shown in Figure 11.3.3. Miihleisen caused condensation at a point in the room in the first pha e of the test. In the second phase this water was evaporated by means of an electric heater. During the test the space charge in the room was mea ured. From the figure it can be seen that under conden ation conditions the space charge in the room is negative, while in case of evaporation it becomes positive. This corresponds very well with the ideas of Volta, but has other consequences, too. For example, our body is sensitive to the sign of this space charge. In case of a negative sign you get a fre h feeling under warm conditions, while in winter it gives you that chilled-tothe-bone impression, even if the temperature is not that low. On the other hand, a positive space charge gives you a warm feeling and even eau e excessive transpiration, as is often the case when wearing shirts or socks made of certain synthetic fibres. The effect is also caused by a certain brand of underwear keeping you 'warmer' than ordinary underwear due to the po itive charge it obtains through tribo-electricity. So when it comes to the appreciation of the indoor climate, the sign of the space charge is of great importance. Radiometric forces I 200 LN - C Dangerous wavelength LN - 8 causing burns and skin cancer. Unshielded halogen lamps produce it 400 LN - A tans your skin without danger Visible light When a temperature gradient is established in air, then the airborne dust particles that form a natural part of the air experience a force in the direction of decreasing temperature. This force is a radiometric one, called thermophoresis. It i , for example, the reason behind the Chapter 2 The habitat puzzle Section 1 The Forgotten Pollution Figure 11.3.3 Charging of condensation nuclei during artificial moistening and drying (after R. MOhleisen, 1958) Fresh Moistening by air evaporation in a dosed room + 1000 5 .~ :;; "- 0 E." .E "- ~ '" c " .~ Drying by electric rndiator "-g'" '" 15 M 1) El I I I I + selective deposition of large quantities of dust on the cold walls close to hot radiators. Another radiometric force of interest is the so-called Stefan flow, which was ob erved for the fir t time more than 100 years ago. Particles in the air en e this force, which is caused by evaporating or condensing surfaces. The Stefan flow is directed away from the evaporating surface and towards the condensation surface. So when we combine this radiometric force with the previous described observations we get the following table: Condensation point in a room 0 -g :;;'" E .D Evaporation point in a room Space charge: negative sign Space charge : positive sign Physiological impression : fresh/cold Physiological impression : warm Particle flow from walls towards the condensation point Particles flow away from the evaporation point ::l Z 11.3.5. Electrical heating -1000 85 21 22 24 Time (hour) 80 75 +17 +15 Temperature +12 Chapter 2 Electrical heating comes to us in a great variety of forms, of which the following main groups can be distinguished. direct heating of the air This is done in general by open, electrically-heated wires or tubes. The air flow is either induced through convection or by means of a fan. indirect heating Here the air is heated by means of a substance which, in turn, has been heated by electrically heated wires. examples are oil-filled radiators and stone-filled storage heaters. radiative heating Here the heat source in an open or screened form is intended to produce heat in the form of radiation, instead of the convective way used in the two previous groups. Examples are infrared reflectors and radiative ceilings. The habitat puzzle Section 1 The Forgotten PoUudon Let us now take a closer look at how these variou forms of heating can influence our indoor environment. Wien's displacement law, thus reducing the absorbtion of the heat by water molecules, as stated by the manufacturers of such sy terns. Surfaces, on the other hand, become heated giving a comfortable feeling in spite Direct heatine of the air In general the electrical wires in these devices have temperatures below lOOO°C. Dust particles touching them will be burned pyrolytically. The particles produced in this combustion process will generally be neutral and, if charged, they will carry a small positive charge. In case of the convector rype of heater without a fan, temperature gradients dm be quite considerable and thermophoresis is likely to occur. This will be less likely for the models having a fan. Figure 11.3.4 Continued on following page A Indirect heatine of the air El Here the surfaces coming into contact with the air and the particles it contains are 0 cool that no combustion phenomena take place. On the other hand the temperature i high enough that important temperature gradients can occur and so selective particle deposition will occur through thermophoresis. Wooden • Insulation beams lVIII/ViII/Uti Plaster board Infrared Radiative heatine Here the temperatures involved vary over a wide range, as does their influence on the environment. Three different forms of this kind of heating are shown in Figure 11.3.4. They are: A • Heated ceiling Here heated wires are imbedded in large insulating sheets. Dimensions of 1.20 x 4 meters are currently available. A wooden frame is fixed to the ceiling and is used as support for the heated sheet. The space between the sheet and the ceiling is filled with insulating material, like rockwool or gla sfibre. This new ceiling is covered with plaster plates which reach a maximum temperature of BOoe when the sheets are heated by e1ectriciry. Thi low temperature cau es radiation in the far infrared part of the spectrum, near Bpm according to Hotair B 'r- Oosed radiator , ... Combustion isPOSSi::l ~;..... f·' , Chapter 2 The habitat puzzle Section I The Forgotten Pollution of a relatively low air temperature. From the point of airborne particle behaviour the low temperature gradient of the system reduces thermophoresis. This is also the case when a metal cover is used, also shown in the figure. Then, however, the heat distribution will be less directional. B. Radiator C • Lamp heater Here open wires, metal tube or quartz tubes are heated to a level of the order of 1000 dc. The infrared radiation produced is gathered by a reflector and directed towards the region to be heated. The sensation in that area will be imilar to sunshine in cold urroundings, i.e. the effect on dust particles is similar to the direct heating of the air. Figure 11.3.4 Continued from previous page III c n.3 Photoionization ~~' -+---~, 66 Dust partides neutral Chapter 2 " .. Here air flows through a space between a powerful light bulb and a reflector directing its radiation back into the bulb. The idea i to treat the air by means of intensive radiation. This way of heating is con idered to be different from more well known type of heating, and is surrounded by some mysterious claim. One of them is that it should produce a latent feeling of heat, even though the air temperatures remain quite low. Another is that it is capable of drying wet clothing in the same room with remarkable speed. All this under the condition that the heater is operated continuously in the room. The high temperature of the lamp and the reinforcing effect of the reflector means that it is likely that some photoionization will occur on particles with low ionization potentials. Under such conditions these particles will become positively charged and the heater acts like an evaporation point, creating positive space charges and the impression of heat. This corresponds well with the first claim. Now, if we put wet clothing in the same room we create a condensation point, acting as a humidity generator and producing negative space charges in the air. It will be clear that the positive charges generated by the lamp heater are attracted to them. Charge recombination will be the consequence, liberating water molecule fixed to the ionized nuclei, ensuring that they dissipate quickly throughout the room by Brownian motion, decreasing humidity levels around the condensation point and favouring a faster drying of the cloth. This behaviour confirms the second claim. Halogen lamps of the type having no secondary envelope will behave in a way quite similar to that of the lamp heater, due to their high temperature and their capacity to ionize the atmosphere. The habitat puzzle III The Forgo"en Polludon Section I 11.4. Electrical fields During the combustion praces , water, carbon dioxide and an impres ive number of carbon containing substance are relea ed in either ga eou or particulate form. The ionization process initially creates electrons and po itively charged particles. These particles are almo t immobile compared with the electrons, which rapidly move away from their point of creation. This behaviour means that they, as well as the negative ions formed by them, are ea ily removed by the walls, hearth 11.4.1. Introduction In the section on electriciry we discussed the electromagnetic fields caused by the indoor distribution of electriciry. These alternating fields are in fact quite exceptional when compared with the ones I will discuss in this chapter, which are mainly static. The fir t fields to be discussed are caused by a phenomenon that ha Geen with us ince prehistoric times, namely the open fire. The other two generators of electric fields in the habitat are much more recent. These are the cathode tube used in TV sets, computer screens etc., on one hand, and the highly insulating materials that are used for upholstery, on the other. An attempt will be made to understand the combined effects that these fields can have on our habitat. Figure 11.4.1 Continued on follOWing page II1II Smoldering fire Open fire 11.4.2. Open fire An op n fire fascinates a lot of people and is also related to a certain wellbeing. It is perhaps for this reason that it has survived in this world of continuous 'improvements' of the indoor situation. When you try to light a fire, you understand quite rapidly that this is far from easy and that controlling a fire is something of an art. This is becau e of the heterogeneous character of the combustion involved. Wood, for example, has to become so hot through mutual infrared exchange between two blocks f kindling that it is capable of releasing combustible gase . The amount of oxygen should be not too low, nor too high when it has to form an open flame with combustible gases. So, in fact, the wood itself is not burning. The temperatures involved in the proces are high enough to cause thermal and photoinization in the flames, Figure 11.4.1. Chapter 2 IR IR IR Infra·red (IR) radiation causes high surface temperature , A ;.~.. J> ~~~ @J (~ Combus~ble O~ @) Combustible vapour,; are released IR ((~@) @@JJ I Oxygen level (OJ determines the fire mode V~J The habitat puzzle Section t The Forgotten Pollution Figure 11.4.1 Continued from previous page E 5 E « I o.,#'~ I l - re ./ o / 1 Comb. vapor ./ 6 // Right mixture 2 "" o 6 o 1 3 No flames - too much air 3 Open fire Smouldering fire -~6+l ----_ +It __ - ---- ®"" ) o~L) ·"r r:.+\ ~. .",L No flames - a lack of air 1.+', '···Therm~;;:nization ,++ , 88 ... "r ©~ Particles carry quite an amount of charge ~•.. ...L 8 Through recombination only one in ten canies a charge : .J.. ! and chimney of the fireplace, leaving a predominantly positive charge on the flames. In case of a smouldering fire, the combustion region remains very compact due to a lack of oxygen and the charge separation is far le s than in flaming fires, leaving the particles mainly neutral or slightly positively charged. What happens with this cloud of positive particles in an open fire depends, among other things, on the flow of air involved. Oxygen is needed for combustion, so there has to be a constant flow of air towards the fire. The heated air will leave through the chimney, taking the positively charged particles with it. In case this air circuit i obstructed, the fire will start to smoulder and smoke, releasing these particles into the indoor air. One can detect such a cloud of charged particles by means of classic in truments, like the field mill, because they ... produce an electric field. The behaviour of this field is . . . . illustrated in Figure 11.4.2. Here we see the natural field in a test chamber and the variation of it caused by the combustion of twO different materials. Plate A shows us the action of an open alcohol fire, while B is due to a smouldering paper fire. Although the alcohol fire produces no visible moke, it still emits a great number of invi ible carbon containing particles carrying a predominantly positive charge. On the other hand the particles released by the smouldering fire are close to neutral and hardly influence the natural electric field. However, the application of a high artificial field, gives direction to this particles as indicated by the following text: "It may not be generally know, for instance, that in the process of kippering (smoking) herrings a much more economic use of smoke particles results making them attractive by charging the racks from which the fish are suspend to a high potential," Weinberg (1968). By using a similar process in combination with our open fire the author for quite some time produced deliciously smoked pike and almon, but he stopped when the process caused him to smell well smoked, too, according to comment from his neighbours. Chapter 2 The habitat pIlule Section t The Forgotten Pollution The heat rransfer from an open fire is mainly radiative. The combustion products are carried away by convection. The presence of an imporrant po itive space charge in a room tends to activate the physiological feeling of warmth experienced by its occupants. The order of magnitude of the electric field and the sign of the space charge involved are of the same order as observed in nature on a sunny summer day, where radiative effects are also imporrant. Another reason behind the widespread acceptance of an open fire during a cold winter's day? Figure 11.4.2 Field mill for electrical field ----, (E) observation ~ Smouldering wood fire "~ 1- Electric field (E) Alcohol +200 0-1-1 -----.-----..,------'1---~-----, o 3 Time (minutes) Chapter 2 A fundamental change in our habitat has come with the TV set. The change from black and white to colour and the increasing picture size has meant that the accelerating voltage for the picture tube had to be increased substantially. This is a positive voltage needed to increase the speed of the electrons emitted by the cathode of the tube, which when hitting the face of the tube, produce there a b!ight spot of light. This causes the whole TV screen to normally carry a high positive charge. This charge can easily be observed by bringing your forearm close to the screen, causing the small hairs to move, producing a strange sensation. That this charge also influences particle deposition is also quite obvious: TV screens are generally covered with dust. In order gain a better understanding of the influence of the electric field produced by the TV set, a number of measurements were carried out in different indoor situations. Results obtained in a room heated with a central heating system and those obtained in a room heated by a wood fire will be discussed here. Both rooms contained very little material capable of becoming electrically charged, such as synthetic rugs. The room heated by a central 3 meters +400 11.4.3. The TV set 4 heatin~ Here, of course, the temperature remained very stable during the ten-hour observation period. It has to be mentioned that the room was occupied by non-smokers. The situation of the furniture, as well as the results obtained, are shown in Figure 11.4.3. The electric field measurements were made in the vicinity of the screen, close to the sofas. The measuring height was that of a siting person. Also pre ent were an experimental sensor for charged particle measurement of the electrostatic charged aerosol monitor (ECAM) type as well as a humidity meter. From the figure it i clear that the TV set plays a predominant role in this room. It produces field levels in The habitat puzzle Section I The Forgotten Pollution Figure 11.4.3 Electric field (V/m) +500 &I exces of the values found outdoors in case of fair weather. Once switched off during the period from t= 1.5 h to t = 4.15 h, the electrical field in the room tended to reach the negative values of the outdoor electric field, something that is not uncommon in wintertime. The sharp peak immediately after switch off is caused by polarity inversion, a phenomenon caused by the interruption of the high voltage and the sudden 'visibility'of the negative charge contained in the particles collected by the screen. During a part of the period, namely between t= 1.5 and t=3.15, the room was empty of occupants. UPon their return an increase in charged particles occur which are removed when the TV set is switched on again. The event near t=7 is also interesting, when a small ga -heated hot water boiler, used for washing up, released a cloud of combustion gas _ into the room due to a violent burst of wind. The charged particle sensor noticed this event very clearly; on the other hand the electric field is very little affected by this event, as we can ee. +100 0 - 300 Tv. on Space charge equivalent ECAM(pA) 50 Boiler on Relative humidity (RH%I 50 40 30 I I I I 0 4 5 6 Time (hours) 7 9 10 The room heated with an open wood fire Here the electric field meter was placed on a tripod near the fire at the height of a sitting person. Observations were made in different directions every quarter of an hour. The level of activation of the fire was also noted. A small, working colour TV set was present in the corner of the room. The indoor situation as well as the results obtained are shown in Figure 11.4.4. From the figure it becomes clear that the electric field values in the direction of the open fire were almost independent of its activity. This is, in fact not such a surprise because the whole fireplace is covered with a thick layer of smoke particles, which are capable of retaining their positive charge for quite a while. However, when turning in the direction of the TV set, not only the field becomes related to the activity of the fire, it also changes sign. This is caused by the strong electric field of the TV screen which, with its positive Chapter 2 The habitat puzzle The Forgotten Pollution Section t Figure 11.4.4 Electric field (V/m) • charge, attracts the negatively charges produced in the fire and repels the positive ones. Thi also explain why the electric field values varied so little during the event with the gas heated boiler when a cloud of combustion gas wa released in the room. In that case it was not a continuous flow of negatively charged particles flowing towards the TV screen, but only a burst, the effect of which was reduced by dispersion of the particles caused by the predominantly positive charge throughout the room. An important consequence of this charging effect of the TV set on its surroundings in case of a central heating system is that it behaves as if it were an evaporation point. This causes humidity and neutral particles to drift towards the walls, an example of Stefan flow. This will gradually reduce the humidity in the room, thus increasing electrostatic nuisance. The non-smoker syndrome o - 200 -400 ~t-:::L ~ o I 1 TIme (hours) Chapter 2 Non-smokers complain quite often that they seem to attract cigarette smoke. Smokers regard this as a fairy tale, or else a method to make them stop smoking. However, as usual, things are slightly more complex. Measurements carried out with an ion counter show that cigarette smoke carries a predominantly positive charge. The negative charge are flowing to ground through the hand or the mouth of the smoker. Now let us assume the situation sketched in Figure 11.4.5, where we find a smoker and a non-smoker ide-byside on a sofa before a TV set. The smoker produces a cloud of positive charged particles and, because previous clouds have also charged the smoker's clothes positively, the particle cloud i repelled. Because the TV screen is also charged positively, it also repels the cloud. On the other hand, the non-smoker is not charged, being more or le s neutral. The repelled smoke particles will thus indeed flow in the direction of the non-smoker. In case the non-smoker wears clothing containing polyethylene or rayon fibres, then it is likely that he or she is charged negatively, according to the triboelectric serie , thus The habitat puzzle Section I The Forgotten PoUution Figure 11-4-5 attracting the smoke particles. So the story about the make that follows the non-smoker, and the one that the house and clothing of a non-smoker smell for a long time after the visit of a smoker are in fact well fonded. The gravitational etding of smoke particles means that children, especially, will be affected by this selective deposition. It is inexcusable ignorance of the scientific community that electrical effects are still not taken into account when it comes to the study and claims about the danger of passive or econdary smoking. The apparent situation Non- smoker The real situation Positive charged TV - screen repels the positively charged smoke particles _ _ _ _..... Combustion produces predominantly positively charged particles Positively charged clothing repels positively charged smoke particles Chapter 2 The habitat puzzle Section 1 The Forgotten PoUution 11.4.4. Upholstery T ribQelectricitv As has been mentioned, certain materials can easily become charged when they come into CQntact with each other. This effect is called triboelectricity. The triboelectric series is a list of materials that can obtain charges in this way. If two materials from the series make contact, then the one that is higher up will be charged positively and the one aear the lower end negatively. A quite extensive series is: (posldve) dry air asbestos glass mica hair nylon wool fur lead silk aluminium paper cotton neel amber sealing wax hard rubber nickel brass silver gold sulphur acetate, rayon polyester cellulOid orlon polyurethane polypropylene • PVC silicon tenon (negadve) So it is no wonder that, when walking over a synthetic rug with leather shoes, we can get charged. This means that there is a potential difference between our body and other objects. When the voltage difference remains below a few kilovol ts we are able to touch the objects withQut an electric shock. However, synthetic carpets give average values of 12 kY and under dry conditions you can be charged up to 40 kY. Under these circumstances touching a grounded object can give yQU a nasty shock. Sometimes even a spark can be seen between you and the object. This is very interesting, becau e the length Qf the spark is an indicatiQn of the voltage you carried. To bridge Imm a voltage of about 3 kY is needed, so when you draw a 13 mm spark, you were charged almost to the maximum value. Electronic circuits like computer can be destroyed by such a discharge. But that i not all. By walking on the rug, the latter also becomes charged, but with an opposite sign. And so are the dust particles and the mites found in it. The repulsive force between particles and carpet will help them to suspend them in the air when whirled up by the walking action. Once airborne the particles will also sense a force directed towards your body due to the fact that you carry an opposite triboelectric charge, see Figure 11.4.6. The electrical field strengths involved in this process are such that quite large dust particles will follow the field lines, tending to concentrate Qn pointed objects, like your nose, for example. But synthetic materials are not the only source of high electric fields. An example of real health consequences is that of people with an allergy to cats. Discussions held at the Pasteur Institute of Paris made clear that the particles have been found which are responsible for this allergy. The Qnly thing that remained unclear was why, when someone sensitive entered a room with a cat in it, the allergy was revealed within the next five minutes. The olution tQ this problem is quite simple. The transport of fine particle is often governed by electrical fields. This Chapter 2 The habitat puzzle -- The Forgotten Pollution Section 1 , Figure 11-4-6 ... + -- Specially pointed parts like the nose serves as preferred deposition site El The manager will attract these partides 1 r I Triboelectric , effects between the carpet and the manager .... L .••: Chapter 2 Charges for example: the manager positive and thus the carpet negative, so the dust and the acarids also swirl - up. :J :••. means that such a field should exist between the cat and the visitor. Because this allergy occurs under a great number of circumstances, it is unlikely that the field is caused by the visitor, 0 it should be generated by the cat. And indeed some simple measurements showed that when a cat moves, very high voltages, up to 50 kV, can frequently be observed. Similar measurements done on dogs revealed values more than one order of magnitude lower. So this makes it clear why the ancient Greeks rubbed amber with a cat skin in order to obtain the triboelectric effect. Th" possible scenario is hown in Figure 11.4.7. Particles emitted by the cat will be repelled because they carry the same sign as the cat. They follow the field lines and will tend to concentrate on pointed objects, such as the nose of the entering visitor. So the particles will be depposited there, where they are most effective at inducing the allergy. It now also becomes clear why cats 'see' in the dark. The fact that they can easily become charged means that their hairs move when passing close to an uncharged object. This is caused by the electrostatic attraction of their hairs and the object; a wall for example. You yourself can become a cat by clo ing your eyes while trying to 'see' the position of a TV screen with the back of your hand. In general this work very well because the high electric field generated at the face of the picture tube will make the hairs on your hand move, a sensation that can easily be detected Test room It will be clear from the different examples that the propagation and deposition of particles in an indoor environment is very complex and cannot be predicted in a simple way. In order to better understand the different mechanisms involved, as well as to investigate the influence of apparatus and materials causing high electric fields, a special measuring chamber has been constructed, Figure 11.4.8. Here it is possible to create different electric fields in order to observe the generation, Tbe habitat puzzle The Forgotten Pollution Section 1 Figure 11.4.8 Figure 11.4.7 The controlled condition measuring chamber at the laboratoire d'Aeroactivite I Enlly to I~ eutralizer measurement chamber. Dust cames the same sign as the cat and is thus repelled (example for positive panides) III Air cleaner Fan Opacitometric and nephelometric particle observation + guidl~ Unes of brce the fine panides concentrate on pointed objects like the nose ':r measurement . . Dustproduced Tnboelectnaty chamber. Entry to cloth chamber -=-------.;.. - - -__ , :••. 1JifJ· . .;L .J;-.. Chapter 2 Enlly to Entry to neutralization chamber The habitat puzzle Section 1 The Forgotten Pollution transport and deposition of particle under controlled circumstances. The role of ventilation and that of synthetic materials in the habitat can also be studied in this test chamber. 11.5. Electrostatic air cleaners and ionizers 11.5.1. Introduction In the industrialized world people tend to remain in confined situations such as rooms, cars and trains for between 70% to 90% of their time. Various pollutants are found in the habitat and their concentrations are sometimes unacceptably high. These contaminants have their origin in a great number of sources like, for example: - the presence of humans or animals who produce or transport a great quantity of particles and microorganisms; - cigarttte smoking; - the presence of synthetic materials or chemical substances releasing fibres or dangerous vapours; - lack of maintenance of installations, faults with ventilation and climatization systems (this can cause, for example, the proliferation of microorganisms throughout the system); - the presence of allergens: mites, pollen, viruses coming from outdoor sources and concentrating in the habitat; - radon and its daughter products which are radioactive elements capable of attaching themselves to suspended dust particles and which are a real danger in regions with granite soil. The electrostatic air cleaner has been proposed to remove these pollutants. Another device, technically very similar to it,the ionizer, is promoted in quite another way. Here are some excerpts from a typical folder: "Air is life, why do you feel better in the mountains or at the • Chapter 2 beach! Did you notice tlIat your respiration there is much easier! That you are in a better shape and less ill there! This is due !O tile quality of tlIe air which is rich in negative ions or oxions there. TlJanks !O ionizer Brand A, you are able !O have a high-altitude air treatmellt in your home or in your car. Negative ions are tlIe vitamins of the air, so breathe health, 24 hours per day." Quite a difference in approach, although both pieces of apparatus have quite a lot in common. < 11.5.2. What do they have in common? Both are in fact electrostatic precipitators. This is a method for removing particles from an air stream through the application of a high electric field between two electrodes. The principle was discovered in 1824 but ~ it was at the beginning of the 20th century that Cottrell transformed the idea into an industrial installation, initially used to remove plumes from smokestacks, but now also used in indoor situations. The ba ic configuration of such a system is a sharp electrode, wire or needle on one side and an almost flat one, cylinder or plate on the other side. Now, when a high voltage is applied between the electrodes, the field lines will concentrate on the pointed one and cause a local discharge in the air there. This produces a great number of ions, which are in fact a mixture of the constituents found in the air, like oxygen, nitrogen, argon and carbon. A part of these complex ions will be drawn \owards the other, flat electrode. On their way they mix with the dust particles found in the air, which also become charged and tart to drift in the same direction as the air ions where they will all be deposited on the flat electrode. Figure [1.5.1 hows the principles of the electrostatic air cleaner. As can be seen, both the pointed and the flat electrodes are contained inside the air cleaner. [n the case of the ionizer only the pointed electrodes are found R!II The habitat puzzle The Forgotten Pollution Section 1 Figure 11.5.1 "r The air deaner Charging electrode .. •• r; ••1 L· ..J ~ !}..p 0 -f' 'O-DUst ~,/. ' ~,r ':1() -Ions "! 0·······0.. : "'0 Particle ,?Chargin g by ions modify J their traJ.J' ectory 0 Line of force :'0' Dust charging electrode aean~ -- III Dirty~ ':r Trajectory change forces , : ,.. dust to become colieeted on the dust coliecting ';r Taytorcones can produce , :... liquid poliution, (Marijnissen et al. 1993 Q. '::.:.::,=:,-" .......... a.;r:=?r1 LW ..•: Electrical discharges can give dust resuspenslon :J~ in the apparatus; the walls, the ceiling, the upholstery and the habitants of the room in which the ionizer is placed serve as flat electrodes for dust deposition. Electrostatic precipitation is efficient in the removal of certain pollutants such as tobacco smoke. It has also been shown that discharges in air have bactericidal effects. Microorganisms are likely to be killed in the presence of an electrostatic air cleaner or ionizer. However, research on this has shown that this effect was less related to the pre ence of the ions than to the production of chemically active but electrically neutral pecie also generated oy the electrical discharge. One of the species formed is nitrogen dioxide (Nq). This gas kills cilia, the microscopic hairs that line the nostrils and the windpipe. These cilia beat backward and forwards, carrying mucus and dust particles out of the body through the nostrils or mouth. It has been shown that concentrations of nitrogen dioxide as low as 4 volumes ofN0 2 to 10 million volumes of air damage the cilia, which get killed when the concentration increases fivefold. Whether it is this aspect of the ga discharge that is also responsible for the death of the bacteria is unknown, but it i clear that it can cause serious problems after some prolonged use with people having pulmonary problem. Gas discharges are capable decomposing certain chemical substances. The reduction in the use of CFCs as propellants for spray cans has meant that other chemicals are now used to do the job. Apart from the hydrocarbon fillings, like propane, other commonly used propellants together with the products they form when decomposed, are listed in the following page. ... : Apart from unwanted gases, air deanelS can also produce poliution Chapter 2 The habitat puzzle The Forgotten Pollution Section 1 Figure 11.5.2 Propellant Decomposition Dimethyl ether Highly dangerous; keep in closed container away From heat and open flames Methylene chioride Dangerous when decomposed; emission of phosgene· Ethyl acetate Highly dangerous; forms phosgene·, reacts with water and steam to give toxic and "':r The ionizer Undesirable gas emissions , :••. take place when the points are dusty or corroded I 1 not~'" jm~:Jk: ,~ - Only when the dust has disappeared are i ~, .. ~ IIiII ions produced in the air under condition that, ..' "':r i Ions are produced and dust , :•.• get charged (-) o = Ions O=Gas ~... Chapter 2 The protective grid has .. • Phosgene is a highly toxic gas, used in chemical warfare. So these ozone layer friendly spray cans are less friendly to their direct surroundings when used in the vicinity of equipment producing electrical discharges. A clear warning on this subject, permanently attached to the equipment, seems a necessity, especially because they are often promoted for use in areas where many odours are produced, like hairdressers. Most of the producers of air cleaners and ionizers claim that their equipment produces only very small amounts of irritant gases like nitrogen dioxide or ozone. However, the precipitation of dust on and the wear of the electrodes means that their shape varies with time and so does the amount of unwanted gas. It will be clear that the use of this type of equipment in badly ventilated spaces should be avoided and that periodical or, even better, permanent monitoring of the performances of such apparatus is necessary. See also Figure 11.5.2. The positive thing both items of apparatus have in common is the rapid reduction of air pollutants like cigarette smoke, as illustrated for an air cleaner in Figure 11.5.3 "':r In contrast to the air deaner. dust is deposited 011 the walls, upholstery, etc. The habitat puzzle The Forgotten Pollution Section 1 11.5.3. What is the difference? Figure 11.5.3 0.5 Typical behaviour of an electrostatic air cleaner, after Panol ... The main characteristic of electrostatic air cleaners and ionizers are listed below: ionizer electrostatic air cleaner Typical decrease without air deaner electric field outside the unit electric field inside the unit .: negative ions are emitted positive or negative ions are used for precipitation 0.1 Air cleaner on I 1.0 Time in hours dust particles are internally deposited dust is deposited outside the unit on walls, upholstery, ete. efficiency changes with properties and thickness of dust layer ions charge surface causing selective dust deposition oppositely charged ions can be produced through reverse ionization ion production will reduce with time when protective grids become conductive particle emission is possible through Taylor cone effect negative ions are good for your health and give you mountain fresh air???? So the real. fundamental difference is the health claim. When we look into the references often cited in the literature promoting ionizers we generally find few scientifically reliable author, related to the following subject; Author P. Lenard (1892) ]. Elster and H. Geitel (1900) A.P. Kreuger (born J 902 - died J 985) Chapter 2 Subject to be promoted That negative ions are produced by waterfalls That these ions are dominant in the mountains Researcher and promoter of the beneficial effects of negative ions on health. The habitat puzzle ... ~ Section 1 The Forgotten Pollution Because the health effects are very difficult to judge and need specialized knowledge, we concentrate on the claim concerning physics. The work of the Nobel prize winner Lenard makes it clear tha t, indeed, a negative space charge is formed by splashing water, under the condition that it is very pure. Ordinary tap water did not produce these negative ions. But whel: it comes to the article of Elster and Geitel, then it becomes clear that they are incorrectly cited and that in the mountains there are far more positive than negative ions pre ent. T,his often causes important positive field values, a can be seen from the table shown below, from data recently obtained in the French alps. III Altitude Field (V/m) Remarks Date 1600 +350 18 July 1993 1200 +400 same 900 +250 same in the vicinity of a small waterfall same 900 +40/-80 2350 + 1040 25 July 1993 2200 +1100 same 2200 -100 1600 +800 close to a waterfall same same Now, when we look into the technical side of the work of Kreuger we find: "Electrostatic, ultraviolet and thermionic generators are capable of producing high densities of gaseous ions initially but they tend to undergo a rapid deterioration of the output. Furthermore, ozone, a very undesirable pollutant, is almo t always a byproduct of high voltage and ultraviolet generators." So he condemns the generation system used in almost all ionizers and he prefer ions produced by means of radioactive sources. Chapter 2 o it must be said that when we investigate the physics on which modern ionizers are based, then we find that the claims made for them are far from solid. How far this is al 0 the case with the health effect is difficult to say. However, the claim on the fre hness of the air is quite simple. For almo t a century it has been known that negative ions are very effcctivc condensation points for water m lecule. 0 an ionizer creates a multitude of fine condcnsation points for water m lecules, in turn creating a multitude of fine droplets in the surrounding air, giving the physiolo&ical impres ion of fre hness. It will al 0 reduce electro tatic effects which can be harmful to one's health. A very interesting approach to this and other fundamental que tion come from Ma-Liang (1992) who indicates the nece iry of the pre ence of a great number of free electrons on the earth' surface to sustain life on this planet. Concerning the promotors of the negative ion idea, it is neces ary to point out that although electrons and negative ion have the ame electrical sign, this does not imply that their action are imilar: probably far from it. 11.6. Health effects 11.6.1. Introduction Quite a number of health effects have been discu sed in the previou paragraphs. In general these effects were een to be negative and a con equence of ituations in which not enough attention has been paid to the real nature of airborne panicles in the indoor environment. However, health is al 0 affected by outdoor effects capable of penetrating the habitat in a variery of way. The combined effects of natural and man-made pollution on our health are terrible, cau ing more than one person in ten to have severe pulmonary problems in Western Europe. It i only with a better knowledge of the behaviour of the particles involved that thi ituation can be improved, but it will be a difficult, uphill truggle. The habitat pw:z1e Section t The Forgotten Polludon 11.6.2. Air conditioning and climate control The outdoor climate has an influence on the indoor situation. This is illustrated by the observations carried out in a car with a completely closed ventilation system where, in spite of thi , a space charge sensor of the electrostatic charged aerosol moniror (ECAM) type was capable of following the level of outdoor pollution, on a trip from France to the Netherlands, as shown in Figure 11.6.1. In modern cities a great number of people live in buildings where the influence of the outdoor climate on the habitat is controlled through climate control. However the re ults are often far from ati factory. At a recen t congress devoted to aerobiology, it was the representative of the French Ministry of Health who told the participants that the objective of climate control, namely an equilibrated and healthy habitat, was still far out of reach, even after the fifty years that the technology has existed in France. Figure Il.6.2 shows a rypical air treatment unit used for climate control. As we can see, it contains a great number of processes, such as filtering, humidification, and heating or cooling of the air. Apparently an ideal system, in other words. However, measurements carried out on quite a number of these installations, and especially the humidifier section, produced less ideal results. In fact, as soon as the humidity passes 60% relative, the number of bacteria and moulds increased dramatically (Perdrix , 1993), and so did the possibility of their proliferation through the building. So from an aerobiological point of view, 60% RH should be the limit. However, to combat electro tatic effects it would be favourable if humidity could be higher. The danger of water as a source of microbiological contamination has been shown by the death of a number of people from legionaire's disease. This is caused by a bacterium, Legionella pneunwphila, which is often present in great numbers in water supplies of badly maintained cooling towers, such as are often used in combination with air conditioning units. These Cbapter 2 Figure 11.6.1 Influence of outdoor pollution on the indoor dimate of a dosed car in a highly industrialized area in Western Europe 15 ocE! 25 I o 35 45 I I Space charge equivalent (pAl Damville Vemon 100 200 III Highway_ 300 Lille 400 Gent Antwerp 500 ~ Also called: 'Randstad' -Rotterdam -Delft -Den Haag -Amsterdam -Haanem -Alkmaar 600 700 Kilometers The habitat puzzle The Forgotten Pollution Section 1 Figure 11.6.2 Principle of a climate control unit III Ventilator Recycled air out Chapter 2 bacteria escape from the tower along with the water vapour. By acting as condensation nuclei, they keep a protective water layer around them. This allows them to cover a large area and can cause severe health problems at a distance, especially when they are able to enter the ventilation systems of buildings. Another weak point of air conditioning installations, of course, is the 'fresh' air intake. As we have seen in the chapter on vegetation, during certain easons a great quantity of biologically active material can be released during certain moments of the day. Tests carried out to understand the nature of these emissions showed that thi material could not be filtered, either by standard or electrostatic means. So this means that such material will also enter the air conditioning system and contaminate it. The pollution entering a building in this way will cause complaints from its inhabitants for quite a while. The best way to deal with this problem is to install a sensing system capable of regulating the fresh air intake, shutting it down when the level ofbiocontamination becomes too high. The reasons behind the penetrative capabilities of this material are still unclear. The best scenario is that fine droplets containing the material, probably in the form of polymeric chains, is emitted by the vegetation, see Figure 11.6.3. The filters of the air conditioning unit intercept them. However, the liquid envelope will leak away to the fibre of the filter and the biomaterial will again become a condensation nucleus, once it is airborne again. When passing the humidifier of the climate control system, it will once again become a droplet. One is tempted to call such ah aerosol a 'ghost-aerosol' because its size varies from molecular to fine droplets. The source of this biological material is not necessarily the vegetation itself. It is possible that it has been transported by pollen. These sponge-like charged particles contain a fluid which is thought to be able to escape through electro-spraying before the pollen itself is intetcepted by the filtering system. The habitat puzzle Section t The Forgotten Pollution Another possibility that has been proposed recently is that when pollen become deposited on a wet surface, its uptake of water is such that it bursts. This causes the release of biomaterial, which is often highly allergenic, into the water of the surface and these allergens will have the chance to become airborne again once the water has been evaporated. Discussion at the Pasteur Institute on this subject has made it clear that the allergenic properties of the material can remain, even under these wet circumstances, for quite a long time (Peltre, 1992). • Figure 11.6.3 Continued from previous page 'rL "': Figure 11.6.3 Continued on following page "r . , Biological ...... particle with a bio nucleius I . .:L Lotsofwater~ "'r -.ID .J However water envelope seeps away. the bio nude re- suspend and pass through the filters C"fjf( .... , " . " ... +'.' ....... ... '.' ° 0 In case of pollen: Electrical charge produces an e1ectrospray of allergens :'" 6@'"" ~ //11\\\ @ In the humidifier the nudei again become bio particles and ~ contaminate the system and. . . "': habitat :'" I I ' .