Study of electric field, Aitken nuclei, gaseous...
Indi an Journal of Pure & Applied Physi cs Vol. 40, February 2002, pp . 141-148 Study of electric field, Aitken nuclei, gaseous concentrations and ionic conditions in contrasting environment S S Kandal gao nk ar, M I R Tinmaker, M K Kulkarni & Asha Nath In dian In stitute of Tropical Met eoro lo gy, Pune 411 008 Recei vcd 25 April 200 i; revised 12 December 200 I; accep ted 4 Janu ary 2002 Ground based observa ti ons of e lec tri c fi eld , Aitken nu clei (A N) and co ncentrati on of trace gases in fai r weather cond iti ons we re made at four locati ons hav in g different e nvi ro nmental status (oceanic, hill-top , se mi-urban a nd industri al). Th e effec t o r co nce ntration s of Aitken nuclei and trace gases on atmospheric electric field at these iocations was exa min ed and an atte mp t was made to obtai n e ffec ti ve att ac hment coe ffi cient s and mea n life time s mall ions at th e lo ca ti ons. The results showed that in clean and relatively less polluted regions th e diurnal as we ll as monthl y mea n va ri ati on of fair weather electric fi eld wa s significan tl y (0.0 1%) correlated with Aitken nucl ei co ncentrati on. An examination of gaseo us concentrati ons suggested th at th e elec tri c fi eld was observed to be adversely affected in the reg ion s whi ch were enriched with th e S0 2 load in g and th e parti cu late matt er from th e industri es. The va lu es of att ac hment coe ffi cient s and mean li fe time or sma ll ions ob ta in ed in th e present se t of study re vealed that environmental statu s is an import ant factor to affe ct th e air pollutants whi ch in turn affect th e electri ca l paramet ers. 1 Introduction The avera ge value of the earth's surface vertical electric field in fair weather co ndition is conventionally taken as positive 1 • Generally fair weather surface electric field may exhibit variation in it s mean value in accordance with the tropographic and lo ca l features of a place2-1. Reports of short and long term influence of s moke and loading of charged and uncharged nuclei and gaseous co ncentrations in the lowest atmospherex -u suggests that the electrical properties of the lower atmosphere may be modified by its environmental status. Th e authors had a set of short period observations of electric field and Aitken nuclei concentration at oceanic, industrial, hill-top and semi-urban locations. It was thought, worthwhile to study few aspect of their variation and project the results thereof. 2 Observational Sites and Measurements During the years ( 1981-1987) field experiments were conducted in fair weather conditions for a period of about eight to ten days at the following locations whose details and environmental status are given below and also in Table I. I Off-shore oceanic region (0)- Arabian Sea, Indian Ocean and Bay of Ben gal regions around the Indian coast in the distance ran ge 25-135 km during May 1983 ( I 0 days). 2 Hill-top regions (H) - Over the Sinhagad fort ( I8°32'N, 73°45'E , 1315 m ASL) situated - 20 km so uthwes t of Pune during Januar y 1982 ( 4 days). 3 Semi-urban lo cation (SU)- At Pashan nearl y 12 km N of Pune (18°32'N, 73° 5l'E, 559 m ASL) during November 1986 to December 1987 . 4 Industrial location (/) - In the close and near vicinity of a thermal power station Sarni, MP . Indi a (22°0 7'N, 78° I O'E, 436 m ASL) for I 0 days in October 1981 and 8 days in May 1982. During the field experiments, at above locations continuous record of electric field was taken and Aitken nuclei (AN) concentration was also monitored. Electric field was measured by employing P" -21 0, 6 1..1. Ci sensor as a potential equalizer and solid state electrometer operational amplifier. The output from the electrometer system was fed to I rnA ink recorder with chart drive speed of I em per min . The accuracy of the recorder is 2 Vm- 1 • Details of the instruments, and recording techniques have been described elsew here 14 - 19 • For the measurement of AN concentration a portable expansion type counter was used and gaseous
