Chemistry of monsoon and post-monsoon rains at a high altitude location, Sinhagad, India

Abstract

Rainwater samples collected at Sinhagad on 65 rain occasions during monsoon season (June -September 2005) and on 23 rain occasions during post-monsoon season (October-November 2005) with standard rain collection instruments, i.e. wet-only (WO) and bulk collectors (BC), were considered for the present study. Sinhagad is a hill station on a mountaintop in the Western Ghats, located about 40 km southwest of Pune. The following ionic components were determined: H +, NH4+, Ca2+, Mg2+, K+, Na+, SO42- NO32-, Cl- and F -. The pH analyses showed that rainwater in both the seasons were alkaline. The major neutralizing component was associated with Ca2+. In monsoon rains, the major anion was Cl- and the major cation was Na+; whereas in post-monsoon the major anion was SO42- and the major cation was Ca2+. The concentrations of nss SO4 2-, NO32- and NR4+ were found to be higher during post-monsoon than monsoon. Surprisingly high concentrations of Ca 2+ and SO42- were found during the monsoon season. Since no large upwind sources of these compounds are expected, one is led to conclude that long-range transport may be involved, possibly even including African sources. Since the local sources didn't seem to influence the samples significantly, this rural site is useful for obtaining regionally representative precipitation data.