~ ..-..'::.. Pollen lands on humid surface increasing volume until it breaks open and releases the allergens ••• Recirculation: catching a cold ':r "Fresh" air intake of c1imatizer 'b". re $~ I Ibr Recycled ~ I Large b,o particle Intercepted by "':~ Chapter 2 the filter • ~ •• Another very important point is the fact that filtration of the recirculated air in the air conditioning system will mainly remove the larger particles. This means that fine particles will be intercepted to a lesser degree and will spread freely through this paradise of virtually clean air. Filters are incapable of removing them here because they are neither intercepted through impaction nor by Brownian movement. These particles follow the streamlines around the filter fibres and can so proliferate almost everywhere. Particles like viruses and certain The habitat puzzle III Section 1 The Forgotten PoUution microorganisms have sizes that atisfy these criteria for non-interception. This means, for example, that very serious problems are often encountered in quite a number of hospitals, namely the uncontrolled spread of disease. Figures in thi case are staggering: you have a one in five chance of getting another illness than the one you were admirred with in quite a number of Western European hospitals. The situation looks very similar [Q that concerning the emission of aerosols, spores and pollen when the vegetation is active. These particles are efficient interceptors of•viruses and other microbiological particles which effect our health. In wintertime, when the vegetation becomes inactive and thus the intercepting particles are removed from the air, then the way i free for viruses of all kinds. The fact that you get a cold during win tertime has nothing to do with the temperature, but everything to do with the absence of large intercepting particles of vegetational origin. All these remarks make it clear that good air conditioning, which i in fact an imitation of what happens in our atrno phere at low altitude, is highly complex and needs quite a lot of basic research. The need f\lr such research will increase, driven by the increa ingly complex indoor situation. If air conditioning is to do its job effectively a never-ending number of puzzles have to be solved continuously. 11.6.3. Equipment The ionizer Thi apparatus has been discussed in a previous section. The claimed health effects are difficult [Q verify, probably due to the interfering activity of unwanted gas products caused by the ion generating discharge. The capacity for creating dangerous products through decomposition of harmless airborne products found or used in the habitat al 0 has to be mentioned. On the other hand, the ionizer will remove pollutants like microorganisms and tobacco Chapter 2 moke from the air. A reduction of certain electric fields, like that of TV screens, can also be expected. Its capability to act as a condensation point for water vapour is also interesting because it will reduce triboelectric effects. The bactericidal effect of such equipment, together with their particle removal capability, is used nowadays in the food industry for the removal of airborne bacteria. However, once again, the lack of basic research here is also frightening. In any case, it has [Q be said that there are a number of positive. aspects related to this type of equipment, as well as some negative one. When an ionizer is used thi can cause an important change in its environment, with possible influences on its habitants, so clear information on this point should be issued. Also the variation in efficiency of the unit should be monitored and a timer or other form of control be added so that the . . . . ionizer functions only when it is really efficient. Ill!'-- Figure 11.6.4 It will be clear that when one wishes to treat effects cau ed by air pollution, such a pulmonary problems, the inhaling of medicaments seems a logical approach. A very simple form of such an inhaler is shown in FigureIl.6.4 Here, warm water is used to vaporize certain aromatic substances which have beneficial effects on certain respiratory problems. A quite similar, but more sophisticated method, is hown in Figure [1.6.5. Here a small aquarium pump is u ed [Q produce Emission of aromatic vapour bubbles in the water, which is not necessarily warm in order not to harm the medicament mixed with it or floating on its surface. Similar to the effect of bursting sea water bubbles, which introduce salt and iodine into the air by a jet effect, here it is the medicament caught in the droplets ejected by the jet that becomes airborne and ready for inhalation. [n circumstances where such a stationary, slightly complex but reliable approach is impossible, for example T i The habitat puzzle Sectlon t The Forgotten Pollution Figure 11.6.5 Figure 11.6.7 Figure 11.6.8 Air sucked into the mouth Medicament in liquid form n.'Y °° •• • "'r ; ,:.. Air buble method Drug floating on or dissolved In qUite cold water \ 0 Jet of droplets °0a/With drug 0 •• @ ~ . .!L Figure 11.6.6 Propellant Liquid containing the drug Chapter 2 --H"-" 11 Mounting bubble "Jrsting bubble .J:.. in ca e of an asthma attack, then a portable version in the form of an aerosol spray can is commonly used. The principle of this method is shown in Figure 11.6.6. The medicament is contained in a liquid, which is compressed by a propellant, often CFC or nitrogen. When the valve is activated, a mixture of propellant, solvent and medicament is ejected from the spray nozzle, forming fine droplets which become deposited in the respiratory tract. It will be clear that a complex mixture of components i inhaled under such circumstances. This limits the inhaler's use, either because the medicaments cannot be mixed, or because the mixture has adverse effects on the respiratory tract. Furthermore, the droplet size is difficult to I:--t- +-'\-'flurbulent flow Control electrode 00 ·-·:0 Fresh air Counter electrode Very fine and uniform partides [Tayior cone) - Air input Discharge elctrode III control. An interesting approach to overcoming this problem is the dry powder inhaler, the principle of which is shown in Figure 11.6.7. The pulverized medicine is contained in a small hopper near the centre of the disk. Now, by turning the bottom, a fixed amount is removed from it and deposed into a small hole. When the patient ucks air through the inhaler, this air will be made turbulent, thus resuspending the powder from the hole, which will thus enter the pulmonary system. It will be clear that this method resolve some of the problems encountered with the aerosol inhaler. A very interesting future approach to the problem is the use of the so called Taylor cone spray, Figure !I.6.8. Here the medicament is mixed with a liquid and kept in a container with a fine tube as output. Now when a high voltage is applied between the container and one or more electrodes, the drops leaving it change shape and become cone-like. Numerous droplets are formed at the tip of the cone, with almost uniform size. The electrode system removes the electric charges carried by the droplets, which thus become available for inhalation. However, by The habitat puzzle Section 1 The Forgotten Pollution retaining a mall charge on the droplets, it is possible to influence their behaviour and one may expect that by doing so elective lung deposition can be accomplished. But it is not only medicaments that are beneficial in the ca e of pulmonary problems. Oxygen, too, plays an important role. In the inhaler shown in Figure 11.6.9, air is pumped through a bottle containing Terebenthine. This action produces a mi t of fine particles, which will become charged with oxygen. A second step modifies the T erebenthine in such a way that it starts to act as a medicament. At that precise moment we obtain a double action, namely that of a medicament and the capability to transport oxygen into tho e regions of the pulmonary system which have been virtually deprived of it for various reasons. Here, too, electric charges could be used to improve selective pulmonary deposition. So the technology of treating health problems by means of inhalers is progre sing well, fortunately, because an ever-increasing number of people are coming to depend on it. For severe cases one could even consider the release of medicaments into the air when the circumstances caused by outdoor or indoor pollution makej; it necessary to do so. However this is only possible if we have a far berrer knowledge then today of natural and manmade outdoor pollutants, and the influence our habitat has on their behaviour. And there will be also an urgent need for far more sophisticated air activity detection systems than those available today. lID 11.6.4. Charged particles and health Here we have to define what i meant by 'charged particles' in this context. On an atomic scale we find the ions: gas molecules lacking an electron (thus carrying positive charge) or having an electron in excess (thus being negatively charged). eutral water molecules have what is called an electric dipole and are attracted towards the gas ion and end up covering it. Positive ions Chapter 2 Figure 11.6.9 :oo. Increased.r-& ~. surface / • • improves • Partid oxygen • O. e ~ attachment - Air -+ I . .:L Therebentine OUpwelling drop Pollution analyzer .. ... .A"'111 -. • • ~ Active Active aerosol treatment apparatus Holiste (1993) Electrode ~~ ..: .. .. "':r ctive aerosol out Aerosol ~:: ::.: :.~.: .. 1 Terpene 'oo. ~-" Ultrafine active aerosol particles I !L. Mollinger 1992) can reach the I wwest parts of the lung liliiii Electrode '.': fO' The habitat puzzle Section 1 The Forgotten Pollution thus form clusters of a few water molecules. Depending on the humidity, negative ions are capable of binding 40 to 80 water molecules. In other words, in atmospheric air pure gas ions are more the exception than the rule. Fine airborne particles are also often charged, either by nature, or by picking up gas ions. For instance, combustion smoke is generally charged positively upon origination; on the other hand, particles emitted by vegetation often initially carry a negative charge. A comparison between these different charged particles is shown in Figure 11.6.16. The difference in health aspects between the two categories of charged particles is probably due to their electric mobility, which means in fact the speed they can attain in an electric field. This depends first of all on the size of the particle: the smaller particles, such as gas ions, have higher mobility. However, a small particle is limited when it comes to the number of charges it can carry. So a large particle, which normally has a low mobility, can become far more mobile than a small particle, when it is capable of intercepting a great number of charges. So everything here i relative. But in general, fine airborne particles also carry a limited number of charges and their size is gigantic compared with that of a gas ion, which means that their mobility is very low and that they can be considered to be stationary compared with a gas ion. What happens now if we inhale charged particles? In the case of ions the presence of high humidity levels in the pulmonary system will ensure that they are covered with a coating of water molecules. When these particles reach the cells in the lungs, a high electric field is created betwe~n the particle and the cell wall. This forces the cell [Q mobilize electrical charges of opposite sign, the socalled mirror image. The electric charge between particle and cell could become so high that, upon landing, a spark could occur between the two, with possible damage to the cell. However charge building takes time and it is likely that the high mobility of gas ions means that they will land before this happens. The presence of water Chapter 2 Figure 11.6.10 Ionizing energy ~ ~~~ 0 Gas ~ ..... (negative) ~ The electron molecule Neutral gas molecule 0 ;; .....~ A negative ion (±) Positive Ion ~~o ~ \ (t/ Positive ion in the atmosphere Size comparison ' ...,.,.', 1;L The gas ion the size of a fly The fine airbome particle, the size of aT· Rex ." • • " 0 = Gas ions 1>" to .. 1> Although the dinosaur prefers other things than flies, they land on him And so do the gas ions with the particle, giving it an electric charge The habitat puzzle Section 1 The Forgotten Pollution clusters probably also diminishes the risk of cell damage by screening off the electric charge, which is a point in favour of negative ions, which form far bigger clusters at high humidity than positive ones. Once present, the water behaves like a transporter for the charges, bringing them into intimate contact with the cell wall. In case of charged airborne particles the tory is quite different. First of all it should be stated that, in spite of their low mobility, test! have shown that their retention in the lungs increases considerably due to electrostatic effects. Let us now take a look at a type of charged particle we all know, namely cigarette smoke. The particle often carries a positive charge. Fortunately for the smoker, its size is of the order of 0.3 J.Lm, meaning that there should be relatively low deposition in the lungs. This is because its size is too large to impact by the random movement, also called Brownian motion of the particle. Such Brownian motion produces important deposition in the case of very fine particles. See also Figure 11.6.11. On the other hand, the smoke particle is small enough to follow the streamlines of the air in the 1ung, so preventing deposition through interception and impaction. So most of the moke that goes in should also come out of the smoker, were it not for the fact that the particles are charged by the fire of the cigarette. As has been mentioned, the mobility of these particles is low, so before deposition they hover over the cell, which is forced to produce a mirror image charge. The water molecules attracted by the charge carried are too few to entirely cover the surface of the charged particles, thus implying a lack of protective covering. Thus, when the embedded charge of the particle is directed towards the cell wall, a violent recombination process between the two charges can take place. Such a process is known under the name of electropuncture and is used in genetic engineering for the transfer of foreign material into cells. . If the charge is embedded on a part of the particle directed away from the cell wall, then the mirror charge Chapter 2 Figure 11.6.11 Continued on following page ··:r., ~ .:L ,. ~:J:.. Smoke is a real T·Rex partide; not only covered with positive chcuges but also with nicotine and lAB. The tobacco rod and cigarette filter take away some of thAe partides. The airways should act as an inefficient filter for partides of this size 50 almost evel)1hing inhaled shouid come out. buL... "':r + ,:.. .... /~ ~ -++ III /" /' .J:.. .,L .:L The efectro charge induces a mirror image in the eeD. increasing deposition High electric fields during landing can cause e1ectro poration of the cell bringing TAR in. will remain, so influencing the functioning of the ionic channels used for the metabolism of the cell. Let us now take a clo er look at the nature of a smoke particle. It is formed from fine carbon particles and covered with a tar-like liquid containing over 3000 substances. However, it is probably not this component that makes the cigarette smoke particle so harmful. Also present in the tar are a group of compounds called polycyclic aromatic hydrocarbons (PAHs). As their name indicates, these have a cyclic molecular structure and therefore look very similar to a human hormone. So when, either through electropuncture or modified metabolism, these components slip into the cell, then The habitat puzzle Section 1 The Forgotten PoUution Figure 11.6.11 Figure 11.6.12 Continued from previous page "or- '" ~ :;! ., '0 .s ~... Or retained charges changes cell metabolism JAR contains polycyclic aromatic hydrocarbonsl'AH's '" .J B- Cell receptor molecule C = Natural honnone molecule P&fi are structurally similar to natural :E u , •. .."E : .:.< o hormone '" .s ... lID "0r- .~ .~, <=> M M o !!! n; &, Vi § ~o •• Receptor ...-fAI:I attaches to cell DNA. the complex manipulates bio switches producing a cascade of sometimes fatal cellular changes they will act as a false honnone in the cellular multiplication cycle. That this can lead to cell mutation and eventual lung cancer should come as no surprise. It has to be mentioned, that from an electric point of view, a great difference has been observed between variou brands of cigarettes. Figure 11.6.12 shows us the equivalent charge released by cigarettes from the brands G and P, smoked on a machine constructed similarly to the one proposed in the international standard ISO 3308. From the figure it is clear that the shorter the cigarette Chapter 2 . c ..... '0 ~ ;; ill :; '0 ~ Iii o "E 1:: '"::>0"Iii M > c .2 .E ~ . c E c"- ·s"- '6 c "c c i-g~-5-5 ~~ ·S g-~1l~ ~~~~ -5~;~ ~~~~ .~ -~ -g ~ ~ .FJ3~ 1 ... <=> <=> <=> g<=> <=> <=> <=> The habitat puzzle Section 1 The Forgotten Pollution gets, the higher its electrical output becomes. This indicates that the tobacco rod serves as an effective filter,the efficiency of which diminishes as the rod become shorter and shorter. A remarkable ob ervation during these tests was that another brand, M, could not be measured in a similar way because the electrical output was so high that the equipment saturated. From the foregoing it will be clear that it would be very interesting to reinvestigate these results in order to see if they are correct, to understand the reason behind them, and the probable difference on health of this brand which, when characterized by its amounts of tar and nicotine, is very similar to the two others shown in the figure. These observations were also ent to the French office of a major American television network in order to support them in a lawsuit initiated by brand M in response to the claim by the network that their cigarettes were 'spiked' with nicotine in order to force addiction of the smoker. The same data were sent to a major American newspaper in order to supply additional information for the Congressional hearing that later on took place on this important subject (Hilts, 1994). A highly simplified calculation, based on measured particle charge levels and electrostatic lung retention, show that, even at one pack per day, the internal ioni:ation cau ed by smoking easily surpasses the safety limits set for people working in and near nuclear plants. The recommendation in the article by Roos (1989), is that not only tar and nicotine should be indicated on the cigarette packs but also the estimated energy dissipated in the lungs by ionization, through the smoking of for example one pack of cigarettes per day. Although the smoke particle discussed here is a highly complex one, it clearly shows that inhalation of electrically charged particles can have numerous consequence and that great care should be taken with their use in a therapeutic mode. 11.7. Conclusion From this chapter it will be clear that the situation concerning pollution in our habitat is less rosy and simplistic than is generally thought. In fact, there is a growing feeling that a skeletal finger is tapping one on the shoulder, causing one to turn around. That is very good because with the pollution of our habitat we are in a pit and, instead of continuing to dig in order to get out, we hould look around. Then we would be able to see that extra but 'forgotten' dimension we need to make our habitat worth living in. Chapter 2 The habitat puzzle The Forgotten PoUudon • •• • •• • ••• The atmosphere is not what it is popularly believed to be ••••• •• •• • • 111.1. Introduction The study of atmo pheric e1eccricil:)', as a science, ha been involved with the eleccrical behaviour of the lower acrnosphere for over two centuries. In particular, phenomena like the influence of fair weather on the sign and strength of the earth's electric field and the behaviour of thunderstorms were studied in depth. However, the electrical behaviour of the acrnosphere when confronted with different pollutants, like pollen, spores, fog, combustion products, etc., was ofren left aside as being too complex. So when, in the sixties, the scientific communiI:)' became interested in the effects of pollutants in the lower atmosphere, the acrnospheric electricians failed to come up with useful contributions. This, of course, drastically reduced the interest in their subject, so funding dried up The atmosphere is not what it is popularly believed to be Section 1 The Forgotten PoUution to a great extent, making the study of atmospheric electricity a dinosaur subject. The hole in the scientific market was rapidly filled by people who considered the lower atmosphere to be an enormous chemical reactor where gases are stirred by winds and activated by the ultraviolet fraction of the sun's light. Such people are called atmospheric chemists. The problem with this approach is that, even with a few ga eou compounds involved, the possible reaction pattern becomes highly complex, and when one includes all po sibilities offered by the atmosphere, then the concept became unmallageable. So drastic simplifications are needed in order to keep things more or less comprehensible. Thus the following aspects of our lower atmosphere are in general omitted or treated in an oversimplified way: - airborne particle; - atmospheric electricity; - role of vegetation. The sources of atmospheric pollution in this concept are mainly of human origin, such as cars, factories, CFCs from spray cans, etc., thus leaving out the main polluter, namely nature. Another problem with atmo pheric chemi~try is that the processes involved are so rapid and that quantities involved are so minute that almost no analysis is possible, even with modem instruments. Thus the reality of the atmospheric chemistry concept is: - an overly complex situation; - a lack of fundamental data. In order to remain in the race, the atmospheric chemists assume that this chaotic situation can be managed by using compu ters, and a Cartesian way of operating them by me3.9s of models, the validity of which should be updated regularly. However, the discrepancy between this concept and that of Descartes is that the latter proposed it for fur less complex situations with an abundance of historic data. However, what is even worse is the idea that this way of thinking could even be used to forecast the future climate of our planet. Chapter] Climate variations occur regularly, even without a significant modification of the atmosphere by man. A striking example is given by the Norwegians who, several centuries after the beginning of our era, found an island in the Atlantic Ocean covered with ice, which they called Iceland. Some hundred years later the climate had become so much milder that, when they discovered another island far more to the north, near the North pole, the island's vegetational aspects meant that they called it land of green, or Greenland. Anyhow, in spite of these scientific speculations and the doom they predict for our atmosphere, it is very likely that this simplistic view of the atmosphere is itself doomed, as was the case with atmospheric electricity a generation before. A really multidisciplinary, unbiased approach including disciplines like atmospheric electricity, atmospheric chemistry, biology, meteorology, geology, etc., is necessary to obtain a better understanding of what really happens in our atmosphere. But that this is a Utopian aim wa illustrated by the Dutch. Launching an ambitious national programme on climate change, the occasion was used by Marijnis en (1994) to present a modest multidiciplinary programme to investigate the consequences of the forgotten pollution in the projected framework. Quite a number of internationally renowned scientists agreed without hesitation to support the exciting proposal. To the great surprise of Marijnissen, the programme wa rejected without any comment. In a 'sub rosa' meeting, the decision was later justified by a representative of the main opposing institution, itself of course participating in this sumptuous exercise, in that his proposal was "an insulated one", obvious incapable of interfering with the insular state of mind reigning in the etherlands concerning this important subject. But change i in the air and it will be interesting to see how long this bastion of institutionalism can cope with discontented murmuring of its clients, the Dutch people. Data gathering, too, has to be changed fundamentally, The atmosphere is not what it is popularly believed to be The Forgotten Pollution Section t with more real observation and fewer computer produced averages and invalidated models. Another prerequisite for escaping the present scientific treadmill is increasing the exchange with the nonscientific observers, who can be found all over the world. Lots of people observe nature, as their ancestors did, and are able to provide useful information to everybody capable of listening to them. Then there is a real job to do for those modellers, squeezing the right information out of such patchy data instead of rejecting it as anecdotal. But a philosophical context is also necessary, to allow as great a participation in this imeortant subject as possible. James Lovelock did it with 'The Gaia Hypothesis' (1990). This book is another attempt to discuss real aspects of our atmosphere, stripped of the trendy dogmas uITounding it at this moment. It will become clear that what is pre ented is in fact only the tip of an iceberg and that indeed additional real study on this ubject is urgently needed. 111.2. Particles in the atmosphere 111.2.1. General Although, even in clean air, almost 1000 particles are present in each cubic centimeter, in general their existence is omitted horn scientific work on the earth's atmosphere. This, however, is strange, because without the e particles our earth's atmo phere would be completely different. An example is the blue sky, which disappears with the particles, to become replaced by a black one as we have seen from the photographs taken from the moon. Another fundamental difference is that rain, fog, snow and hail, cannot exist without the pre ence of these minute airborne particles. So let us take a closer look at the e two phenomena. Chapter 3 111.2.2. Panicles and albedo The optical phenomena in the atmosphere are governed to a great extent by the scattering and absorption oflight by airborne particles. Apart horn the blue sky they are also responsible for effects like coloured sunsets, rainbows, halos, and coronas. Smoke horn a diesel car is black becau e the particles effectively absorb light, while den e rain clouds appear black because, although the cattering of the particles is intense, their great numbers mean that the light gets lost inside the cloud. To return to the blue sky. This effect was studied in the late 1800s by Tyndall and Rayleigh. It became clear that it was caused by very small particles with diameter le s then 0.05 !Lm. These particles effectively scatter light of short wavelength, Le. blue as well as ultraviolet light. This means that these fine particles are of great ~ importance for the chemistry in the atmosphere and that they affect the radiation budget of the earth. The general term used for the later is 'albedo'. Albedo = 1 means that all incoming radiation on the earth is reflected back to the universe, while Albedo = 0 means that all incoming radiation is absorbed by the earth. Albedo e timates are fundamental to the results of the different climate models and thus to the prediction of whether the earth will become colder or warmer in the fu ture. Because it is well known that certain natural and manmade pollutants are able to enter the hee atmosphere, like volcano emissions or jet plane plumes, but also lots of others as we shall see, this means that they influence absorption and reflection and that their omissiop from predictions is a form of oversimplification. BIll 111.2.3. Condensation nuclei It was Coulier and Aitken in the 1880s who found that water condensed around fine airborne particles when the air is saturated with water vapour. This is the prelude to The atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution the formation of raindrops, fog and snowflakes. It should be pointed out that this process does not take place on the larger smoke or dust particles but only on particles imilar to those respon ible for the blue sky. If the nuclei are made of hygroscopic material, like for example the salt emitted by bubbles bursting at the surface of the seas, then this condensation process can rake place at humidities less than 100% relative. The ubiquity of these nuclei in ordinary air is easily demonstrated by cooling the air through adiabatic expansion, which is ackieved when a rapid volume increa e takes place from a ga or vapour. At that moment the temperature drops rapidly and condensation will take place around any condensation nuclei that may be present. Figure IlU.l shows three different examples of this effect. Plate A shows how clouds are formed in the atmosphere as large masses of humid air rise by buoyancy and expand adiabatically with the decrease in pressure due to altitude. Plate B shows the cloud of fine droplets Figure 111.2.1 Plate B Pressure drop - cooling Atmospheric Pressure Figure 111.2.1 Plate A (Q} sunrise ~ Upd~ I Thus condensation around the nudei found f!IIery where in the air. Process is • adiabatic expansion- Hot humid air + nuclei ~\"I&I~~r:~r:~~{;a~: Figure 111.2.1 P1ateC Earth Cold o o '~o"''''-= \ High Pressure Condensation of water around the nudei Chapter 3 Condensation of water around the nudei ~ doud Inhaling in quite cold air Blowout pressure drop produces condensation. again adiabatic expansion The atmosphere is not what it is popularly believed to be Section 1 The Forgotten PoUution formed around the nuclei present in the atmosphere when the internal vapour is rapidly released by opening a champagne bottle. Plate C illustrates the condensation produced by yourself through the adiabatic expansion of the vapour of your breath in a cold climate. It is nor only fine neutral particles, but also ions that are highly effective condensation sites for water vapour. egative ions or negative fine particles, in particular, are among the best we know. But microorgani ms, too, with their complex surface structure, are highly effective in this regard. This easily explains why elderly people in the Normandy area tell you tell that cider should nor be bottled during a foggy period because the contents will often undrinkable through the action of microorganisms present in the fog. Because fog, mist, rain and snow are fundamental ingredients of the earth's atmosphere and their presence greatly affects the radiation balance, this once again underlines the fundamental role airborne particles play in the atmosphere. III 11I.3. Pollution sources 111.3.1. General There are two main sources of atmospheric pollutants, namely manmade or anthropogenic, and nature itself. Although the largest, nature is the source that is studied least. The reason for this is not clear, but one reason could be that nature still is synonymous with wellbeing. That is an over simplification, as everybody knows who gets a prodigious attack of hay fever when going to the countryside during a weekend. So it comes as no surprise that probably the mo t important field of all, i.e. how nature is influenced by manmade pollution and how it reacts to it, thus the question of synergy, is almost untouched by cientific studies. Concerning the magnitude of the problem, the following figures are often found for the different pollution ources: Chapter J Natural sources Tg/y (mill. metric tons/year) ± 65% Soil dust 300 Salt emitted from the sea 150 ± 95% Polymerized vapours from vegetation 140 ± 40% 90 ± 65% Volcanos 75 ± 95% Forest fires 600 ± 50% Particles formed from gases Tg/y (mill. metric tons/year) Manmade sources 50 ± 90% Cars, factories, heating 200 ± 25% Particles formed from gases Photochemically formed particles 50 ± 80% The process by which particles are formed from gases includes, for example, ulphates from H /5 or 50/, nitrates from NO, 0/, etc. In the following paragraphs the discussion on ga emis ions and conversions from a chemical point of view will be as brief as possible because this ubject ha been treated in extenso by atmospheric chemists. The behaviour of vegetation has also been left out to a great extent because a complete chapter of this book has been devoted to thi pollution source. 111.3.2. Forest fires This a very particular type of emission, as we shall see. Recent events have helped to unveil some of the consequences of such large-scale combustion. ear the end of the Cold War, in the 1980s, the number of atomic weapons was so large that in case of a war a great number of explosions over a vast area had to The atmosphere is not what it is popularly believed to be -- Section 1 The Forgotten Pollution be expected. The infrated emissions caused by the explosions would be able to ignite large-scale fires, not only in forest areas but also cities similar to Leipzig in the Second World War. The particles emitted in this process would be able to modify the energy balance of the earth for a long period. Obscuration of the sunlight was thought to be likely, leading to a decrease in surface temperature, the so-called 'nuclear winter' concept. A number of experiments were carried out to verify this theory, amongst others, with large-scale forest fires. However, the reduction of the cold war also entailed a reduction of interest i~ this nuclear winter concept. This, unfortunately, halted research on particle behaviour in the atmosphere. Another, less scientific, large-scale combustion project was the burning for a period of months of a great number of oil wells in Kuwait at the end of the Gulf War. Although not a forest fire (the type of combustion and the duration of the event differed considerably), very useful observations about large-scale combustion could still be obtained from it. The first fact to be discovered was that the cloud of soot particles did not spread out ea ily into the atmosphere, in spite of the constant release of heat from the burning wells. This, however, is easy to understand if we know that combustion processes generally produce positively charged particles. However the elecrrosphere surrounding the earth is also charged positively and will repel the cloud of soot particles back to the earth, flattening it, but mainly preventing vertical distribution. The oot particles are composed of fine carbon particles, whic could serve as condensation nuclei. However their tar-like covering means that they become hydrophobic, which thus reduces this capability. However, laboratory experiments have shown that such tar is affected by ultraviolet light, causing the particles to become hydrophilic with time, so it is likely that this also happened with the particles produced by the burning oil wells. So that when winter arrived in the Middle East, lID numerous conden ation nuclei were available in the humid air, producing unexpected snowfall in Jerusalem and Athens. Snow gathered from the Himalayas howed that it was indeed soot that served as condensation nuclei. The process is schematically illustrated in Figure Hl.3.t. And finally we come to an event concerning real forest fires. At this very moment fires are being used in the Amazon to clear large areas of trees. As we have seen from the Kuwait oil well fires, the effects of this action will remain quite localized. In an article, a leading British Figure 111.3.1 Continued on following page . or I + + + + &. + Oil ~well Desert ElectrIcal situation Thermal M 0smOk0.J partides - I :... Well at fire Chapter J The atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution scientific journal proclaimed: "Puzzle of mystery ozone cloud over Brazil". It turned out that satellite observations revealed that there existed an unexplained increase in atmospheric ozone over the Amazon area where large, scale fires are used for clearing the forest. Now, by taking the particle release into the atmosphere into account, this observation immediately becomes less puzzling. Unlike the burning well situation, in case of the Amazon the fires will last for only a limited time. So that when the thermal buoyancy disappears, the particles produced will drift: back to the earth through gravity, helped by the QPposing electrosphere. An increa ed large particle load near the ground limits the conductivity of the air there, similar to what occurs during fog periods. This apparently insulating layer forces the electric field lines between earth and electrosphere to become more concentrated on objects passing through this layer, i.e. the remaining trees. Under such circumstances, taking into account the impressive height of the trees involved, gaseous discharges near the tops occur, producing ozone and nitric oxides. The situation described here is illustrated in Figure IIU.2. Figure 111.3.2 Figure 111.3.1 III Continued on following page Continued from previous page "'F + ep Electrosphere .~I, + + ep . .:L -:J:'" (Q) .' ','. Amazonian forest 0- : Sun rays ; ~"""""~ ~~ r .' ····::··~···:·····:···::····:A··_··.,·_:_··/·· ··~ ,.,"/\'••••• .: .. ' ... i .J:.. .. ..., ., ., .'