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Indian Journal of Pure & Applied Physics Vol. 40, February 2002, pp. 141-148
Study of electric field, Aitken nuclei, gaseous concentrations and ionic conditions in contrasting environment
S S Kandalgaonkar, M I R Tinmaker, M K Kulkarni & Asha Nath
Indian Institute of Tropical Meteorology, Pune 411 008
Recei vcd 25 April 200 i; revised 12 December 200 I; accepted 4 January 2002
Ground based observa ti ons of electri c fi eld , Aitken nuclei (A N) and concentrati on of trace gases in fai r weather cond iti ons were made at four locati ons having different envi ronmental status (oceanic, hill-top , semi-urban and industri al). The effect or concentrations of Aitken nuclei and trace gases on atmospheric electric field at these iocations was examined and an attempt was made to obtai n effecti ve attachment coeffi cients and mean life time small ions at the locations. The results showed that in clean and relatively less polluted regions the diurnal as well as monthl y mean vari ati on of fair weather electric fi eld was significan tl y (0.0 1%) correlated with Aitken nucl ei concentration. An examination of gaseous concentrations suggested th at the electri c fi eld was observed to be adversely affected in the regions which were enriched with the S02 load ing and the particu late matter from the industri es. The values of attachment coeffi cients and mean li fe time or small ions obtained in the present set of study revealed that environmental status is an important factor to affect the air pollutants which in turn affect the electri cal parameters.
The average value of the earth's surface vertical e lectric field in fair weather condition is conventionall y taken as positive 1
• Generally fair weather surface e lectric field may exhibit variation in its mean value in accordance with the tropographic and local features of a place2-1. Reports of short and long term influence of smoke and loading of charged and uncharged nuclei and gaseous concentrations in the lowest atmospherex-u suggests that the electrical properties of the lower atmosphere may be modified by its env ironmenta l statu s. The authors had a set of short period observations of electric field and Aitken nuclei concentration at oceanic, industrial , hill-top and semi-urban locations. It was thought, worthwhile to study few aspect of their variation and project the results thereof.
2 Observational Sites and Measurements
During the years ( 1981-1987) field experiments were conducted in fair weather conditions for a period of about eight to ten days at the following locations whose details and environmental status are given be low and also in Table I.
I Off-shore oceanic region (0)- Arabian Sea, Indian Ocean and Bay of Bengal regions around the
Indian coast in the di stance range 25-135 km during May 1983 ( I 0 days).
2 Hill-top regions (H) - Over the Sinhagad fort
( I8°32'N, 73°45'E, 1315 m ASL) situated - 20 km southwest of Pune during January 1982 ( 4 days).
3 Semi-urban location (SU)- At Pashan nearl y
12 km N of Pune (18°32'N, 73°5l'E, 559 m ASL) during November 1986 to December 1987.
4 Industrial location (/) - In the close and near vicinity of a thermal power station Sarni , MP. Indi a (22°07'N, 78° I O'E, 436 m ASL) for I 0 days in October 1981 and 8 days in May 1982 .
