\\-t \~~
IndianJournalofRadio&SpacePhysics Vol.22,August1993,pp. 2{)7••214
*This paper was presented at the National Space Science Symposiumheldduring11-14March1992at PhysicalResearch Laboratory,Ahmedabad380009.
5"'5\ '53
Air pollution and acid rain problems in the Indian region*
---
~Ot - \1
L TIKhemani
(Indian Instituteof TropicalMeteorology,Pune411(08)
~ Ii 8eptembcc't992yreWed-Z9IM:emhert992;accepted9'March 1993
I~
problems of air pollution and acid rain in India are reviewed.Gaseouspollutants like802 and N~ are high in a few large cities in India, whereas at other locations their concentrations are in the range of background levels.The concentrations of total suspended particulates in coastal Kerala and forest regions are within 100 ~ m -3,but in north-west and central India they are quite high and vary between 200and 550 J.tgm -3• The concentrations of soil-oriented components (AI, Fe, Mn,ea,_K
and Mg)., are higher in aerosolsand the concentrations of componentsfrom anthropogenic sources(pb, Ni, Cd, Zn, Cu, Sb, S04 andN03) are lower than those reported for western countries which are industrially more developed. There are more cations (Na, K, Ca and Mg) than anions (S04 and N03) in the aerosols reported from different environments. These aerosols, which are potentially basicin nature, influencethe acidificationof rain water.
The mass size distribution of aerosols reveals that coarse particles (natural sources) dominate over the submicron particles (anthropogenic sources) in India. It is observed that precipitation in India is, by and large, alkaline. It is of interest to notice that rain water in Chembur, a highly industrialized area in Bombay regionwhich was reported acidicfrom 1974to 1980,turned alkaline in 1990.Thi!lcould becomepossibled~
to proper pollution control measures taken by industries in the area. Acid rain, wherever it has occurred in India, is purely a local phenomenon and is restrictedwithin2 km distancein the upwind and downwind of the industrial complexes. If (
15'"
\(l ~t )
1 Introduction 2 Gaseousand particulatepollutants
There is sufficient evidence available to prove that The principal precursors of acid rain are emissions large anthropogenic emissions of sulphur and of sulphur dioxide (S02) and oxides of nitrogen nitrogen oxides to the atmosphere have a profound (NOx)' In addition, a variety of other emissions also influence on the chemical climate of Europe and influence acidity, notably among them are hydro- North America which have shown harmful effects on chloric acid, ammonia, volatile organic compounds, aquatic and terrestrial ecosystems of theseregions1•2• and alkaline dust. These species have both natural But even today very large differences exist in the per and anthropogenic sources. Natural emissions capita emissions. of air pollutants between in- include biogenic emissions from terrestrial, tidal and dustrially developed and developing countries. For neutrient-rich oceanic areas, and non-biogenic example, the per capita emission ofS02 in India is less emissions from natural combustion, geothermal than 5% of that in North America3• However, there activity, lightning, and airborne soil and water are apprehensions that due to increase in population aerosols. The main anthropogenic sources are and large-scale industrialization in developing man-made activities like industries and vehicular countries like India, per capita emissions will increase traffic.
by a factor offour which will bring the level to 30% of As urban areas are the main centres of man-made the per capita emissions in North America and activities, the levels ofS02, N02 and total suspended
Europe4 -6. particulates (TSPs) at these locations will show how
In view of the above, it is pertinent to examine the far they are affected by pollution sources. For this air pollution problems in India and their influence on purpose average monthly concentrations of S02, acidification of rain water. For this purpose, N02 and TSPs for ten large cities in India, namely, published data on gaseous and part~cu1ate pollutants Ahmedabad, Bombay, Calcutta, Cochin, Delhi, andprecipitationchemistryhavebeenexamined,and Hyder~bad, Jaipur, Kanpur, Madras and Nagpur, the results of the study are presented in this paper. are given in Fig. I (Ref. 7). The monthly average
concentrations are representative of industrial, commercial, and residential areas. The concentra-- tions of S02 and N02 are higher in industrial and commercial areas as they are directly affected by the
Ten Large Cities in India (1982-85) Fig. I-Average monthly concentrations of S02, N02 and TSP for 10large cities in India (AHM, Ahmedabad; BMB, Bombay;
CAL, Calcutta; CHN, Cochin; DHL, Delhi; HYD, Hyderabad;
JPR, Jaipur; KNP, Kanpur; MDS, Madras; and NGP, Nagpur).