.l..: : .: ~.:J Earth So cloud remains quite low and spreads "'r un horizontally I: 11'" C.L~ ray . .. . .... High particle density L.J~ Surface ...:L.:0dificatiOn Molecules break- uP.J:... Hydrophobic becomes hydrophilic; So lots of effective condensation nudei produce snow where it normally never falls Chapter 3 Gravitation + repelling of the electrosphere The atmosphere is not what it is popularly believed to be Section I The Forgotten Pollution So a straightforward and sound explanation for this phenomenon is available; one which is perhaps not much appreciated by those who view the atmosphere more as a religion than a scientific subject. It will be clear that the examples cited above are too limited to give us a good insight into what happens with large-scale combustion at the earth's surface. But they show once again that the processes involved are much more complex than can be as umed on a simplistic point of view. Figure 111.3.2 Continued from previous page ''':11~~~\ \ l +J, ·~r:r./~ , ... Particles . : : . . . . . . . { Low 'ntercept ' . " •• ' , co d et' ions •: ' • • Ill, • "" lay~r u ,ve . .:l. T~ee s~~,~,l ~ .._ _ -.I:.. F'eld lines directed towards st,lI standing tree stumps 'r+\/.1.",/ +++,:. . / : t! L-./ I .' .... _~ "': Chapter 3 Concentration of field lines causes gas discharges and thus ... I OZONE :'" I / ~,~"' ~ America Ozone cloud through forest clearing 111.3.2. Car emissions Cars are easy targets, not only for politicians but also for environmentalists. This combination means that measurements taken to limit the impact caused by their ever-increasing numbers are often less scientifically based then the lobbyists who try to have certain rules imposed on us want to believe. So perhaps it is useful to place a question mark by the proclaimed usefulness of green petrol and catalytic exhau t systems. Let us start with the scientific data, which are not as reliable as one tends to assume. For example, at the start of a recent conference on photochemistry in the atmosphere, the audience was told that the previously published estimates on the emission of nitrogen oxides ~ produced by cars were ten times too high. Quite an important error, one might say, and the question .... automatically arises: are there other emissions that could be held responsible for an overestimate of this magnitude! It is these nitrogen oxides that are held to be responsible for the formation of the grey-brownish domes which often cover our cities, through a so-called gas-toparticle conversion process in which the ultraviolet part of the sunlight plays an important role. The latter is also as umed to be the reason behind the increased levels of atmospheric ozone found in polluted cities. Apart from these gas emissions, cars also produce lead emi sions coming from the lead used in petrol as an additive for the improvement of motor performance. Lead is known to have serious health consequences, because it is a socalled heavy metal, capable of accumulating in the body. Also, the nitrogen oxides have been proved to be not only highly irritant to the airways, but also capable of blocking the cleaning effect of the cilia found in the upper respiratory track. So the simplistic mode of reasoning tells us that car pollution problems can be solved by taking away the lead and reducing the nitrogen oxides. The fairy believed to be capable of doing this is The atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution called catalytic afterburning. Let us see whether this is a reasonable assumption. Figure 111.3.3 Classic car emissions If combustion takes place according to theory, then we should have the following reaction: combustible Chapter 3 Recorder + oxidant = water + carbonic acid However, things are slightly different in reality. As mentioned before, the nitrogen of the air also becomes oxidized in the process, producing a mixture of gases containing NO and NOz' generally referred to as NO.. The parrially oxidized carbon monoxide is also formed in the process. But particles are also formed. Figure II1.3.3 . shows the electrical behaviour of these particles as mea ured at the exhaust of a slowly warming up Citroen ZCV car. The instrument used was an Electrostatic Charged Aero 01 Monitor (ECAM), which is sensitive to both positively and negatively charged particles. In the first phase we see that the signal representing the electrical activity of the exhaust gases has an oscillating character. This is because the water produced by the combustion condenses in the cold exhaust system. This process regularly intercepts all emitted parricles. At the end of the first phase the motor of the car stopped because the exhaust became completely blocked by the water. After removal in phase two we notice a steady increase in the electrical activity of the exhaust gas. This is caused by the increasing temperature of the exhaust system allowing for an increased thermal ionization of the particles. Measurements carried out with a device capable of discriminating between positive and negative particles showed that the main charge carried by the particles was positive, an observation confirmed from the literature. If we now take this car and drive it under normal, fair-weather conditions, what will be the consequences • 200 lOO Motor stops water blocks exhaust / Neutralizer on Aerosol out 200 Recording paper change rjl L!..J lOO Citroen Phase 2 Motor increasingly hot no condensation in exhaust system 201 - 800 Rpm W o I I 7 6 Minutes The atmosphere is not what it is popularly believed to be Section t The Forgonen PoUudon of these observations? Because the electrosphere surrounding the earth has a sign similar to that of the emitted particles, the force exerted on them will be twofold: one is gravity, the other is of electrostatic origin. Both forces are directed towards the earth, meaning that the main part of the particle emission containing lead and the carcinogenic tar components like polycyclic aromatic hydrocarbon (PAH) is deposited in the vicinity of the road. Modem car emission It is important to underline that, with the catalyst, which is part of the modern car exhaust system, we are not dealing with a question of which came first - the chicken or the egg. Because the catalyst is poisoned by lead, then if we want to use it we need lead-free petrol, commonly referred to as green petrol. What is this catalyst, in fact, which is used in series with the car exhaust system? It has been known for a very long time that certain components are capable of reducing the time needed for chemical reaction proces es without themselves being consumed. Such compounds are called catalysts. On of them is platinum, which is capable of acting a an extra combustion source for gases released from classic combustion, thus reducing the level of incompletely burned gases. The temperature at which this can take place i some several hundreds of degrees Celsius instead of temperatures far over a thousand degrees found in ordinary combustion. As mentioned, this catalytic combu tion activity is brought to a halt when fuel containing lead is used. However, in spite of this precaution, the catalytic section of a car will not have infinite life because lead-containing particles from the car driving in front of you will pass through your motor and end up in the catalyzer. But mechanically, too, through vibration, dilatation and shrinkage the active surface of the catalyzer will be affected and there is thus a good po sibility that platinum, which is the active substance, will be released into the environment. And once your car is no longer roadworthy, a good po sibility exists that this platinum will find its way into the environment. Platinum is an extra heavy metal in fact some three times more heavy than the dangero~s lead,' and is thus concentrated in the body. It is also interesting to notice that when it comes to the compatibility of the catalytic exhaust system and the particles produced by the combu tion, an almost complete silence appears to exist in the scientific literature. However, the catalytic effect depends on the surface exposed to the exhaust gases, so when this becomes covered with particle its effect will be reduced. Effective filtering of particles produced in combustion is very d~cult, because the larger particles are in fact composed ot very fine particles which are easily released upon in terception of the original particle. It seems likely that thiS process plays an Important role 111 the reported rapid decrease in efficiency of catalytic exhaust systems. Now, what about the combustion particles released by the sy tem? The improved combu tion will make them maller and less likely to carry an electric charge, helped by th lower temperature of the exhaust system. However, smaller particles are less susceptible to the force of gravity and, with the electric force almost absent, these particles will not be deposited close to the roads but will remain airborne for quite a while. The health effects caused by this behaviour are far from trivial. On one hand the absence of lead makes the particles less harmful, on the other hand the unleaded fuel produces quite an important amount of benzene, a substance bannedlworldwide due to its carcinogenic effects. Adding to this to the direct and indirect release of extra heavy metals from the catalyzer itself, the lack of reliable scientific data gives the impression that we are dealing here more with a trendy politicized makeshift than with a well investigated solution to the serious problem of car emissions, and that it is more a fairy tale than a fairy in which we are assumed to believe. III Chapter 3 The atmosphere is not what it is popularly believed to be : Section 1 The Forgotten Pollution The nitrogen oxide puzzle Numerous studies have been carried out on the influence of cars on the quality of the air in the cities. A very interesting study has been carried out recently in and around the city of Freiburg in Germany. A number of pollutants were observed for quite a period, using passive samplers. The behaviour of nitrogen oxides as a function of time is very interesting. As shown in Figure 111.3.4, the level of this pollutant ilJ,creases in winter because, apart from cars, other combu~tion sources are presen t for heating. However, it is then less clear why this pollutant peaks strongly on days when the temperature is low and condensation of the water vapour in the air is likely to happen. The high humidity and the great numbet of condensation nuclei found in urban ateas lead, under these circumstances, to fog fotmation. Such a layer effectively blocks the conduction near the ground, forcing the field lines between the electrosphete and the earth to concentrate on extremities. These, of course, are numerous in such ah urban area, with churches, high buildings, tree, powerlines, etc. Such concentration causes gaseous discharges, with nitric oxides and ozone as by products. Ozone in such humid surroundings is likely not to survive in its original form for a long time, but nitric oxides do. So, from this point of view, there are no problems with this sudden increase in nitric oxides, which are not a result of combustion but are caused by pollution in general. This effect also gives a plausible explanation of the astonishing reduction in car related nitroge~ oxide emissions announced at the congress mentioned above. lID Similarity Figure 111.3.4 (After B. Kreissl, 1992) 40 20 = Periods where dew condensation becomes point temperature very likely and increased NO, production through gas discharges is likely to occur falls below C and 0 >:; c: '" E '" 1988 1989 1990 !,2. l:' ::> .J:J '0; <t 20 ;.; .: l!! .3 15 10 ~ 'E" f" Cl. Dew point temp. 0 -5 There is quite a striking similarity between what has been described in the paragraph on forest fires and what happens in urban areas. Cars act as continuously burning mini oil wells, with particles confined in height due to 1988 1989 1990 Chapter J The atmosphere is not what it is popularly believed to be - Section t The Forgotten Pollution electrical effects and gravity. The high particle concentration, helped by the presence of humidity, promotes the production of air decomposition products similar to the situation described in the Amazon. This analogy easily explain the pollution effects observed in den e urban situations, without the need for recourse to a number of possible phorochemical reactions, including gas-to-panicle conversion processes. It also makes it clear why you smell ozone on days with a high traffic density in those areas of the city where wall and roofs are covered with sharp points in order to prevent pigeons from landing - here too, all ingredients are present for gaseous discharges on a large scale. It is frightening to see how reducing the pollution caused by the pigeons creates a new pollution in the form of ozone and nitrogen oxides. The ions on their way to the cylinder will collide with the relatively slowly moving dust particles entrained by the gas stream. This means that these particles become charged with the same sign as the ions, causing them to drift in the same direction, namely toward the cylinder wall. When ions come into contact with the wall their electrical neutrality is swiftly restored by the acceptance of a charge of oppo ite sign, thus once again becoming ordinaty gas molecules. When the charged dust particles reach the wall, it takes the intercepted charges some time to leak away, meaning that during this time Figure 111.3.5 The idealized world of electrostatic precipitations Continued on follOWing page 111.3.3. The electrostatic precipitator It was eorterel, in 1905, who constructed the first electrostatic precipitator. This was a device capable of removing particles from a gas flow and it is not urprising that recent attempts have been made to use it in car exhaust systems. The basic device is very simple and consists of a fine metal wire placed in the centre of a conductive cylinder through which the particle laden gas flow. Now, when we apply a high voltage between the wire and the cylinder, field line will concentrate around the wire. In this process ions of both polarities are produced, see Figure 111.3.5. Ion with oppo ite polarity to that of the wire will be attracted by it and neutralized as they fall onto its surface. On the other hand, the ions with the same polarity as the wire will be repelled by it and drift towards the cylinder wall, which starts to attract them. In general the high voltage applied to the wire has a negative polarity, thus producing negative ions, while the cylinder, for practical reason , is connected to the earth. After installation of electrostatic Before (~~ High voltage (negative) applied to wire :L LM-e-ta-l -cyi""',-'lIlder = ground -, •.. ...-... +: wire; - C(_):~-..• :~ + Positive ions Chapter 1 precipitators r M , I I..• _ ~ - Negative ions The atmosphere is not what it is popularly believed to be Seaion 1 The Forgotten Pollution important electrostatic forces exists between the particle and wall, causing a very intimate contact between the two. At that moment, short-range molecular forces will take over, causing the dust particle to remain stuck to the wall even after charge neutralization has taken place. So the particles are removed from the gas and fixed to the wall, making it an almost ideal filter, and indeed when it comes to efficiency, figures near 100% particle removal are often given for such an installation when it comes to the clean up of polluted air as produced by smokestacks, for example. So from the simplistic point Figure 111.3.5 Continued from previous page -) l B ..,L El Dus~~~' , ~Yr~" '. ("If: ~. ~ Even after the charge disappears dust remains stuck Chapter :5 •.. ~ 1;; ." c: ~I / Local pollution When it comes to industrial airborne pollution, it has to be mentioned that for a long time plumes leaving chimneys were related to progress and the domination of mankind over nature. It is in the former East block states that this image has beeFl sustained until quite recently, Figure IlIJ.6. Figure 111.3.6 ... + + Dust + particle (-) - - + (_) Ions charge dust; dust goes to cylinder wall , of view once again we have a miracle that, when used on a large scale, should be able to free our atmosphere from the pollution caused by the industry. · ~ ~ c: J.. , Electrostatic force causes very good contact between particle cylinder and wall ···;r •.. Filter efficiency 95 - 99% .J:.. . .:L ~... Let us now take a closer look at these plumes. We find that, apart from gases, they are in general composed of a great number of particles, ranging from ultrafine to coarse. The latter will fall back to the earth as soon as the thermally induced buoyancy disappears. The fine particles are constantly moving in all directions, due to Brownian motion. This increases their chance of colliding with less mobile particles and adhering to them. Indeed, the finer part of the emission is intercepted by The atmosphere is not what it is popularly believed to be Section 1 The Forgouen PoUution the coarser part, which thus become even heavier, accelerating its sedimentation. If combustion processes are involved in the formation of the plume and the particles are predominantly positively charged, then the repelling field of the earth' e1ectrosphere will reduce the height of the emitted plume. So the interception of smaller particles by larger ones is a really effective way of cleaning up. Did you ever notice the improvement in visibility when airborne particles have been scavenged by a rain shower? However, the concentrated deposition of the airborne pollutants near the emission site can pose serious health problems. First of all there is the direct intake into the lungs. Fortunately, however, our pulmonary system is fitted with an ingenious way to reduce this. Another way of intake is through the food chain, directly by eating vegetables grown under the plume, or indirectly by drinking milk or eating meat from animals grazing in the polluted area. Another problem is the infiltration of the pollutants into the underground water system. At that moment the problem is not restricted to the emission area but affects regions beyond its boundary, affecting drinking water, fish stocks and other elements in the food chain. It is thi form of more or le local pollution that i found on a large cale in the countries which formerly were a part of the East Bloc. .... ~ Long range pollution In the Western world the psychological link between plumes and progress ha in general been lost for almost a generation, and efforts were made to remove these plumes. One popular way to do this is by adding an e1ectro tatic precipitator to the stack, taking away the plume. But is this device indeed doing so? By using an aircraft fitted with equipment capable of measuring charged particles in the air, so-called ion counters, it was established a few years after the end of the Second World War that the smokestacks cleaned by electrostatic Chapter :J precipitators were still emitting kilometer-long plumes, but now invisible to the eye. The reason for this is quite simple, as we will see when we go back to the charging mechanism involved. See also Figure lIU.? The ions drifting from the wire to the cylinder are capable of charging large dust particles quite easily, becau e their low mobility causes them to act as almost stationary targets. The high charge level they are able to acquire in this way means that they will head for the cylinder and become depo ited there. The small particles of the condensation nuclei type have their own fast - Brownian - movement. This makes them a target which is difficult for the ions to hit, so their charge level will be low. On the other hand, it has been shown that it is just these fine particles that have the highest amount of dangerous substances (on a weight basis) when compared with their larger counterparts Friedlander (1993). Besides this, it has been known for almost half a century that gas discharges, such as those taking place around the wire, are themselves powerful fine particle generators. So these fine, low charged particles easily pa s through the precipitator without interception. But fine particles are also formed by other processes like, for example, when larger ones are disintegrated upon impact at the cylinder wall. Unwanted discharges also occur in the dust layer formed, thus creating a dust layer on the wire which will break down in its turn. This process, which is called back ionization, is also a powerful producer of fine particles. Particles of all sizes are emitted in large quantities when the particles collected on the cylinder have to be removed in an electrical or mechanical way. So there are indeed a great number of particles produced in these precipitators. What about the high level of efficiency claimed for these devices? This is easy. Efficiency is defined as: effc~IC:J' weight of particles lmving !he predpiuuor x 100% weight of particles entering !he precipitator The atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution so with an efficiency of 99% this means that only 1% of the incoming weight in particles comes out of this precipitator. However, the relationship between particle size and weight is in principle a cubic one, so, assuming a spherical particle with a diameter of 10 IJ-m, then thi particle has the same weight as 1000 particles of the same matter with a diameter of IIJ-m or over a billion particles of the size of a condensation nucleus. So even with very high efficiency figures, based on particle weight and not on particle numbers, the production of a tremendous quantity of fine particles is still possible. This is well known by the manufacturers of the electrostatic precipitator, who have for years been looking into the possibility of intercepting these fine particles. However thi has not changed their statemenrs about the "fantastic" efficiency of their product. Let us now see what happens with this invisible plume. Because the larger particles have been removed with good efficiency, this means that there is no interception of the finer ones, making it possible for the Figure 111.3.7 - The real world of electrostatic precipitators Continued on following page Figure 111.3.7 Continued from previous page Back to nature .~'. "'->~ ~ Wire, . (-I + + -. "• --:.. (0 ,--...~ , + 10pm Small particles - + easily pass o 0.1 pm But what about that super efficiency: -: .::. - Exchange + la~er + ··0····· ~ ,) -----t;\--------~~~-- + + + r~ LNO ./ -It is based on weightnot on numbersone 10 pm particle has the same weight as 1 000000 particles of 0.1 pm (0'"'\ Solarrays ; : finally ) ..,........ remove ~ the charge . e' ~ CV ! - Earth Air ionization itself produces particles In the process negative. charged particles are drawn into the sky The sedimenting particle is an effective condensation nucleus o It is easier to catch one 10 pm particle than 1 000 000 0.1 pm particles. Besides that they are invisible· so who worries? Chapter] Aircraft can detect these plumes at great distances Pollution pattern dirty factory Pollution pattern clean factory The atmosphere is not what it is popularly believed to be III Section 1 Tbe Forgotten PoUution plume to spread over a much larger area. This, for example, affects the visibility of the lower atmosphere, giving that grey image to far away objects. This concerns the uncharged part of the emission. As mentioned before, the polarity used in precipitators is such that the escaping particles carry a negative charge, meaning that they are actually drawn into the higher parts of the atmosphere. Here they become subjected to air movements far different from those ob erved near the earth's surface. The residence time at high altitude will be long; because of the \"eight of the particles,gravitational settling will be low. Effects like conden ation of water vapour or intense photoionization will be needed to increase the settling of this pollution. Investigations on the effects of these plume started directly after the Second World War. By using a 7 km long wire, IO m above the ground, Vonnegut (1958) produced a negative space charge plume. This caused a clear modification of the rainfall in the downwind direction and at a considerable distance from the plume. However, as is often the case with electrical effects, these are easily forgotten. So it comes as no surprise to read of the observations made by the Environmental Protection Agency (EPA) in the USA where they sampled two types of pollution at the same spot and moment; one with the source in line with the wind direction and the other one at the other side of the continent, see also Figure IIIJ.8. So by cleaning up in this simplistic way we have transformed a local pollution problem into a long range one. The greatest worry concerning the atmosphere over the long term is the possibility that this inadequate method of particle removal is applied on an even larger scale than today, for example using it in the fonner East Bloc countries and newly industrialized areas. At that moment the long range pollution will be generated over almost the whole earth and so become a global problem. As we know, the particles involved are often very dangerous and effective condensation sites, thus Chapter J Figure 111.3.8 Wilson,1993 Modern methods can localize pollution sources. Measurements at M identified source Iwhose pollution was carried by wind at low altitude and the same moment source 11 whose pollution traveled outside the boundary layer' - ","ong cleaning methods turn a local problem in a continental one'After EPA. spreading the pollution everywhere and affecting the albedo of the earth in the interim. It will be clear that the current way of expres ing the efficiency of industrial filters by means of weight is completely inadequate and should be replaced as soon as possible by one that takes account of the number of particles that are released. Such an approach has been in use for years in the case of clean rooms without any problerrts. 111.4. Transport and sinks 111.4.1. General The importance of transport has already been discussed briefly in the paragraph on electrostatic precipitation. It Tbe atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution is only quite recently, since the accident with the nuclear power plant at Chernobyl, that we have got a better insight into the dispersion properties of airborne particles. However, we have to bear in mind that what happened there was not an ordinary fire, where the electrosphere opposes the vertical proliferation of particles, as was discussed in the paragraph on forest fires. The particles emitted from Chernobyl were radioactive, capable of ionizing the air around them and so profoundly modifying the influence of the electrosphere, not only during emission but also during transport. In fact it mdmt that the plume acted as if it consisted of mainly neutral particles. An interesting observation is that a great amount of the emitted and easily traceable material sedimented in the Northern part of Western Europe, a form of selective deposition. But as we will see in this paragraph, this is only one form of selective deposition or sinking of atmospheric pollution. - 111.4.2. Dust Wind effects As we have seen from the list of natural particle sources, it is soil dust that is among the largest contributors. Contrary to the intuitive idea that this then produces a few dunes, it has to be said that the effects of volatile dust are more far-reaching. One of the main sources is the action of wind in arid areas. So what happens here is that dry air rubs a surface, namely that of the earth. This is an action with a lot of similarity to that of rubbing a glass r~d with a cat's skin. In that case both objects become oppositely charged by this action due to a process called triboelectricity. In the list that indicates what sign an object gets when you rub it with another, you will find that on the top of the list is dry air, which easily acquires a positive charge, leaving the material touched by it negatively charged. As we know, the Chapter 3 earth's e1ectrosphere carries a positive charge and the earth a negative one. This means that when a desert wind whirls up soil dust, it will be repelled by the earth and attracted by the e1ectrosphere. The level of charge that can be put upon an object by means of triboelectricity can be very high. The comb with which you combed your hair easily lifts up a hair and, when the air is dry, charges can be so high that a spark occurs between the comb and the hair. The electrostatic force acting on a dust particle is directly related to the number of accumulated charges on the particle. For a negatively charged particles this force is directed upwards and when it equals or surpasses the force of gravity, then the dust particle will float in the air. A cloud of these particles will th us create a negative space charge in the air. However this space charge will . . . . . draw positive charges to the earth's surface under the __ cloud. So when the wind continues to whirl up particles, a positive space charge is created below the cloud and the mixing due to turbulence will make both charges recombine and drift back to the earth through gravitational sedimentation. However, this is not always the case. So-called dust devils in the Sahara and New Mexico clearly behave as electric dipoles with the negative charge on top and the positive one underneath, see Figure 111.4.1. If the negative space charge can escape neutralization, for example by rising very quickly, it is ready for long distance transport because, in the absence of vegetation or other pointed objects, no particle discharge will occur through the action of point discharges. So the only important discharge mechanism is the photoionization by the ulthviolet part of the sunlight. However, this action has only a limited penetration depth in case of a dense cloud. When arriving in less arid areas it is the condensation of water vapour, which will occur preferentially on the negatively charged particles, that will help the sedimentation of the cloud, and it will thus come as no surprise that The atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution large territories of Western Europe are regularly covered by dust particles from the Sahara region which were able to make this long trip only with the help of the interaction between particle charge and the earth's electric field. means that it not only intercepts particles carrying an opposite sign with high efficiency; neutral particles, too, are intercepted effectively because mo t of them behave like an electrical dipole. A similar effect can be observed with the so-called electret filter. This, however, is not the only similarity. Another resemblance is that with the behaviour of airborne pollen, which becomes charged by intercepting the negative charges emitted by the vegetation at the moment of release. This enables the pollen to be transported over long distances, in spite of its weight. The differen.~e between pollen and dust is that Health effects It will be clear that a huge cloud of charged dust floating through the atmosphere acts like an enormous electrostatic vacuum cleaner. The sign of its charge Figure 111.4.1 continued + + + + 011 + Figure 111.4.1 following page continued from previous page + + + + + .....- - :.-:.: ••~ Wind .. • -• A nice day in the desert ./ + + I + --- -- --- ---- ---- - - + + I Tribo electricity A less nice day in the desert. Wind blows up (negative) dust + + ~C!) + + -. - - ~+++\~ Sy movin g upwards positive cha rges are sucked up + l- + .' .:... Such kind of movement is rare! y stable and can end up as a dust devil / I --"- -Y""'" --/ - -+ -- ......... + + + + - - The dust cloud induces opposite charges in the sand Chapter 3 -~ + Charged particles repel each other creatmg a bubble lighter than surrounding air Dust devils are highly effective air c1eanelS, because they are electrostatically active and make them effective as transporter for aerobiological material • Strong ~ Moderate ~ Possible The atmosphere is not what it is popularly believed to be III The Forgotten Pollution Section t Chapter] pollen is biologically active and has a very complex surface structure. Dust particles, on the other hand, are often minerals and act as a more or less inert substrate. Thu , in contrast to pollen, which tends to interact with intercepted biological material like micro-organisms and viruses, thi is not the case with the dust particles, which act more as a transporter. So when a dust cloud intercepts biologically active material and the transport circumstance are not too harsh to kill it, then the biomaterial can spread our over a large area. If the material involved is capable of inducing illness, then this action can cause a widespread epidemic that is difficult both to explain and to stop, because the static electricity involved in the process will ensure that the deposition of such particles is often selective, as we shall see below. This capability of propagating diseases on desert dust has been the subject of recent investigations in the Arizona area, where isolated Indian tribes were affected by an unknown illness during the same time period. Electro tatic resuspension of desert du t as carrier and the biological content of an Iraqi Scud missile as activator i probably the origin of the "unexplained" illness that appeared after some time among American oldiers, even those serving at quite a distance from the impact in Saudi Arabia. However the knowledge available at the scientific centres of the major military powers on aerosol propagation means that this 'unknown'is an understatement. Their action has to be seen as an effort to keep the general public in the dark and label the forgotten.pollution as unknown .50 when we look back a little in history to the massive attack of the German army on Moscow in the Second World War, and the army's inability to reach the city, hampered by mud and the very early snow in which it virtually sank, this in fact comes as no surprise. You cannot inject a great number of condensation nuclei into the aonosphere without serious climatic consequences. Man.made effects 111.4.3. Selective deposition A we have discussed previously, wind is able to release charged particles from the earth's surface. Explosion are also powerful dust emitters, as we shall see. Their effects could be studied recently during the Gulf War, when a tremendous amount of explosive was dropped onto a limited area, known to be very arid for years. For example, lake Aral contained almost only ships lying on their sides on a crusty bottom before the Gulf War. After the massive injection of effective condensation nuclei, Le. the dust cloud produced by the explosions, into the atmo phere things changed rapidly because it started raining. And while, at the beginning of the war, television images were regularly shown of so-called surgical airstrikes against all kinds of targets, at the end of the war the weather had become so bad that aircraft had to remain on the ground. The riddle of the dead crayfish Quite suddenly in the early I960s, there was a marked acidification of the small lakes scattered all over Sweden. This drew a lot of attention, and you may wonder why. This was because in these lakes there were crayfish, a famous delicacy and the pride of the Swedish cuisine. The acidification killed these crayfish and the scientific community was asked to determine who was the villain causing such a national disaster. See Figure III.4.2. These investigations showed that the probable source was located in the German Ruhr area, which is in fact quite trange because this region has been a notorious polluter for over a century, thus also during the time that the crayfish were still alive. However, these results were probably not so wrong as they seemed. At the end of the 1950s an enormous quantity of natural gas was found in The atmosphere is not what it is popularly believed to be • Section I The the province of Groningen in The Netherlands, Le. slightly further north than the Ruhr area. In a few years almost the whole population of the Netherlands, some 15 million, was warmed by this new source of energy and so too were millions of flowers, tomatoes and other vegetables growing in greenhouses. So in a few years a great variety of combustion sources were replaced by a single source type. This change was promoted by the authorities because it was thought to be pollution free. Indeed, if one looks.at the chimneys of natural ga heaters, no smoke is visible, 0 from a simplistic point of view, this is a real clean energy source. However there is smoke involved, although it is not visible to our eyes For~otten Pollution because the particles are very fine indeed. They are mainly formed from carbon, but al 0 contain some sulphur. The reduced size of the particles means that, in contrast to most combustion particles, they carry almost no electrical charge, and behave a if they were neutral. This means that the earth's electric field has no influence on their sedimentation. It was the Chernobyl accident that produced interesting information about the sedimentation under Figure 111.4.2 continued from previous page Figure 111.4.2 III continued on following page The situation Cold water in --::-_~.., Cooling causes condensation intercepting the sulphur At the end of the fifties natural gas was found 111 The Netherlands. Natural gas contains sulphur that can form an acid ,.., Invisible sulphur containing cloud ... ......... ••••••• . (...... ." : .., The Ruhr area was notorious polluted even when crayfish were alive Chapter 3 ., .. :.. , t( .... .Ae'> , . .;:~~ . . ~: , rr . 15 million people. cats. dogs,cows. flowers, vegetables such as tomatoes all are kept warm by the gas in the etherlands The high efficiency central heater removes pollution The atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution the virtual absence of the eanh's electric field. The radioactivity of the emitted particles produces a highly ioni:ed environment, thus increasing the conductivity of the arrnosphere and in this way decreasing the influence of the electrosphere. Because these particles are quite easy to detect when deposited, it became clear that the sedimentation pattern was far from uniform and that selective deposition occurred in the Scandinavian region. So it is not unlikely that the fine, neutral particles generated by the Dutch on a nation-wide scale and carried thermally to a high altitude, deposit in a similar way in the Nonhern E~ropean regions. Their size makes them ideal condensation nuclei when they reenter the lower pans of the arrnosphere. Although the natural gas found in the Netherlands is relatively free of sulphur, the massive use and the selective deposition means that it is very likely that sulphuric acid is formed under the influence of atmospheric chemical reactions, leading to the fate of the Swedish crayfish. This theory gained even more substance when the initial natural gas heaters with a thermal yield of the order of 70% were replaced on a large scale by the high yield types (HY), which with their efficiency of almost 100% produce almost no thermal lift for the emitted panicles. Even more imponant is the fact that this gain in yield comes from the extraction of heat from the flue gases leaving the chimney. This causes them to condense in a similar way as they did previously over Sweden. The liquid produced in this process is so acid that special regulations had to be put into place by the authorities to dispose of it without harmful effects to the environment, and of ourse all parts of the installation coming into contact with it are made of special polymers or stainless steel. If this action ha made it possible for the crayfish to come back and once again play their pan in the Swedish cuisine, then this effect is trivial because in the mean time, the use of this environmentally friendly source of energy has spread over Europe like wildfire, thus creating an acidification source with the size of a continent. So, &I Chapter J for the Swedes, the remaining solution to this environmental aggression will be to develop a taste for surstromming. Oasis and islands Let us assume a plain surface, like a de ert or a sea. The absence of pointed objects means that the venical potential gradients above these surfaces can reach very high values. The reason behind this is the following: when the vertical poteRtial gradient wants to increase for some reason and pointed objects like trees and buildings are present, then the lines of force will become concentrated on them. Now, when their number passes a certain value, then gas discharges occur on those points and ions are produced. Ions carrying a charge of opposite " ' - ' sign to the field that initiated their production will move _ _ upwards and so reduce the value of the vertical potential gradient. This means, for example, that in a coastal region the local venical potential gradient is lower over the land then over the sea. ow, when we have particles like pollen or desen dust which, during their release or transpon, have become charged in such way that they float in the air, then when passing the border between land and sea, these panicles will ense an increased upward force, thus increasing the altitude of the particles. An island will have a reduced vertical potential gradient for the same reasons as that for the land, thus causing the panicle to reduce its altitude by lowering the upwardly directed force. This effect is illustrated in Figure 111.4.3. It will be clear that this effect favours the deposition of particles on sites which penurb a flat surface, like an oasis in the desert or an island in the ocean. This form of selective deposition increase over accidented regions is of course of great imponance for the vegetation, pollination, fertile oil deposition, etc. It helps one to understand why on such an enormous surface like the Pacific Ocean an impressive flora is possible on islands The atmosphere is not what it is popularly believed to be Section 1 Tbe Forgotten PoRation Figure 111.4.4 Figure 111.4.3 Trajectory of charged partides Pollen trap Sea High rising buildings change equipotentiaJ lines and thus the trajectory of pollen .- .- .:"'~ ~'--------------'--' _ _- - r - - Pollen get charged by intercepting negatively charged particles "'r + .f / :~:::::::::7:::::::::::~~. 11h::::::::::"" .,;:. .~.'" Equipotential 0 line .