Influence of local sources on rainwater chemistry over Pune region, India

Rainwater samples were collected at five locations in the Pune region, an urban area in the south-west part of India, during 2006–2009. These locations; viz., Swargate (Traffic), Bhosari (Industrial), Pashan, Sangvi (Urban) and Sinhagad (Rural and High Altitude), represent different environments in this region. The study based on chemical analyses of these samples reveals that, on average, rainwater was alkaline at all the locations with pH values of 6.7, 6.16, 5.94, 6.04 and 5.92, respectively. Higher pH value of rainwater at the traffic location than those at the other locations is due mainly to the abundance of Ca2+ caused by vehicle-driven road-side dust. The maximum SO42− and NO3− concentrations were found at Bhosari and Swargate respectively caused by local industrial and vehicular emissions. The average Fractional acidity over Pune area is 0.024, indicating about 98% acidity is neutralized by alkaline constituents. Factor analysis of the results indicated the influence of various sources, such as anthropogenic, soil dust, sea salt and biomass burning.

Research Highlights
► Alkaline rain at all the sites with appreciably higher pH at traffic and industrial locations.
► The major acid neutralizing ion is found to be calcium.
► Very few occurrences of acid rain at all the five locations.
► Maximum concentration of SO42– at the industrial location and NO3– at the traffic junction.
► Major contribution from marine source to rainwater composition at all the locations.