INDIAN J RADIO &SPACE PHYS, AUGUST 1993
208
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3 Chemical and physical characteristics of aerosols Atmospheric aerosols are important in various fields, such as agriculture, defence applications, environmental pollution, meteorology, cloud physics, acid rain, climate change, etc. The knowledge of the mass size distribution of atmos- pheric aerosols is of fundamental importance to any discussion of their measurement, chemistry, physics and aerosol air quality. We know that atmospheric aerosols have three modes with respect to their sizes . First is called the nucleation mode, second the accumulation mode, and third the coarse mode. The coarse mode is built of particles greater than I J.lm radius which are produced by disintegration of sea spray and/or mineral dust. The nucleation mode (size
<
0.1 J.lmradius) of the particles is generated from gas-to-particle conversion of precursor gases. The nucleation mode is not stable and is converted by coagulation into the accumulation mode (size between 0.1 and I J.lm radius).Although investigation on aerosols in India was initiated in the early sixities, yet the research in this direction was limited to the physical characteristics of aerosols till recently. Of late, studies of chemical composition and mass size distribution of aerosols have been conducted over the urban regions7.10-18, and at remote locations and forest areas9,19,20.
11.11
J
sources which are close to them. Calcutta is the highly polluted city and Cochin is the least polluted. Barring three metropolitan cities, namely, Bombay, Calcutta and Delhi, the concentrations of S02 and N02 are quite low in the remaining seven cities. However, the concentrations of TSPs are, by and large, very high and vary between 200 and 500 f.lgm-3 except at Cochin where the concentration is below 150f.lg m -3.
Khemani et al.8have taken observations of trace gases (S02,NH3, N02 and 03) from 1981to 1984at 6 different locations representative of urban industrial, urban, non-urban, thermal power plant and marine environments. They concluded that average con- centrations of N02 and 03 were in the range of background values. Except in urban industrial environment, the concentration of NH3 was in the range of background value. The concentrations of SO.2were substantiany higher (by nearly 7 times) in urban industrial and thermal power plant environ- ments compared to those in other environments studied. However, the levels are much lower (by nearly 6 times) than those reported for western countries. Recent observations on trace gases referred to above have indicated that the forest areas in the Nilgiri Biosphere Reserve located in South India are so far free from the influence ofindustrial pollution9.
4 Chemical composition of aerosols
The average concentrations ofTSPs and their acid soluble components at different locations are given in Table I. It is seen from this table that there is a large variation in the concentrations ofTSPs in India and they have varied from 39 to 507 J.lgm -3 •Such large variations have also been reported for 10large cities in India where the levels varied from 200to800J.lgm -3
(Ref. 12). Soil in north-west and central India is, by and large, loose and most of the time is not covered by vegetation. The winds erode this type of soil easily and raise a lot of dust which contributes to high levels of particulates in the atmosphere. The areas which are influenced by dust will record high levels of TSPs.
This inference is also supported by the chemical composition of aerosols given in Table I. The concentrations of soil-oriented elements, namely, AI, Fe and Mn, were much higher compared to those contributed by anthropogenic sources (Pb, Cd, Zn, Cu, Ni and Sb). The concentrations of Pb at the locations referred to in Table I were quite low because of the locations of sampling sites. The Pb con- centration will be high at those places where the traffic density is ~more. The concentration of Pb was reported 560ng m -3at King's Circle, Bombay, where vehicular traffic density is very high. The lowest value
, 1'1
I
"II
'I' ., nll'I'" 'II I~ I U 1;'Ult 1111111111' 111111,·1111illl,HlIII Ulhl' IIIL , "Table I-Average concentrations of TSPs and their acid-soluble components at different locations in India and
in some western countries Location
of samples Al
Sea areas
Sinbagad Thumba
Raichur Pune Delhi Sarni West Virginia
(USA) Milan (Italy)
Washington D C Lancaster (England)
Table 2-Average concentrations of water-soluble components of TSPs at different locations in India and
in some western countries
Location No.
