L. T. Khemani

Spread of acid rain over India

Abstract Rain water and aerosol samples were collected at a few locations representative of urban and non-urban regions in India. Also, rain water samples were collected in and around a coal-fired power plant. All the rain water and aerosol samples were analyzed for major chemical components along with pH. The rain water at all the places of measurement, except near the industrial sources, has been found to be alkaline and was characterized by the presence of excess cations, particularly by Ca2+. The acid rain near the industrial sources was associated with excess anions, especially SO42−. The atmospheric aerosols at all the places of measurement were found rich with basic components, suggesting that the alkaline soil dust and fly ash are responsible at present for preventing the spread of acid rain in India.

Influence of alkaline particulates on pH of cloud and rain water in India

Abstract Cloud and rain water samples were collected on board aircraft by specially designed equipment, during three monsoon seasons, 1983, 1984 and 1985 in the Pune region in India. The samples were analyzed for major ionic components and pH, and the concentrations of all the ionic components were found to be significantly higher (35–161%) in cloud water than in rain water. In cloud water Cl contributed most (35%) to the total ionic concentration followed by Ca(21%) and Na(17%). Sulphate and nitrate concentrations, on the average, were low and were found to account for only 6% of the total ionic concentration. pH of cloud water and rain water was substantially higher than that of the CO2-equilibrated value (5.6). The findings suggest that influence of anthropogenic sources is negligible and that of soil dust which is alkaline is substantial on the pH and chemistry of cloud/rain water in India.

Impact of alkaline particulates on pH of rain water in India

Rain water samples were collected over a period of a decade from 1974 in Pune, a city which is relatively free from industrial pollution. They were also collected at 4 places during 1974 in the region of Bombay which is highly industrialized. The samples were analyzed for major chemical components and pH. The ionic balance was computed. Samples were collected at Delhi during 1965 and 1966 and were analyzed for pH. The values were compared with those reported for 1978. The total suspended particulates (TSP) were measured at Delhi during 1980 and analyzed for water soluble components. The rain water at all the places except near the industrial source was not acidic and was characterized by the presence of excess cations, particularly Ca. The acid rain near the industrial source was associated with excess anions, especially sulphate. The difference between the cations and anions was inversely proportional to the H+ ion concentration. The pH of rain water at Delhi which was in the alkaline range during 1965 and 1966 remained alkaline even after a period of 12 yr when the city developed industrially. The TSP in the region was rich with the basic components, mainly Ca, suggesting that the alkaline property of the soil dust is mainly responsible for neutralizing the acidic effects resulting from the anthropogenic gaseous pollutants.

Study of surface ozone behaviour at urban and forested sites in India

Abstract Surface ozone concentrations were measured continuously at Pune for a period of one year during 1991–1992 and for a period of 10 days in January 1992 at Upper Kargudi and in April 1992 at Bandipur, core zones of the Nilgiri Biosphere Reserve forests located in Tamil Nadu and Karnataka States, respectively, in south India. There is a marked diurnal variation in the concentration of surface ozone which clearly follows the diurnal variation of surface temperature. The monthly maximum concentration was observed during the summer season (March–May) and minimum during the monsoon season (June–September). The annual average concentration of ozone was 27 ppb and hourly values varied between 2 and 69 ppb at Pune. However, in the forest environment the 10-day average concentration was 15 ppb and hourly values varied between 5 and 31 ppb. The values of surface ozone at Pune and forest environment are below the U.S. EPA standard (113 ppb, maximum 1 h permissible concentration).

Rain water and throughfall chemistry in the silent valley forest in South India

Rain water and throughfall samples were collected at the Silent Valley forest during the two consecutive southwest summer monsoon seasons (June-September) of 1989 and 1990. All the samples were analysed for Cl - , SO 4 2- , NO 3 - , NH 4 + , Na + , K + , Ca 2+ , Mg 2+ and pH. The average pH of rain water was 5.31 and that of throughfall was 6.38 indicating that the throughfall is 10 times more alkaline than the rain water. The buffering of H + in throughfall was due to interaction with canopy. It was found that the ionic concentrations in throughfall were higher than those in rain water, except for NH 4 + . Enrichment of ionic components in throughfall is attributed to the interaction of precipitation with the forest canopy.

