Precipitation chemistry over the Indian region

Abstract

The present study is based on the precipitation chemistry data from the Background Air Pollution Monitoring Network (BAPMoN) in the Indian region, for the period 1976-87. Sampling is made on an event basis and the pH and electrical conductivity of the samples are determined from filtered samples immediately after cessation of rain. The chemical analysis is performed on monthly mixed samples.
 
 No trend is found in the pH of rainwater from background areas except at Allahabad, Pune and Visakhapatnam which suffer from sizable anthropogenic influences. The pH seems to be related more to NO3 ions compared to SO4-2 ions. A natural buffer appearing in the form of alkaline soil-derived species seems adequateat most places (except Mohanbari), in keeping a check on progressive acidification despite steady increase in concentration of nitrates. The ion balance cannot be achieved without including the presence of HCO3, which when done explains the observed electrical conductivity of rainwater. The interaction of marine aerosols with acid aerosols has also been studied for the marine regions in the Indian areas and reveals a substantial removal of chloride from sea-salt. Inland sources of NaCl have also been identified from the BAPMoN data.

Monsoon Rainwater Chemistry and Its Potable Status: A Case Study From South-East Coastal Belt of Bangladesh

“…Das (1988) advocated that the major, minor and trace elements monsoon rainfall over Calcutta had greater influence of marine inputs. Mukhopadhyay et al, (1991) pointed out that the occurrence of acid rain is virtually absent over the Indian region. It is now believed that neutralization of acidic components in rainwater by calcareous aerosols species in the atmosphere acts as the main buffer mechanism against acid rain (Nanda, 1984;Mukherjee et al, 1985;Khemani et al, 1989).…”