Long Term Variation in Precipitation Acidity over the Indian Global Atmosphere Watch (GAW) Stations
Acidic precipitation is a serious environmental hazard because of its capability of damaging environment worldwide. In this paper monthly variation and long term trend in pH, SO4-2 and NO3 have been studied over a network of ten Global Atmosphere Watch (GAW) stations in India for the period from 1981 to 2002.
The analyses reveal that at Jodhpur and Allahabad precipitation is predominantly alkaline due to the influence of soil originated components derived from the Thar Desert and their transportation to these locations. Higher SO42 and NO3 concentrations in precipitation at Visakhapatnam and Nagpur in most of the months in a year can be attributed to industrial and vehicular pollution. Higher concentrations of calcium, magnesium and potassium at Minicoy (Arabian Sea Island) cause its pH to be alkaline, whereas relatively lower concentrations of these basic cations at Portblair (Bay of Bengal Island) make its pH in the acidic range. During the period of 1981-2002, significant shift in pH towards the acidic range and increasing trend in sulphate and nitrate concentrations have been observed at most of the GAW stations. Further, decadal variations revealed drop in pH and substantial rise in sulphate and nitrate concentrations in 1991-2000 decade as compared to that in 1981-1990 decade at majority of the Indian GAW stations.
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