Chemical composition of precipitation in India and Nepal: A preliminary report on an Indo-Swedish Project on Atmospheric Chemistry

Abstract

Rainwater and dustfall are being collected for chemical analysis five sites in India and on e in Nepal on an event basis with wet-only and bulk collectors. Special attempts are made to obtain regionally representative values and in particular to avoid local sources of alkaline dust. Sampling and analysis are described and data are given from four of the stations, Delhi, Pune, Sinhagad and Goa. Rainwater is on the average alkaline (contains more bicarbonate than hydrogen ion) with a pH of between 6.2 and 6.8 based on mean hydrogen and bicarbonate concentrations. Major acidifying and neutralizing components have rather similar concentrations at three of the four sites (except Delhi): SO sub(4) sup(2-) (12-18 mu q/L), NO sub(3) sup(-) (5-7 mu eq/L) and nss Ca sup(2+) (32-40 mu q/L). Concentration of NH sub(4) sup(+) varies from 5 at the coastal Goa to 12 mu q/L at the inland stations and nss Mg sup(2+) from 2 to 8 mu eq/L. Sea salt components very clearly decreases with increasing distance from the coast. Delhi deviates in peculiar fashion with higher concentrations of SO sub(4) sup(2-) , NH sub(4) sup(+) and K sup(+) and lower in Ca sup(2+) and Mg sup(2+) . Amount of dustfall (as collected by funnels which probably only give a fraction of dry deposition to real surfaces) was estimated at Delhi. The dustfall greatly exceeded wet deposition of Ca sup(2+) and Mg sup(2+) , made a significant contribution in case of NO sub(3) sup(-) and was rather unimportant in case of NH sub(4) sup(+) (20%)