Atmospheric pollutants and their influence on acidification of rain water at an industrial location on the West Coast OF India

The chemical analysis of rain water samples at 11 locations along with measurements of atmospheric aerosols and their size distributions were made to study the influence of pollutants on acidification of rain water during the monsoon season of 1990 at Chembur-Trombay area, a highly industrialized belt in Bombay region located on the west coast of India. The concentrations of acid precursor gases, namely, SO2 and NO, emanating from industries were low and their influence on acidification was limited to a few kilometer radius of their sources. Whereas, the deposition of ionic components (Na+, K+, Ca2+, Mg2+ and CI−) whose sources are natural (sea and soil) were uniformly distributed throughout the region as compared to those released from man-made sources. The high concentration of alkaline components, especially Ca2+ from natural sources and NH3 released from a fertilizer plant, were responsible for neutralising H+ ion concentration generated from the acidic components (SO42− and N03−). The variation from acidic (1970s) to alkaline (1990s) nature of rainwater in the area maybe due to the change in the use of fuel from coal to natural gas, which contains less sulphur and also, the pollution control measures taken by the industries.

Long-term effects of pollutants on pH of rain water in North India

Abstract The ionic composition and pH of rainwater samples collected during the summer monsoon seasons of 1963 and 1965 at Agra and Delhi, respectively have been compared with those collected during the summer monsoon seasons of 1984 at both these cities. The pH values at Agra and Delhi have been found to have decreased by 2.8 (9.1-6.3) and 0.9 (7.0-6.1) units, respectively after the period of two decades during which the cities developed industrially to a great extent. The main cause for the decrease in the pH values is a significant increase of acidic components and decrease of soil-oriented components in the rain water. For the first time in India, long-term effects of pollutants on the pH of rain water have been observed but the effects are comparatively slow compared with those in western countries.

Rainfall Variations in an Urban Industrial Region

Abstract The rainfall data, for the period 1901–69, of three stations in the region downwind of the urban industrial complex at Bombay and of two stations in the nearby non-urban region, have been analyzed. The study has indicated that, with respect to the non-urban region, the region downwind of the urban industrial complex recorded an increase of rainfall by about 15%, significant at less than the 1% level, during 1941–69 which is the period of increased industrialization.

Trace elements and sea salt aerosols over the sea areas around the Indian sub-continent

Abstract The nature and the characteristics of trace elements and sea salt aerosols in the ocean atmosphere around the Indian sub-continent was studied. For this purpose, concentrations of the total suspended particulates (TSP) as well as of its various chemical components together with their mass size distributions were measured on 11 days in May 1983. Over the sea regions around the sub-continent, sampling was done on board the research Vessel Gaveshani using a high volume air sampler and a multistage Andersen sampler. The concentrations of soil-origin elements (Al, Fe, Mn and Ca) were found to be at a maximum over the Arabian sea region suggesting the presence of dust particulates, transported from the Arabian peninsula. The near sea water ratio of CI/ Na was observed in giant size (> 2.5 μm dia) sea salt aerosols suggested that there was very little fractionation in these aerosols. The ratio value considerably decreased in the case of sub-μm sea salt particles. The chemical components originating from soil and from sea salt showed a unimodal distribution whereas those from anthropogenic sources showed a bimodal distribution.

Trace elements in the atmospheric aerosols at Delhi, North India

The total suspended particulate (TSP) levels at Delhi (north India) were measured on 116 days between February and October 1980. The observations were stratified according to season and the values of cross-correlation of the TSP and its components were evaluated. High TSP (209 μg m-3) levels were found during the summer period associated with hot and dry weather in the region and low TSP (109 μg m-3) were found during the monsoon period. Most of the TSP mass was associated with natural soil elements, such as Fe, Al, Mn, Ca, and K. Only a fraction of the mass of the TSP was comprised of elements from anthropogenic sources, e.g., Pb, Ni, Cd, Sb, Cu, and Zn. The aerosols at Delhi were potentially basic in nature, unlike those in European countries which are acidic in nature and cause acid rainfall.