Source apportionment of rainwater chemical composition in wet precipitation at Kelaniya in Sri Lanka

Abstract

Rainwater quality is of utmost importance as it can be used to predict atmospheric quality which of course governs, to some extent, the health of the ecosystem. In this regard, the research reported here was to study chemical characteristics of precipitation in Kelaniya, Gampaha District, one of the most populated and most urbanized districts in Sri Lanka. This study was conducted during the period from 2012 to 2014, and wet precipitation was analyzed for pH, conductivity, Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, NO3−, SO42−, Pb, Cu, Mn, Al, Zn, and Fe for a total of seventy-eight (78) samples. Volume-weighted average concentrations of the major ionic species present in precipitation samples were in the order of Na+ > Ca2+ > Cl− > SO42− > NH4+ > Mg2+ > NO3− > K+ > F−. Neutralization of the acidic species would take place due to the presence of NH4+ and CaCO3. When considering marine contribution, SO42−/Na+, Ca2+/Na+, and Mg2+/Na+ ratios are higher than the reference value suggesting that contribution of sources be possible other than marine. Among metallic constituents, the concentration of Al is the highest while that of Mn is the lowest. Significant correlation is observed among certain ions and elements (Ca2+, SO42−, Mg2+, Al, Cu, Fe, Zn, and H+) which indicates their source of origin and chemical interaction. This study reveals that chemical composition of rain water depends on both anthropogenic activities and natural phenomena.