CI Sea areas
Thumba SinhagadRaichur Tuticorin PuneDelhi Sarni
West Virginia (USA) England
Berlin (Germany) Vienna (Austria)
(16 ng1ll- 3)was reported at Matheron, a hill station located in Maharashtra State, where vehicular traffic is very low24•
The average concentrations of water-soluble components ofTSPs at different locations are given in Table 2. The concentration of sea salt in the aerosols was maximum near the coastal regions and decreased with an increase of distance from the oceans. The concentration of sulphate was, by and large, in the range of background values. The concentration of nitrate in the aerosols was quite high. The high concentration of nitrate normally indicates the influence of anthropogenic sources. But, it has been
shown that most of the nitrates in aerosols are originated from the soil and hence do not playa role in the acidification of aerosols28, Among the cations, concentration of calcium seems to be quite high. Very high values of Ca concentration are reported in aerosols as well as in rain water throughout India.
Even though the concentrations of remaining cations (NH4, K and Mg) in aerosols are low, they play an important role in the neutralization of hydrogen ions caused by acidic sulphates and nitrates.
It is seen from the above discussion that soil and sea salt are the major natural sources of aerosols in India and the concentrations of nitrate and sulphate
210 INDIAN JRADIO &SPACE PHYS, AUGUST 1993
released from industrial sources are quite low. As soil in India is highly alkaline, alkaline aerosols released from it have large influence on thepHof rain water in India.
Khemani28 has surveyed the physical and chemical compositions of aerosols for a few locations in India which are representative of urban, non-urban, marine, and thermal power plant environments. The conclusions derived from this survey are:
(i) The average levels of TSPs in India are quite high than the recommended standards in USA and European countries. In most of the large cities in Europe and USA, major sources of TSPs in atmosphere are industrial plants and vehicular efuissions, whereas in India most of the TSPs are from dust particles carried by winds from arid zones and nearby surroundings. The concentrations of soil-oriented elements (AI, Fe, Mn, Ca, K and Mg) are higher, and concentrations of components from anthropogenic sources (Pb, Ni, Cd, Zn, Cu, S04 and N03) are lower in India than those reported from the western countries which are industrially more developed. The concentrations of some of the above components reported from western countries are given in Tables I and 2 for com- parison21 - 23.25- 27.
(ii) There are more cations (K, Ca and Mg) than anions (S04 and N03) in the aerosols in India. These aerosols are potentially basic in nature and hence influence the acidification of rain water in India.
(iii) The mass size distributions of atmospheric aerosols have shown bimodal distributions in all the environments. The lower mode has been observed in submicron size range (0.4-0.6 /lm diam.) and the higher mode in the giant size range(5.6/lm diam.).
The particles in submicron mode are formed by gas-to-particle conversion processes, whereas those
in giant size mode originate mainly from soil. In India, the giant size mode always dominates the submicron size mode, whereas in western countries submicron size mode dominates the giant size mode. This observation indicates that the natural sources of aerosols are very strong and anthropogenic sources of aerosols are weak at present in India.
5 Acid rain
Acid rain is one of the most widely published environmental issues of the day. Vast areas of the northern hemisphere including central Europe, Scandinavia, north-east United States, and Canada are affected by acid rain. There is a great concern that acidity of rain can have adverse environmental impacts.