During the field experiments, at above locations continuous record of electric field was taken and Aitken nuclei (AN) concentration was a lso monitored. Electric field was measured by
employing P"-21 0, 6 1..1. Ci sensor as a potential equalizer and solid state electrometer operational amplifier. The output from the electrometer system was fed to I rnA ink recorder with chart drive speed of I em per min . The accuracy of the recorder is 2 Vm-1
• Details of the instruments, and recording techniques have been described e lsewhere 14
• For the measurement of AN concentration a portable expansion type counter was used and gaseous
142 INDIAN J PURE & APPL PHYS, VOL 40, FEBRUARY 2002
concentrat ions (S02, NH3 and N02) were measured by wet scrubbing method211
3 Results and Discussions
3.1 Association between electric field and Aitken nuclei
In fair weather and c lear sky condi tions and in the normal atmospheric conditions the atmospheric electric fie ld is conventi onall y positive and its magnitude mainly depends on the value of local conducti vity-the electric fie ld could be anywhere in the range 50-200 vm·1 as the place is remote, nonurban and active urban respective ly 17
• Table l shows the fair weather average electric field (Vm-i);
concentrati ons of AN (Z) and small ions (n); rate of small ion production (q); effect ive attachment
coeffi c ient (/3) and mean life time of small ions (8) at the above said locat ions . From Table I , it is seen that on an average the magnitude of e lectric field and Aitken nuc lei is increased as the site of measurement is shifted from m re clean and isolated locati on (0 and H) to semi-urban and industrial location (SU and 1). T hese va lues are 70, 150, 170 and -534 Vm- 1 and 580, 680, I 0,000, 54,000 cm·3 respective ly at above locations. At an industrial location the electric !fie ld values undergo a change in its polari ty (Table 1). Th is may be due to corresponding increase in Aitken nuc lei , presence
Table I- Fair weather average electri c field (Vm.1), concentrati ons of AN (Z) and small ions (n); rate of small ion production (q);
effective attachment coefficient (~); and mean life-time of small ions (8) and gaseous concentrations in clear sky conditi ons at different environmental locations
Electric fi eld (Vm-i)
Concentration of AN (Z) (N cm.3)
Concentration of small ions n (cm"3)
Rate of small ion producti on q (cm·3 sec-i)
Effective attachment coefficient ~ (cm·3 sec- 1
Mean life- time e (sec)
Off-shore oceani c region (0)
May 1983 (10 days)
4 .6 X 10·~
3.0 1.6 1.8
Locat ion and Period
Hill -top region Pashan (6 km NW of Industrial location Sarni Singahad Hill Pune IMD observatory) (H) semi-urban location (f)
18 January 1982 November 1986 to October 198 1 ( I 0 days) (4 days) December 1987 (winter May 1982
season) (8 days)
150 170 -534
680 10,000 54,000
1100 780 80
1.9 14.4 14.4
0.18 X J0-6
76 54 5.5
Gaseous concentration (Jlg m·3)
1.5 5.8 14.0 2.8 1.8 4.0 0.5 2.0 1.5
KANDALGAONKAR et ai.:STUDY OF ELECTRIC PARAMETERS IN CONTRASTING ENVIRONMENTS 143
OIST Zero J' 10 km
~ ~ 69000 Neg.
~ RECORD IN COCHIN KARBOUR N cm·J
mo 1740 I 18 I 8 I 0
Pas. 429 N cm·3
Zero -t OIST. ... 12 0 kin
__. .___. Neg. __., 9·5-1983 ~
980 H cm ·3 Pos. ·
.,- 7~~~ Zero
17ZO 17!0 I 4 I 0 1800 1810 18 20
Fig. I - Sample records of electric tield in harbour environment and at large coastal di stances
and di spersal of negatively charged aerosols released into the atmosphere during the combustion process15
• It also indicates that as compared to oceanic region (0 ) at a hill top location (H) , for a sli ght or negligible increase in AN concentration the corresponding increase in the e lectric field (from 70 to 150 Vm-1
) is noticed . This increase in the e lectric field at a hill top stati on is attributed mainly due to two reasons. Fi rst ly as proposed2
\ the lowest part of the columnar resistance is absent at a mountain station which in turn is the like ly reason for higher value of electric fi e ld . Secondly the applicabi lity of electrode effect25 over-vegetated land21 at Sinhagad. The average value of electric field at Sinhagad was
150 Vm·' which is al so in close agreement ( 149 Vm') with that reported e lsewhere24
At a semi-urban (SU) location the AN concentration is seen to be enhanced and compared to this increase in AN. There is a lso increase in e lectric field value from 150 to 170 Vm·' . The observed simu ltaneous change in elec tri c f ie ld and AN suggests that the two parameters are close ly correlated . This feature can be clearly seen in Fig. I which shows the sample record of offshore sea surface electric field observations for three days i.e ., 9'h, 13'h and 19'h May 1983. It is seen that on 9th and 19th May the surface e lectric field was low and positive and AN concentration was also low due to
144 INDIAN 1 PURE & APPL PHYS, VOL 40, FEBRUARY 2002
clean environment as the observation ship (ORV Gaveshani) was 120 and 70 km respectively away from the coast 1x. While on 13'h May the ship was anchored amidst the exhausts due to marine traffic in the harbor and as an effect the authors noticed that AN concentration had markedly increased and a lso that e lectric field tended to be frequently negative (Fig. I). Thus, the effect of marine pollutants on above parameters can be c learly seen.
