Study of chemical composition of rainwater at an urban (Pune) and a rural (Sinhagad) location in India

Abstract

Data are presented on the chemical composition of rainwater collected at a rural site (Sinhagad) near Pune, India, between August 2002 and August 2003 and at an urban site in Pune between April 2002 and August 2003. Both bulk water samples and wet‐only samples were alkaline at both sites, with an average pH of 6.6 (both bulk and wet‐only) at Pune and 6.4 (bulk) and 6.2 (wet‐only) at Sinhagad. Only one case of acidic rain was recorded: at Sinhagad with pH of 5.2 (bulk) and 4.9 (wet‐only). The major cations were Ca2+ and Na+, and the major anions were Cl− and SO42−. Higher concentrations of both SO42− and Cl− at Pune compared to Sinhagad were balanced by higher concentration of Ca2+ such that the pH remained approximately similar and, on average, well on the alkaline side. The difference in ionic composition between the two sites, available so far only for the monsoon period, is quite small (especially in case of wet only samples) and interpreted as an influence of local sources at the Pune site. At both sites the concentrations in the bulk samples were only slightly larger than those in the wet‐only samples. Our analysis demonstrates that the Sinhagad site provides useful data representative of the regional situation. The data are also analyzed in terms of seasonal (monsoon versus postmonsoon) variations and air mass trajectories. Surprisingly high concentrations of SO42− at the rural site (Sinhagad) during the SW monsoon period may indicate transport from the African continent.