The free acidity of solution such as rain is
determined by the concentration of hydrogen (H+) ions present. It is commonly expressed in terms ofpH scale. Pure water has apH of7 which is neutral and on the borderline between acidic and alkaline. Natural, unpolluted rain water is frequently assumed to be slightly acidic with pH of 5.65. This is the pH of distilled water in equilibrium with atmospheric carbon dioxide, as determined under laboratory conditions. It has never been etablished that 5.65 is real pH of unpolluted rain in nature. Nevertheless, many researchers have accepted this assumption and refer to rain water having apH of less than 5.65 as acidic. Hence, the term acid rain has come to mean rainfall with pH of less than 5.65.
Contamination in the atmosphere can shift thepH of rain water either way. Alkaline soil particles containing carbonates can increase the pH. In contrast, the presence of acidic particles of suIph uric or nitric acid would lower the pH. The processes affecting the acidity of rain water are many and very complex. They includegas-to-particle trans- formations, photochemistry and catalytic chemistry, aqueous chemistry within cloud drops, precipitation, regional and global integrated atmospheric transports. ThepH of precipitation is an integrated measure of the relative contributions of all of these complicated processes29.
Most research efforts dealing with precipitation acidity have been directed towards understanding the influence of acid materials or chemical reactions in the formation of acids in precipitation. As a result, the role of alkaline substances in determining precipitation acidity has largely been overlooked.
Precipitation acidity is a function of its contents of both acids and bases, and any attempt to understand the processes causing acid precipitation must deal with the potential acid neutralizing capacity of alkaline materials. The major cations in precipitation associated with alkaline compounds (other than ammonia) are Ca, K, Mg and Na which are mostly released from crustal sources.
The influence of dust particles in India can be seen better where concentration ofTSPs has varied from 200 to 800 /lg m -3.Soil in India is rich with alkaline components like Ca, K and Mg, and is the major source for the observed high levels of aerosols in atmosphere. Therefore, chemical composition of precipitation in India can indicate the influence of man-made pollution and natural pollution on thepH of precipitation.
6 Chemical composition of precipitation
The average concentrations of major ionic components along with pH values in precipitation
lo.
I ,,', I
(rain, cloud, fog and snow water) collected at different locations in India are given in Table 3. The concentrations of all the ions are higher in fog and cloud waters than in rain and snow waters. This observation appears to be logical since fog and cloud droplets are very concentrafed solutions of soluble condensation nuclei.
Besides sea salt (CI and Na), S04 and Ca are present in substantial amounts in rain water. It is known that concentration of sea salt decreases with an increase in distance from the sea. The contribution of sea salt in rain water at coastal as well as inland stations is mostly from the sea. Sea salt has beeen considered neutral and its presence does not influence thepH of rain water. Except at industrial locations (Chembur and Kalyan), the concentrations of S04 at other locations are quite low in rain water. Also, the concentrations of N03 are quite low in rain water
except at a few locations, namely, Indraprastha thermal power plant, Delhi, and Muktsar. High concentration of N03 at Muktsar, a non-urban location, is little surprising. It was found that N03 in rain water at M uktsar was originated from soil, since it showed significant positive correlation with soil-oriented elements like K, Ca and Mg. The maximum concentration ofCa in rain water has also been observed at Muktsar. High concentrations of Ca in rain water have been reported for coastal as well as for inland stations in India30• However, the concentrations of Ca in rain water are substantially low in north-east (Goraur in Bihar) and South India (Trivandrum). It seems that in these regions the influence of dust on TSPs is quite low; concentration of TSPs in these regions is reported to be about 75 Ilg m-3• Low concentration of Ca and high concentrations ofS04 andN03 in rain water reported