··C·::::::::::::·:::::.:·.:·::.., +,;. Particle line/ \\ \~~._ j:~ . .):l:nd -: '''''~ . . .J:.. Sea Pollen will follow the equipotentiallines which are lower over land - higher over sea Chapter J and again lower over an island CD _ . which normally should have none, if the distribution would have occurred according to probability calculations. On the other hand it will also help to concentrate pollutants when the e are available in the air, so atomic tests in such an area, because of its ability to concentrate pollutants, cause a far greater effect than one might suppose, were one to consider the problem in simplistic terms. Another important consequence of the vertical potential gradient on the trajectory of charged particles is the so-called reduction factor. This happens, for example, in the vicinity of a house, a skyscraper or another obstaclt; which tends to seriously disturb the equipotentiallines. These are imaginary lines connecting the different altitudes where the observed vertical potential gradient has the same value. This effect is illustrated in Figure 1II.4.4, which shows us a building on which a pollen/spore sampler is placed. The concentrationof equipotentiallines just over the building profoundly increases the vertical potential gradient and thus the electric force. So when a Tbe atmosphere is not what it is popularly believed to be Section I The Forgotten Pollution floating charged particle arrives in front of the sampler, this increased force will lift it up, thus severely reducing the possibility that the particle is trapped in the sampler. The reduction factor, in other words, probably underlies the observations that samplers often receive markedly different quantities of particles, even when operated in the same sector. It will be clear that this effect depends on a number of factors like, for example, whether the sampler is connected electrically to the earth or allowed to adapt itself to its electrical environment.This has been clearly illustrated by a number of experiments carried out on this subject in Antarctica by Benninghoff (1985). on higher objects, i.e. mainly trees in the rural areas. This stresses the trees and affects their metabolism. See Figure 111.4.5. Things become even worse when low layer conduction becomes almost nonexistent, for example when the effect is enhanced by ground fog. At that moment the concentration of field lines can become so high that small discharges occur in the air near the tree tips. A result of this action is the production of ozone and nitrogen oxides. A consequence for the tree is that it becomes ubject to the selective deposition of certain Figure 111.4.5 Continued on following page 111.4.4. Visibility, ozone layer, and nitrates By visibility we mean the clarity with which distant objects can be seen. The visibility in the atmosphere depends directly on the pollution and its capacity to affect the light by scattering and extinction. It will be clear that visibility is in general lower in the vicinity of regions with large emi sions, like industrial sites and cities, 'than in rural areas. Apart from some local exceptions it is generally observed that visibility, even in rural areas, has decreased in the Western industrialized world and Grassl (1989) has proposed that the particle weight in Western Europe has doubled in the last 20 years. This is not only an aesthetic problem; it goes much further than that. An increased particle load in the lower part of the atmosphere also means that the ions created through cosmic ays or natural radioactivity become increasingly intercepted by these particles. This means that the ions are recombined and thus neutralized and can no longer take part in the conduction of the lower layer of the atmosphere. A decrease in conduction means that the field lines from the electrosphere have problems in reaching the earth's surface, causing them to concentrate Chapter 3 o c CFC's are assumed to reduce ozone at high altitude + + + OZONEt~ I ..,,;1 / + + + JV C Ozone is produced in gas discharges Gas discharges are intensified by CFC's The atmosphere is not what it is popularly believed to be Section t The Forgotten Pollution airborne pollutants. From laboratory experiments it is known that the moment that these discharges occur can be changed when certain pollutants are added to the air in very small quantities. In case of fluorine-containing substances, like CFCs, these discharges take place at lower voltages. This explains those ob ervations which show that an increase in airborne CFCs in rural areas coincides with an increase of ozone in the air. But if we are to talk about ozone in the case of gas discharges, we also have to discu the presence of nitric oxides which are produced simultaneously. These tend to be transformed , Figure 111.4.5 Continued from previous page ... ------------, Tree tips are covered by fluorine containing products found in CFCs So the recent reduction in CFC's should reduce gas discharges. and nitrates in rural water ways let's see... Nitrates enter waterways Chapter :5 by various processes into nitrates and are, of course, the reason behind the observations made in the United Kingdom for more than a century, which show that one hectare of land, unaffected by fertilizers, still produces some 40 kg of nitrates per year. A consequence of this is that with the sudden reduction of the 1980's of the CFC's used for propellant and other purposes, at the end of the 1980s a reduction of the number of natural gas discharges and, as a consequence, a reduction in the level of nitrates in surface waters, seems to be logical. And it will thus not come as a total surprise that this is indeed the case when we observe the results measured in the small river called the Dive, which flows through our highly rural department, the Orne, see Figure IlI.4.6. Here it can be een that, over 20 years of steady increase of nitrates in the water, ~ coinciding very well with an Increased CFC use, a clear ~ dip occurs when the level of CFCs used diminishes at the end of the 'eightie . So the reduction in the use of CFCs is a good thing from the point of view that it reduces the stre s on the trees, which are in very bad shape in Western Europe. However, it is far less obvious that the CFC sub titutes, which still contain fluorine and which are said to be inoffensive for the ozone layer of the upper atmosphere, are also favourable for its lower part. It is, after all, the conversion of the fluorine-containing gases that is responsible for the reduction of the discharge threshold. Laboratory tests show that electrodes involved in gas discharge processes involving CFCs become covered with fluorine-containing deposits. Similar selectivedeposits have been found on the leaves near the tips of trees. I 111.4.5. Torrential rains It would, of course, be too naive to expect that nature would give no response to the modifications in the lower atmosphere caused by human activity. Of fundamental The atmosphere is not what it is popularly believed to be The Forrotten Pollution Section 1 Figure 111.4.6 M '" ~ co '" ~ "tl 0 .~ -. -. ~o. ~ .2£ G ~.!: 20 .s :: .~~ :lJ . .~~ III o~ III :;ijli) .. E,:,: '" c .. ~o ~ "El . - ::l C"tl .S! ~ "eo ..c:.s- .o~ °E .2:1.5 co <X) ~ gc . . . ~n 00 ::l ~~~ ~~~ E~ is !i] .. ~a ~~~ _u.: 0 0 - .. ..... '" '" ~~-E ~.?:-'" o.~::l .!!! is r; '::z-: N ..... co '" Chapter J co ..,. ;::; co ~ importance is the doubling of me fine particle load in a span of some 20 years and the use of electronegative gases like CFCs on an everincreasing cale. In fact what has happened is that the effect of the CFCs in promoting the formation of electrical discharges in me lower armo phere, thu giving it a better conductiviry has to a great extent obscured the effecrs of me increased particle load which, by conrrast, reduces me conductiviry of me lower armo phere. The only dlcingS to suffer in this process were of course me tree , which had to sUPPOr[ these increasing discharges, and which showed some fatigue, called un cientiflcally 'acid rain'. ow, although ir wa never the purpose, by removing me CFC load from the lower armosphere, we are back in me days of our grandparents, when a thundersrorm could rurn around a hill for hours withour discharging due re a lack of effective di charge points. But once it did discharge, its violence was frightening and ascendent air movemenrs, also called electric wind . swept airborne particles high inro me atmosphere. These particles are effective condensation site for water vapour and when me elecrric field that initiated the discharge wa caused by a laye)" of cold, wet air sliding over a layer of warm air o-called rriboelecrriciry - men me e particles caused rorrential rain in the cold air due ro instantaneous condensation of water vapour around memo owadays, by removing the CFCs from our environment, we are back ro the violent discharges of the time of our grand parents, with the difference that the weight or load of particles has doubled, but because their size has dimini hed their numbers have increased by orders of magni ude due ro our inabiliry to correcdy clean our indu trial emi sion . The number of condensation nuclei determine me number of drops mat can be formed and so the level of rorrential rains caused. So once again me 'forgotten' pollution with irs electrical dimension explains where omer hypothese remain silent. However, once again, a bony finger .... If.lw fON) sal1!.Q 1N The atmosphere Is not what It is popularly believed to be Section I The Forgotten PoUution 111.5. Interesting atmospheric phenomena 111.5.1. Self-sustained electrical storms Vegetation and atmospheric electricity have a very intimate relationship, but in general it is the electricity that provokes a reaction in the vegetation. However, recent observations indicate that, under certain circumstances, it is possible that a real synergy takes place between atmospheric electricity and vegetation, creating an amplified reaction causing storm damage of a magnitude rarely found in the Northern Hemisphere. The following storms were analyzed in this context: III This storm started during daytime in the Bordeaux area and went over the Western and Northern part of France and finished the next day, 9 August 1992, over Belgium and the southern part of the Netherlands. This torm caused substantial damage mainly to trees, through tor iOIl of the trunk and the removal of the crowns. The trail of the storm was remarkably limited, in general some 20 km wide, and it propagated through valleys and clearings. When these circumstances were absent, the storm jumped over that area without great damage and continued its terrible activity where the terrain became accidented again, i.e. a behaviour completely different from a classical storm, where the damage is more on hilltops than in valleys. Although thunderstorms had been active in the area the day before, this storm started in the morning near the city ofVaison la Romaine in the south-east of France on September 22, 1992. It inundated the region, causing a flood that killed 37 people and caused great structural Chapter :I damage. The storm died out at the end of the same day. So the two storms seemed to have little in common. However, because the first one passed over the Atmospheric Aerosol Observatory at oce, it was po sible to observe its electrical signature and correlate it with meteorological and vegetational phenomena. Although part of the electrical observation was unavailable during the second storm, the reaction of the vegetation and the meteorological data made it clear that the underlying mechanism of this storm was the same as the first one, namely: r Synergy between vegetation and amwspheric electricity. In the following part of this section ome typical aspects of this type of storm will be discussed. The rain Meteorologically, both storms started under similar conditions. The temperature had been high for quite a while, when a cold front charged with water vapour from the ocean started to come in. It is well known that under such circumstances cloud electrification occurs through friction between the two air masses with very different characteristics, so-called triboelectricity on a large scale. Thi causes very high potentials, meaning that the observations of the vertical potential gradient at the observatory at oce saturated regularly, well in advance of the storm, see Figure 111.5.1. The same figure shows the point discharges occurring almost one hour before storm 1 reached the observatory. These effects are not limited to the measuring masts with a height of even metersi the surrounding vegetation is also affected by them. The trees respond to this condition in the following ways: - Emis ion of gas ions produced at the tips. The sign of these ions is opposite to the sign of the overhanging space charge which initiates them. - This flux of ions also entrains ordinary air molecules, thus initiating a wind, called the electric wind. The speed The atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution Figure 111.5.1 -Recording saturated +0.5- «' Current through a metal point ~ ~ t:: 11 0 a 11 I1I '1 '-Storm -0.5- 11II -Recording saturated 8 August 1992 -Recording saturated 100 E ~ ~ '0 . ~ ."c: 0 l'l 0 a. Vertical potential gradient "El 't 01 > -1000 -Recording saturated I 18.00 12.00 6.00 24.00 Local ti me (h) I 6.00 12.00 Universal time (h) Chapter 3 I 18.00 of this wind is related to the number of ions and thu the current of the discharge. Even at low current levels wind speeds ranging from breeze to storm are easily obtained. - High electric fields will produce so-called electroevaporation of the sap contained in the leaves. The fine droplets produced in this way will also move upwards, entrained by the electric wind. So in fact we have an almost volcano-like emission of a mixture of air molecules, ions, neutral and charged particles. From a meteorological point of view the cold air cau ing these phenomena should also produce an important drop in air p;essure, because cold air has less volume than warm air. However it is here that we find one of the signatures of this special type of storm: the temperature does indeed drop, almost 10 °C in less than a quarter of an hour, but the barometric pressure ~ increa es quite remarkably, as shown by Figure IlI.5.2 for ~ both storms. From an electrical point of view this is not so curious. The rapid drop in temperature will produce important triboelectric effects and the great number of electrically charged and thus mutually repelling particles . generated by the vegetation in response to it will need a much greater volume than if they were electrically neutr~l. However, this electrostatic pressure increase is so powerful that it can wipe out the expected pressure drop for quite a while, and this is astonishing. Similar to hot air, this electrified air will move upwards. When entering the cold air it will continue to rise, in this way injecting a great number of condensation nuclei into the cold air laden with water vapour. This is a classic situation, capable of producing droplets almost ins tan aneously, and it comes as no surprise that a torrential rain starts. That this rain had less disastrous effects during storm 1 is because the wind of the storm caused it to propagate over a large area, while storm 2 remained virtually in the same place. This made it possible to study intensively the effects of storm 1 on the vegetation, while the floods initiated by storm 2 meant that a lot of useful material was swept The atmospbere is not wbat it is popularly believed to be The Forgotten Pollution Section 1 Figure 111.5.2 Storm 1 start Storm 2 start mBar mBar Pressure ------,>------l1000 ~ , - - - " r - - , - ! - - - - - ' 990 12 18 h(TU) 24 ·C 25 20 15 Temperature III ------::I-\------l1000 · --.---+-,---r---' 995 10 • 9 ·C : h (TU) 25 · ~20 Temperature 15 90 I 12 18 h (TU) 24 Pressure data: Meteo Aleneon Temperature data: Atmospheric Aerosol Observatory - Noel! 7 9 h(TU) 10 Data: Meteo Carpantras TU - universal time away or modified in uch a way that distinction between cause and effects became impossible. The propagation As mentioned, storm 1 propagated through valleys and jumped over flat terrain. Storm 2 turned around in a limited area, being imprisoned by the surrounding mountain tops, remaining all the time in the same valley while in the mean time emptying the clouds laden with water vapour which were coming over. Here too, the electric phenomena helped us to understand certain observations. Returning to the recording of the observatory, Figure 111.5.1, we notice that in the afternoon small discharges occurred at high objects for some time, the vertical potential gradient Chapter 3 showed major variations, indicating an electrical storm in the vicinity. Data obtained from the Meteorage network (Tourte, 1992), showed that this was indeed the case and that it occurred ome 30 km west of the observatory. However, there was an important time lag; it took almost one hour between the electromagnetic observation by Meteorage and the appearance of the discharge current at Noce. How is this delay possible? It is because it took the cloud of electrically charged particles that rime to move from the point o£emission to the point of recording due to the light breeze. A clear indication that thunder torms produce clouds capable of producing discharges far away. The importance of valleys is also illuminated; they tend to concentrate the discharge products, helping to initiate new discharges, and thus thunderstorm activity, as soon as circumstances allow. The generator Figure 111.5.3 schematically shows a valley with a row of trees bordering a brook in the centre. The cloud of chargc;d particles produced by the thunderstorm activity at a distance and transported by the wind will concentrate in the valley. This will initiate gas discharges near the tree tips, followed by a vertical flow of electric wind containing a partly charged mixture of gas and particles. It will take some time before this cloud reaches the cloud that initiated it, which has been drifting away under the infl uence of the wind. So in fact a succession of oppositely charged clouds is created, something I like to call ze~ra charging of the overhanging cloud, which is typical of thunderstorm activity in Western Europe. This causes intercloud discharges and, indeed, during both storms the sky showed constant illumination, to such an extent that the fire brigade of the village of Longny, some 20 kilometres north of the observatory, did not need extra light to do their job in the midle of the night. The fact that the glow was very con tant makes it likely that, apart from light caused by the discharges, The atmosphere is not what it is popularly believed to be Section 1 The Forgotten PoUution other luminous phenomena were also present. A possible candidate is chemilumine cence caused by the reaction between the ozone and the nitrogen oxide. both produced in the discharges. This effect is also called air afterglow. However. even in the time of year when the vegetation activity is at its peak, the production of particles under the influence of the electric field still has it limits, and so has the possibility to obtain charged clouds according to the mechanism under discussion. However, in a valley die number of particles is virtually unlimited, because when used they will be aspirated once again by the electric wind for another cloud charging exercise. This effect should mean that two horizontal, oppositely turning cyclonic gusts flow through the valley. Thi has been confirmed by the position of crops flattened by the storm, as well as by eye witnesses. The reuse of particles as transport mechani m for electrical charges makes the generator of this storm very similar to that of well known very high voltage generating machines, such as have been constructed by Pauthenier Figure 111.5.3 Figure 111.5.3 Continued from previous page Continued on following page But initiating cloud drifted away and an oppositely charged cloud takes its place Typical valley landscape Invisible charged cloud drifts in / + - Wind Lines offorce install on tree Chapter :5 + " This causes a sequence of oppositely charged clouds. These 'zebra' clouds give intercloud discharges. glow in the sky and the typical thunderstorm records .. ~:~J lA Tree produces negatives ions .J,.. The electric wind causes rotation Storm moves as a horizontal double tornado The atmosphere is not what it is popularly believed to be Section t The Forgouen Pollution and van der Graaff. Their principle is shown in Figure 111.5.4. It also explains the remarkable pressure increase of these storms: not only is the mutual repulsion of ions is due to it, the centrifugal force created by the electric wind will also cause a depression inside the turbulence, but an increase in air pressure outside it. Concerning the electrical activity and its analogy with the van der Graaff generator, we notice that an insulated belt is charged electrically by means of a gas discharge. Now. by turning the handle, these charges will be brought upwards and finally reach a large metallic sphere, to which they jump over. This process means that the sphere is capable of collecting an enormous quantity of electrical charge, causing its potential with respect to the ground to rise far in excess of a million volts. Some of the machines of this type are capable of storing energies up to 50 kW. A highly simplified diagram situating these extra acrivated storms amol1~ other atmospheric electric phenomena is shown in Figure III.SA. The destructive character of this type of giant electrical storm came to light in the forest of St Victor de Reno, were thousands of full-grown oaks were destroyed in a Figure 111.5.4 Continued on following page Chargeq cloud " ............................ III ••••••w•••••• . . •••. .: ~( Figure 111.5.4 ~ Simplified diagram situating the different atmospheric electrical discharges \~i t\~ElectriCWind 1 Continued from previous page '. Self sustained electrical storm §l> ::E Ordinary thunderstorm Valley Valley More schematically it starts.. ,,/ C Sphere ·0 //' r'CR Disdiarge ~ I ~ ..,. ...: '~ ,;, I't '1~ .. -- '. ' . Lowpresure -High presure ~~~ ~. - _.' -' ' ...... <V > ~ .: '" ::J i!! ~ « g ~ ""E0- ~ Electrified clouds <: 0 .£''" co';:; ~ :J ~~ <>. 0- ~ . 0 <: Handle ...to look like the Van der Graaf high voltage generator charges from discharge are accumulated on sphere by moving insulated belL Sphere obtains more than 1 000000 volts "0 Z Rotation moves air away allowing for very high discharge current 0 u 0:: Kilo Voltages involved Chapter J The atmosphere is not what it is popularly believed to be Section 1 The Forgotten Pollution quarter of an hour, without the observation of a classic lighting stroke between sky and earth. Although this type of storm is often referred to as a once-in-a- century occurrence, research in journals and the meteorological service, as well as historical data, show that, on the contrary, they in fact occur quite often. It is probably the fact that the width of the territory affected is relatively small, making it go almo t unnoticed outside it, that causes such ill founded remarks. The electrical signals obtained by the Atmospheric Aerosol Observatory show that it is possible to construct early warning systems for this type of event. 111.5.2. Fair weather lightning Literature on lightning generally describes the situation with large overhanging thunderclouds, the setting of classic lightning discharges. Descriptions of ball lightning that is sometimes associated with it are fare more sporadic, and when it comes to fair weather lightning almost all reliable sources are silent. This type of often silen t discharge is also referred to as lightning caused by heat, in French: eclairs de chaleur. It can manifest itself as a faint light near the horizon. Even without clouds a sudden flash appears, quite often with deadly consequences. Observations performed more than one hundred years ago made it clear that such events coincide with the presence of thunderstorms at a great distance. So once again it seems that we are dealing here with t1ie possibility that thunderstorms propagate by means of invisible clouds of space charge. In one of the older books devoted to meteorological phenomena there is a mention of the presence of eclairs de chaleur, which are said to occur over Belgium, caused by thunderstorm activity in the centre of France. A more recent illustration of the exi tence and the danger of this fair weather lightning comes from the high mountain guide, Mr Franc Astore, who describes the Chapter J event to which he and his two colleagues were expo ed on 22 july 1974 on Mont Blanc. It happened during very fine weather, very cold and with no sign of a classic thunderstorm. During the day they observed from the mountain luminou effects all over the Aoste valley, which had a fairytale appearance. Later on, when trying to regain their Vallot refuge, they got tired and decided to take a rest. When sticking their ice axes in the snow they fell unconscious for 2 to 3 hours. When awakening for a while Mr. A tore, although paralysed, saw the light of electrical discharges from various parts of his equipment and heard his colleagu~ at his side complaining as if he were in pain. The third unfortunate member of the party hung uncon cious at the end of a rope which was fixed to the mountain and which showed a glow over its length due to electrical discharges. Later on, in hospital, it was found that he has suffered several holes burned in his back. He never regained the health he had before the event and died some six months later. After a second blackout Mr. A tore regained consciousness the next morning, suffering frozen body parts. Stumbling, he reached the Vallot refuge, where he alerted the rescue services. It is highly probable that this tale concerns a space charge cloud emitted by the distant thunderstorm in the Aoste valley. Buoyancy would cause it to hover over the barren mountain face, see Figure Ill.5.5. The absence of extremities like trees as well as a snow layer means that no major discharge can take place from this cloud. When it encounters the unfortunate party of high mountain guides, the cloud finds discharge paths through the pointe9 ice axes, metal parts and even ropes, which fortunately are bad conductors, saving the hanging guide from direct electrocution. Less fortunate, although also subject to low current discharges, were the three soldiers who in 1838 in the village of Vic sur Ainse heltered from a thunderstorm under a lime tree. Even in death they remained standing, but when touched they fell and turned to ashes. The main The atmosphere is not what it is popularly believed to be Section t The Forgotten Pollution 111.5.3. Aircraft accidents constituent of the human body, as is well known, is water. As we have discussed befate, high electric fields are capable of inducing electroevaporation in tree leaves, which then will become brittle, falling to ashes when touched. Measurements at the Atmospheric Aerosol Observatory have shown that space charges are capable of inducing very high electric fields even under trees, making the strange death of the soldier less puzzling than at first sight. In fact it teaches us useful lessons about the unexpected dangers that can be encountered in relation to thunderstorms. A we have discussed previously, foggy circumstances can produce very high potentials, mainly at trees, inducing discharges in the air. The electric wind produces a mixture of ions and particles, which also become electrically charged through a different effects, directed towards the sky. Now when an aircraft passes Figure 111.5.5 continued from previous Figure 111.5.5 Continue on following page Mont blanc , •.. , ... ···0· .. ····· ~~~ ..,"~~..= ... Chapter 3 , Lines of force concentrate on pointed objects causing gas discharges and thus ions. These discharges give a buzzing sound •.. ...-... ...The mix carries the same Echarge sign and repel each other , ... Resting climber High electric fields makes vegetation produce a mix of ions and particles page This gives the charged invisible cloud buoyancy The ions produce a conductive path between the invisible cloud and the earth passing through the climber The electric current through the climber can become deadly. Some protection can be obtained by sitting on a coil of rope insulating the climber from the earth The atmosphere is not what it is popularly believed to be 11II Section 1 The Forgotten Pollution over such an active area, these particles will deposit on it in a similar way as happens with so-called electrostatic painting. In that case paint particles are charged via a gas discharge and/or triboelectric charge. An electric field guides the particles to the object to be painted, see Figure III.5.6. Fortunately the speed of an aircraft is in general far superior to that attained by charged particles in an electric field, making it almost impossible for them to hit it. However, if the aircraft is obliged to fly slowly over such an active area as part of a take-off or landing manoeuvre, such precipitation can become possible. It can be enhanced if the aircraft has also obtained a charge by flying through a cloud of space charge, or has been charged by triboelectric means, such as a deicing procedure. So when flying over the active area, a form of electrostatic painting can occur, where the paint is in fact fine water droplets. This will cause a sudden increase in weight of the airplane. But this is probably not the Figure 111.5.6 Figure 111.5.6 Continued from previous page Continued on following page III + + + + + + + + + + + + ~ (.) r:r:¥5r:n Flying slowly over the foggy forest the plane attracts cloud Under dense fog conditions lines of force Ions produced serve as condensation nuclei concentrate on tree tips - a charged doud- .... . ~I+) ~ -) .::::::.. " (+) ~. . ~} '--' .. . (+) ...:..:.::.:.:. ... (+) ,.0. ·c ..... • '. . .:L Combustion releases(+) charged particles giving unacceptable (-) charge to plane Chapter J Pointed bars give small gas discharges making the plane almost neutral ~ §$". Wings and tail of planes have movable flaps for flight control ~. .-....,.J; ~ ' I .J:.. The charged water droplets will enter flap cavities and block flap movement when they freeze due to low aircraft temperature So sudden weight increase and lack offlight control can cause crash. The origin is difficult to verify; high voltage lines can also behave as foggy forests The atmosphere is not what it is popularly believed to be Section 1 The Forgotten PoUution worst part of the picture, because similar to electrostatically emitted paint droplets, the water droplets will not only depo it on surfaces lying in a straight line to the emitter, but they will also search for unpainted surfaces, even if they are located for example inside a wing section. At that moment flap movements will be hindered or, in the worst case, blocked. The latter depends greatly on the temperature; when it is near the freezing point it will cause water droplets to accumulate like the rime you find on trees under such circumstances. Verification of this mechani m is very difficult afterwards: either the rime has disappeared or it is mixed with the snow and ice covering the region where the plane has come down. It is not impossible that it is this process that is behind the quite recent and more or less unexplained aircraft acciden t of 20 Jan uary 1992, where an Airbus A3 20 suddenly went down near Strasbourg, when obliged to fly slowly over a hill covered with snow, with the trees surrounded by thick fog. Other accidents of this type have happened over forest areas with aircraft which took off after the ice coveri{lg the hull had been removed. Evaporation produces positive charges, as we all know after reading this book, making the aircraft a really attractive object for the negatively charged particles, this time emitted by a Swedish forest. Also the crash of a highly reliable aircraft, a Fokker F-27, over a high voltage line in France under freezing conditions could become less mysterious than the official explication of the accident suggested, when efforts were made by the same authorities to suppon the aircraft industry to perform a number of tests to investigate this phenomenon. That airfields and eventually even aircraft hould be oumtted with equipment capable of measuring such fundamentals as space charge or vertical potential gradients could be a logical consequence of such research. Chapter 3 111.5.4. Earthquakes Although earthquakes seem to be remote from atmospheric electricity, to such an extent that the author of a well known book on this subject mentioned in his foreword that he had omitted as irrelevant everything that concerns electrical currents through the earth, a number of observations have been made describing glow phenomena in advance of and during earthquakes. Abnormal radio signals are al 0 related phenomena. These effects are very similar to those in respect of lightning, but also with the presence of high levels of space charge. So it is in fact no surprise that measurement of the vertical potential gradient under earthquake conditions does indeed show important variations. This explains why observations of the behaviour of animals can give indications about a possible earthquake. Animals are sensitive to the effects of the earth's electric field. For example, before the appearance of the self-sustained electrical storm in the Noce area, birds left the trees in great numbers at about the same instant that the observatory measured electrical discharges from pointed objects. When it comes to the storm near Vaison la Romaine, where the evening before the air was highly electrified, here certain inhabitants complained of severe headaches and animals like dogs displayed strange behaviour. Similar observations have been reported from Romania before a large earthquake hit the country on 4 March 1977. An explanation can come from those earth or telluric currents. The e currents vary under pre-earthquake condit'ons in such a way that they are used by certain researchers as predictors. These currents will prefer to flow through underground water supplies, instead of the often highly resistive rocks. However, as soon as an electric current flows through water, it will start to decompose. Hydrogen atoms will appear at one pole and oxygen is released at the other, see Figure 111.5.7. The hydrogen atom is the smallest and also the lightest one we know and will escape from the earth's The atmosphere is not what it is popularly believed to be The Forgotten Pollution Section 1 crust through pore and cracks. 0 it is logical that a sharp increa e of the hydrogen concentration in the atmo phere is reported in certain fault zones. The electrical charge carried by the hydrogen atoms will cau e a space charge cloud in the atmosphere, similar to the one generated by lightning, and which is capable of producing powerful electrical effects at a distance. Because the buoyancy of a pure hydrogen cloud is very high, the po sibiliry of carrying over its charge signature and remaining in suspension near the earth's surface will depend to a great extent on the number of particles suspended in the atmosphere. The higher this number the more likely it is that they become charged by the hydrogen ions. The particles will become charged in such a way that they are repelled by the electrosphere surrounding the earth, causing the cloud to spread horizontally and cover an increasing area. Strategically placed space charge measuring stations in a fault area Figure 111.5.7 Figure 111.5.7 Continued from previous page Continued on follOWIng page + + + '00' III + + Electrosphere -€!etonatin ggas:/1- . .:L Earth , Telluric a.rrents H 7/7/ ~. . But not all gas escapes! cavities are filled with a mixture of hydrogen and oxygen - a terrible detonating gas - When earth crust moves.the path of the cUlTent changes ... I o ' + + ++ + ++ +++ q. :l L~~ CUlTent flowing through water decomposes it oxygen (0) and hydrogen gas is formed: water is a better conductor than rods SO cUlTent goes there Cbapter] Hydrogen calTies + charge Hydrogen gas + oxygen· water Hydrogen (H2) will bubble up easily· smallest molecule we know. normally it goes up very quickly but when pollution is present it behaves like charged cloud Slamming two rocks together produces sparks capable of igniting the detonating gas causing local shock waves adding to the effect of the earthquake. No traces are left So when the earthquake takes place shockwaves are noticed far away The atmosphere is not what it is popularly believed to be Section I The Forgotten Pollution should be able to monitor sudden space charge variations, induced by events that occur deep inside the earth crust: astonishing? 65 million year ago after they had existed for some 130 million years. Why did this happen? I do not know, but of about eighry theories on this subject a great number assume a fundamental climatic change caused by volcanic eruptions or impacting comets, ee Figure III.5.8. Assuming that this is the case, then the earth has been confronted with an increased particle load, quite similar to what happens in highly industrialized areas nowadays. 111.5.5. The dine climate For those readers who are still with me, despite the impact of modern dogmatic doom thinking, and thus flexible enough to accept a fundamental change in their opinion, I have added this last chapter. It concerns the world of the dino aurs that ended very uddenly some Figune 111.5.8 Continued from previous page Figune 111.5.8 Lines OffO~Cf:~:~'1I1 / end on the~ ./ Continued on following page I Ferns are sensitive to pollution . ..•• " M '" '" Gas discharges themselves produce partides So an infernal cycle where pariides produce discharges which in tum produce partides causing terrestrial dyno's to die Only pollution resistant vegetation will survive. Also, acids are produced polluting marshes and lakes, and killing the nautic dyno's Only those dyno's that where mobile and small enough to find food under these terrible cirrumstances have escaped extinction Quite a number of theories on the disappearing of the... dinosaur involve production of a high global partide load.... Chapter :5 resulting in an insulating layer The atmosphere is not what it is popularly believed to be The Forgotten Pollution Section 1 Similar to the observations in the Vosges forest, such a situation will increase the stress on the vegetation, causing it to suffer through acidification. Modem trees, which proliferated after the disappearance of the dinosaurs, resist this aggression relatively well. However, the ferns which fed the vegetarian dinosaurs did perhaps not have that capability and died out with them. As we have seen, vegetation responds to air pollution by creating new pollution itself and in that process a flood of toxic substances is produced, capable of killing fish. Transposing this to the- time of the dinosaurs, when large lakes existed, the same effect could have poisoned them, killing off aquatic life. So the only survivors of this apocalyptic world are those dinosaurs, small enough to have a limited need for food and mobile enough to find it, namely the present-day birds which are the only dinosaurs left on a large scale, according to scientists. However, what is the fundamental difference between this sketch of the vanished dinosaur world and ours: our intelligence..... ? There-is more in heaven and earth than you ever dreamed of in your philosophy, Horatius William Shakespeare, Hamlet. IV. References ASPA, Association pour la Surveillance et l'Etude de la PoUution armospheric en Alsace. Astori, F., The accident on 22 July 1974 on the Mont Blanc. Discourse. Cie des Guides de Chamonix Mon< Blanc, France. Aumont, F., Project Agri.Activite 2CXXl, Vers une agricultute ecologique, Etude DEA, University de Caen, France, 1993. Aurela, A, New approach to old problems about poin< discharges in nature, TIJRKU-FL-R4 Repon Series, Turku University, Finland, 1992. Barde, H., Quiet sufferers of the sUent spring, New Scientist, pp. 30.35, 18 may 1991. Becquerel, Anwine, Memoire, 1850. Benninghoff, W. S., Benninghoff, AS., Wind cranspon of eleclrostaticaUy eharged particles and minute organisms in Antarctica. Antarctic nutrient cycles and food webs, Ed. Siegfried, W.R., Springer Verlag, Berlin, Germany, 1985. Borra, J-P.ln<ensive collaboration. __ Capsor S.A, 38 Rue M. Douville, 78270 Cravenr, France. Chalmers, ].A, Poin< discharge currents through a living Iree during a thunderswrrn,]. Arm. Terr. ~ Phys., VoJ 24, pp. 1059-1063, 1962. Cerceau-u.trival, M.T., NUsson, S., Cauneau.Pigot, Berggren, B., Derouet, L, Verhille, A.M., Carbonnier~ Jarreau, M-C., The influence of the environmem, natural and experimental. on the composition of the exine of aUergenic pollen with respect w the deposition of pollutant mineral particles, Grana 30: pp. 532·546, 1991. Dary, G., A cravers I'Electricite, Libririe Npny et Cie., Paris. EPA, Presentation by WUson, W.E., Workshop "u.w on the Armosphere", European.American Center for Policy Analysis, Delft, The Netherlands, May 1993. Friedlander, S., private discussion, Workshop on nanosized particles, TIJ Delft, (NL), 1993. Griissl, H., Krypton 85, Bayerisches Staats Ministerium fur u.ndesenrwicklung und Umwehfragen, Mlinchen, 1989. Gregory, P.H., The Leeuwenhoek Lecture 1970, Airborne microbes: their significance and distribution, Proc. Rey. Soc. Lend. B. 177, pp. 469·483, 1971. Hermanr, A, Discussion, Muse. de la Foudre, 15190. Marcenat, France, Feb. 1993. HUts, P.]., Tobacco Firm Halted Nicotine Study, Inrernational Herald Tribune, pp. 3, April 30, 1994. Holiste, Artaix, 71110 Marcigny, France. Jamet, E., Co-founder of the u.borawire d'Aeroactivite. Keen. M., Natural nitrate prcxlucrion figures, Letters, New Scientist, 1993. Koning, M. de, Bosbescherming: de leer der Ziekten en Beschadigingen, Zutphen, The Netherlands, 1922. Kreissl, B., Staubdeposition und NO, Konzencration in Aullen und Innenluft in Abhiingigkeit von meteorologischen EinIlli!lgrossen, Diplomarbeit, UniversitJit Karlsruhe, 1992. Levelock. ].E., Les Ages de Gaia, Robert u.ffont, Paris 1990. Chapter 3 The atmosphere is not what it is popularly believed to be Section 1 Ma liang, Q., Questioning on the universally accepted e1ecoical neutrality concept, Static E1ecoidty, No. I, pp. 59-, 20 March 1992. Marijnissen, J.C.M., Influence of e1ecoidty on air Pollution and climate change, propooal for the Dutch ational Reseatch Programme on Global AirpolIution and Oimate Olange (Nap), June 1994. Marijnissen, j.C.M., Mollinger, AM., VetCOU1en, P.H.W., Generation of droplets in electrostatic predpitators by e1ectrospraying, J. Aeroool sa. 24, Sup. pp. 39-40, 1993. Meteo A1en9>n, Mr. Pierre Gayan~ 1992. Meteo Carpantras, Mr. Gerard Bouby, 1992. Milner, J.W., ChaImers, JA, Point discharge from natural and attifidal points, Quatt. j. R Met. Sac. 87, pp. 592·596, 1961. Mollinger, AM., The Holiste, experiments, questions and com:nents, Repott. Delft, The Netherlands, 1992. Miihleisen, R, The influence of water on the aanospheric elecoical field, Recent advances in atmospheric e1ecoicity, Eel. Smith, LG., pp. 213-222, Pergamon Press, London, U.K., 1958. Obolenski, W.N., Ober e1ektrische Ladungen in der Aana;phare, Ann. Phys. Lpz. (77), pp. 644·666,1925. Panol SA, BP 5.• 78373 Plaisir Cedex, France. Peltre, G. Discussions.Perdrix, A" Air condition and microbiological contamination, influence of hygrometry and humidifying systems, Proceedings Building Design, SateUite Sympa;ium, Ste. Ftan<;aise d'aerobiologie, Bruxelles. 17-19 Feb. 1993. Popovid. I.. Discussions. Renard. D., DEFORPA Programme, Recherche sur le role de H,o,lors du processus d'addilkation des retombees au col de Donon, Universite de Paris VU, Laboratoire de Physico-chimie de I'atmosphere, Paris. Rooo, A·j., Personal Din","ur library. Rooo. RA, GoIdman, M., On the behaviour of activated particles in cigarette smoke, j. Aerosol Sd. 20, Vol. 8, pp. 1337-1340, 1989. Stoe!inga, M., Experiments with the Taylor cone, Laboratoire d'aeroactivire, 1992. Surra, J~P" The "PoUen" man, numerous discussions. Tourre, J-1., Meteorage data, 1992. VetCOU1en, P.H.W., Rooo, RA, Marijnissen, j.C.M., Scarlet~ B., An instrument for measuring e1ecoical charge on individual particles, j. Aerosol Sd. 22, SI, pp. 335-338, 1991. Vonnegut, B., Morre, C.S' Preliminary attempts to influence convective electrification in cumulus clouds by the introduction of space charge into the lower aanosphere.