3.2 Diurnal variation of electric field and AN concentration
Fig. 2(a) shows the diurnal variation of atmospheric el ectric f ield observed during the oceanic measurements of the Carnegie and Maud Expedition s. The diurnal variation curve of the e lectric fi e ld and the AN averaged for I 0 days is shown in Figs 2(b and c) , respectively. From Figs 2(b and c) it is seen that e lectric fie ld and AN concentrat ions exh ibit parallel variations giving the first maximum around 0200 hrs UT. Comparison of Figs 2(a and b) shows that there is shi ft in the time of occurrence of first maximum. Thi s difference in the time of occurrence of the maxi mum, may be due to the shorter time averages used in the present study'' which shows the great departure from the Carnegie curve. Further it is also noticed from Figs 2(b and c) that the two parameters i.e .. e lectric field and AN are correlated and the correlation coeffic ients between them IS 0.35 which IS
s ign ificant at less than 0.1% level.
3.3 Monthly variation of electric field and AN concentration
Figs 3 (a-b) shows the monthly variation of electric field and AN concentration at Pune on fair weather days for the one year period. From these figures it is seen that during the annual course, the two parameters exhibit a trough shape variation with maximum during winter months (NovemberFebruary) and minimum during monsoon months (June-August). This result is in good agreement with earlier studies21
• Thei r studies revealed that during the winter season the transport of nuclei of continental origin by air masses passi ng over land from the east. The lower concentration of AN during monsoon period were due to maritime characterist ics of prevailing winds coupled with washout effects. The correlation coefficient between these two parameters is 0.931 which is
significant at 0.0 I % level. These observations corroborate the results 1 and the di rect relationship between e lectric field and Aitken nuc le i.
c 0 u
0 12 I ~ . 6 1!3 20 22 [<
Ti~r,e (UTC j
Fig. 2(a)- Diurn al variat ion of potential gradient over oceans (from Whipple and Scrase, 1936)
E ::: 80-
ii: 70 -~ ~ m 60
- • - Electric Field
~~--~~~~~-.~~~~~ 9 11 13 15 17 19 21 23
Time (U TC}
Fig. 2(b)- Diurnal variation of electric fi eld in the oceanic atmosphere around the Indian sub--continent
- • - Aitken Nuclei
1\ . I .\ .-· ~. -· ~ · ~ J -· I ,/ . ".-·,.
\ i • I \ . ,,~
11 13 15 17 19 21 23
Fig. 2(c)- Diurnal variat ion of Aitken nuclei in the oceanic atmosphere around the Indian sub-cont inent
KANDALGAONKAR et al.:STUDY OF ELECTRIC PARAMETERS IN CONTRASTING ENV IRONMENTS 145
- Aft ken Nuclei
Jill Feb Mil Apr May J111 Jul AUJ Sep Oct Nov Dec
Fig ure 3a
Fig. 3(a)- Monthly variation of electric field at Pune
.. 250 ~
i150 ~ u E 100 w
-- Electr~ Field
Jill Feb Mr ~r May Jm Jul Alll Sep G:t NO¥ Dec
F. Jb Months 1~ure
Fig. 3(b)- Monthly variation of Aitken nuclei at Pune
3.4 Influence of gaseous concentrations on electric field and Aitken nuclei
Gaseous concentrations (S02, NH3 and N02) at four locations is shown in Table I. It is seen that out of these three gases the variation of NH3 and N02
does not show any specific trend with respect to environmental status of the location . However, S02
concentration showed cognizant increase (i.e. 13.6 ~-tg/m3) and this is perhaps consistent with the status of the location. Studies regarding the gas concentrations in contrasting environments were also available in literature 13·26'27. These studies
revealed that the variation of NH3 and N02 are sitedependent but the concentration of S02 and smoke pollution depends on the material and mode of burning fuel in the industry23 •28 · 2~ along with some meteorological conditions. In some other studi es30
suggests that an industrial location the concentration of so2 is higher due to direct emission from the industries .