Table 3-Average concentrations in mgjlitre of major ionic components and pH values in precipitation collected at different stations in India
Station CI Na
RAINWATER
K Ca Mg pH
H
.IiCqjlitre
Coastal Trivandrum Industrial Kalyan
·Chembur36 Power Plant Indraprastha' Koradi Urban Pune Delhi Non-Urban Sirur Muktsar Goraur Forest region Masingudi
4.22 3.95 5.00 2.06 2.35 2.57 2.54 2.64 2.66 0.95 0.67
1.71 5.20 20.20 2.10 1.78 1.78 2.73 1.53 1.59 1.85 1.85
0.98 1.92
3.30 1.52 0.48 2.54 2.64 4.38 0.60 1.69
0.25 0.38 2.10 0.93 0.39 0.10 0.53 0.07 0.16 0.25 0.49
2.25 2.36 2.20 0.98 1.78 1.84 1.75 1.84 1.84 0.59 0.44
0.27 1.02
UO
0.25 0.31 0.20 1.28 0.95 1.70 0.67 0.73
0.77 1.86 3.10 2.03 3.13 2.07 2.95 3.53 5.56 1.54 1.43
0.35 0.47 0.68 (}.31 0.48 0.45 0.62 0.80 0.63 0.22 0.23
5.30 5.70 4.80 5.00 6.70 6.30 6.10 6.70 7.30 5.30 6.04
5.01 2.00 15.85 10.00 0.18 0.50 0.79 0.20 0.05 5.01 0.91
Pune
Delhi
Gulmarg
8.91
8.20
0.64
1.50
4.38
0.65
1.80
11.65
0.56
CLOUD WATER
0.99 4.5 1.44
FOG WATER
2.90 16.13 12.55
SNOW WATER
0.30 0.36 0.19
5.48
17.53
0.61
U5
3.95
0.07
6.90
6.91
6.68
0.13
0.12
0.21
212 INDIAN J RADIO &SPACE PHYS, AUGUST 1993
from the western countries are the major causes of acid rain. The relative contributions of primary aerosols (Ca, K and Mg) and secondary aerosols (S04 and N03) in rain water will decide the acidity in rain water. It has been seen that the presence of Ca neutralizes the H ion concentration and increases the pH value. However, S04 to some extent increases the H ion concentration and decreases thepH value31.
N03 in rain does not show any relationship with H ion concentration since the source of N03 is soil.
However, at Goraur N03 was responsible for the increase of H ion concentration along with S04.
Among the three crustal elements, K, Mg and Ca, the last one has maximum acid neutralizing capacity32. Influence of alkaline particulates from soil dust onpH of rain water has been reported in the United States and European countries32 - 35.
7 pH of precipitation
Except at Chembur, a highly industrialized area in Bombay region, thepH of rain, cloud, fog and snow waters is alkaline at other locations in India. Also, the pH of rain water at Trivandrum and Goraur (near Patna) is near the CO2-equilibrated value. The rain water at these two places cannot be called acidic because not only the concentrations ofS04 and N03 are quite low, but the concentration ofCa is also quite low compared to other locations in India. It is reported thatpH of rain water in unpolluted areas can be around 5 due to the presence of naturally produced organic acids like formic acid and acetic acid29. It is presumed that the lower pH at Trivandrum and Goraur is not due to pollution sources but may be due to formic acid and acetic acid which are able to bring down the pH from 5.65 to around 5.30.
The first acid rain in India was reported from Chern bur , where average pH of rain was 4.8 in 1976 (Ref. 36). Recent results of chemical analysis of acid rain in Chembur-Trombay area conducted during the monsoon period of 1990 have indicated that the rain in this area has become alkaline and thepHvaried between 6 and 7 (Ref. 37). Acidic pH (4.8) was reported earlier (1976) in the rain water samples coll~cted at Bhabha Atomic Research Centre (BNR C) and the trend continued up to 1980 (Ref. 32).
The change from acidic to alkalinepH of rain water in this area is due to change in fuel from coal to natural gas and pollution control measures adopted by industries which are reflected from the declining S02 emission trends reported for Chembur. The average concentrations ofS02 and N02 during 1971-73 were around 65 and 49 Jlgm - 3 which reduced to around 15 and 29 Jlg m - 3 respectively in 1990. Also, concentration ofS04 which was around 20 mg/litre in
1976 (Table 3) came down to around 5 mg/litre during 1990 (Ref. 37).