• Recent advances in aanospheric elecoicity, Ed. Smith, LG., pp. 317-332, Pergamon Ptess, London, U.K., 1958. Weinberg, F.j., Elecoical aspects of aeroool formation and control, Discussion on science and technology of aera;ol poUution, Proc. Royal Sac. London. A 307, pp. 195·208, 1986. WiIson, W.E., discussion, Intemational Conference on the Law of the Aanosphere, Rand/TU Delft, The Netherlands. 1993. I The Forgotten Pollution Section 2 The second section ofthis book was intended to treal in grealer depth the electrical phenomena that arefundaJllentalto the forgotten polluJion concept. However, in order to keep a balance between both sections, it was necessary to Cu1 down on the number of subjects. So only those subjects that are not easilyfowld in other textbooks are incorporated The reference list althe end ofeach chapter is extensive enough to allow a broader treatment ofmore general aspects. Rein And,. Roos _ The Forgotten Pollution ••••• Vertical potenti~1 gradients and III electric fields 1.1. History . Let us look at the DicOOllnaire des Pltys~ Paris, 1905 for what was at that moment the understanding of atmospheric electrical phenomena and eSIEcially that of the earth's electric field. This work states that there is an electric field near the ground. The ground is charged negatively and the electric potential increases with increasing height in the atmosphere. Numerous studies have been carried out on this subject, among one of the first was that of Saussure (1779). He used a sensitive electroscope with a dome, (Figure 1.1. 1) to protect it against rain. The measuring electrode was a fine copper rod. By lifting up the electroscope swiftly above one's head in an open field, the two tiny strips move in such a way that, in the case of fair weather conditions, the potential has to be positive. Vertical polential gradients and eleclric fields The Forgotten Pollution Section 2 of the air. If we make up the balance of what we now know about this subject, compared with 1905, then we have to admit that it is not much more. Indeed, UV radiation has been linked to a certain behaviour of the lower part of the atmosphere, especially from a chemical point of view. Also, a little more is known about the behaviour of water vapour, which does indeed seem to contain positively charged ions of the type HJO+, surrounded by a cluster of neutral water molecules (Lee et aI., 1990). This is coherent with the observations of Wilson (1989), who showed that water condenses much faster around negatively charged nuclei than around positively charged ones. Also salt, as produced by the sea, shows an increase in condensation that can occur at humidity levels lower than 100% RH, as shown in Figure 1.1.2 The reason underlying this phenomenon has puzzled a lot of minds. Among one of the most famous we should mention Volta (1782), who believed that it was caused by the evaporation of water, especially water coming from the sea. His ideas were supported by the well known French scientist Andr" Peltier in the middle of the 19th century. They assumed that the vapour was charged positively by evaporation, leaving the liquid negative. The Dictionnaire des Physique considers this to be sufficient and also gives the explanation of Brillouin Figure 1.1.1 SaU5sure's electroscope l1li Figure 1.1.2 1----+ Electrode Relative humidity versus droplet diameter for droplets containing the indicated mass of salt at20 'c (after Hinds, 1982) 110 ->,----+ Protection ......_=~-; Fine melal 4--+-+.\ leaves against the rain 100 .". " co '"~ -+---+Glass box .& C '5 90 .~ ~ Ol (1897), based on observations of the intensity of solar radiations - actinometry. He proposes that it is the ultraviolet (UV) part of the solar emission spectrum that causes gas borne particles to lose their negative charge (note that the 'electron' had not yet been discovered and become positively charged. He cites ice particles which do so, losing their charge through increased conduction Chapter 1 '" 80 . , . , , :·10· 1Sgram .c .' .. io '16gra~.· E ::l ' , , .", 10· 1-4 gram 70 -t---~----rl----r--r--~-----, 2.0 0.2 0.4 0.6 0.8 1.0 Droplet diameter (micrometers) Venical potential gradients and electric fields - The forgotten Pollution Section 2 Conden ation increases the weight of the particle, so a higher sedimentation of negative particles becomes probable, leaving the atmosphere with a dominant positive character. So Volta becomes more convincing at the end of this century than he was at its beginning. According to Ma Liang (1992), the solar wind reaching the earth also has to be taken into account in the explanation of the activity of the electrosphere. Figure 1.2.1 1 ==t+~ 1 Needed force f V 1.2. Definition What in fact do we mean by 'Electric Field'? The term means: a field of forces caused by a potential difference. This is illustrated in Figure 1.2.1. Here V represents a voltage source, for example a battery. This device produces a potential difference between the two parallel plates. When we take a positively charged, small particle, it will sense a repelling force from the positively charged plate and an attracting force towards the negative plate. Now if we want to move this particle from the lower potent4al to the higher potential, then we have to make a certain effort, we sense a force. This force is in the opposite direction to the potential difference, as indicated by the arrow in the figure. The direction of this force is defined to be that of the generally accepted electric field, E, which is measured in . volts/meter. However when we assume that the low potential plate is the earth's surface, then the higher we are above it the higher the potential difference becomes. This means that the electric field becomes increasingly negative. This is very confusing, although it agrees with the definition in case of atmospheric electricity. Nearly all of the publications in this field regard the field as positive in case of fair weather conditions. The proposition put forward by Chalmers (1967) seems to be very logical. If the electric field definition seems not to be logical, then use the term vertical potentii:zl gradient, also expressed in volts/meter, but Chapter 1 1 Electric force /---J;:-,....--...-.-~ Forces sensed by positively charged particle 1 /=t+/?; jjjjjjj!! V 1 7 J;: -~ Direction of the electrical field lines ~ 22+~ V 1 'IIlll111 y? Direction of the vertical potential gradient (\IPG) Vertical potential gradients and electric fields .. The Forgotten Pollution Section 2 having opposite polarity. To reduce confusion, the letter E is used for the electric field, while the letter F is used for the vertical potential gradient. It is only for atmospheric electricity situations that the verrical potential gradient is used; in all other cases, such as indoor situations, the term electrical field is employed. It is important to indicate that often field measuring instruments are indicating a Verrical potential gradient instead of an electric field. Figure 1.3.1 Daily variations of the vertical potential gradient VPG (earth electrical field) at Kew near London, winter and summer values (after 5carse, 1934) Winter E ~ 1.3. Earth's Vertical Potential Gradient t .3. t. The electrosphere If we move up in the sky during a fair weather situation, the potential difference with the earth's surface increases; at lower levels this is quite fast, some hundreds of volts per meter. This continues until we reach the socalled exchange layer, whose height depends mainly on meteorological conditions, varying between 0 and 3 km. Above the border, the voltage increase with height decreases dramatically, probably due to an increased condu.ctivity (Sagalyn, 1956). Potential increase with height stops when we enter the electrosphere, situated some 50 km above the earth, carrying a potential of some 280000 volts (Clark, 1958). This is considered to be the boundary of atmospheric electricity. It is imporrant to know that the ionosphere, known for its reflection of radio waves and the Northern lights, is situated above the electrosphere. t .3.2. Fair weather variations The value of the vertical potential gradient near the earth's surface is far from stable. In fact it changes all the time, in such a way that it took Beccaria (1775) twenty years of observations to confirm the existence of daily Chapter 1 Summer + 350 + 585 +485 ~ -/-_~-=-:;I- -\- + 250 -4:---+------l,;----1'---------\ lJ c.. > + 150 + 385 o I 6 12 18 nme (hours - GMT) I 24 o I 6 12 18 24 nme (hours - GMT) variations. Observations made today are not much better. Typical winter and summer variations during fair weather are shown in Figure 1.3.1 for the Kew observatory near London. It has to be underlined that these urves were obtained by filtering out all high frequency variations. As can be seen from the figure, there are two peaks. The second, somewhere between 18 and 24 h UT, is observed almost everywhere on earth at the same time and this is thought to be related to a maximum of thunder torm activity (Whipple, 1929). This corresponds with the exposure of the Pacific region to the sun. The first peak is of local origin. It does not exist over the oceans (Whipple, 1936). It is related to solar heat dissipation, vegetation, rush hour traffic and other activities like the roasting of small pigs on Samoa. t .3.3. Thunderstorm variations Thunderstorms give rise to very high values of vertical potential gradients, which is not much of a surprise. One Vertical potential gradients and electric fields Section 2 The Forgotten Pollution interesting fact that is the polarity of the vertical potential gradient varie very often during the storm as can be seen from Figure 1.3.2, obtained at the Atmospheric Aerosol Observatory at Noce (F). In general values of some 5000 V/m or more are typical of ordinary thunderstorms. 1.3.4. Normal weather variations For most of the year we have normal weather. In industrialized area this means that vertical potential gradient values vary behveen those of the fair weather siruation, with some hundred volts per meter, and those of a thunderstorm, with several thousands of volts per meter. Such values can be caused, among others thing, by; - fog formation; - air pollution; - pollen and spores in the air. Box 1 The EleClrosllllic SysU!m of Units (ESU) has beell used 011 a large scale in older Ucerature for electric applicatiollS.· HOlyever it has lost ground III lite SI sysfem of units. Because access III hislllrical PUbUCOliDlIS is of great imparLance in regard CO atmospheric electricity, conversiDlIS for both me systems are given in this box. Figure 1.3.2 III From SI system of Units to Electrostatic System of Units (ESU) Typical vertical potential gradient variations - Zebra charging - caused by a passing thunderstonn atmospheric aerosol observatory at Noel!. 27 IV 1991 SI QuantitY ESU Charge I Coulomb (C) 3·10' (StC) Current I Ampere (A) 3·\0' (stA) Potential I Volt (V) 3.33·IO· J (stV) Capacitance I Farad (F) 9·10" (stF) ResistivitY I Ohm (0) 1.11·10'" (stn) ConductivitY I Siemens (5) 9·10" (stS) From Electrostatic System of Units (ESU) to SI System of Units ESU QuantitY o SI I Coulomb StC 3.33· 10"0 (C) Current I Ampere stA 3.33· 10·'0 (A) Potential I Volt stV 300 (V) Capacitance 1 Farad stF 1.11·10'" (F) ResistivitY I Ohm stn 9·10" (0) ConductivitY I Siemens stS 1.11·10'" (S) Charge ·111 188/ the Incemational Congress of ElectriciallS, Paris. tried III establish an intematiollOlly agreed electrical sysU!m of units. However. the following systems coexisted for a very long time: ElectrosLatic System of Units, Electromagnetic System of Units. and the System of Practical Units. - 2500 12 16 20 h (Gm~ I Chapter 1 Vertical potential gradients and electric fields .. Section 2 The Forgotten Pollution But also certain storms, snow layers or steam from classical locomotives can cause important values of the vertical potential gradient. Fib~Jre 1.4,1 + + + + A 1.4. Consequences of high electric fields Let us return to the parallel plate shown in Figure 1.2.1 Here the field lines are uniformally spaced, as illustrated in Figure 1.4.1a. This will still be almost correct even if the lower electrode is not ideal, but shows some surface irregularities as shown in Figure 1.4.1b. The situation changes dramatically when the lower plate is covered with an insulating layer, except at the extremities. This is illustrated in Figure 1.4.1c, where we see that the field lines are concentrating on these extremities. This causes an enhanced local increase of the electric field. The multiplication factor varies from 50 to 2500, as can be seen from Box 2. Can the electric field increase without limits in atmospheric air? The answer is no. There is a critical field strength which, once surpassed, causes the air to become conductive. This can sometimes be seen in the form of a spark or a glow. The value of this critical field depends on a number of parameters such as humidity, but in general a value of 3 000 000 Y/m can be used. At first ight this eems a formidable value. However, reality shows us that it is not. Assume the lower plate of Figure lA.lb to be the earth's surface, with trees as extremitie . Here we found field multiplication factors up to 2500. When an insulating layer is installed, for example in the form of a mist layer, this value will be increased even further. Under such circumstances vertical potential gradient in excess of 500 V/m have been measured in the French Vosges (Roos, 1992). Here the trees are some 30 m high and the voltages found at their extremities should be in excess of 15 kY, a sort of high-voltage line. Although precise modelling is difficult, it will be no great Chapter t kleal distribution of force lines + + + - + B Distribution caused by irregularities (trees) of the lines of force + c '+ + + Distribution with irregularities and an insulating layer: fog. pollen, spores, air pollution Vertical potential gradients and electric fields The Forgotten Pollution Section 2 surprise that this high voltage, with the high field multiplication factors, is capable of producing gaseous discharges under such circumstances. This has been confirmed for the modification of the gas content of the atmosphere by Reiter (1958) and acidification of fog (Fuzzi, 1985). Laboratory tests using air corona discharges confirm these observations (Goldman, 1989). Figure 1.5.1 The decay of an initial voltage (V = 392 V) as function of time on an 400 epoxy resin targe~ (after Jestin 1987) Box 2 The relalionship used is: A • .,---;-=-,,2::;h~/R::...--=­ In(4h/R) - 2 &1 Field strength increase, A, due Radius Height h= I h=2 h=3 h=4 h=5 h=6 h=7 h=8 h=9 h=lO R=O.OOI 318 572 812 1042 1265 1484 1699 1911 2120 2326 R=0.OO2 179 318 448 572 693 812 928 1024 1154 1265 R=0.OO5 85 1.49 207 '264 318 371 422 473 523 572 R=0.010 50 85 118 149 179 207 236 264 291 318 1.5. Triboelectricity (tribo (Gr) = friction) An equilibrium exists in the atomic structure of materials when the number of protons matches the number of electrons. In case of metals this situation is in general easily reinstalled after a perturbation, due to high electronic mobility. The case is different for insulators. Processes such as heating, stress or rubbing make them lose or gain electrons, but the lack of conductiVity means that it can take quite a time to reinstate equilibrium. This is illusrrated in Figure 1.5.1, which shows the ratio Chapter t ID irregularities with height h(m) and radius R(m) (Berger, 1992). to o -t---------;I------,---10 o 5 Time (minutes) between the initial potential on an epoxy resin target and the remaining potential as a function of time Oestin, 1987). Numerous generators producing static electricity based on this triboelectric effect have been constructed in the past. A very powerful one was constructed by van Marum in 1785, which is shown schematically in Figure 1.5.2. The triboelectricity is produced by two leathercovered blocks of wood, rubbing a glass disk. The charges so disposed are picked off the disk by two metal combs, storing them on the spherical output of the generator. This generator was so powerful that it easily created gas discharges in a closed vessel, which when opened emitted the characteristic odour of lightning discharges. The gas was later on analyzed by Schonbein in 1840 and found to Venical potential gradients and electric fields The Forgotten Pollution Section 2 The ability of materials to acquire charges is illustrated by a triboelectric scale: Figure 1.5.2 Schematic construction of the van Marum triboelectric generator Most positive (+) Dry air Bakelite High voltage output sphere Silicon wax Glass, Mica r;;..-"'_~---I-I--Charge Nylon pick up combs Wool Glass disk diameter >1 m Human hair Silk + - Leather covered wooden block Paper, Cotton, Wood Amber Scyrofoam, Polyethylene Rubber be ozone. It is interesting to see that this machine is almost a prototype of the van der Graaff generator, flrst constructed in 1931 and capable of producing several million volts with a power of several kilowatts. Although the tribogenerator was replaced by a gas ion charger and the glass disk by an insulating transport belt, the charge transfer and pick off principle remained. Chapter 1 Rayon PVC Silicon Most negative (-) Teflon The materials clo e to 'most positive' will take a positive charge when they come in contact with a material closer to 'most negative' of the scale. Although not mentioned, dry warm air and cold humid air also produce triboelectric effects,las illustrated in Figure 1.5.3. This shows that a small rapid decrease in temperature, due to an incoming cold front, sets up an important variation in the vertical potential gradient at the Atmospheric Aerosol Observatory, Noce (F). And some of us are reminded on a daily basis of the existence of tribo-electricity, when walking on insulated carpets, we regularly draw a nice spark between our finger and the door we want to open. Vertical potential gradients and electric fields .. The Forgotten Pollution Section 2 Figure 1.5.3 Vertical potential gradient (VPG) variation induced by a rapid temperature variation caused by frontal passage. Atmospheric Aerosol observatory, Noc~ (f) Rapid temperature variation Vertical potential '---+-gradient variation after a number of balloon measurements and vertical potential gradient observations at the Observatory of Lyon. If we take the concept of lines of forces for the earth's atmosphere, see Figure 1.6.1, then each line should commence on a negative charge and end on a positive charge. The density of lines of force across any area gives a measure of the potential gradient. If we move vertically, there is a change in the density of lines of force, but they remain vertical everywhere. Then there must be charges presen~ on which the extra lines of force have commenced or on which missing lines of force have ended. Thus a change of potential gradient with height involves space charges, see Box 3. Box 3 In case of the atmosphere, we can write mathematically: &I eo dF/dh = .p 6 I I 12 18 24 h (GMT) where: F . vertical potential gradient (Vim) h . vertical distance from the earth's surface (m) p . volume of density of charge (Clm') eo· permittivity of free space (8.85.10' 12 F/m) When the lines of force end on a conductor, and in our case thus the earth, then there must be a surface charge density 0 (C/m') of: 1.6. Space charges This is a quite confusing term, referred to a flowing charges between two electrodes in case of gas discharges by Vor! Engel (1965) and as free, unbalanced charge in a volume of air, taking no account of the charges of both signs which balance one another (Chalmers, 1967). It was Le Cadet (1897) who viewed the electrosphere as a space charge, produced by positively charged mineral dust particles. This charging should be caused by the ultraviolet part of the sun's light. He arrived at his theory Chapter 1 A mor~ general way to express space charge is: eo div E = p where E is the electric field strength (Vim). For surface charge density we can simplify this expression to: Vertical potential gradients and electric fields The forgotten Pollution Section 2 So if we put a space charge somewhere, then we are able to modify the vertical potential gradient or the electric field values. Space charge in nature may be carried on small ions, dust particles, cloud or fog droplets, precipitation particles, etc. As can be een from the table on the next page showing the value of space charge in the aonosphere as observed by different author , values do vary greatly. Figure 1.6.1 + ++ + + + + + .. + + DAY/NIGHT YEAR AUTHOR 1907 1921 Norinder 1925 Obolensky + 1.2 1927 Kahler +193 SUMMERlWINTER MEANlY +/. +38 _40 1/+ 2 Daunderer 1930 Brown +28 1935 Scarse Smiddy +10 1959 Lines of force for the earth normal potential gradient (after Chalmers, 1967) ++ Variations in the value of the atmospheric space charge as reponed by Chalmers (1967) -20 3 + HO/·20 4 1963 Law 1963 Crozier 0/+500 5 1966 Bem +60 All values in picoCoulombs per cubic meter, (I )h=0·3m, (2)h=8·9m, (3)h= 1-3m, (4)h=0.5m, (5)c1ose to the ground. + • + + + f • f Earth • Figure 1.7.1 Protection from lightning (after Schonland, 1964) 1.7. Field-free space FARADAY CAGE An insulating chamber entirely covered with tinfoil was used by Faraday to investigate whether electric fields occur in side such confinement, when the external foil was connected to a very high potential. In spite of this, no electric field was observed inside the room. However, a charged object taken into the room loses its charge as soon as it is put in contact with the foil. Chapter 1 ==== ==== ==== ==== ==== Rod to moist earth or in trench Ground to metallic water pipe Conductor connected to cooper plate Vertical potential gradienu and electric fields .. Seeeion 2 The Forgotten Pollution Similar effects can be obtained when wires are used instead of plain metal surfaces. Such a construction is called a Faraday cage. It is used for electric field measurements, eliminating external fields such as that of the earth. Also the classic lightning protection is viewed as a partial form of Faraday's cage, Figure 1.7.1, however, in case of a thunderstorm this is far from reality. 1.8. High voltage lines Although the earth's electric field sometimes shows rapid variations, especially during thunderstorm activity, in general it can be considered stationary on a time scale of minutes. Most high voltage power lines carry alternating fields, changing their sign some SO to 60 times per second, which is why they are called AC power lines. The inten ity and shape of the electric field on such lines is shown in Figure 1.8.1 (Martsumoto, 1987). Although the values are far higher near the earth than are found under fine and normal weather conditions, their alternating character makes it impossible to make comparisons. However, when it comes to power grid loss, quite a lot is due to gaseous discharges, amongst others the sOI·called corona discharge. A great variety of ~ partic es are produced in these discharges, depending on ~ the electrical and atmospheric circumstances. Returning to the measured high electric fields found under high FARADAY CUP Thi is in fact a metal chamber with a hole. When a charged body is dropped inside the chamber, its charge leaks away to the ground through a sensitive galvanometer This is called a Faraday cup and it is in general surrounded by a grounded screen, see Figure 1.7.2. In the example given, the metal bubbler serves as a Faraday cup. The galvanometer measures the net charge transported by the particles retained in the liquid. Figure 1.7.2 Figure 1.8.1 Example of a Faraday cup for aerosol measurements -----+ ==~==:;l =------+ ~ Air in with charged particles Air out Intensity of the electric field obs~rved by a worker passing under a high voltage line (after Martsumoto, 1987) 6000 Q ....H - 0- Water 4000 Q.-~ o 0-_ o 0-,,-- . . - - Metal cup 2000 CO 0° Insulator o 0.5 Time (minutes) Chapter 1 Vertical potential gradienu and eleeerie fields Section 2 The Forgotten Pollution voltage lines and their influence on health, this is a subject of continuous study. However, knowing the different aspects of these losse , that influence is not restricred ro the direct vicinity of the power lines as is generally thought, but in the direction of the most likely deposition region, as for example the dominant wind direction. When you look carefully in that direction you Figure 1.8.2 Instrumenls and rurious cows as used in the Grizzly moul).tain high voltage DC line experiment (Grizzly Mountain. 1986) will often be amazed by the trees which are partly dead, dried up, or lack leaves. Also disfigurations can be observed, like trange twists of the trunk and branches or the presence of 'antennas' at their tops. The latter are in fact leafless twigs, assumed to screen off the high electric fields from the rest of tree, thus protecting its metabolism. Figure 1.8.2 shows us the instruments used for measuring the electric field, small ion concentration and ion current density under a +500 kV/ - 500 kV De power line at Grizzly Mountain HYDe Research Facility. The cows in the background are also part of the experiment. t .9. Outdoor and indoor fields 1.9.1 In general a house resembles a Faraday Cage. This means that under such circumstances, the electrical situation of the earth's atmosphere near the surface should have no connection with indoor situations. However, simplifications are very dangerous when your subject is the earth's surface, so let us take a somewhat closer look. Figure 1.9.1 shows the observed electrical fields jnside a house. No synthetic carpets, furniture, wall paper, shutters or smokers were present. Between time t = 1.75 and t = 3.15, the house was not occupied. The fair weather field at that moment was, as often occurs in winter, some 100 - 200 V/m, negative. From the figure it becomes clear that a very important role is played by the TV set in this confinement, even without high insulating surfaces or powerful air pollution. When switched off, the electric field reverses immediately. The possible reason1for this is shown in schematically in Figure 1.9.2: the positive accelerating voltage of the cathode-ray tube necessary to cause electrons emitted from the cathode to gain enough momentum to release enough photons from the phosphor inside the viewing screen of the cathoderay tube, to get the brightly coloured spot necessary for a coloured image. Chapter 1 Venical potential gradients and electric fields _ The Forgotten PoDution Section 2 which remains at the inside of the picture tube is grounded, which means that the outside surface all of a sudden shows a negative charge. These charges will gradually leak away and an equilibrium is achieved between the surrounding space charge and the TV creen. From Figure 1.9.1 it becomes clear that under the actual circumstances, the final field value approaches that of the field observed outdoors. Figure 1.9.1 Electric field values found in a room at different distances from TV set 500 d m 1.5m d = 2.5m d - 3.5m Figure 1.9.2 o + + + III -300 I I o 4 I TIme (hours) It i this voltage that charges the inside, but also the outside of screen positively and to such a level that you can feel the electrostatic attraction when you approach it with that part of your hand covered by small hairs. But it not only attracts these hairs but also atmospheric dust particles, and of course preferably those which are charged negatively. The glass surface of the screen is a good insulator and it will thus come as no surprise that once switched off the high electron accelerating voltage Chapter t 1.10. Other indoor fields 6 OPEN FIRE Combustion is a powerful ionizing process, creating visible and invisible particles floating in the air. The visible ones are also called smoke. The number of charges deposited on these particles by the combustion process depends strongly on the type of fire involved. In any case, these charges could form a space charge and thus produce and electric field. Efforts have been made to observe this in a specially constructed test room, as shown in Figure 1.10.1. Here two test fires were generated, one flaming using alcohol as combustion Vertical potential gradienu and eleettlc fields The Forgotten Pollution Section 2 Figure 1.10.1 Figure 1.10.2 Special test room for indoor field measurements Field measurements in a house with open fire. Field mill height 1.2 m i~ . .. ~oo~ I I o 1 Time (hours) 2 I 3 400 E ~O-t--+-\-------:;"L-----=,~.--------.,.L- Gm -400 . 4m Tv. set W sIN ope~ fire ource and a smouldering one created by putting small dried oakwood blocks on a heating plate of about one kilowatt. The results obtained show us that although the particlts are invisible, the flaming alcohol fire produces a noticeable space charge in the test chamber after some time, while the smouldering fire does not change the local electric field situation. Now we consider a real indoor situation as shown in Figure 1.10.2. Here we have an historic stone house in a state not far removed from the middle ages, Le no modern materials. A wood fire is used for heating and a small TV set connects the inhabitants to reality. A field Chapter 1 mill was placed before the fire and directed each fifteen minutes in the four indicated directions inside this room. As might be expected, the field meter shows a positive charge when directed towards the fire. However when pointed towards the TV set, the charge reading becomes negatige. although the creen charge is positive when the set is on. The reason for this behaviour could come from the negatively charged particles also produced by the fire which are preferentially attracted towards the TV screen, thus producing the negative space charge observed by our field mill. This could also explain why the observed field levels depend little on the intensity of the flames of the wood fire. Vertical potential gradients and electric fields The Forgotten Pollution Section 2 SPRAY CANS The classic "ozone layer unfriendly" pray cans, containing chlorofluorocarbons (CFC) as propellants, produce high electrostatic charges on the droplets generated. This situation has become worse when they are replaced by some "friendly" propellants, such as butane. For a long time certain hydrocarbons have been known for their important ability to acquire electrical charge from particles issued by them due to triboelectricity in the tubbing and the release valve. The cloud so formed will produce a high mutual repulsion between the particles and between the particles and the surface being sprayed. The resulting space charge produces important electric field levels, see Figure LlO.3. This has been shown by Electric field values observed with hairsprays containing different propellants Butane Dimetil ether Freon 1• 11. Field variations through motion 30 J!I cQ) > Q) '0 Q; .D E IONIZERS This apparatus produces powerful electric fields in the surrounding space. It also creates a lot of unipolar ions, causing atmospheric dust to become charged. This, together with the generation of various gaseous molecules and particles, mean that such equipment profoundly modifie its immediate environment. Figure 1.10.3 40 Awu (1990) in the case of hair lacquer applied to a great number of persons. Very high repulsive fields were observed, with the ozone-friendly substitute butane, of such a magnitude that the goal, putting lacquer on the hair, could nor be achieved in some cases. The degree to which these particles return to the hairdresser who sent them off, and what their health effects are on the environment involved, has not been established in this investigation, However the high levels of pollution involved, as well the long exposure time, cau ed by these ozone-friendly spray c~s means that the health effects are probably far worse than those assumed to come from a "hole" in the ozone layer. .., . 20 :> Z 10 ! 0 -20 -10 -E(kV/m) 0 Suppose you are seated in front of a computer screen, repelling positive space charges like cigarette smoke to you, as shown in Figure 1.11.1. This will give you a surface charge, when the charges cannot leak away througq the high resistivity of your clothing, which is often the case with synthetic materials. This surface charge will mean that there is a potential difference between you and your chair. In fact this is similar to a charged capacitor, having a large surface and a little space between the plates. Now when you stand up, the capacitance to the ground will drop sharply. However the charge collected will remain the same. This means that the potential increases by the same proportion as Venical potential gradients and electric fields Chapter 1 Section 2 The Forgotten Pollution the capacitance diminishes. This, in turn, means that a field increase has taken place between you and the ground. This you will notice when you sense an electric shock, when you try for example to open a grounded door. The level of the acquired voltage can be deduced from the length of the spark between you and the grounded object, by taking 3000 V/mm for the breakdown value of air, see Box 4. Box 4 Aguet (1985) relates the possibility of acquiring electric charges to the dielectric constant, E:" of the materials. He proposes for the surface density P,: P, = 15.10- 10 (E: rl - E: r 2) C/m 2 (MKS) where e rl and er2 are the relative perrnittivities of the two materials. For instance, if we take two rubber-soled shoes (E: r = 2.5) representing 500 cm J and a nylon carpet (er = 5), the maximum total charge is then: Figure 1.11.1 Q = p,A Potential increase mechanism where A is the area concerned. Q ++++++ = 15.10- 6 -2.5.5.10- 4 = 1.86.10- 6 C If the corresponding foot-to-ground capacitance is 200 pF, the acquired voltage is: v = Q/C = 1.86.10However if only one foot is kept are walking, we get: o V /\+ + + + + + = Q/C = to 6 /200.10- 12 = 9300 V the ground, which happens often when you 1.86.10. 6 / 100.10- 12 = 18600 V 1.12. Electrical field measurements Although many people tend to believe that electric fields are something imaginary, the reality is that they can be measured by differem methods. The induction method The principle is shown in Figure 1.12.1. The electric field induce a charge on the surface of the metal probe. The quantity of charge is proportional to the applied field. Chapter t . Vertical potential gradienu and electric fields - The Forgotten Pollution Section 2 Figure 1.12.1 Figure 1.12.2 The electric field mill concept The electric field mill concept Chopper vane Motor Rotor Amplifier Meter Electric field 1 Electric field Input capacitor When we let this charge leak away through a very high resistor, then a voltage is obtained, which after amplification gives a deflection of a connected galvanometer. The meter should be zeroed without field before and after the measurement. The indication is affected be atmospheric ions (Seeker, 1984). A = Light emiting diode B = Photo transistor The aItematine field meter The field mill This is in fact a complicated form of the induction method. Here the zero setting is done repeatedly by means of a grounded vane shutting off and exposing the measuring probe to the electrical field to be measured, see Figure 1.12.2. In this way an alternating signal is obtained the amplitude of which is proportional to the . applied field (Seeker, 1984). A very important point to be observed with these instruments is their polarity indication, which is often such that, when you point the instrument towards a positively charged surface the instrument gives a positive reading. However, according to the definition of an electric field, a minus sign should be given. So in fact, electric field meters are often measuring the vertical potential gradient. Chapter 1 Here the probes consist of two hemispherical electrodes on which the electric field induces alternating charges, see Figure 1.12.3. In this instrument the information obtained from the two halves is fed to a differential current/voltage converter and send to a remote indicator, through a fibre optic system. This is done in order to reduce the perturbation of the electric field caused by the in oduction of the probe (Kirkham, 1987). Water dropper This method was used by Kelvin in 1895 to measure the vertical potential gradient (VPG) , and consists of a bucket filled with water having a hole to let small drops out. The whole is placed on an insulated pole and connected to an electrometer. Vertical potential gradients and electric fields - The Forgotten Pollution Sedion 2 Figure 1.12.4 Figure 1.12.3 The Lord Kelvin water dropper An alternative electric field probe with one half of the spherical electrode removed + + + + I + + + + + Let us consider that the dropper is at ground potential. Then the lines of force in a fair weather field end on the dropper and the drop, see Figure 1.12.4. So if the drop falls, off a negative charge is carried away. The more drops that fall, the more the dropper will reach the level of the local VPG. Radioactive equalizer I This consists of a disc or a wire covered with tadioactive material emitting mainly alpha particles. This causes ionization in the small volume of air around the source. When the source is not at equilibrium with the surrounding VPG, the potential gradient will cause ions of one sign to be drawn away from the source. This will charge the source oppositely until an equilibrium is reached with the surrounding VPG. A combination of Chapter 1 this method and the field mill is shown in Figure 1.12.5 (Kirkham, 1989). Opto electronic effects If we submit certain materials to high electric fields, molecules with a large electric dipole will become orientated by the field and the way light passes through the material will be modified. This effect is called the Kerr effect. Venical potential gradients and electric fields The Forrotten Pollndon Section 2 In case of the Pockels effect, the optical variation is obtained by ionic displacement in a crystalline structure due to an applied electric field. The optical variations can be monitored at distance by using, for example, a fibre optic connection. figure 1.12.5 Example of an air driven field mill with radioactive source for vertical potential gradient measurement - Chapter I t. t 3. References Aguet, M., Bertuchoz, J., lanovici, M" Perrurbations eleccromagnetiques dues aux decrorges statiques et aux impulsions c1ccO'Ol'T13gnetiqucs d'origine nud6ire, Compatabilil~ EJecuomagn6tique. 2nd ed., Presses Polytechniques Romandes, 01, 1985. Awu, K.W., Olarge dans Ics cheveux el repulsion e1ecrrosratiquc, DEA Paris, VIU , 1990. Beccaria, G.B., Dell elettricita terrestre aonosfcrica a delo sereno, Tuno, Italy. 1775. !lerger, G, PelSOOlll Conununication, Gif, F, 1992. Brillouin, M., L'Electicile atmospherique, Eel. Elect., 12, pp. 517-599, 1897. Cadet, G le, Etude du champ e1ectrique nonnal de I'atmosphere. Cause et origine de cc champ, Ass. Franc. pour l'Avanc. des Sei., 260 Session, Se Etienne, pp. 202-203, 1897, Chalmers, ].A, AlTnospllCic Electriciry, 2nd edition, PergamonPress, Oxford, UK, 1967. Qark, ].F., The mlr-weather atmoopheric potential gradien~ Advances in Atmoopheric Electricity, ed, LG mith, Pergamon Press, New Yark, USA, 1958. Engel, A von, Ionized Gases, 2nd ed., Oarendon Press Oxfcxd, UK, 1965. Fuzzi, ., Orsi, G., Mariotti, M., Wet deposition due to fog in the Po vaUey, lady, ]. Arm. O1e01., 3, 1985. Goldman, A, Goldmnn, M" igmond, R.S., Sigmond, T., Analysis of air corona products by means of meir reactions in water, 9th 1nl. Symp. on Plasma Otem., Belgrade, Yugoslavia, pp. 1654-1658, 1989. Grizzly Mountain HVDC Research Faci1i<y, Bonneville Power Administration, US Depamnenl eX Energy, BPA Project Brief, 1986. Hinds, w.e, Ae""'" Technology,]. Wiley.nd Sons, New York, USA, 1982. ]estin, P., Analyse du vieillissement sUPernciel de la Tesine epoxyde soumise ?t un plasma fToid de type dCcharge couronne, ThC5e de Doctorat, Univ""ite P. et M. Curie, Paris, 1987. Kirkhmn, H, Johnston, A, The measurement of OC electric fields away fTom the ground, 6th Symposium on High Voltage Engineering, 44.04 New Orleans, USA, 1989. Kirkham, H., ]ohnston, A, Jackson, S., Shell, K., AC and DC electric field melers developed for the US Depanment eX Energy, jPL Publication pp. 87-20, 1987. Lee, Y., et al.,]. O1em. Phys" 91, pp, 7J31-fT, 1990. Ma. Uang, Q., Questioning the univers,illy accepted e1ectricalneutrali<y conccp~ Statistic E1ectrici<y, No.!. pp. 58-fT, 20 March 1992. Marsumolo. T., Measurement of humah exposure to AC elecmc fields using intelligent data acquisition system, 5th Int. ymp. on High Voltage Engineering, Braunschweig, 1987. Reiter, R, Reiter, M., Relations between the contentS of nitrate and nitrite ions in precipitations and simultaneous atmospheric electric processes, Recent Advances in Atmospheric Elecaicity, Ed. LG. mith, Pergamon Press, New York, USA, 1958. Roos, R.A, Pic. R., Renanl, D" La",r, H., Vie le Sage, R., GoIdman.. M., Goldman, A, Borra, ].P., Nocrum.,l hydrogen peroxide observation in a pine forest .lOd the elecaic.1.1 behaviour of the Venlcal potential gradients and elec:trlc fields 1111 Section 2 atmosphere, Euromtc, SPB Academic Publishing bv, The Hague, The Netherlands, 1992. Sagalyn, RC., Faucher, G.E, Space and time variations of charged nuclei and elecoical conductivity of the atmosphere, Quart.]. R. Met. Soc., 82, pp. 428-443, 1956. Saussure, H.B., VOY3ges dans les Alpes, Geneva, 1779. Schonland, B.].F., The Right of Thunderbolts, 2nd ed,. aarendon Press, Oxford, UK, 1964. 5er.lse, F.j., Oboervations of atmospheric electricity at Kew oo.ervarory, Geophys. Mem. London, UK, 60, 1934. Seeker, P.E., Chubb, J.N.,lnstrumentation for electrostatic measurements, J. ElectrostaC, 16, pp. 1-19, 1984. Volta, A, Del mooo render sensibilissima la piu deoole electricica sin narurale sia artifici.'1le, Phil. Tram. Ray. Soc., pp. 237-280, 1782. Whipple, E].W., On the llSSOCiation of the diurnal variation of electric potential gradient in fine weather with the distribution of thunderstorms over the globe, Qum.]