In the present study, the authors also observed that, higher concentration of S02 at semi-urban and industrial location where the electric fi e ld and AN
concentration was found to be hi gher. Earlier studies13·26 mentioned that in the presence of so2 plumes and when the concentration of so2 exceeded 250 !-lg m·3, the concentration of large negative ions was greater than that of positive ions and the difference between small positive and negative ions reached nearly zero. In the present study when S02
concentration at semi-urban, oceanic and hill top is much less as compared to industrial location, it may be possible that the balance between positive and negative ions is not much disturbed and this may be the possible reason for getting the positive electric field at these locations.
However, at an industrial location (f), where so2 concentration and smoke pollution are more, the observed negative electric field is quite expected as the smoke aerosols have been recognized as the negatively charged particles8
·30 due to chemical
combustion ionization process at an industry34•
Hence the observed negative electric field at an industrial complex appears to be consistent and reasonable 17
4 Attachment Coefficient and Mean Life Time of Small Ions
Knowledge of Ion aerosol attachment coefficients and mean life time of small ions is important for aerosol size distribution7 and for understanding of the electrical properties of the lower atmosphere in different environments and also for studying environmental problems particularly in relation to pollution. In the lower atmosphere, the ions are produced by the emanations from radioactive elements of the so il and by radioactive gases . The normal processes of production of ions give small ions and not direct ly any large ions 1
• Large ions can be produced only by the attachment of small ions to nuclei. The small
146 INDIAN J PURE & APPL PHYS, VOL 40, FEBRUARY 2002
ions thus fo rmed in the atmosphere dissipate in three ways. Firstly by the recombination with small ions of opposite sign giving neutral mo lecul es, secondly, by comb ination with large ions of opposi te sign givi ng a neutral nucleus and neutra l molecules (more than one if the small ion has attached mo lecules) and lastly, by the combination with a nuc leus to give a large ion. In the aeroso l free environment the ions are destroyed by the ion-ion recombination . Large ions can be destroyed by the combinati on wit h small ions of opposite sign or by combinati on of large ions of oppo ite sign and in each case neutral nucl e i are formed. The number of combinati ons that occur in unit time in a given volume is proportional to numbers present in the two types of particles concerned and the factor of proportionality de fines the attachment coeffic ients. The interval between the ion for mati on and d iss ipati on is broad ly termed as the li fe-time and it van es under different atmospheri c and environmental conditions in the range of few tens of seconds. For the mean life time or ion depletion calculation the important requirement is the abso lute values of ion ae rosol attachment coeffic ients . The au thors worked out the values of
attachment coeffic ient CP) and mean li fe-time (8) at above sa id locat ions (0, H, SU and l) by using the formulae given 12 and di scussed in the literature".
T he following equations are used to obtain the
above va lues:
q I f3 =- and fJ =-
where P is the effecti ve attachment coefficient between small ions and Aitken nuc lei (em·' s·1
); q the rate of small ion production (cm·3 sec-1
); n the concentrati on of small ions (cm 3
); Z Aitken nuc le i concentrat ion (N cm-3) and 8 is the mean life time of small ions (seconds).