It will be of interest to know the
pH
of rain water at other locations in India during various monsoon periods (1970-90) reported by other investigators.For this purpose, the average pH values measured and reported for different stations in India during various monsoon periods are considered (Refs 31, 38-45). ThepHvalues are high (pH
>
7.0) at Srinagar, Allahabad, Jodhpur, Muktsar, Amritsar, Bikaner, Jaisalmer, Lucknow and Ahmedabad. The values are comparatively low but still in alkaline range (pH=
6-7) in industrial towns and cities, namely, Nagpur, Visakhapatnam, Delhi, Agra, Bhopal, Calcutta and Chandigarh. At Trivandrum and Goraur, pH is still lower (pH = 5.3). However, the rain at Chembur which was acidic during 1974-80 turned to alkaline in 1990.The pH values of rain water have been compared with thepH values of soil of different regions ofIndia published by ICAR46. The pH values of soil are reported quite high between 15°N and 35°N, and substantially low in the longitude belt of8YE to 95°E.
HighpH values (pH = 6.5--10.5)of soil are reported in Jammu and Kashmir, Punjab, Haryana, Uttar Pradesh, Rajasthan, Madhya Pradesh, Gujarat, Maharashtra, Karnataka, Andhra Pradesh, and some parts of Tamil Nadu. Quite low pH values (pH
=
4.8-5.3) of soil are reported in coastal Kerala and also at Kodaikanal in Tamil Nadu. In Bihar and West Bengal, thepH values are between 4.8 and 6.0;pH values are still lower (4.0-5.4) in the east of these two states. It is noticed that the dust load in the atmosphere over north-west parts of India is high and a significant amount of dust is incorporated into rainfall either as condensation nuclei or by collision with falling rain drops. However, the extent to which airborne dust influences the precipitation chemistry of certain geographic regions vaJ;les with its composition and abundance. Neutralizing effect of airborne dust31,37.47- 54has been attributed as one of the reasons for higher pH values (pH > 5.6). Higher atmospheric temperatures in the tropics, lower solubility and dissolution rates ofCO2 added to rapid processes of cloud formation and precipitation are also responsible for higher pH values. Greater depth of saturated air during south-west monsoon over the Indian subcontinent could be yet another factor for higher pH (Ref. 55).
8 Conclusions
The neutralizing effect of airborne dust on rainfall acidity is now well documented. The alkaline properties of soil particulates have so far sustained
I I"H I
KHEMANI: AIR POLUJTION & ACID RAIN PROBLEMS IN INDIAN REGION 213
the alkaline nature of rain water(pH
>
5.65)and have to Sadasivan S, Studies of some important trace constituents in thebeen controlling the spread of acid rain in India. This ,,' mo~oon r?ins ~ their role in atmospheric processes, PhD has been possible due to low concentrations of acidic ~theSIS, Umverslty of Bombay, Bombay, 1977.
. . /11 Sadasivan S, Sci Total Environ (Netherlands-), 20 (1981) 109.
compo~ents (S?4 and ~03) and high concentratlO~s 12 Air quality in selected cities in India, 1978-79 (National
of alkalIne particulates m the atmosphere. Also, acld /' Environmental Engineering Research Institute, Nagpur),
rain, wherever it has occurred in India, is purely a 1980.
local phenomenon and is restricted within 2 km 13 Air quality in selected cities in India, 1980-81 (National
distance in the upwind andlor downwind of the, Environmental Engineering Research Institute, Nagpur),
. d . 1 1 Lo
f
1983.m ustna comp exes. Jig-range transport 0 14 Kha d ka RN Sud' A h' LeadDII' .
'd' 11 .. h' f'd"'" n e r ,t les on tmosp erlC rO utlOnIn
aCI lC po utant~ IS t e mam cause.o aCI ram m ,...,.Greater Bombay,Ph D thesis, University of Bombay, Bombay,
western countnes. However, this process
of
1981.long-range transport of pollutants (S04 and N03) 15 Khemani L T, Momin G A, Naik M S, Vijayakumar R &
does not seem to be effective in India during the'-' Ramana Murty Bh V, Tellus (Sweden), 34 (19~2) 151.
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north-east and south-west are classified as and their deposition through precipitation, Ph D thesis,
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