. R. Mec Soc., 55, pp. 1-17, 19Z9.Whipple, F.j.W., 5er.lse, F.j., Point discharge in the electric field of the <atth, Geophys. Mem. Lond., 68, pp. I-20, 1936. Wilson, C.T.R. On me comparative efficiency as condensation nuclei of positively and negatively charged ions, Phi!. Tmns A, 193, pp. 289-308, 1899. n, - Chapter 1 The Forgolten Pollution • • • ···r Gas and electricity 2. t. Ionization In general a gas is considered to be composed of molecules bouncing off each other as they collide through thermal movements. The behaviour of the gas is determined to a large extent by the nature and frequency of the collisions whicH takes place continually between pairs of atoms or pairs of molecules. If the temperature of the gas is raised sufficiently, if it is submitted to electromagnetic radiation or particles, the collisions become increasingly violent and a number of supplementary effects occur. When the collisions are no longer elastic, then it can happen that the atom becomes excited to a higher energy state or it can dislodge an electron from the atom, making it into a positive ion. Sometimes the electron is captured by another atom or gas molecule, thus forming a negative km. The collision can also cause a molecule to vibrate, to rotate or even to break up. A number of possibilities occurring when an electron hits a diatomic molecule are illumated in Figure 2.1.1. When the striking particle is a molecule instead of an electron, the number of possible reactions becomes even greater (Massey, 1965). Gas and electrldty - The Forgotten PoUution Section 2 Figure 2.1.1 An electron that hits a molerule may initiate a rich variety of reactions (after Massey. 1965) The ionizing efficiency greatly depends on the energy of the striking particle. At low energy levels the electron wave character means that the chance of collisions, the effective cross section, increases. However when the electron energy or that of other striking particles increases, the ionization efficiency decreases gradually until it reaches an almost constant level, as illustrated in Figure 2.1.2 (Cachon, 1961). Figure 2.1.2 (after Cachon. 1991) The initial impact leads to ... &I Excitation Dissociation - 4 Dissociative ionization Ionization Double ionization No ionization 7 6 Speed of impacting particle I Radialive attachment Chapter 2 Dissociative attachment Ion pair A gas containing a great number of electrically charged particles, ions, is called a plasma. In contrast to an ordinary gas, in which most of the constituent particles carry no electric charge, the main force between the particles is the short range gravitational one. However, in a plasma, oppositely charged particles, also called bipolar ions, are attracting each other through the long range Coulomb forces. This causes recombination and thus ion loss. When the ions carry the same sign, Gas and electricity Tb.e Forgotten Pollution Section 2 so-called unipolar ions, they will repel each other and a virtual increase in gas pressure will occur. Another aspect of a plasma is the fact that the charged particles cause the gas to become a conductor. The hotter a plasma becomes, the better it conducts. In Figure 2.1.3, a number of well known plasmas are shown as a function of their temperature and charge density (Gottlieb, 1965). Gas pressure is of great importance when it comes to plasma physics: unless marked differently, the pressure.referred to in general is assumed to be atmospheric. Figure 2.1.3 Electron Volt The electron volt is a unit of energy especially used on an atomic scale. It is the energy gained by an electron when passing through a potential difference of 1 volt. Mobilities as used in physics and aerosol technology are compared in the table below. The denotation lIsed for mobility is 1.L for small gaseous ions, all other ions and charged particles will be referred ion group'} to as Z name mobility range (cm'/Vs) particle diameter (pm <2) mobility of particles (cm'/Vs) small ions >1 neg air ion 1.56 neg air ion 1.40 Temperatu,e and charge density of various plasmas (after GottJieb, 1965) - 10 22 11 small Intermediate ions 1 . 10" 0.01 2 ·10-' III large intermediate 10"· 10" 0.1 2.7 .10" 1.0 I. I .IO- s co 10 9.6 ·10" '0 100 9.3 ·10' electron 660 p;- lot' ions IC IV Langevin ions 10-' . 2.5 .10-1 V ultra-large ions < 2.5 .10.1 'in co '" '0 10'· ~ .S! ;ij ~ g u w'" 10'0 10' (1) Classification of ions as a function of their mobility according to Bruyant (1985). (2) Electrical mobility of ions, aerosoi and electrons according to Hinds (1982), when charged with one elementary charge. 10' In this chapter only small gaseous ions and electrons will be treated. unless otherwise stated. To obtain mobiliry in the MKS system the values from the table should be and is then expressed in m'Ns. multiplied by LO'" 10" 10' 10' 10' 10' Temperature (K) Chapter 2 Gas and electricity III Section 2 Tbe Forgotten PoUutlon 2.2. Cosmic rays Figure 2.2.1 At the end of the 19th century, Elster and Geitel observed that a charged plate gradually lost its charge, even if all precautions were taken to prevent leaks. A similar observation was made when radioactive sources were present, so it seemed that atmospheric air contained some form of highly energetic particles. The subject was studied by Wilson (1901), who made the experiment portable by Jlsing an ingenious method to charge a plate placed in a bottle, which was directly connected to an electrometer. He observed that this charge decrease happened virtually everywhere, even in deep railway tunnels, so it seemed to be independent of location. Wilson concluded that it had to be caused by ionization of the air due to energy-rich particles, coming from space. Wilson estimated this production to be about 20 ion pairs per cubic centimetre per second, a figure still found in most literature on the subject. The existence of these cosmic rays was established in 1911. They are atomic nuclei of extremely high energies: 100 000 000 eV to 100 000 000 000 eV are on one hand produced by the explosions of supernova in our galaxy before being submitted to a random acceleration through collisions in the interstellar environment. They are called Galactic Cosmic Rays. The other source are the solar eruptions, producing the so called Solar Cosmic Rays. Due to their very high energies the cosmic rays are only slightly deviated by the earth' magnetic field, see Figure 2.2.1 (Blanc, 1992). When smashing into the atomic nuclei of the earth's atrnosl1"ere, neutrons are ejected, a small number disintegrate into an electron and a high energetic ion. Some of these particles are intercepted by the magnetosphere, where they become the main source of the radiation belts surrounding the earth. The others are directed towards the earth's surface. About 80% of these particles carry a single electric charge. Their ability to produce ions in the lower part of the atmosphere - Outer space ionizing agents (after Blanc. 1992) -Sun Chapter 2 Gas and elec:trldty Section 2 The Forgotten Pollution depends on this charge: the higher it is, the more ions are produced. 2.3. Radioactivity Here we di tinguish two main sources, namely: - radioactivity in the earth's crust and its transport mechanism; - radioactivity in the air. Among the great nun~ber of energetic particles emitted by radioactive material, the two most well known are the alpha and beta rays. In general the stability of an atomic structure, consi ring of protons, which would all repel each other under normal circumstances, and neutrons, is achieved &I by the presence of mesons. These mesons can be regarded as the cement which holds the nucleus together. In some elements, however, the structure of the nucleus is so complex that spontaneous changes in the structure may arise. The most usual changes are the following. - A combination of two protons and two neutrons is emitted from the nucleus. These so-called alpha particles form the alpha rays which are emitted by some radioactive substances. The combination of two protons and two neutrons occurs in the helium nucleus, and is therefore sometimes called a helion. - In some cases where the number of neutrons is too large compared to the number of protons, a neutron may be transformed in to a proton and an electron, the electron being emitted. A beam of electrons from such a source is known as beta radiation, and the electrons are referred to as beta particles. Both of the above forms of radiation are usually accompanied by a rearrangement of the particles remaining in the nucleus. The excess energy which previously held the emitted particles in place is therefore called binding energy. This energy is also released as gamma radiation (Van Dijck, 1964). Chapter 2 The alpha rays produce a large number of gaseous ions in a volume quite close to the source. The beta rays produce a trail of gaseous ions along their track, the distance of which to the source is some orders of magnitude longer than for alpha rays in atmospheric air. Both forms of radioactive decay are often highly energetic. If we take for example Americium 241 ('"Am), which is often used in ionization chamber fire detectors, this is a mainly alpha ray emitting element, whose rays remain within some 5 cm of the source. Their mean energy is some 5000 000 eV. As we have seen, the ionization efficiency of highly energetic particles is quite low and it takes about 35 eV of the ray to form an ion pair in atmospheric air, although the ionization potential of the main constituents, oxygen and nitrogen, is much lower. This means that one disintegration, also called a Becquerel (BqJ, produces ~ some 150000 ion pairs along its trail. A modem low ~ activity ionization chamber fire detector still uses sources of some 40000 Bq, which means that inside the measuring chamber 6 000 million bipolar ions are created per second. It will be clear that when no charge separating electric field is present, most of these ions will be neutralized through recombination. Crust radioacdvirv Although, for example, vertical potential gradients of the earth's electric field are influenced by the radioactivity of the earth' crust, when observed close to it (Ebert, 1904), its activity is greatly enhanced when certain rock types are present, like granites, for example. These often contain quite large quantities of uranium, thorium and radium. It has been shown that high levels of outdoor radioactivity can produce substantial dose levels indoors, but this is certainly not the only source. Indoor radioactivity is also thought to be caused by upwelling gas formed as a decay product, which is found almost everywhere, but very often in granite. This decay product of uranium 238 produces radon, an invisible, Gas and elecaidty The Forgotten Pollution Section 2 tasteless and odourless gas. It is easily absorbed in ground water and liberated when it wells up. Radon in turn decay after a few days and, after some intermediate steps, forms a stable radioactive element, lead, Pb 210. This, if it becomes attached to airborne particles or deposited, produces ionization in the lower atmosphere and it becomes quite dangerous when it remains confined inside a building. Figure 2.3.2 Various natural ionization sources as function heigh above earth (after Grassl, 1989) E ~ <11 ~ "'Rn emission from the earth (Radon) a '€ Figure 2.3.1 O'l ~ Different sources of the "Kr isotope (after Grassl, 1989) .... ~ 1: .,..... 00 'iij :c Plutonium production ~ .'" Earth surface . Natural radioactive decay on earth crust 0 0.1 1.0 10 Ion pair production (#/cm' s) , ' ' " Nuclear energy production A~omic bomb tests /' • ••• t" .. .. .. ... '. ". :... -.. -.. o -I----=---.---....:..;.:::.!.!....--=..:.=r-.:=.=....:...:.....-....:.;.:I:""':":"--..,.-- .. .. .. .. .. .. .. -.. .. 1950 1970 1960 Time (year) Radioactivity in the air Apart from the already mentioned radon emission from the earth's crust, another major radioactive source in the atmosphere is krypton 85 gas. This isotope, initially a product of nuclear arms tests and plutonium production, is nowadays produced in even greater quantities by the Chapter 2 nuclear energy industry, see Figure 2.3.1. Although it has a relatively short half life of 10 years, this beta radiating very stable gas is practically not removed from the atmosphere, mainly because of its insolubility in water. This means that its disrribution world wide is far more homogeneou than radon, whose activity is reported to be a hundred times higher over the continents than over the oceans. According to Grassl (1989), this increasing radioactive gas load of the atmosphere will modify its conductivity and modification of the lightning distribution balance between the continents and the oceans as well as an increase in atmospheric electricity discharge frequency can be expected. Figure 2.3.2 shows a compilation of the different natural sources of air ionization as function above the earth crust. Gas and electricity - The Forgotten PoUution Section 2 2.4. Electrical gas discharges Figure 2.4.1 Different electrode configurations 2.4. t. Collection of atmospheric charges If we take two plane electrodes or one plane and one pointed electrode, as illustrated in Figure 2.4.la and b, and we place a variable voltage source and a sensitive ammeter in series, then we notice at low voltage levels that a very small current, less then 0.000 000 000 001 A, flow in the system. The reason behind this current is the interception of gas ions. the positive ones go to the negative electrode and the negative ones go to the positive electrode. As we have seen, the production of these ions is limited to some 20 pair per cubic centimeter per second. Because this figure is independent of the applied voltage, the observed current will remain constant for a large range of applied voltages. This current is also called saturation current for this reason. If we now bring a small radioactive source, for example the already discussed 40000 Bq241Am source, into the gap, the level of the saturation current increases substantially, because a great number of the 6 000 million bipolar ions will be prevented from recombination and land on the respective electrodes, increasing the gap conduction. If we increase the applied voltage to some several thousand volts, even the collection current caused by interception of atmospheric gas ions will suddenly increase. This is called the Townsend regime. A Plane - plane high voltage configuration Protection resistor Rat electrode / F l a t electrode 7 Variable high voltage power supply High voltage voltmeter B Point - plane configuration Protection resistor Rat electrode Variable high voltage power supply 2.4.2. The Townsend regime Pointed electrode{s), Figure 2.4.lb, tend to concentrate electrical field lines. This causes the field close to the point to increase substantially, as is illustrated in Figure 2.4.2. If the value of about 3000 00 V/m is exceeded, another conduction mechanism appears in the gap. This fieldstrength is also referred to as the critical field strength. If an electron or ion appears through natural ionization Chapter 2 - Pico - milli ammeter Pico - milli ammeter Gas and electricity The Forgotten Pollution Section 2 Figure 2.4.2 Field strength variation as function of the distance to a conducing pointed electrode 0.5 1000 00 V/m 0.4 - E .s '" ":J 0 tl 0.3 proce es inside the critical field strength volume, it will be accelerated to uch levels that, when colliding with neutral gas particles new electrons or ions are formed. The initial electron or ion is also referred to as a seed particle. The seed particle and the newly formed ones will collide again and newly charged particles will appear. If such an event happens in a gap with an almo t uniformly distributed field line structure, Figure 2.4.la, due, to for example, to a projection on one of the electrodes, then the avalanche tends to produce a conductive channel beEween the plates and a park will be the result, Figure 2.4.3. In case of a so-called heterogeneous field, Figure 2.4.lb, the high field strength is concentrated around the pointed electrode and it is only in this vicinity that the avalanche takes place. Because the field in the rest '" Qj "0 ~ Figure 2.4.3 " '" -5 '0 Q. The arc discharge in the atmosphere .9 -0.2 '"u ~ 250 000 V/m 0 500000 V/m 0.1 1 000 000 V/m o~\ ( Chapter 2 POint 1500000V/m 2 000 000 V/m 3000000 V/m ~ breakdown of atmospheric air \ Gas and electricity The Forgotten Pollution Section 2 of the gap is below the critical value no avalanche take place here and the extra conduction will die out when no other seed particle is available in the critical field volume. Now by increasing the gap voltage, the current will acquire a more sustained character. The necessary seed electron come from the electrodes, released through ion bombardment, and are al 0 formed in the gas through light emission near the pointed electrode. It is this effect, the soft glow that crowns a pointed object, that gave its name to the discharge: the Corona (crown) disclwrge. It can also be observed in nature, often at the extremities of ships, see Figure 2.4.4. Then it is called Saint Elmo's fire. &I Figure 2.4.4 The corona discharges (St Elmo's Fire) on the caravel of CoJumbus (Dary, 1900) 2.4.3. The Corona discharge The corona discharge is a widely employed method for producing air ions (Whitby, 1961). The energy needed to create an ion pair is similar to that of radioactivity, some 35 eV. Oxygen and nitrogen have ionization potentials of 13.6 and 14.5 eV, respectively so the rest of the energy is dissipated in another way. The primary particles formed in the ionization volume in case of a negative corona, are ions which in turn pr~duce carbon, o;Ygen and nitrogen. These ions normally immediately become hydrated through the humidity of the air. The main pecies are: COJ-(HP)n' 0Z-(HP)n' 0J-(HP)n' HOZ-(HP)n Here it is interesting to note that the main peak is ~ produced by a carbon containing component. However, . . . of all the gases present in the earth's atmosphere, the carbon containing ones are only a minor fraction and are for this reason called 'trace gases'. So the corona di charge is a selective mechanism. For a positive corona, the principal observed species are (Peyrous, 1982): H+(HP)n' 0+ ° (HP) n' O/(HP)n It is interesting to recall that both polarities are producers of nitrogen dioxide. Gas-to-particle conversion proces e are also a part of the corona discharge, (Nolan, 1958). Depending on the polarity of the most pointed electrode (it is this polarity that determines whether the discharge is called positive or negative), the discharge once again shows a certain form of instability. In case of a positive corona this is caused by streamer formation, a fine conductive channel which repeatedly bridges the gap. In case of a negative corona, it i mainly the successive layers of ions drifting towards the low-field electrode that causes electrical field variations in the critical volume giving rise to an unstable current (Loeb, 1965). The corona discharge is considered to be a coul plasma. Chapter 2 Gas and electricity The Forgotten Pollution Section 2 Figure 2.4.5 Characteristic. It was Townsend at the beginning of the 20th century who established the general fonn of the current-voltage relationship of a corona discharge: Condensation nuclei production during corona discharge as a function of workpoint and electrode radius (point - plane configuration) (after Nolan. 1958) A 1= kV (V - V,) where 0.4 k V V0 = a mainly geometrical constant = gap voltage = threshold voltage also called corona onset voltage. c ~ 0.3 :::; u The value of the corona onset voltage varies with the presence of airborne particles in the gap (Lawless, 1988), an important phenomenon in electrostatic precipitators. ~ ..c 0.2 u £5 Particle oroduction 0.1 Very small uncharged nuclei are produced by the corona discharge; when atmospheric nuclei are drawn past the discharging point dley become multiply charged (Nolan, 1957). Figure 2.4.5A show the IN characteristic of the gap used for two different point radii. Figure 2.4.5A i hows the concentration of nuclei observed in the outflowing air. The nature of these particles has been investigated by Peyrous (19 2), who assumed them to be HNO, (nitric acid). Electric wind and electrohydrodvnamic pressure Although the corona discharge has a low efficiency in the production of gas ions (only 1-5% of the applied energy is used for it (Sigmund, 1983», their momentum is still such that while drifting in the electric field charge is transferred to a great number of neutral air molecules, because their masses are about the same. As a result the neutral molecules also acquire a velocity in the direction of the electric field. Thi flow is referred to as corona or electric wind and was first described by Hauksbee (1719). It can easily be felt by placing your hand in the vicinity of a corona discharge point. It has been quantified by Robinsin (1961) who found a square root relationship between wind speed (v) and the corona di charge current (IJ o I 3000 8 4000 5000 6000 V o '""-E .l:'0; lJ :::; c c o .~ @ :5u '0 Blunt point '" .D E ~ v -.,; I, An indication of the wind speed involved can be seen from Figure 2.4.6 (Ballereau, 1980). The pressure increase caused by this phenomenon has been described by Slaughnessy (1991). Chapter 2 Gas and electricity The Forgotten Pollution Section 2 Electrode material Current (A) Te (K) T, (K) C 2 - 12 3500 4200 Cu 10 - 20 2200 2400 Fe 4 - 17 2400 2600 E Ni 4 - 20 2370 2450 i W 2.4 3000 4250 AI 9 3400 3400 Mg <10 3000 3000 Zn 2 2350 2350 Figure 2.4.6 The electric wind speed as function of the discharge ament (after Ballerreau. 1980) :c (10) [36) ~ -0 Cl> QI Point - plane configuration ~ -0 .~ .. U (5) [18] 'S u Cl> u::; I o I 50 100 These temperatures are higher than the melting temperature of the electrodes. Thi means that evaporation and condensation can take place, making the arc a powerful generator of (mostly) metallic aero 01 . ~ ... 150 Discharge current (uA) 2.5. Photoionization 2.4.4. The Arc When we continue [Q increase the applied voltage the conductive channel (in case of a positive discharge) becomes permanent. The same thing happens in case of a negative discharge after it has passed through a glow regime. The conductive channel is called an arc and at atmospheric pressure it is characterized by a small, intenseJy brilliant core surrounded by a cooler region of flaming gases, also called the aureole. The voltage needed to keep an arc going is often less than one hundred volts. The temperatures found in the arc are very high. Examples of the observed different cathode and anode temperatures, T, and Ta' in air for atmo pheric pressure are given in the following table (Cobine, 1958). Chapter 2 Above the earth there is a series of electricaUy charged layers, called the iono phere. They start at a height of some 1000 km and descend down to about 60 km. The processes taking place there are very complex, but one of the main mechanisms involved is the production of electrons and ions under the influence of the absorptionof ultraviolet light and X-rays from the sun on th ionizable constituents, like 0, O 2 and N 2• The density of the atmosphere diminishes with altitude, while radiation and spectral richness increase. So at a certain height an ionization optimum will occur for an individual atmospheric component, as is the case for ozone, shown in Figure 2.5.1 (Seinfeld, 1986). Ion production is caused by collision between photons from the sun and neutral gas molecules. These are broken up into an ion and an electron. Photons in the Gas and electricity The Forgotten PoUution Section 2 wavelength region of 990 to 105 nm, for example, are effective ionizers of oxygen, because their energy is almo t the same as the ionization energy of oxygen. However. in the lower part of the atmosphere it is only the UVA (315-400 nm) and the UVB (280 -315 nm) fraction of the solar UV pectrum that penetrate. Herethe radiative energy (3.1-4.4 eV) will not produce much ionization in most elements. However, it has been shown that even low radiation energies can cause ionization of certain gases through the action of intermediate states Figure 2.5.1 High altitude ozone concentration (after Seinfeld.1986) 100 \ \ , \ E ~ '" " 50 2.6. Ionization by combustion "0 .~ ~ "\ / ,,- ,,- / / 0 0 2 4 6 Ozone content (ppm) Chapter 2 (Loeb. 1965). When it comes to inorganic particles contained in the air, they are easily ionized when they are contaminated or oxidized. Some organic particles can also be ionized at low energy levels. However Burtcher (1988) reports high levels of ionization energy, at 4.9 eV. in the case of combustion particles. But even when no ionization takes place, UV Light is still a powerful chemical agent. and is responsible for the natural smog formation caused by polymerization of the terpene vapours emitted from trees. The explanation of Le Cadet (1897) that the positive electrosphere is caused by the ionization of dust particles under influence of the UV part of the sunlight is thus quite plausible. It also explains Why Elster and Geitel (1900) observed a preponderantly positively charged atmosphere in the high mountains. Because their work is _ often wrongly cited. as if there should be a dominantly negatively charged atmo phere at high altitude, I have given a copy of their work in Figure 2.5.2. the current produced by the effect i sometimes incorrectly explained as coming from point discharges instead of (correctly) from simple charge collection (Reiter, 1992) . .... .It became clear that on mountain tops the 10 s of negative electricity (of an electrified body) is in general larger then that of a positive one. 8 10 Fire is a chemical chain reaction that needs a combination of several factors in order to be ustained: - h~at source; - combustion; - oxidizer; - the availability of free radicals. There are several modes of combustion, such as: - pyrolytic or smouldering; - flaming or open combustion; - deflagration; - explosion. Gas and electricity • The Forgotten Pollution Section 2 A number of 'standard' fires have been established, for example, in the testing of fire detectors. The following list is u ed on a European scale: Figure 2.5.2 J-?HYSIKALISCHE. ZEITSCHRIFT No. LJahrgang. 2.2. ..--............... CkII,_.'lUu..••• : ..., _- J. t\h.u - ' U. C.luJ. J",,",&c--.~ t'''''U,__,- Ji", 64'..:. ... - ..... ..-1.1 -.. &. J CJIt,M!+ II. u- l-"W-- r G. C. S••• ~III. 0 ......... a..ft_ lIlUAX.,.. T~a.&o._r .." ~ ~.r..u..tlu"'l,ue.-. lIi. '11. .... "-Ill "'" : "' •••••• "'.............. J.. ~ So ~ 1}4. .- \:t.... ~ r~~~1'a. Lotj ORIGINALMITTEILUNGEN. < DcitrScc .Iv,t )ttn,O,U'Iu, du .tmoapbS.tiK!K1l Ek1ctric:i.tlt. l ) VOri J. Eluel' W\d H. CchcL Jahr:;wc. No.. Die TbcGric del' IoncnJcihwC' dClr G.uc lit VOA Hum W. Gleu') ;w( Grutw.l voa. flu. dclctlischCQ W~ca.~ vca Fla&Dmclt~" a'4.oat.l:1lt W'Ordcn. .lpliI:c.r Hc:rr. A. ScJ,It.. tcr'l wcilCticlUlut. 'II'd 21. ... .It became clear that on mountain tops the loss of negative electricity (of an electrified body) is in general larger then that of a positive one. ....This ratio became clear on the "Brocken" and on the "Santis" the numbers had a ratio of 4: I. When fog appeared on the mountain it immediately diminished the scattering to very low values. .... In the earth's electric fields the free ions are partly separated. On the mountain tops, where the negative earth electric density is highest, it is mainly positive ions which are plentiful available.... Chapter 2 Cellulosic (wood) open fire TF2 Cellulosic (wood) pyrolytic fire TF 3 Cotton glowing-smouldering fire TF 4 Plastic foam (polyurethane) open fire TFS Combustible liquid (n-Heptane) fire TF 6 Combustible liquid (methylated spirits) fire went ~c.kwal'l;i. '1Nl J. TFI 4IIWIrc'IUk .., .......,..,_ . . M Co Material and mode .. .r.:=..,pl. A. • Fire tests What takes place chemically in a fire is perhaps best illu trated by Figure 2.6.1. This reveals a complex network of combustion routes involving so many elementary reactions that the use of a flow diagram is really needed to keep track of the overall course of the reaction mechani m. The figure shows, in a comparatively simple way, the major transformations that take place in the combu tion of small hydrocarbons, methane (CH~), ethane (C2H 6) and ethylene (C 2HJ The intermediates, 0, H, HI' and OH, as well as the combustion products CO2 and H 20, have been omitted from the figure for the sake of clarity. Also not shown are the further reactions of acetylene (~H2) and the reactions of intermediate hydrocarbons, CzH, CZHl' and CHz' some of which lead to the formation of larger hydrocarbons or combustion aero 01 (soot) . Combustion processes are a major source of airborne particles, and have been studied intensively mainly in terms of concentration, ize, mechanical and optical properties. However the characteristic electrical signature of such processes is less well understood. Theoretically, in equilibrium the combustion aerosol particles should be charged according to the Boltzmann Gas and electricity Section 2 The Forgotten Pollution Rgure 2.6.1 Row diagram of the decomposition of some simple hydrocarbons when burned. The intermediates: 0. H. H, and OH as well as the combustion products H,O and CO, are left out (after Gardiner. 1982) CH + 0 CH,o /" 0 • t CH, I I Ethane "' CH, CH,O' CO CHO r---- \ #--~--~~~-I C,H. C,H, C,H,O C,H,o ! ,/ ' /' I ~ ~• ~ Carbon Ethylene o' ',r'" 0 0 ~---=teo C,H, o Oxygen o Hydrogen C,H, ) .~CH, ,/ Acetylene 0 C,H, C,H,O "0 CO C,H I distribution (see the chapter on airborne particles) with ome deviation for particles with diameters close to the mean free path between the air molecules. Under the assumption of equilibrium, the final particle charge depends on the particle size and the ambient temperature However, in reality the charge distribution will reflect the characteristics of the burned material as well as the mode of combustion (Guyonnet, 1983). Chapter 2 -+ CHO+ + e· 'a o --.--~~-- Methane Particle charge involves ions and the main sources in the combustion process are the chemical reactions between the gasified fuel and the oxidizer in the flame front. The 'clas ical' reaction: is still considered to be dominant for charge separation in hydrocarbon flames. In case of premixed hydrocarbon 8 flames, local ion and electron concentrations of 10 to J 10" per cm have been reported. Soot formation and growth takes place in and near this highly ionized region, something that at first sight looks similar to the conditions in a 'neutralizer' where aerosol particles are confronted with a large quantity of bipolar ions and where is assumed that the equilibrium charge distribution is conferred on _ _ the particles. However, this can only take place when ~ the ratio between ions and particles is at least 10: 1. With particle densities of the same order of magnitude as that of the ions; in the case of a pyrolytic fire, this means that particle charge should be below the Boltzmann level. The low charge level of smouldering fire particles does nO[ mean that smoke is uncharged. The high particle density means that the number of charges per volume can be quite impressive. In the case of a flaming fire, particle density is far less than the ion density and Boltzmann charge levels on the particles are often reported. Another ionization mechanism, apart from the thermal one that has its effect at some distance, is photoemis ion. The main branching reaction, including the OH radical, emits UV radiation, which is capable of ionizing hydrocarbons covering the particle's surface. H + -+ OH + -+ o + -+ OH OH + o + H + H Gas and electricity The Forgotten Pollution Section 2 From Figure 2.6.2 ir is clear that particles generated in a fire differ by several orders of magnitude in size, this greatly depends on: - the nature of combustion; - the circuit material. But the si:e is far from constant. Krafthefer (1984) reports increases up to a factor 4 in diameter some time after the generation of particles by fires such as smouldering and flaming cooking oil and smouldering polyurethane. This is a form of coagulation. Figure 2.6.3 Typical sool partide Figure 2.6.2 Typical particle size produced by differenl fires (after Guyonnel elal.. 1983) El F' Raming S- Smoldering -- celone (F) \ _ - - - - - - - - - - - Firwood(F) Petrol (F) Methanol (F) ~ . . /0', I~'f I\\'+-~\- - - g / I U I I I I I , I I '.,. I 1.': / I :'/ • '\ \ ." \ ,.,--------- \ \ \'\, ,\ '\', I \ , '" .... Catdboard (5) . ..' , I 0.1 1.0 Partide diameter (micro meters) Transformer(5) Sodium (F) '. .... '-.. 0.01 PVC cables (5) '' \\':.~'-------- 10 • 1.3 micrometers Gas oil (F) If wc now look at the shape of such an enlarged particle (diesel soot in Figure 2.6.3) then it is clear that this does not look like the ideal, spherical particle. One of the reasons for this could be that shear or gradient coagulation took place in the motor or the exhaust system. Anop,er explanation is of an electrical nature. Here it is assumed that the basic particles have a unipolar charge. Now, if gradient coagulation were to take place, only those particles will coalesce which undergo a headon collision, the others will be repelled. This could explain the formation of the pearl-like strings. Too high a charge level on the string will halt the process and other strings will be formed, which will become interconnected later on, forming the large, non-spherical structure shown in the figure. Gas and electridty Chapter 2 The Forgotten Pollution Section 2 Chapter 2 Such an agglomerate can be characterized by assuming that it is a self-similar structure (Mandelbrot, 1977). Self similar clusters imply the relationship It will be clear that there is a relationship in combustion aerosols between particle charge, fire mode and burnt material and thus, if we are capable of measuring the particle charge and the fire mode we should be able to gain an indication about the burned material. where N is the number of primary particles composing the agglomerate and 1\ a static radius, e.g. the radius of gyration. Of is called t~e fractal dimension. Schmidt-Ott (1989) has related the fractal dimension to the dynamic shape factor for ultrafine silver agglomerates through electrical mobility measurements. Burtscher, et al. (1986) examined the particle charge in combustion aerosols and found also that it depends strongly on the material burned and the combustion mode. They distinguish three classes of fires. 1) The particles generated by a smouldering fire. They show charge levels far below the eqUilibrium value at room temperature. 2) Large flame fires producing large amounts of black smoke, like a polyurethane fire. Here the fine particles (18-32 J.Lm) carry a large charge corresponding to a Boltzmann temperature of 500-700°C. 3) Smokeless fire like alcohol fires, here the particles are charged almost according to the Boltzmann law. From these observations it does not seem impossible that electricity may indeed play a role in the formation of agglomerates. Another important factor could be the presel ce of water, which is of course a normal end product of combustion. Chen, et al. (1986) showed that chain agglomerates could become spherical at higher humidity levels. They explain this by assuming capillary condensation between the spheres, causing them to float. This then causes the chain structure to collapse. However, it is not clear whether it is this mechanism that is causing the bimodal character of the cardboard smoke of Figure 2.6.2. 2.7. Various effects of ionization 2.7. 1. The Lenard effect By observing the sign of atmospheric electricity at altitude, which is predominantly positively charged, Elster and Geitel (1890) observed that it changed sign and became negative in the neighbourhood of waterfalls. Phillip Lenard, in 1892, investigated this phenomenon ~ scientifically at Bonn University. He pointed out that the ~ effect, which later on came to be called the Lenard effect, can ill1lY be observed when the water involved has a purity imilat to that of distilled water. It was for this reason thar he used only pure mountain water in his experiments, because drinking water proved to be too impur.e to produce any effect. His conclusion was that, when a water drop falls on a surface, the water itself becomes positively charged and the surrounding air negative, see Figure 2.7.1, which is a figure from the original article. So we may conclude that negative ions are moving faster then positive ones, although the relative humidity in case of these experiments is, of course, very high. 2.7.2. Zeleny's observations John Zeleny, in 1898, repeated the experiments of Rutherford (1897) on the electrification of gases exposed to Rontgen rays. He established a difference in mobility between negative ions, which are faster than their positive counterparts in all gases except organic ones. Thi effect could be caused by the hydrophobicity of Gas and electricity The Forgotten Pollution Section 2 these organic gases. Zeleny took precautions to prevent airborne particles and electric charges from reaching the measuring chamber. Under these circumstances, and although he does not mention the humidity of the gases used, he finds a general pattern quite similar to that of Lenard; negative ions are faster than positive ions. Figure 2.7.1 Generation of negative air ions by means of sprashing water (Lenard.1892) .. Figure 1 o Ionizing energy o ,~C) oCq~ Positive ion Negative ion CJ o<:-~ 0e.cJS ,) ~ -~ Electron path III C c c j\ h w Chapter 2 h w In case of a simple ionization, an electron and a positive ion are formed at almost the same point. If the electron manages to escape before recombination, then its mobility is some 400 times larger than that of an ion. This and its small size means that it will likely slip through the intermolecular' space of a great number of molecules or atoms before it attaches itself to one and becomes a negative ion. So it seems probable that negative ions are formed more towards the exterior than their positive counterparts, Figure I. It is interesting that such an effect not only occurs with falling water droplets or gases irradiated with Rontgen rays, but also with combustion gases. By smoking a cigarette through a measuring coaxial cylindrical capacitor, Figure 2, and applying a polarizing voltage of either + 100 or -100 V, the electrometer shows that the re~eived current on the central rod (Roos, 1989) is predominantly positive, Figure 3. Here too it seems that the positive ions remain more concentrated in the air flux coming from the cigarette, while the negative ones disperse and become trapped by the cigarette paper, or any available tubing. Similar observations were made by Kittelson (1986) in the exhaust pipe of a diesel motor. He also observed a majority of positive charges when using a real-time measurement sensor. Gas and electricity The Forgouen Pollution Section 2 Figure 3 Figure 2 Pica ammeter 100 (output curren~ Insulator .-' ,\ . .-' \.,- _-------}J Cigarette 1 : .. " ' l , Ventilator 1 « .& 50 ai + 100V Polarizing voltage " :; ~ ~ S- 8 ..t -100V *-~ Polarizing voltage for intemal cylinder 2.7.3. The Wilson's observations Wilson, still known for his cloud chamber, found in 1899 that in saturated air from which he had carefully removed all condensation nuclei, condensation occurred more re;adily on the negative ions than on the natural or positively charged ones. Mass spectrometry has been used to study the behaviour of water molecules in air. Carlon (1980) showed that for various temperatures, water cluster ions of the type H+ (HP)" (hydronium ion) are continuously formed in water vapour and moist air. This explains the importance that negative ions have in humid air. Chapter 2 - 20 I 2.7.4. Miihleisen's observations Richard Mlihleisen showed in 1958 that there is a correlation between atmospheric electric phenomena during the formation of mist and fog, the modification of the earth's vertical potential gradient after sunrise, and the generation of electric charges during the evaporation Gas and electricity The Forgotten Pollution Section 2 2.7.5. Possible coherence and condensation of water. Some of the water molecules leaving a surface must be negatively charged according to Muhleisen. He checked this statement by creating temperature and moisture changes in a closed room and then measuring the electric space charge produced. The results are shown in Figure 2.7.2. Here, water is evaporated quite violently by means of a dish pan heated up to 80-90 qc. This produces a negative space charge. When the air is dried by means of an electric radiator, a positive space charge occurs. One interesting observation is that both effects become stronger when the content of condensation nuclei in the air is higher (for instance through cigarette smoke) and if the relative humidity is rapidly changing. However, both effects were only observed with relative humidities higher than 65%. 11II Figure 2.7.2 The results on evaporation and condensation as published by Richard MOhleisen in 1958 Fresh air ...:... Moistening "Eu 85 1000 E Q. C c '" 500 "0 ~ '" .s::: u 'u" '" ",., ,/., u 0 0. o o /' ....: / . . . -'.. '" . , ...:_ Drying .......... R.H.