Out of these above parameters, the parameter z (i.e., Aitken Nuclei concentration) at these four locat ions was already available21
• The parameter n i.e. small ion concentration for above said locations was adopted from elsewhere 111
.32 si nce the
observati onal s ites in both cases were identical. q values (i.e. the rate of small ion production) for oceanic , hill-top and land regions were taken as 1.9, 1.9, and 14.4 respecti veJy 1. 12
• These va lues are beino 0
most commonl y reported in literature for the environments under study.
Table I shows the location-wi se values of the
above two parameters CP and 8). Ta le I shows that
the maximum values of P and e were obtained at the clean and pollution free environments and then these are markedly reduced at an industria l location where the leve l of pollution is the highest (max imum). It is seen that in the present set of observational site (i.e. at 0, H , SU and I) the va lues of attachment coeffic ient are in the range of 0.1885 - 4 .6798x I o-fi em' s·1
• Hope i ( 1985) made study of ion aerosol attachment coeffic ient in both cont inental and oceanic atmosphere and showed that over ocean aerosol size di stribution is found to be nearly constant for a peri od of many hours. Thus marine environment will usuall y be in charoe equi librium. Further the same stucl y31 r.evea lecl th~t in oceanic atmosphere where part icle concentration was 27370 em·', the va lue of effecti ve attachment coefficient was observed to e 0. 89x I o·fi cm3 s·1
while at 161 nautical miles in the oceans where
particles concentrati on was 400 em·', the va lue of p was 5.84x I o-fi cm1 s·1 and in more remote regions where the partic le concentrati on was 200 em·', the
value of P was 3. 18x I o-fi cm3 s·1• ln some other
st d. 33 12 f N U · · u tes · or agoya mvers1ty , Japan these were in the range of 0.7-7 .0 and for locati ons such as mountain and island, they were in the range 1.9-6x 10-fi em' s·1 and 0.7 to 9.0x JO·fi em' s·1 respectively A comparison of the above values reported elsewhere suggests that, the values reported in the present set of location appeared to be consistent. The higher value of p over the ocean in the present study may be due to large number of surface generated sea salt partic les 31
It is mentioned 1 that mean life-time (8) va lues are higher for cleaner and re latively pollution free environment and these are reduced with respect to polluted locations. In the present study mean lifetime for above set of locations was obtained by
using P values for respective locations and given in Table I. The mean li fe-time at the cleaner and pollution free environment (oceanic) was maximum (368 sec) and its magnitude decreases with the level
of pollution (Table J ). The min imurn va lue of e was obtained at an industria l location (5 sec). This maximum mean life-time of ions over the oceanic
KANDALGAONKAR et a /.:STUDY OF ELECTRIC PARAMETERS IN CONTRASTING ENVIRONM ENTS 147
region may be due to constant aeroso l size distribution over a period of many hours and thus keeping the marine env ironment in charge equilibrium and also to some extent low turbidity of the air over the sea surface31
If simultaneous measurements of electric parameters especially conductivity, particle sizes and ionization rates etc. are made at point locations in different environments, a functional relationshi p of these parameters could be studied in detail.
A case study of the results and discuss ions on the electric field , Aitken nuclei and gaseous concentrations, in the contrasting environments over the Indian region suggests the following:
(i) In clean and relatively less polluted regions the seasonal fair weather average electric field was observed to be positive in the range 70-170 Vm' 1
Also at such locations diurnal as well as monthl y mean variation of fa ir weather electric field to be significantly (0.01 %) correlated wi th the loading of Aitken nuclei concentrations. The regions experiencing substantial loading of sulphur dioxide and charged particulate matter from the indust ries, the vari ations in the electric field were irregul ar and indicated a possibility of getting adversely affected.
(ii ) The values of effective attachment coefficients and mean life-time of ions obtained in non-industri al locat ions in the present study were in good agreement with the reported ones. At an industrial location these values were reduced which may be due to the charge and size di stribution of aerosols in that environment.
The authors are thankful to the Director, Indian Institute of Tropical Meteorology for planning the field experiments. They are also thankful to the supervi sors of respecti ve locations for providing the facilities during the period of field observations .
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