~ o "- ~ 'in % ]-g '. bO .' :~':" ~ ~ os ~ 23 i3'" 'ij - 500 '" w J20 '. ••••• , " .,.... ",.. __ . c==J nme (hours) 24 -R.H. -1000 ---=p ....... -T Chapter 2 T(oq 15 Negative ions have something in common with the God Janus, namely they have two ways of acting. At high humidity levels they act as condensation sites for neutral but polar water molecules, as observed by Wilson. The atomic arrangement will be such that a large, stable cluster is formed with negative charges exposed to the outside. A consequence of the condensation action is that the electrical mobility of the negative ion cluster become very low. Positively charged hydrated hydronium molecules will help the cluster to grow even more, although the neutral sites they create in and on the cluster will limit its size. Depending on the impurities present, this condensation action can take place even at relative humidity levels slightly below 100%. This ... condensation will create the negative space charge ~ observed by Muhleisen (1958). Below this critical humidity level there will be a steady coming and going of neutral water molecules. So the organized build-up around the negative ion does not take place. As a consequence, the cluster reduces in size, makinI:: the influence of the electrostatically drawn-in stable, positively charged, hydrated hydronium molecules greater and so, increasing their capability to neutralize the cluster. Once this happens the negative ions, and thus their capability to serve as condensation sites, can escape from the scene by showing a higher mobility than their positive counterpart, as shown by Zeleny near the end of the 19th century. The low mobility of the positive ions is caused by the presence of a few, tightly connected water molecules attached to it, as observed by Carlon in the 1980s. The higher mobility of the negative ions will mean that they get lost to a greater extend to for example the walls of a room, leaving its inside with a positive space charge, as shown by Muhleisen (1958). But what about the presence of negative ions in the highly humid environment ofLenard? Here it is the purity of the water that is the key. Condensation around Gas and electricity Section 2 The Forgotten Pollution Figure 2.8.1 negative ion can take place below 100% relative humidity. At that moment the negative clusters will how low mobilities and are scavenged by the droplets returning to the earth. It is only with very pure water that the Lenard-effect can be observed, because the critial humidity level needed for condensation will be higher, meaning that even under these high humidity conditions, the negative ions remain mobile and so produce a negative space charge in the surrounding air that i helped to spread by the elevated positive vertical potential gradient pres€nt in mountainous areas. Measuring capacitor of Gerdien Type Output current (I) .-- Insulator ~ V'!"tiI.Jr 2.8. Measuring Methods 2.8.1. General Charge mea urements and sign determination of atmo pheric particles have been performed for more than a century, by different means. The most frequently used methods are a follows. - Observation of the decrease with time of the charge place on an in ulated plate. This method was first used by Elster and Geitel and wa uccessfully used by C.R.T. WiI on to determine the amount of natural ionization in 1901. - deflection of the charged particle towards a collecting electrode under the influence of an electric field. The current ob erved depend on the number of charges that are intercepted. The method was used for the fir t time by Rutherford. It was improved by Ebert and is known under\the name of the Gerdien (1905) ion counter. The method is capable of giving sign and charge number information and i still in use as a major aerosol mea uring instrument, the EAA (Electrostatic Aerosol Analyzer). - Interception on a high efficiency filter. The current flowing from the filter i in fact the difference between the number of intercepted positive and negative charges. Thi method wa introduced by Obolensky in 1925 and Chapter 2 Charged smoke partide Inte]--c}'iinder . . . . Polarizing voltage on internal c}'iinder(Vm} L valuable atmospheric space charge information has been obtained by it. 2.8.2. The ion counter The ion counter consists of a coaxial cylinder, with the outside plate polarized and the centre rod connected to a sen itive current meter, Figure 2.8.1. Charged particles are drawn in by the suction unit and will be collected on the centre rod when they carry a charge opposite to the polarization of the outer plate. It can be shown that the ion density n is: n = Gas and electricity Section 2 The Forgotten Pollution where ro and r, are the outer and inner electrode radii, v the air velocity, e the mean charge per ion and I the Figure 2.8.2 presents the number of charges as well as the space charge per unit volume as observed by the ion counter. Clean air contains less than lOO negative gas ions per cm' in the LPD laboratory, corresponding well with the values reported by Berger (1980) for the same laboratory. The reduction in the number of smoke particles reaching the centre rod at higher air speeds is well illustrated. measuring current. It can be shown (Alien et al., 1977), that an ion counter can only collect particles from within a cylindrical region with radius r: Figure 2.8.2 Results obtained with Gerdien ion counter exposed to light smoke where J.L is the particle mobility, Vm the polarizing voltage and L the length of the counter. This means that we have to inject large particles very close to the central rod. The other methods less commonly used nowadays. III 500 80 Eu :;; :0 Cl 400 60 ~ ~ " u ~ E " ""5 combustion .!d 40 ~ Q; '0 '"C. .D o o u light smoke caused by 300 u Measurements were carried out in the Laboratoire de Physique des Decharges (LPD). The smoke was obtained by burning 25 g of perforated computer tape and 50 g of light cardboard. The distance between the fire and the Gerdien ion counter was approximately 2 m. The volume of the room was 125 m'. The smoke diffused quite uniformly through in the room and was considered to be 'light'. The Dutch Standard NEN 3883 gives the following classification for smoke clarity in tearms of the mean attenuation coeffictent: ~ E u c. 2.8.3. The ion counter and a combustion space charge ~ 8 'Q. .: 200 _ :;; .t::I E z" 20 100 0 -r--,--,----,---,----,-I----,-----,-----,------J-- 0 0 4 5 9 Air velocity, v. in m/s I Smoke light medium Attenuation coefficient (dB/m) m < 0.5 0.5 < m<6 strong very strong Chapter 2 15 < m Gas and electricity - The Forgotten PoUudon Section 2 2.9. References Alien, N.L, Allibone. T.E., Dring, D., Effect of corona on me density of ionisation in a high~voltage laboratory, Proc lEE, 124(2), 1977. BaUereau, P., Etude du vent electrique. contribution a I'crude et a' la realisation d'un detoctcur de pollution, these 3"· cycle, Univetsite Paris-Sud Cenue d'Otsay, 1980. Be'!!er, G., These, Univetsire de Paris Sud, Cenue d'Otsay, no 2310, France, 1980. Blanc, M., L'Environnement ionise des vehicules ,paOaux, DGA Science et Defence 92, Dunod, Paris, 1992. Bruyant, ).L, Conaibution • I'erude d'un mobiIimeue ionique • repulsif, These 3"· cycle Universite P&M Curie, Paris France, 198;' Bunscher, H., Sclunidt-On, A, Siegmann, HC, Monitoring ~niculate emissions from combustion by photo emission, Aerosol Sci. ""d TeduL, 8, pp. 125-132, 1988. Bunscher, H, Sehmidt-Ott, A, Reis, A, Panicle cha,!!e in combustion AeroooIs, J. aerosol Sci., 17 (I), pp. 47-51,1986. Cachon, A., Daudin, A., )auneau, L, Les Rayons Cosmiques, Presses Univetsitlires de France, Paris, (F) , 1961. Cadet, G. Le, Etude du champ electtique nom131 de \'atmospherc; OlUse et engine de cc champ, k.s. Fran.,. pour l'Avance. des Sei., 260 ,ession, St. Etienne, pp. 202-203, 1897. Carlon, H.R., Harden, C.S., Mass specrrorncay of ion induced water dusters: an explanation of the infrnred continuum absorption, Appl. Opt., 19, pp. 1776-1786, 1980. Cabine, ).0., Gaseous ConductOts, Ed. Dover Publ. Inc., New York (USA), 1958. Chen, N.C).. Longest, A.W., Adams, R.E., Spheroidization of chain-agglomerated aeroools in nearly ..rurated environments by capillary condensation, 2nd Int Aeros. Conf. Berlin, Ed. P<'1!Bmon, Oxford (UK),1986. Dary, G., A tr..wers l'E1ectriote, librairie Nony ct Qe., Parisr (F), 190:>. £ben, H., Ober die Ursache des nonnalcn atmOSpharischen Potential geflilles und dct negativen Erdladu08, Phys. Z. 3, pp. 135-140, 1904. Elster, )., Geitel, H., Wien Ber, 99, 1890. Elster, J., Geitel, H., Beitriige zur Kenntnis der armosphiirischen 8ekmcitiit, PIry,. Zeitsehrift., 1(22), 1900. Garcliner, W.C, The chemistry of flames, Sci. Am., Feb 1982. Gerdien. H., Demonstration eines Apparates fUr ein absoluten Mes.sung cler elektrischen Fahigkeit cler loft, Phys. Z. 6(23), pp. 800-802, 1905. Gotclieb, M.B., Plasma, The Fourth State, Int. Sei. and Techn., pp. 44-50, Aug 1965. Grassl, H, Kryl'ton 85, Bayerischs Staats.lunisterium fur Landesennvickelung und Umweltfragcn, 1989. Guyonnct, J.F., Deoiche, P., Lanore, J.c., Lauwick, B., L, maitrise de l'incenme clans les ootimenrs, Ed. Maloine, Paris, (F), 1983. Hinds, W.C, Aerosol technology prope<ties, behavioor and measurement of airborne panicles, J. Whiley, New York, 1982. Hauksbee, F., Physico-mechanical experiments on various ,ubjects, 2nd ed., London, 1719. Kittelson, O.B., Moon, K.C, Collings, N., 8ecmcal charge on diesel panicles, 2nd lnt Aeros. Conf. Berlin, Ed. Pe'1!Bmon, Oxford, (UK), 1986. Chapter 2 Krafthefer, B.C, Lee n, G.E., Panicle distributions for smolderi08 and flaming fire 'iNations, 1st Int. Aer",. Coni:, Minneapolis, Ed. Elsevier, New York, (USA), 1984. Lawless, P.A., McLean, K.)., Sparks, LE., Ramsey, G.H., Negativc corona in wire-plate e1ecu"'tatic precipitators. Part I: Characteristics o(individual [uft corona discharges, J. of ElectTOStatics, 18, pp. 199-217, 1986. Lenarcl, P., Ober die Elekmcitiit der Wasserfiille, AmL PIry,., Lp:, 46, pp. 584-636, 1892Loeb, LB., E1ecmcal coronas, Univetsity ofCalifomia Press, Berkeley, (USA), 1965. Mandelbrot, 8.B., The &actal geometry of narure, Freemann, San Francisco, (USA), 1982. Massey, H., When atoms coIllide,lllL Sci. ,"Id TeduL, pp. 44-50, July 1965. MGhleisen. R, The influence of water on me acnospheric eleccical field, Recent advances in 3ttnospheriC electricity, Ed. LG. Smith, pp. 213-222, P<'1!Bmon Press, Lopdon, 1958. NoIan, P.)., Kuffel, E., Metal point discharge nuclei and the production of multiple cha,!!ed ions from condensation nuclei, Geofis. Pur. Appl., 36, pp. 201-210, 1957. Peyrous, R., Lapeyre, R-M., Gaseous products created by e1ecmcal discharges in the atll105phere and condensation nuclei resulting from gaseous ph."\Se reactiON, Aunospheric Environment, 16(5), pp. 959-968, 1982. Reitcr, R, Phenomena in Atm05pheric <lnd Environmental Electricity, Fig 5.3 and 5.4. pp. 260-261, Elsevier, Amste<dam (NL), 1992. Robinson, M., Movement of air in the elecoic wind of the corona discharge, TraIlS. Am. InsL Elec. E08., 80, pp. 143-152, 1961. Roes, R.A., GoIdman, M., On the behavioor of the activated panicles in cigarette 'moke, ). Aerosol Sei., 20(8), pp. 13J7-1340, 1989. Rutherford, E., On the e1ectrillcation of gases exposed to Rontgen rays, and the absorption of Rontgen radiation by gases and vapouts, Phi!. Mag. SS (VoI43, No 263), April 1897. Seinfeld, J.H., AtmOSpheric chcmistry and physics of air pollution,). Wiley and Sons, New York, (USA),1986. Sehmidt-Ott, A., New approaches to in-siru characreri:ation of ultrafine agglomerates, J. Aerosol Sei., 19 (5), pp. 553-563,1988. Sigmund, R.S., Goldman, M., Inst Physics Conf. Series No. 66, Session Ill, Electrostatics, Oxfotd, (GB), 1983. SIaughnessy, E.]., Solomon, G.S., Elecrrohydrodynamic pressure of the point re plane corona discharge, Aeroool Sei. and Techn., 14, pp. 193-200, 1991. Van Dijk, J.G.R., The physical ba'is of e1ecdunics, Cenuex Publishing Company, Eindhoven, (NL), 1964. Wilson, C T.R, On the comparative efficiency as condensation nuclei of positively and negatively charged ions, Phi!. Tram. A., 193, pp. 289-308, 1899. WiIson, CT.R., On the ionisation of atmOSpheric air, Proc. Ray Soc. A, 68, pp. 151-161, 1901. Whitby, K.T., Generator for producing high concenuations of 'mall ions, Rev. Sci. lnst, 32 (12), pp 1351-1355, 1961. Zeleny, J., On the ratio of the velocities of the two ions produced in gases by Rontgen radiation and some related phenomena, Phi! Mag., S5(VoI46, NQ 278), pp. 120-154, 1898. Gas and electridty - The Forllotten PoUudon / L ...J The electri~ field, mixture of ions and airborne particles .., r 3.1. Introduction· 3.1.1. What's in a name? Airborne particles are also called aero ols and are considered to be a two- phase system, comprising both the particles and the gas in which they are suspended. The word aerosol was used for the fir t time in the 19205 as an analogy to hydrosol, meaning a stable suspension of solid parricles in a liquid. However, with the passage of time, the word aerosol has become firmly anached to spray cans in a great number of countries, producing quite a confusion between the public and the scientists. But a great number of people concerned with, for example, milk powder, pesticides or foot and mouth disea e also fail to under tand that their problems are related to aerosol technology. ·Quote from Shakespeare The electric field, mixture of Ions and airborne pardcles - Section 2 The Forgotten Pollution On the other hand the term airborne describes with a striking simpliciry what we try to bring over by using the word aerosol, so let us promote the term airborne for the sake of clarity in case of atmospheric aerosol. Mist. A liquid-particle aerosol formed by condensation or atomization. Particle size ranges from submicrometer to about 20 !Lm. Fog. A visible mist. 3.1.2. Definitions Aerosols can be subdivided according to the physical form of the particles and their method of generation. The following definitions correspond quite well to common usage (Hinds, 1982). Aerosol. A suspen ion of solid or liquid particles in a gas. Aerosol are usually stable for at least a few seconds and in some cases last a year or more. The term aerosol includes both the particles and the suspending gas, which is usually air. Their particle size ranges from 0.001 !Lm to over 100 !Lm. III Dust. A solid-particle aerosol formed by mechanical disintegration of a parent material, such as by crushing or grinding. Particles range in size from submicrometer to visible. Coarse Particle. A particle larger than 2 !Lm in diameter. Fine Particle. A particle smaller than 2 !Lm in diameter. Fume.! A solid-particle aerosol produced by the condensation of vapours or gaseous combustion products. Particle size is generally less than 1 !Lm. Note that this definition is different from the popular use of the term to refer to any noxious contaminant in the atmosphere. Smoke. A visible aerosol resulting from incomplete combustion. Particles may be a solid or liquid and are usually less than 1 !Lm in diameter. Chapter 3 Smog. Photochemical reaction products, usually with water vapour. Particles are generally less than 1 to 2 !Lm. The term is derived from the words smoke and fog. ~ Cloud. A visible aerosol with defined boundaries. 3. 1.3. Particle sizes If we take a careful look for example at the smoke that leaves a cigarette, as shown in Figure 3.1. I, we can see that just above the pyrolytic region, the smoke is invisible. Then it becomes bluish and finally ends up as the well known white cigarette smoke. During the short time between their release and the formation of white smoke the size of the particles has increased almost a hundred-fold, from several nanometres to almost a micrometer. Another example, but in the reverse direction, can be observed in the countryside some time after sunrise. In the morning, you can observe a white fog over the vegetation, which gradually disappears. In the afternoon, the fog comes back as a blue haze. How is this possible? In the morning, large particles contain vegetational nuclei, negatively charged and su~rounded by a water layer. This layer will disappear at noon under the influence of the sun and so will the negative charge. The down drifting nuclei are much smaller and capable of producing the bluish T yndall scattering. But particle size also plays a very important role in other ways. Let us consider the inhaled fibreglass particle, which easily enters the pulmonary tract because it follows the streamlines of the flow. However, when the flow The electric field, mixture of ions and airborne particles The forgotten PoUution Section 2 3. t .4. Particle modification and activation reduce, wp and rever e when exhaling, the lack of lift of the particle mean that it has problems in finding a route out of the pulmonary ystem, so it depo its or becomes intercepted. From these daily experiments it becomes clear that is difficult to put a size to the particles involved. However, particle ize is of fundamental importance in aerosol technology, to such an extent that special types of airborne particles with uniform izes have been created for mea uring purpo cs: 0 called monodispersive aero ols. These particle 'are nowaday used on a large cale to test filters, cyclones, lung models etc. However, it will be clear that we are dealing here with an over implification and it i for thi rea on that re ults obtained with the e particles have to be lIsed with extreme care. But is only a part of the problem facing the classical aero 01 approach. El To keep it simple, airborne particles are just particles suspended in the air. However when you suspend particles in air, you are modifying the behaviour of the air itself. For example, its electrical conductivity changes, visibility is reduced, thermal behaviour modified, etc. In fact, you notice that your air is in fact polluted. This in turn means that the particles receive another part of the solar spectrum, that they repel or intercept other particles differently, evaporation and condensation changes, ete. So not only the air has changed, but so have your particles, i.e. the particles are in fact modified by this process. However, a great number of particles also experience one or more of the following activations: Activation Characteristics Shape or morphological Spheres, hollow spheres, fibres, agglomerates, .... Figure 3.1.1 Different aspects of cigarette smoke Chemical A cigarette smoke particle is a carbon nucleus covered with tar. Biological Pollens are already morphologically activated, but contain a great number of allergens, capable of leaving through tiny holes, Fig 3.1.2. Radiological . •• ••• ••••• ~ Blue - Inll1sible - Chapter 3 r The particle that intercepts the radioactive Pb-21 0, produced through radon disintegration, now becomes surrounded by a great number of modified air molecules. So in fact we should look at our airborne particles as often very active particles suspended in polluted air, see Figure 3.1.3. The electric field, mixture of ions and airborne particles _ The Forgotten PoUution Section 2 Figure 3.1.3 Figure 3.1.2 Schematic approach of the interaction between air and suspended particles Pollen Cerceau - Larrival (1991) Particles 1 Photoionization Particles in the air 'Betula Vel7l1cosa' -Birch- I Electric field modification I 3.2. Electrical activation 3.2. t. Extra particle activation But there is one activation that even fundamentally modifies the mechanical behaviour of airborne particles, namely: Electric discharges In the earth atmosphere. we have the following formula: Electrical activation Thi activation can be added to all particles, even when they al eady carry other activations, even down to atomic size. It is this electric activation you ee running through everything that comprises air pollution. This overriding activation is also referred to as: Extra particle activation One of its effects is illustrated in Figure 3.2.1, which hows the terminal settling speed, VTS ' caused by gravity for different particle diameters. Also shown is the speed a Chapter 3 Airborne particles Polluted air + very active particles single charged particle of different diameters obtains when submitted to a fair weather vertical potential gradient of 180 V/m. In case of a positive charge, this additional speed means that the particle will drift downwards, even faster than by gravity. However, when the charge is negative, the electrical speed is opposite to that of gravity and, The electric field, mixture of ions and airborne particles .. The Forgonen PoUudon Section 2 Figure 3.2.1 Influence of gravity and Coulomb force on airborne partides in the atmosphere (after Hinds, 1982) Electrosphere + + + + + v.. I Particle with one elementary negative charge V. Vertical potential gradient - 180 V/m Earth 0.1 &I 0.01 Vu Downward speed due to gravity 0.001 below a certain diameter, the particle should go up instead of dQwn. This i the ca e with particles smaller than 0.2 lUll, which should remain flQating in the air. However by dQing SQ. the particle will regularly intercept the small ions CQn tandy created in the atmosphere. This means that if a layer of these particle exists, the cQnductivity decreases around the layer. This in turn means that the vertical potential gradient increases, helping the particle layer to remain aloft. So this activation alsQ produces a synergetic action between the particle and its surroundings. AnQther example is'that Qf people who are allergic to cats. In general, when they enter a rQQm cQntaining a cat, their allergic reaction is triggered off remarkably hordy afterwards. The e reactions are cau ed by minute protein particles produced by the cat as it moves. _ However this is not the only thing the cat produces: it also generates high electric fields; values of 50 000 V/m are ea i1y observed, ow thing become clearer. The tiny particles will be charged by the action of the cat and follow the electric field lines. which end in principle everywhere. but which concentrate on pointed objects, like the no e. Measurements carried out with dogs showed field values that were more than one order of magnitude below that of a cat under the same circumstance. 0.0001 V.. Upwards speed due to electrosphere attraction 0.00001 0.000001 0.01 0.1 1.0 Partide diameter ~m) Chapter J 3.2.2. Electrostatic forces Quite a number of attempts have been made to establi h a relationship between the force observed when two electrically charged objects are influencing each other at a certain distance (r) a a function of the charge carried by each object (ql' q2)' It was finally Coulomb (J 736(806) who established that for two.l2Qim charges this force (F) is proportional to rhe product of the charges involved and inversely proportional to the square of the distance between the two charges, thus: The electric field, mixture of ions and airborne panides The Forgotten PoUution Section 2 F Where k is a constant, whose value depends on the system in which we work. In the MKS system k = 41tEo = 1.11'10- 10 F/m If we now take one point charge and bring it into an electric field, then the force th is charge notices is defined to be: F = qE Airborne particles are in general small enough that they can be considered as a point charge, so Coulomb's law can be applied. The charge carried by the particles is at certain times (n) the smallest charge we know 19 (e = 1.6'10. C), so we can also write: F = charge, but also because its size cannot be neglected in relationship to the mean free path between the air molecules. It was Langevin (1905) who proposed a mobility relationship that takes account of the larger charged particles, also called Langevin ions. Another approach comes from aerosol technology. For airborne particles, their average speed will depend on the value of the Stokes drag force, Fo: ne E where 1) d v viscosity particle diameter particle speed Cunningham's coefficient It is the Cunningham's correction coefficient that adapts the Stokes drag force to particles with diameters less than 10 nm. By equating the electrostatic force to the Stokes drag force, we find for the particle speed: 3.2.3. Mobility neECc 11 When we consider an ion moving in the air under the influence of an applied electric field (E), then it will be submitted to a great number of collisions, resulting in an average drift velocity (v) that depends directly on the strengt.h of the field and inversely on the density of the gas through which the ion moves. It has been found convenient to define a reference velocity, also called ion mobility (p.), which is the mobility of an ion submitted to a unit electric field (E): 11 = !-LE In the case of airborne particles, the situation is different, not only because such particles are often multiply charged, while an air ion normally carries only one Chapter 3 31t1)d In analogy with the mobility of gas ions (j,L): 11 = !-LE an airborne particle mobility (Z) is also used: 11 = ZE where Z The electric field, mixture of ions and airborne panicles The Forgotten PoDution Section 2 h will also be clear why two different symbols are used for the mobility. That for ga ions assumes them to carry one elementary charge, while for airborne particles the number of charges has to be known. For liquid droplets there is a much smaller charge limit, related to the surface tension, y. This is called the Rayleigh limit: n e 3.2.4. Particle Charging One way to charge airborne particles is by having them intercept another charged particle, for example an air ion. Another way is wHen a neutral particle loses a charge, for example an electron. This means that the remaining particle carries a positive charge. This is for example the case with beta radiating particles (Charuau, 1982). Different means of particle charging will be dealt with. However, corona particle charging will be especially highlighted because of the ever-increasing u e of it for this purpo e. Charge limits: When we sub titute the Coulomb force for two identical charges by the force cau ed on a charge by an electric field E, we find: Electrons can be drawn out of a surface when the 9 limit field strength, EL. surpasses the value of 10 V/m. In case of a proton emission the field has to be 2· 1010 V/m. When this happens at a particle with diameter d, then the number of charges needed to reach this limit is given by: n 4e Chapter J 3.3. Natural extra activation of airborne particles 3.3. 1. Energy rich particles A part of the ionization in the earth's atmosphere is caused by the interaction between energy rich particles and air molecules. The mean energy needed is about 35 eV. However generally less than half is transferred to the ion pair formed, meaning that the rest must be dissipated in another way, such as kinetic energy, molecular dissociation, excitation etc., thus also creating a number of electrically neutral but chemically active particles. The origin of the energy rich particles is: - decay of natural radioactive material in the earth's crust; - upwelling of 22l Ra and daughter products from inside the earth; - cosmic rays, photon . Once formed, the main loss of gas ion pairs is the recombination of the oppositely charged components. Ifwe a sume: q I the ion production, which is between 7 and 20 cm-\-l; the instantaneous densities of positive and negative ions; the recombination coefficient, which is 2.36-10- 6 cmJs -I at 22 DC and atmospheric pre sure. The electric field, mixture of ions and airborne particles The Forgotten Pollution Section 2 Another los comes from the fact that the ions tend stick to aerosol particles when they come into contact with them through the Brownian movement. Uncharged aerosol particles become charged by this process, while initially charged aerosol particles will lose their charge with time, becau e of their preference for ions of opposite sign. These competing processes can, due to stagnant aerosols, lead to a situation of charge equilibrium, also called the Boltzmann charge equilibrium. Then at equilibrium we have: to The ion density near the earth's surface should lie J between 1700 and 2900 cm- , a value often found in the literature. However, when we look at the densities observed for small negative ions some 30 km outside Pari , see Figure 3.3.1, we see that the quantities are much lower (Berger, 1980). One of the reasons for this los is the fact that ions are promoting droplet formation by acting as condensation nuclei, thus becoming les mobile. This has been clearly shown by Goldman et al., (1976) for laboratory air, see Figure 3.3.2. Figure 3.3.2 Mobility spectrum of negative ions in corona discharge (after Goldman. 1976) Figure 3.3.1 Negative ions in atmospheric air at30 km from Paris. Sampling rate 2 per minute (after Berger.1980) Day 2 Day 1 ~ 30 30 20 20 5 .~ ~ :.> c 0 Cl Air c .2 "J!! e '0 2 .!: 10 10 V> Ql 0.66 0.5 Mobility (P) in cm'/V' sec E .Z' 0"Ql ~ Ql ~ oD" E z " ;a E 0 Ql I 75 100 25 50 0 Negative ions per cubic centimeter Chapter 3 0 50 100 0 25 75 Negative ions per cubic centimeter The eleci:ric field, mixture of ions and airborne partides The Forgotten Pollution Section 2 3.3.2. The Bolumann charge equilibrium If we look at the quantities of aerosol particles in industrialized areas compared with the theoretical ion denSity (see table below), then it will be clear that this is a major gas ion removal proce . Concentration in number and mass of two types of atmospheric aerosols condensation nuclei d p = lOnm particles larger than 5 pm micrometer particles where ~, fl' .fn are respectively the fractions of particles carrying 0,1, n elementary units of charge and JOI' JIZ ' .•..In(n-I)n are the rate with which particles carrying 0, I, ....n charges will have their charge increased by one elementary unit by collision with an ion of same polarity and JIO' JZI' ····In(n-I) are the rates with which particles carrying 1, 2, ....n charges will have their charge decreased by one elementary unit by collision with ions of opposite polarity (Uu et al., 1986) For equal concentrations of positive and negative ions the fraction of particles, (, of a given size having n elementary units of charge is given by: industrialized regions numbers (#/cm J ) El mass (pg/cm J ) 100000 10 50 25 25 fn Over the oceans n._~e 1000 mass (pg/cm J ) 0.5 0.5 The development of the steady state Boltzmann charge on an initially neutral or charged aerosol on exposure to bipolar ions is a stochastic process and the theoretical calculations involve the solution of the following set of equations: dfo dt dfn = J(n-1)n dt fn_1 - I n (n-l) + I n (n_l) fn + '1 n 2e 2] dpkT 5 Note: theoretical density of small air ions is between 1700 and 2900 per cm J • Chapter 1 ~ ~ numbers (#/cm J ) J(n.l)n fn•1 For large particles (d > 0.02 J.Lm) this equation become identical to a normaf distribution and can be written in a more tractable form: fn This equation can be used for particle diameters larger than Z.o nm at which the estimated error of ~ becomes about 10%. In general the Bolrzmann equilibrium charge is initiated on an aerosol by passing it through a dense cloud of bipolar ga ions produced by a radioactive source. Such an instrument is called, questionably, an Aerosol Neutralizer. The following table (Hinds, 1982), gives the percentage of particles with a given size and the charge level they obtain in case of a Boltzmann equilibrium. The electric field, mixture of ions and airborne partides The Forgotten POUutiOD Section 2 Figure 3.3.3 Particle charge for infinite time as function of ion concentration (after Adachi, 1980) Distribution of charge on aerosol particles at Bolumann equilibrium Percentage of particles carrying the Indicated number of charges Particle Average diameter charge - - - - - - - - - - - - - - - - - - - - - - - - -2 < -3 -3 -I o +2 +3 > +3 +1 (J1m) &I 0.0\ 0.007 0.3 99.3 0.3 0.02 0.104 5.2 89.6 5.2 0.05 0.411 0.6 19.3 60.2 19.3 0.6 0.1 0.672 0.3 4.4 24.1 42.6 24.1 4.4 0.3 0.2 1.00 0.3 2.3 9.6 22.6 30.1 22.6 9.6 2.3 0.3 0.5 1.64 4.6 6.8 \2.\ 17.0 19.0 17.0 12.1 6.8 4.6 1.0 2.34 11.8 8.1 10.7 12.7 13.5 12.7 10.7 8.1 11.8 2.0 3.33 20.1 7.4 8.5 9.3 9.5 9.3 8.5 7.4 20.1 5.0 5.28 29.8 5.4 5.8 6.0 6.0 6.0 5.8 5.4 29.8 10.0 7.47 35.4 4.0 4.2 4.2 4.4 4.2 4.2 4.0 35.4 = 2.37{a. The rate at which an aero 01 reaches the Boltzmann equilibrium is given by: I n{c} 3 An Nit value of 6000000 bipolar ions per cm per second is needed to bring a highly charged aerosol back to the Boltzmann equilibrium level in a few seconds. Such high values are produced in special ubsonic (Whitby, 1961) Chapter 3 2QI Half the particles carry a charge The average charge {il} for particles with diameters {d} larger than 0.1 J.Lm follows the, following relationship with good accuracy: ~ All particles are neutral E '" ij ---- 0.2 ----0.5 ~ ~ 2.0 All particles are charged Ten times more partides than ions umber ions = number partides Ten times more ions than particles and supersonic (Felici, 1980) corona discharges and radioactive neutralizers. It will be clear that the e processes have violent aspects and that fragile airborne particles like micro organisms can have their viability affected by them. The a sumption that atmospheric aerosols are at Boltzmann equilibrium charge levels through the action of natural ionization is a danflerous one for two reasons: - 0 have the equilibrium charge installed takes time, since strong eddy diffusion means that aerosol particles are con tantly moving; - to have equilibrium charge there hould be a certain exces of gas ions, as can be seen from Figure 3.3.3, which will not be attained in industrialized areas. It is probably for this lack of equilibrium that the often proclaimed relationship, that there should exist a certain balance between the number of gas ions Ni and aerosol The electric field, mixture of ions and airborne particles - Section 2 The Forgotten Pollution particles ,in atmospheric air: . N ,.. N x ~ constant shows an important variation in the value for x (0.2 - 0.45) (Chalmers, 1967). 3.3.3. Gaseous discharges For a great number o(years atmospheric electricity scientists have tried to produce an atmospheric electricity balance, shown below. III Place Author Cambridge Wormell (1930) Cambridge Fine weather Point discharge Precipitation Lightning Total +60 -100 +20 -20 -40 Wormell (1953) +60 -170 +20 -5,6 -96 Chalmers and Litde (1947) '+60 -90 +40 -35 -25 Revised +60 -180 +40 -5 -85 Chamler (1949) +35 ·125 +22 -45 -113 Revises +35 -300 +22 -6 -249 Wai ( 1950) +\100 -30 +20 -20 +70 IsraiH +90 -100 +30 -20 0 condition Durham Durham (1957) Kew Kew (1957) World World It is clear that values vary substantially, but all authors agree that point discharges occupy a more important place in the balance than lightning. It is also interesting to see in the table that there has been a dramatic decrease in ligh tning activity and an increase in point discharge current for the same station, when comparing older data with newer. Ions are regularly formed through gaseous discharges near the earth's surface, through ga eous discharges in the form of almost invisible point or corona discharge, and the better known lightning. The relationship between the production of nitrogen oxides and the presence of point discharges has been observed by Reiter (1958). Because such discharge are taking place at pointed objects like trees, then it is no wonder that for example Orthofer (1990) found that nitrogen oxide deposits are in general a factor] higher in a forest ~ than in the open field nearby. ~ The fact that the scientific opinion has decided that these deposits are mainly from anthropogenic origin has meant that little activity has happened to correctly quantify the natural production of these pollutants. Precipitation From the atmospheric electricity balance table, we also see that precipitation adds to the electrical activity of the atmosphere. Certain types of precipitation carry charges and can thus act as a space charge, modifying the vertical potential gradient. The splashing of drops on the ground can perhaps be a source of air ionization, the Lenard effect. It is unfortunate that recent data on thi effect are scarce. 3.3.4. Vegetation (1953) The figures given are in Coulombs per kilometre per year (Chalmers, 1967). Chapter 3 It was William Gilbert, in his book 'De Magnete' in 1600 who stated: "It plainly attracts the body itself in case of a spherical drop of water standing on a dry surface; for a piece of amber held at a suitable distance pulls towards The electric field, mixture of ions and airbome partides Section 2 The Forgotten Pollution itself the nearest particles and draws them into a cone". This, we believe, is the first time that a description has been given of an effect later called the Taylor cone. This is in fact the electrostatic spraying of liquids, and is schematically shown in Figure 3.3.4. When a syringe containing a liquid acts as a point in a point-plane gap configuration, then the initially rounded drop at the end of the needle will be drawn into a cone when a high voltage is applied to the,gap. At the end of the tip, a 8 10 stream of liquid droplets (10 _10 per second) is produced. Although the effect has been studied by Zeleny (1917) and mathematically described by Taylor (1964), after whom it is called, it remained in fact a laboratory curiosity for a long time. It was Marynissen and Meesters (1992) who, by discharging the droplet cloud, realized that the effect could be used to reliably generate liquid airborne particles. But electrostatic spraying is not restricted to the laboratory. Recently it has been observed that a similar effect can occur in nature, where leaves can be emptied of their sap after they have been submitted to high el ctric fields. So although there seems a similarity between what we can do with metal electrodes and what happens in nature, there is however one important difference. Vegetation is in general covered with a wax layer. It was Volta in 1775 who constructed a so-called electrophore, a wax slab which, once charged by triboelectricity, retained it for a long time, enabling a lot of electrostatic tests without the need for an electrostatic generator. The modern form of the electrophore i called an electret. Consisting of a tiny polymer layer charged by mean of corona discharge, it can retain its charge for years. Filters produced by this effect prove to be highly efficient in retaining airborne particles (de Haan, 1986). In nature it is the wax covering the leaves that can behave like an electret when charged through point discharges, for example, and even after the charging effect stops, particles of opposite sign will still be invited to deposit on the charged leaves. Figure 3.3.4 " The Tayior cone "r r , L .J . ,:L r~ L .JI "r High voltage supply cJ . ,:L L fJ Ordinary drop ~, L .J Strange drop called: "Tayior cone" ...-... .. " .. ...-... " ~ ';r "': .. .. ...,',' , "... ~~~:~t~"~i~;des 10 000 are.l produced per second :'" Chapter 3 The electric field, mixture of ions and airborne partides The Forgotten Pollution Section 2 3.3.5. Photoactivity Another plant activity which influences the electrical balance in nature is the release of pollen and spores, which often carry charge, into the air Figure 3.3.5. It will be clear that these often quite large particles are capable of modifying the electrical behaviour of the lower atmosphere. In the exchange layer, situated near the capping inversion and the free atmo phere, see Figure 3.3.6, the solar energy produces energy levels of 3.1 to 4.4. eV, powerful enough to produce a number of chemical reactions such as ozone formation (Rowland, 1988) and particle formation through terpene polymerization. However, it is not only chemical reactions that take place in this region, as "has been shown by Sagalyn (1954). Aircraft observations indicate that the boundary layer is also the boundary for charged airborne particles, (see Figure 3.3.7), and that it is almost only gaseous ions which are found in the free atmosphere above. It is interesting to nQ[e that the ratio between positively charged and negatively charged particles was almost 1 during checks carried out between 300 and 3300 m. But _ Figure 3.3.5 Smoking pistol: puff ball fires a plume of spores into the air (after Simons. 1993) Figure 3.3.6 Exchange layer daily meterological cyde Free atmosphere ( --~-------------Capping inversion .'.~'" • --~------------ :Enlrainmentzone v~ -- Residual layer Convective mixed layer o :... ': ~':. ---. Mid Chapter 3 .. _ _ - ight .··0' ....···. ~.. N·~·~~ ..: -~ ,- • ( ( ... . ................../ Residual layer .. . Ooud~) ( Mid night ---+ The electric field, mixture, of ions and airborne particles The Forgotten Pollution Section 2 there is a lack of reliable electrical data here, and such data are needed to form a coherenr picture of what really happen in this global reactor. Figure 3.3.7 Large charged particle content of the atmosphere as function of height (after 5agalyn.1954) Aigh N° 1 2 3 4 3.0 Free 5 III 6 2.0 Atmosphere 7 8 9 Height (Ft) 5500 8200 4300 4500 3200 7000 8200 9400 8000 Top of 1.0 exchange layer (H) Ground level 0.0 .L 0 ....,..._ _..,1000 ---;-_ _-;5000 ---, 9000 Number of charged particles per cubic centimeter 3.4. Artificial extra activation of airborne particles 3.4.1. Electrostatic precipitation of the major industrial applications of corona discharge. The unipolar ion created in the drift zone are used to charge aerosol particle that move through the gap, and making them sensitive to the electric field that tends to depo it them on the counterelectrode. The charging mechanism involved depends on the aerosol particle size. In general the following regions are distinguished: - particle diameter < 0.1 !-Lm, diffusion charging dominates; - particle diameter> '1.0 !-Lm, field charging dominates; - particle diameter between 0.1 !-Lm and 1.0 !-Lm, combined action of the two charging mechanisms. We will treat the two mechanism in some detail. 3.4.2. Diffusion charging Here the charge on the particles is caused by ions which are deposited on it by thermal gas agitation. Among the different theories about the subject describing the phenomenon, let us discuss the one proposed by White (1951) The charged ions with a numerical mean density No are in Boltzmann equilibrium around a particle with a charge Q and a diameter a. An ion at di tance from the particle has a potential energy U. The numerical ion density at the distance r of the particle is we also know that dQ dt = re a 2 Nqc I The currenr that reaches the particle is: Electrostatic precipitators are used on a large scale in indu try to remove the visible part of the emitted airborne particle pectrum of smoke-stacks. Here we come to one Chapter 3 The electric field, mixture of ions and airborne particles _ The Forgotten Pollution Section 2 where k is the Boltzmann constant, T the absolute temperature, which is the same as the gas temperature, and c the mean thermal ion speed. Figure 3.4.1 Electric field lines for a conductive partide canying various charges in a uniform field (after Hinds, 1982) Uncharged partide At STP the formula holds within a factor 2 for particles 6 with radii of 0.05 to I I'm and for not> 10 (Hinds, 1982). 3.4.3. Field or bombardment charging Chapter 3 = E - 1] + Plate Fully or saturated charged particle F. qE, Q"" {rJ III ~ e In this relationship is the angle between vector rand field E, E, the relative dielectric constant and a the radius of the particle. An ion situated at r is drawn towards the particle and its charge will become collected when the force permits. Figure 3.4.1 hows us the field lines for q=O, for an inrerme iate charge level, and for the case that the saturated charge, Q~,. of the particle is reached. The saturation charge is given by: + Mate Partly charged partide • Plate Or ~ - If a spherical charged particle with charge Q is placed in a uniform field, the field will become deformed in the vicinity of the particle. The radial component E, of the field can be established fot r;' a by the Poisson equation: E, . - 011 ?~ L - Plate - Plate + Plate 2 41tEO 1 • 2 - ' - - a Eo (31) [ Er ,. 2 The electric field, mixture of ions and airborne particles Section 2 The Forgotten Pollution The factor I 1+2_'__ € - €, + 2 is a measure of the deformation of the field by the particle. If E, = I, then no deformation occurs, while for E = co the factor reache a value 3. The latter will, in p~actice, hardly be reached because most dielectric materials have E < 10. An important exception, however, is wate; which has a very high value of &" namely almost 80. In industrial precipitators, No is in general close to 12 J 5'10 m- • Figure 3.4.2 compares the saturation charge by diffusion and field charging as function of aerosol Figure 3.4.2 Number of charges on particles as function of their diameter and charge mode (after Taillet. 1981) 2000 ID u .f' Electricfield value E ~ 3.5 ·10' V/m 0.. Bombarding or field charging '" -5 25 1986). 1600 '" I 'u" ..c 800 c '"E '" Diffusion charging Qj = KV (V - Vo) where K = geometrical constant V = applied voltage Vo = threshold voltage. For the often used wire-cylinder structure with radii r and R, the formula becomes: I -R-z8_:-f-~-~-) V(V - V.) = o o Chapter J By limiting himself to the drift region and assuming an Ohmic relationship between the field and the current density, Townsend, at the beginning of the 20th century established the well known IN relationship for the corona discharge that in its general form is: 1200 ~ ~ diameter (Taillet, 1981). From the figure we notice that bombardment, or field charge is more effective than diffusion charging for particles larger than 1 f.Lm. It is necessary to keep in mind that small particles are very difficult to charge electrically and that when this does occur in electrostatic precipitators, it is close to the end of the sy tem. This means that a great number of these fine (invisible) particles tend to escape. The fact that negative charging i conunonly used in smoke-stack precipitators, means that these particles will be drawn into the atmosphere by the positive vertical potential gradient. Such 'plumes' have been observed by aircraft measurements (Vonnegut, 1958; Reiter, 1992) several kilometer from their source. Their sign causes these particles to be effective condensation nuclei, causing an increased precipitation. Although the impression is still given that no problems exist with electrostatic precipitation of smok-estacks, a remarkable lot of research work has gone into finding ways to improve the charging of small particles (Eliasson, 1986; Niessner, 0.5 1.0 1.5 Particle diameter in microns 2.0 The electric field, mixture of ions and airborne particles ~ ~ The Forgotten Pollution Section 2 Figure 1 where 1J. = ion mobility = permittivity of free space (8.854' 10 -12 F/m) e ee Figure 1. If we now introduce aerosol particles into the gap, which also become charged, we will see an increase in the threshold voltage, in the ca e of a wire-cylinder structure: VIo = V0 .-Vl = V0 • ..E.... r Vo = Vo - Vs = Vo - - p/ r Space charge in micro couloumbs per cubic meter 0.01 o 2 4 6 8 10 0.08 2 4e (p = charge density per volume) However, if an opposite charged aerosol (p /) enters the gap, then the thre hold voltage will be diminished through the increased field strength, thus: I I-V curves with space charge increasingfrom 0 - 10 JiC!m' (after Lawless et aI., 1988) 2 0.06 «oS c ~ :; u 0.4 4e o in general we get: KV(V - Vo - V,) 0.2 KV(V - Vo • Vs) depending on the sign of the space charge. o o I 10000 20000 30000 40000 Applied voltage M 50000 As mentioned, the electric wind reaches a speed of 10 m/s at moderate corona current levels. If we now take the implified impactor model oi Figure 3.4.6, where U represents me electric wind, according to Hinds (1982), me radial di placement of a particle from its original stream line is: 1t -U't 2 \vhere 't is the relaxation time of a particle: 't Chapter 3 = mB The electric field, mixture of ions and airborne panides The Forgotten Pollution Section 2 Here, m is the mass of the particle and B the mechanical mobility. In the table below the relaxation time is given for unit density particles, tandard conditions and the displacement with an electric wind of 10 rn/s: particle diameter (pm) displacement (pm) relaxation lime (s) 0.01 6.8·10" 0.001 0.1 8.8· 10" 0.013 1.0 3.6·10" 0.56 10 100 3.1 . 10" 48.7 10.2 3.1· Figure 2 Deposition in point - plane geometry as function of particle diameter (after Paulou. 1980) 4870 The figure in the table make it clear that selective deposition by electric wind will take place for monodispersive particles with diameters of I /l-m or more. ee Figure 2. However the particles drift in highly ionised surrounding and will become charged by bombardment, giving them an electric mobility Z which is related to the relaxation time: Particle diameter 0.01 pm E E 200 .s '"~ ~ c:: :£ c:: .g c:: -lS £ c:: .g 100 o 0- 0- Q) Q) o o O~-r-I o ----, • Plane radius (mm) Particle diameter 1.0 pm Particle diameter 10.0 pm 200 200 ZE o 5 ne .;:; 'tE m where E is the electric field. This velocity has disrinct values a a function of the charge it carries and is probably . the reason underlying the selective deposition in a point-plane configuration \vith a monodisperse aerosol. In case of polydi persive aerosols the deposition will be much more complicated. Cbapter J 4 4 Plane radius (mm) where e = elementary charge n = number of charges Becau e n i always a whole number, n = I, 2, 3, ... we get sharply defined electrical mobilities Z,. 7." Z" The electrical mobility will give a velocity component to the particle. v, in the direction of the local field line. This velocity i : , .. 100 'v; .~ m IJ 200 .s -lS ne z Particle diameter 0.1 pm 5 100 o ""'v;o ~ ~ 'v; 0- 100 0- o+-...........L;;.+'"'""""'"'-t-'-~~'"-"-'''''-'9 o 4 Plane radius (mm) o 4 Plane radius (mm) The electric field, mixture of ions and airborne particles The Forgotten Pollution Section 2 Figure 3.4.3 3.4.4. Back discharge Different dust load conditions as found in electrostatic precipitators Since 1907, when Frederick W. Cottrell constructed the first electrostatic precipitator, the phenomenon has been used on an industrial scale for cleaning up the visible part of smoke particles through the gas ions produced in a high voltage corona discharge, Figure 3.4.3 plate A. The particles are now also governed by electrostatic forces induced on them by the electric field of the gap and there is a tendency that they become deposited on the less stressed electrode, \vhere they are supposed to adhere, plate B. The adhesion forces are in general greater than gravitation for mo t particle sizes, meaning that the collecting electrode regularly has to be cleaned, mostly in a mechanical way. If, however, the layer is allowed to become too thick and when its resistivity is high, as is often the case with fly ash, then the charge deposited on it by the particle cannot leak away fast enough and an electric field will be built up between the top of the layer and the wall, see plate C. This can go on until breakdown of the layer occurs. This causes adversely charged gas ions and dust particles to be reinjected into the gap, considerably reducing the collecting efficiency of the precipitator through charge recombination processes. This process is known by the name of back ionization, back corona or return ionization, see plate D. Things become even worse when these adversely charged particles can reach the stressed electrode and there create a micropoint or tuft discharge site. The concentrated ionization from this site locally enhances the back ionization effects, which in their turn reinforce the micropoint sites. This kind of ping-pong mechanism is illustrated in plate E. The low mobility of the aerosol particles in the gap will act as a space charge, thus reducing the corona discharge current. But, a discussed before, the particles tend to settle on the electrodes, often covering them with an insulating layer, thu reducing gap conductivity even further. Chapter J A (-) o (-) U Particle laden gas stream lOllS 0-0--0 -0 u c i Layer break/'down 11~ j Dustlayer E (-) ~ Ions 0-0-- The electric field, mixture of ions and airborne particles The Forgotten Pollution Section 2 J What happens in the extreme case, when a whole electrode is covered, has been discus ed by Dancer (1980). Here the plane of a point-plane structure was covered with a number of papers having a different porosities. The light from the spots that appeared on the surface of the paper was reflected by a parabolic mirror and sent ro a monochromaror - phoromultiplier combination for spectral analysis. It turned out that the spots displayed mainly the second, positive sy tern of nitrogen in air and proved to be of the same nature 8S the light produced by a corona discharge. This should mean that, under these circumstances, emissive sites are created on the nonstressed electrode, something that needs some explanation. When the discharge is switched on, ions will deposit on the surface of the paper. The conduction through the paper depends on a number of factors such as humidity, temperature, thicknes , nature, etc. If we now look at the number of charges deposited and the number that move through the paper by conduction, the relationship is: I > VS o d where I = discharge current S = effective area of the paper sample V = the voltage acro s the paper sample o = the conductivity of the paper sample d = the thickness of the paper sample then crere will be an accumulation of charges and V will increase until the electric field in the paper reaches the breakdown level and several partial discharges flash across the paper, raising its conductivity locally. Nearly every charge is neu tralized and charged species are injected into the gap from the local discharge pots. In general it is assumed that this phenomenon occurs when the current den ity through a deposited layer is: Chapter 3 ~ 10-4 Am·2 10 with deposited layer resistivity in excess of 10 Om. It will be clear that electrode coverage and partial breakdown play an important role in gas discharge behaviour. 3.4.5. Conversion and selective deposition Now, a somewhat closer look at both aspects. It is well known that certain types of gases and vapours, such as: SOl' Ox' NH J , HzS, He and terpenes, found in the earth's atmosphere are easily photochemically _ modified under the influence of sunlight, forming the smog aerosol. However, the photoelectric energies, some 3-6 eV, are small compared with the 50-75 keY found in the corona discharge. It is no surprise that the molecules are broken up in the corona discharge process. By giving a special shape to the corona reacror, as shown in Figure 3.4.4, the decomposition can be enhanced. The observed decompo ition of an organophosphorous compound, pho phorofluoridic acid methyl -1,2,2trimethylpropyle ter, also referred ro as PFA is shown in Figure 3.4.5. But it is not always necessary to add pollutants ro the discharge atmosphere to get particle in the volume. Absorbed gases in the walls of the vessel and vapours released from the seals and the insulating materials will also be decomposed. However, the fragments can ho v electrical and/or chemical activation, forming larger conglomerates through different processes The electric wind associated with the corona discharge could promote larger particle formation through gradient or shear coagulation. Once formed a fraction of the particles will deposit. The deposition pattern is often circular for point-to-plane structure when confronted with monodispersive aero 01 particles, Figure 3.4.6. The electric field, mixture of ions and airborne particles The Forgotten PoDotion Section 2 Figure 3.4.4 Figure 3.4.5 Schematic diawam of a triangle-shaped DC corona device for molecular decomposition (Yamamoto et al.,1987) Decomposition in a discharge of PFA in other products and phosphorous acid (after Oothiau,1984) --- CH, CH, I I '" . : H,C - - C - - C - - 0 ·, + -I x· ".: '.. CH, ". III ...' ID T T I \, : HC - - C - - C - - O - - P - - Q j \.. ' "" It is interesting to notice that there is another aerosol impaction region in the point-plane, namely near the point. This is illustrated in Figure 3.4.7, where it can be seen that here the electric wind causes part of the velocity of the particle, while the other part comes from the velocity acquired in the electric field. Once again, the latter has only distinct values, so a size-charge dependent deposit will also occur near the point. However, the origin of the doughnut-shaped particle deposition that has sometimes been observed (see Figure 3.4.8), still remains a mystety (Hadidi, 1990). If the particles are not solid, but liquid, as is often the case with hydrocarbon gas gap fillings, filament-shaped structures will occur either on the point or at the plane, thus replacing the stressed electrode. The cone tends to Chapter 1 I I CH, H I : '// X' - Phosphorous acid F'-- Phosphono ftuoridic acid methyl- 1,2,2 trimethylpropyl ester .. .-,.,.,,, .... CH, -' .·'. CH, I · I , : H,C - - C - - C - - F '.\ I •••••• CH, ". I H + X' ".·.... . · -- ........ 3,3 Dimethyl- 2- ftuorobutane The electric field, mixture of ions and airborne partides The Forgotten Pollution Section 2 Figure 3.4.6 Figure 3.4.7 Impactor behavior of the plane in a point - plane discharge configuration Impactor behavior of the plane in a point - plane discharge configuration C IL Point_ _ : / Electricwind ,, + Resulting velocity ~ __ Resuspended partide J. \. ....... !It Plane #. Plane grow con tandy and eventually bridges the interelectrode gap a is illustrated in Figure 3.4.9. This is also often noticed in practice by those who work with two stroke motors, as a bridge between the spark plug electrodes when using a rich fuel/air mixture. 3.4.6. Electrode behaviour By using a constant current source of 1 pA, a number of small electrodes were formed (Roos, 1992). The results for some electrode metals, when exposed to ordinary laboratory air are shown in Figure 3.4.10. Plate A shows us the behaviour of a new molybdenum 100 J-Lm diameter pair of electrode as a function of time. A can be seen, the voltage that is needed to maintain the 1 pA increases with time and shows three well- Chapter 3 characterized region: a fluctuation free region that is entered directly after the high voltage is applied (1), a second region (2) with large fluctuations and a slow increase in applied voltage, and (3) a plateau without large fluctuations. Plate B shows us the behaviour of a 100 J-Lm diameter tungsten electrode set that had been formed some days before, and that showed a characteristic very similar to plate A. However, now it is clear that region (1) is skipped and that region (2) is quite hort before entering the plateau (3). Plate C shows us the behaviour of a set of new gold 100 J-Lm diameter electrodes. As can be seen no region (1) exists and the duration of region (2) is similar to that of the new molybdenum electrodes. The electric field, mixture of ions and airborne particles Section 2 The Forgotten PoUution Figure 3.4.8 Figure 3.4.10 Remarkable aerosol morphology on the point of a point- to-plane discharge geometry (Hadidi,1990) Switch - on behavior of electrodes made of different metals 3 _Region 2 Molybdenum electrode A T .. I I I o 2 4 TIme (minutes) 6 '" c: .~ ~ 7 .~ ~ S£ 6 1Lf: « • -::l ~~ Tungsten electrode >0 S -"'- .s &1 Figure 3.4.9 fat:: OJ Filament-like deposits caused by the combustion of hydrocarbons B 4 ~ IL ,.-- r o -, ,- j I 2 4 TIme (minutes) 6 7 6 Gold electrode 5 - . . . "' 21". I Chapter J I c 4 T---,-----rl----rj- o 2 4 6 TIme (minutes) The electric field, mixture ~f ions and airborne partides Section 2 The Forgotten PoUution We will tty to interpret the results globally. It is remarkable that such different results are obtained, even though the work functions of the metals used are quite close: - gold 4.00 to 4.58 eV - molybdenum 4.15 to 4.44 eV - tungsten 4.25 to 5.01 eV In fact there is a clear split between oxidizable and non-oxidi:able electrodes. The most remarkable is perhaps the absence ofnoi e with gold. It could be that the others are producing more charge carriers in the gap than gold. If we assume that this is the case, then is seems possible that these carriers are produced when the field strength over a formed oxide layer causes it to break down. The formation of this layer should be caused by electrochemical processes. The oxidation layer seems to be recovered almost instantaneously because no large fluctuations are observed and the voltage that it is capable of withstanding increases steadily. From the figure it can be concluded that each layer is capable of withstanding some 1000 V if one assumes their deposition to be ymmetrical. In order to investigate the adhesion of the layer the following tests were performed. Layer resr A formed layer can be considered as a capacitor. So if we apply a high voltage step on the electrode, an electric field will be induced between the non-charged layer top and the part of the layer touching the electrode. So betweell two particles at the extremity of the layer, with charges q I' q 2' respectively, a force of the type: F = will be experienced, where E, is the permittivity of the layer and is thus also highly dependent on its water content, i.e. the relative humidity. 1 Chapter J Thi force will have a short duration because the layer resistivity will cause the charge to become uniformly distributed after some time, so its action is more or less like a punch against the particle layer. Figure 3.4.11 shows the proposed electrode situation. A is the gold electrode, which has collected a number of airborne particles and B is the electrode covered with an oxide film as well as collected airborne particles. In case of A, the force F will be applied over the whole layer, while in B the force will de divided between the porous particle layer and the sturdy oxide film. The results are show~ in Figure 3.4.12. Plate A shows us the behaviour of gold. The high voltage is regularly interrupted long enough to allow a complete discharge of the layers. This action leaves layer formation unaffected until a certain thickness is reached. At that moment the layer seems to become unstable under theapplied impact, ~ and disappears. This re tarts the formation cycle. ~ Tachibana (1990) proposes anintermediate energization (lE) unit to be added to existing electrostatic precipitators in order to prevent back ioni:ation by electrically stressing the dust layer regularly. The effects of electrode material and dimensions have been studied by Nashimoto (1988). He found that the generation of o:one by corona discharges increases with the increase of the diameter of the wire used in a wireplate configuration. itrogen dioxide production, on the other hand, is more related to hot spots on the electrode, see Figure 3.4.13. He also observed abnormal behaviour with gold plated electrodes. The effect of electrode size and hot spots on the production of ozone and nitrogen dioxide becomes real when \~e know that electrodes tend to modify their dimensions substantially through degradation and particle interception, as is illustrated in Figure 3.4.14. It will be clear that the presence of pollutants, dust layers and different electrode materials have a great influence on the performance of equipment such as electrostatic precipitators, aircleaners, ionizers) The electric field, mixture of ions and airborne particles Section 2 The Forgotten Pollution Figure 3.4.11 photocopiers, etc. Our regular confrontation with them means that further studieij. on such equipment are urgently needed. Influence of electrode material in a point - plane discharge configuration Figure 3.4.12 The "Noble" plane electrode (A) Difference in behavior between a "Noble" and "Ordinary" electrode in a discharge system V(kV) Point Point E o 0 - .....0008,0 p:mmm1 o [ Plane Real situation, dust particles become deformed 0- 0~000 - Theoretical situation of a dust layer under electrical stress on a "gold" electrode ~ - 0080 Plane '" ~7 /' / I QJ -5 .S -a rr / Gold electrode 6 / / / 5 and when the electrical stress is taken away they bounce up again '} ~ V{kV) 10 Time (minutes) ../ 7 The "Ordinary" electrode (B) Molybdenum electrode Point Point Point .) T o 5 10 Time (minutes) '), Dashed lines - High voltage supply switched off for a short moment Theoretical situation of a dust layer under electrical stress but on an oxidized electrode Chapter 3 - Real situation, is that the oxygen takes much of the stress - so once taken away the dust layer without stress remains in place The electric field, mixture of ions and airborne particles -- Section 2 The Forgotten PoUution Figure 3.4.13 Figure 3.4.14 Amounts of ozone and nitrogen dioxide in a positive discharge (after Nashimoto. 1988) , Electrode wear caused by discharge 7 Copper tip point initial aspect 6 ~ 5 o 4 . g •.. 3 2--'------,---...-----, o 50 100 150 Wire (tungsten) diameter in J..Im : 7 7 6 6 0 '"" 6- . ~ 'x c fii • • ~ • (5 .. 65 ~ :.c co ...-... 4 0 ;;, z 3 2 -0 'x 5 .Q u fii co >--l 4 100J..lm 0 ;;, Z 2 0 100 50 150 Wire (tungsten) diameter in J..Im 0 50 100 150 Wire (tungsten) diameter in J..Im • (x 10" mol/min' J..II'V •• {x 10" mol/min' J..II'V Chapter 3 Copper tip aspect the same day after it had been used in a positive discharge The electric field, mixture of ions and airborne particles Section 2 The Forgotten PoUudon 3.5. Measuring methods 3.5.1. General Extra activated airborne particles carrying electric charges are very difficult to measure by using classic methods, uch a their capture on ordinary filters, impactors or, for example, the strips covered with glue used for the standard pollen traps. All these methods instantaneously remove all electrical information. But not only this aspect play an important role: probably of greater importance is the fact that these samplers are installed without any regard for the vertical potential gradient situation, meaning that eventual deposition becomes highly selective Benninghoff (1985). A device which measures the extra activation of the airborne particles before they can be analyzed by classical methods, one which respects local vertical potential gradient circumstances, could be the solution to this problem. The four most probable methods for fulfilling thi mission are: - the measuring capacitor method; - the filter method; - the induction method; - the discharge variation method. A brief description of each method is given below. - 3.5.2. Measuring capacitor This method is similar to the one used to measure gas ion. However, the very low mobility means that the dimen ions of such a measuring system have to be increased to compen ate for the particle interception rate. A typical example is shown in Figure 3.5.1. In the first stage ions and small extra activated particles are collected and mea ured. In the second part the large particles, here called large ions, are intercepted. ore that this section alone is almost two meters long, limiting the device's use as a portable instrument. Chapter 3 Figure 3.5.1 The ion counter (after Reming. 1939) -Electrometer It is ~ important to understand that uch an instrument must not be confused with instruments of the type called electrical aerosol analyzer . In such an instrument the initial electrical particle signature is removed by imposing a forced Boltzmann equilibrium through high energetic particles produced by a powerful radioactive source. A considerable number of charges are then added to the particle through a corona-generated diffusion charge. It will be clear that this action causes all initial charge information to be lost and that the characteristics of fragile particles become dubious under such a harsh treatment. But what is even worse is that these types of instruments tend to generate their own particles, caused by the powerful corona gas-to-particle conversion mechanism, when confronted with atmospheric air (Stelson, 1989). The electric field, mixture of ions and airborne particles The Forgotten Pollution Section 2 3.5.4. The induction method 3.5.3. The filter method Obelenski (1925) wa the fir t to use an instrument that draws in particle laden air and uses a filter to take off their charge. Since then the method has been used by numerous people, adding know-how and reliability. The filter method produces a current that is proportional to what i left of the positive charges when they have been partially neutralized by the intercepted negative charges on the insulated filter element. A modern version of the filter has been describecfby McNight (1982) and an example of a setup to test its efficiency is shown in Figure 3.5.2. Figure 3.5.2 Experimental filter test configuration. The ion interception section detects the particle leak of the filter under test Filter under test Air out -+ When a charged particle passes in front of a conductor it induce an image charge and thus a variation in the current flowing from or into this conductor. Recent development in semiconductor technology has made it possible to measure these minute current variations quite simply (Vercoulen, 1991), enabling us to establish the extra activity signature of airborne particles without intercepting them, thus making this method a highly promising one for furur,e measurements. 3.5.5. The discharge variation method Thi method uses the fact that charged airborne particle tend to modify the electrical characteri tics of a ~ ga dt charge gap, as has been explained in section 3.4.5. - The interception of these particles on the gap electrodes add to a type of back di charge mechanism, giving the sensor an extremely high sensitivity to space charges found in nature (Roos, 1992). The limited dimensions of this new space charge measuring approach are illustrated in Figure 3.5.3. This is in fact the new "real-time" space charge sensor which is the heart of the instrument that gave me the fir t close look into the Forgotten Pollution. If you want to know more about it, you are back to where we started: Chapter 1. Section 1. Rest charge Chapter 3 The electric field, mixture of ions and airborne particles The Forgotten Pollution Section 2 Figure 3.5.3 The new real - time space charge sensor, which is the device giving me the " EXTRA EYE" (see book 1 chapter I) Chapter 3 3.6. References Adachi, M., Okuyama, K., Kousaka, Y., Takahashi, T., ElecoicaJ charging of uncharged aerosol particles at variou bipolar ion concentrations, J. Chem. Eng. Japan, (131), pp. 55·60,1980. Benninghoff, W.S., Benninghoff, AS., Wind transport of electrostatically charged particles and minute organisms in Antarctica. Antarctic nutrient cycles and food webs, Ed. Siegfried, WR, Springer Verlag, Berlin, D, 1985. Berger, G., These, Univelliite de Paris ud, Centre d'O!1iay, No. 2310, 1980. Cerceau·Larrival, M·T., Nilsson, ., Cauneau-Pigot, Berggren, B., Derouet, L, Verhille, A-M. Carbonnier-Jarreau, M-C., The influence of the environment, natUral and experimental, on the composition of the exine of allergenic pollen with respect to the d~ition of pollutant mineral particles, Grana 30, pp. 532-546, 1991. Cerceau, M. Th., Derouet, L, documents. Chalmers J.A Atmospheric Electricity, Clarendon Press, Oxford, GB, 1949. 0-.aIn""" JA, little, E W. It, Currents ci anra;pheric doctricity, Terr. M:Jgn. A= 8= 52, pp. 239-260, 1947. Chalmers, J.A, AtmospheriC Elecoicity, 2nd. ed. Pergamon Press, Oxford, GB, 1967. Charuau, J., Etude du depot des particules dans des conduits, rapport CEA-R-5158, Centre d'Etudes Nucleares de Fontenay-aux-Roses, F, 1982. ClothialLx, EJ., Kolopchak, JA, Moore, R.R., Decomposition of an organophosphorous material in a silent discharge, Plasma Proc. (41) pp. 15-20, 1984. Dancer, P., Goldman, M., he Fur, D., Non-destructive breakdowns in non-impregnated papers, }. PI1YS. D., tJ, pp. 449-454. 1980. Eliasson, B., Egli, W., Hirth, M., Bipolar field and diffusion charging, Aerosol formation and reactivity, Pergamon, Oxford, 1986. Felici, N., Larigaldie, S., Experimental study of a static discharger for aircraft \vith special reference to helicopters, J. Electrostatics, 9, pp. 59-70, 1980. Aeming, ]A, Terrestial magnetism and e1ecoicity, McGraw-l-Wl, New York, USA, 1939. Goldman, A, Haug, R., Latham, R. V., A repulsive field technique for obtaining the mobility spectra of ion species created in a corona discharge, J. App1. Pysics, 47 (6), pp. 2418-2423, 1976. Haan, P.H. de, Turnhout, J. van, Wapenaar, K.E.D., Fibrous and granular filtelli \vith eJecoically enhanced dust capturing efficiency, IEEE, (2tJ), pp. 465-470, 1986. Hadidi, c., PelliOnal communiCation, 1990. Hinds, W.e., Aerosol technology properties, beh.,viour and measurement of airborne particles, J. Wiley, New York, 1982. Israel, H., Bemerkung zum Energieumsarz im Gewitter, Geofis. Pur. App1. 24, pp. 3-11, 1953. Lawless, P.A, McLean, K.]., Sparks, LE., Ramsey, G.H., Negative corona in \vire-plate electrostatic precipitators, parr I: Characteristics of individual tuft corona discharges, J. of Electrostatics, 18, pp. 199-217, 1986. Uu, B.Y.H., Pui, D.Y.H.,"ElecoicaJ neutralization of aerosols, J. Aerosol Sei.. 5, pp. 465-472, 1974. McKnight, R.H., The measurement of the space chatge density using air filtration methods, The electric field, mixture of ions and airborne particles .,. ~ Section 2 BSLR 82-2486, Nat Bur Stand., Washington, USA, 1982. Mee;ters, G.H.M., Vercoulen, P.H.W., Marijnissen, ).C.M., Scarlett, B., Generation of micron sized droplets from the Taylor cone,J. Aerosol Sci., (231), pp. 37-49,1992. Niessner, R, On the improved efficiency by use of a photoelectric charger instead of bipolar charging, Aerosol, formation and reactivity, Pergamon, Oxford, 1986. Nishimoto, K., The effect of electrode materials on 0, and NO, emissions by corona discharging, ). lmaging Sei., 32, 5, SeptJOct, I98B.Orthofer, R, Kienzl, K., Acid precipitation and forest damage research in Austria, OEFZS·A··1849, ieberdorf, A, 1990. Paulou, ]. These Universite de Pau et des pays de l'Ardour, No 102, 1980. Reiter, R, Phenomena in Atmospheric and Environmental Electricity, pp. 232-233, Elsevier, Amsterdam (NL) 1992. • Reiter, R, Reiter, M., Relations between the contents of nitrate and nitrite ions in precipitations and simultaneous atmospheric electric processes, Ree. Adv. Atmos, Elec., Pergamon press, London, 1958. Roos, RA, Electrical gas discharges and the influence of airborne pollution, These Univ. Paris SlId, 1992. Rowland, F.S., Isaksen, I.S.A., Ed. Changing the Atmospere, ). Wiley and Sons, Chicester, UK, 1988. Sagalyn, RC., Faucher, o.A, Aircraft investigation of the large ion content and conductivity of the atmosphere and their relation to metrological tiJctors, J. Aml Terr. Pltys., 5, pp. 253-272,1954. . . . Simons, P., An explosive start for plants, New ScientLSt, pp. 35·37, ]an 1993. Stelson, A, Theoretical and experimental evidence for artifact particulate matter formation in electrical aerosol analysers, Env. Sei. Techn., 23, pp. 125-, 1989. Tachibana, ., Matsumoto, Y., Intermittent energization on electrOStatic precipitators,). Electrostatics, 25, pp. 55·73, 1990. Taillet,)., La precipitation electrOStatique, Onera, Chatillon, F, 1981. Taylor, 0.1., Proc. Ray. Soc., A280, pp. 383, 1964. Yamamoto, T., Lawless, P.A., Sparks, LE., Triangle shaped DC corona discharge device for molecular decomposition, IEEE·1A, Proc, p. 1491-14%,1987. Vonnegut, B., Moore, C.B., Preliminary attempts to influence convective electrification of cumulus clouds by the introduction of space charge into the lower atmosphere, Rec. Adv. in Atrn05. Electricity, Pergamon, London, 1958. Vercoulen, P.H.W., Roos, RA Marijnissen, ].C.M., Scarlett, B., An instrument for measuring electrical charge on individual particles,). Aerosol Sci., 22, SI, pp. 335·338, 1991. Wait, o.R, Measurements by airplane of electric charge passing vertically through thunderstorms to ground, Arch. met., Wien, A, 3, pp. 70-76,1950. Whitby, K.T., Generator for producing high concentrations of small ions, Rev. Sci. Ins., 32 (12), pp. 1351-1355, 1961. White, H.j., Particle charging in electrostatic precipitation, AlEE Trans, 70, pp.II86, 195 I. Wormell, T.W., Atmospheric electricity; some recent trends and problems, Quart. ). R Met. Soc.,79, pp. 3-50, 1953. Zeleny. ]., Phys. Rev., (101), 1917. ~ The Forgotten Pollution INDEX A C acid, 21, 23, 29,33,35,36,58, 59, 70, 178, 202, 361, 380 acidification, 21, 22, 199,202, 234,250 acid rain, 21 actinometry, 240 adiabatic, 168, 170 aerobiology, 75, 142 aircleaner, 83 aircraft, 37, 82, 188, 198, 225·228,347,353,379,380 albedo, 167, 193 alcohol, 14, 117,263,264,308 alveolar, 93 Arnazonia, 66 amber, 51,129,253,343 arc, %, 298, 299 aromatic, 149, 157, 180 asthma, 150 calcite, 10 I cancer, 158 capacitor, 32, 267, 368, 374 car, 133, 142, 167, 177, 178, 180-182, 184 carbonized, 44, 51 carpet, 127,269 cat, 127, 129,331 catalytic, 177, 178, 180, 181 B back discharge, 358, 377 bacteria, 70, 135, 142, 145, 149 bactericidal, 135, 149 biomaterial, 145, 146, 198 biosphere, 86 bleach water, 58 Boltzmann, 303, 305, 308, 337·341,349,350,375 bombardment charging, 350 Brownian, 94, 113, 147, 156, 187, 189,337 bulb, 102, 104, 105, 113 buoyancy, 169, 174, 187,223, 230 cave, 90 ceiling, 100, 110, 135 cre, 150,209,211,266 chamber, 16,42, 117, 129, 132, 256, 258, 264, 287, 310, 312 chemistry, 17,27, 52, 164, 165, 167,320,321 Chernobyl, 14, 194,201 cider, 170 cigarette, 94, 123, 132, 136, 156·158,160,236,267,314, 321,325,327 cilia, 38, 93, 135, 177 cleaning, 91, 93, %, 177, 188, 192,358 clearance, 66 climate, 69, 86, 90, 100, 105, 107, 142, 145, 164, 165, 167, 170, 232, 236 climalization, 132 coagulation, 94, 97, 306, 307, 361 cold,89, 109, 112, 118, 147, 148,170-172,178,211,213, 215,223,253,295 comfort, 105 contamination, 16,99, 142, 236 conversion, 177, 184, 209, 295,361,375 cosmic, 206, 284, 335 counter, 21,123,316·319 critical field, 248, 290, 293, 294 crown, 42, 44, 47, 49-52, 294 cycle, 17,20,74, 158,320,369 cylinder, 133, 184, 185, 189, 317, 353,354 ~forpa, 21, 23,35,36,86, 236 depletion, 58 desert, 66, 195, 198, 199,203 diffusion, 341, 349, 352, 353, 375,379 dimension, 4, 36, 39, 66, 74, 86,90, 161,211,308 dimethyl ether, 136 dino,232 Oonon, 21, 2)·26, 236 downdrift, 20, 74 dust, 80, 91, 96-99, 105, 107, 109, 110, 112, 119, 127, 132, 133,135, [36, 139, 168, 171, 185,186,189,194-199,203, 254,256, 262,267,301,324, 358,369,379 E earthquakes, 229 efficiency, 96, 99, 104, 139, 149, 160, 181, 186, 189-191, Chapter 3 Index __ The Forgotten Pollution Section 2 .. 193, 197,202,276,281,287, 316,321,358,376,379,380 e1ectret, 31, 197, 344 e1ecrric wind, 48·51, 213, 215, 217,219,220,225,321,361, 362 electrolysis, 54, 55,58 electron, 105, 152,262,279, 281·284, 286, 290, 293, 299, 305,334 electronics, 98, 99, 321 e1ectrophore, 344 electroscope, 239 Electrosratic Charged Aerosol Monitor (ECAM), 14, 24, 119. 142, 178 eThyl acetate, 136 evaporation, 17,35.37,51,52, 105,107,109,113, 123,215, 228, 240, 299,313. 327 exchange, 21, 58, 74,89,93, 114, 166,244,347 extra activation, 335, 348, 374 eye, 14, 17,50,56,91, 189, 219 F fair weaTher, 21, 33, 37, 61, 83, 121, 163, 222, 239, 242, 244·246,261,272,329 fertilizer, 33, 35, 70 Held charging, 84, 349, 352 Held strengTh, 33, 61, 248, 255, 290, 293, 334, 354, 368 filrer, 16,24,25,80,96, 145, 147,160,186,197,316,374, 376 flre, 14,78,89,90,114, 117,119,121,123,156, 172, Index 194,217,263·265,287,294, 301,303,305,306,308,309, 318,321 fish,54·59, 117, 188,234 fluorescem, 102·104 fog, 24, 25, 27, 29, 30, 33, 35.37,57,58,61,64,66,80, 163, 166, 168, 170, 175, 182, 207,228,247,250,256,275, 313,325 forest, 25, 26, 35, 42, 57, 59, 63,64,66, 171·174, 182, 194, 221, 228, 234, 275,343, 380 fresh, 107, lOO, 139, 145 fume, 324 G gaseous, 29, 37, 38, 70, 115, 140,164,175,182,184,250, 259,267,287,320,321,324, 342,343,347 geology, 165 glow, 41,102,217,223,229, 248, 294, 298 granite, 132, 287 H hail,l66 halogen, 104, 105, 113 health, 91,104, 105, 127, 133, 139.142, 145, 148, 152, 154, 160, 177, 181, 188, 196,223, 260,267 heating, 78, 90, 105, 109, 110, 112,113,119,123,142,171, 182, 250, 264 heavy metal, 177, 181 high voltage, 14,90,121,133, 140, 151, 184,219,228,250, 259, 275, 344, 358, 365, 368, 369 high volrage lines, 259 hormone, 157, 158 hospiral, 223 humidifier, 142, 145 humidity, 19,26,29,66, 113, 119, 123, 142, 154, 156, 182, 184,241,248,295,308·310, 314·316,360,368 hydrogen peroxide, 22, 23, 26, 27,30,35,58,275 hydronium, 312, 315 I induction, 269, 270, 374, 377 inhaler, 149, 151, 152 integrated, 98, 99 inversion, 75, 121,347 iodine, 104, 149 ionizers, 90, 132, 136, 139·141,267,300,369 ion counter, 21,123,316·319 K Kuwait, 172, 173 L lamp, 100, 102·105, 113 leaf, 30, 33, 42, 44, 51, 61 !.enard effect, 309, 343 lighting, 102, 222 M measure, 17, 255, 271, 352, 374,377 medicine, 151 merabolism, 63, 157, 207, 261 mereorology, 165 meThylene chloride, 136 microwave, 90 mirror, 154, 156,360 mistleroe, 60 mobility, 154, 156, 189, 250, 308,309,315,318, 332·334, 354,358,374,379 model, 33, 47 monodispersive, 326,361 mordam,58 mounrains, 104, 132, 139, 140, 301 mucus, 38, 85, 93, 135 N narural gas, 23, 199,200,202, 209 nerve gas, 39 neutralization, 59, 186, 195, 379 neutralizer, 339 nicotine, 160,235 nitrates, 33, 35, 70, 171,206, 209 nitric acid, 29,33, 58, 59, 70 nitrogen oxides, 26,33,58,61, 66, 177, 182, 184,207,343 normal weather, 246, 259 nuclear, 160, 172, 194,288, 289 nuclei,35, 113, 145, 167·170, 172, 173, 182, 189, 198,199, 202,211,215,241,276,284, . 312,314,321,325,336,338, 353 0 observatory, 16, 17, 19,23,37, 39,41,53,54,69,70,75,78, 213, 2!6, 217, 222, 224, 229, 245, 246, 253, 255, 276 oil well, 173 ozone, 23, 30, 55, 58, 61, 66, 13~,.I40, 174, 175, 177, 182, 184,206·209,218,252,267, 299,347,369 powder, 103, 151,323 precipirator, 184, 188·191,358 probe, 269.271 propane, 135 pulmonary, 36, 37, 84, 135, 141,149, 151, 152, 154, 188, 325,326 Q P parenchyma, 13 particle activation, 328 particle modification, 327 particle size, 190,304, 324·326,349 Pasteur. 17, 19,75,89, 127, 146 Perche, 16, 39, 48, 49. 58·60, 69 pesticide, 36, 38, 39 petrol, 177, 180 phosgene, 136 photochemical, 23, 184,325 photolysis, 23 pigeons, 184 pisciculture, 53 plane, 167,228,290,321,344, 360·362 plume, 188, 191, 192, 194 point discharge, 13, 54, 78, 235,236,276,321,342,343 point·plane, 344, 360, 362 pollen, 17, 19,61,74, 75, 78, 80, 82·86, 132, 145, 146, 148, 163, 197, 198,203,205, 235,236,247,346,374,379 Polycyclic Aromatic Hydrocarbons (PAH), 180 polymer, 344 quarTZ, 112 R radical, 305 radioactive, 13, 14,89, 132, 140, 194,272,284,286·290, 327,335,339,341,375 radioactivity, 91, 202, 206, 286·288, 295 radon, 132,287·289,327 rain, 21, 33, 35,166,167,170, 188,213,215,239 rays, 23, 25, 206, 284, 286, 287,299,309,321,335 reactor, 14,21, 164,348,361 reduction factor, 205, 206 regime, 61, 290, 298 respira tion, 133 resuspension, 33, 36, 199 rerention, 32, 93, 156, 160 rug, 127 S sampler, 17,205,206 sap, 35, 49, 51, 53, 60.62, 215, 344 sapwood, 44, 47, 49, 53 screen, lOS, 119, 121, 123, 129,258,261·263,265,267 selective, 30, 32, 33, 35, 36, Index .. Section 2 - 61, 109, 110, 125, 139, m, 194, 198, lW, Z02, 203, 207, 209,295,361,374 sensor, 14, 119, 121, 142,377 skeleron, 86 smog, 101,301,325,361 smoke, 14,94, 117, 121, 123, 125,135,136,149, 154, 156, 157, 160, 167, 168,200, 236, 263,267,305,308,314,318, 319,321,324,325,327,348, 353,358 smoker, 123, 125, 156, 160 smolderi"ll' 321 snow, 21,61, 166, 170, 173, 199, 223, 228, 248 soot, 78, 172, 173, 303, 305, 307 spectrum, 21, 82, 104, 110, 240,300,327,348 spore, 75, 82, 84, 205 spray, 36-38, 51,135,136, 150,151, 164,266,267,323 starvation, 23, 26, 35, 36 static, 89, 90, 114, 198,236, 251, 308, 379 streamlines, 19, 147, 156,325 sun, 21, 27, 30, 103, 245, 299, 325 syndrome, 91, 92, 98,100,123 synergy,86, 170,212,213 synthetic, 107, 119, 127, 132, 261,267 Index T tape, 17, 19,78,318 tar, 157, 160, 172, 180.327 Taylor cone, 51, 139, 151, 236, 344, 380 terpenes, 20, 361 lhermionic, 140 thundentorm, 13,24,25,27, 29,30.56,60,78,84,211, 217,222,223,235,245,247, 258,259 tip, 33, 70,151,166,344 • tobacco, 135, 148. 160,235 torrential, 209, 211, 215 to"ion, 44, 50, 212 Townsend, 61, 290, 353 transport, 57, 83,127, 132, 152,193.195, 198,203,219, 235,252,286.379 trap, 17,75, 78,84 tree, 13, 23, 30, 32, 33, 35, 36, 41,47·52,54,58,60-62,64, 68,207,217,223,224,235, 261 trOUt, 55·58 1V set, 119, 121, 123,261, 264,265 U ultraviolet. 103·105, 140, 164, 167, 172, 177, 195,254,299 updrift, ZO, 21, 74 upholstery, 90, 114, 126, 135, 139 Wc, 104, 105 V vacuum cleaner, 90, 91, 95·98, 100,196 Vai50n la Romaine, 212, 229 valley, 14. 59, 216-219, 223. 275 visibiliry, 16,94, 188, 192,206, 327 V",ges, 21, 23, 35, 59. 80, 234,248 W waterfall, 140 water dropper, 37, 271 wax, 31, 38, 253, 344 white water, 53, 54, 56 Wilson, 235, 236, 241, 276, 284,312,315,316,321 wind, 19,26,33,38,41, 48·51,64,68,69,75,82. 121,192,194,195,198,213, 215,217,219,220,225,235, 242,260.321,361,362,379 Z Zelenv, 309, 310, 315. 321, 344,380 Rein A. Roos The Forgotten Pollution The Increasing pace of Industrialization throughout the world has brought with It a serious, and ever Increasing threat from air pollution. It Is true that this threat Is being taken seriously, and that many responsible research workers, government advisors and others are working towards Its reduction. But air pollution seems to have something of the nature of a hydra-headed monster: tackle one problem and another immediately grows to take its place. Actions taken sometimes have results that are far from what was envisioned, sometimes even seeming to make the problem worse. In "The Forgotten Pollution", Roos shows clearly and In an often entertaining way, how many of the "unexpected" side effects of pollution by waste gases and particles can be explained by paying attention to the electrical activity of the atmosphere and the earth. Using an Instrument, which he has developed the Electrostatic Charged Aerosol Monitor (ECAM), together with other instruments and reference to the literature, much of it dating back to the early days of science, when electrostatics was appreciated as a science more than It Is today, Roos has succeeded In explaining many hitherto "puzzling" phenomena in a clear, simple and intellectually satisfying way. 1SBN 0-7923-3917-7 Kluwer Academic Publishers I 9 780792 339175 Kluwer Academic Publishers !