Atmospheric chemical composition of bulk deposition at two geographically distinct locations in Sri Lanka

This study presented the research work carried out for the investigation of chemical composition of bulk precipitation in two geographically and economically distinct areas, namely Gampaha and Kandy Districts. This study was conducted from 2013 to 2014 at three sampling stations in each District. The bulk precipitation was analyzed for pH, conductivity, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, F^-, Cl^-, NO₃^-, SO₄^2-, Pb, Cu, Mn, Al, Zn and Fe for a total of 375 samples. Only 8% events of acidic precipitation were recorded in Gampaha District when compared with 3% in Kandy District. The volume weighted average concentrations of the major ionic species present in precipitation samples were in the order of Na⁺ > Ca²⁺ > Cl^- > NH₄⁺ > SO₄^2- > Mg²⁺ > NO₃^- > K⁺ > F^- in the Gampaha stations, while the order was NH₄⁺ > Ca²⁺ > Na⁺ > Cl^- > SO₄^2- > Mg²⁺ > NO₃^- > K⁺ > F^- in Kandy District. Neutralization of acidity of precipitation is much more related to CaCO₃ than NH₃, and high content of Ca²⁺ ions present in both Districts strongly supports this fact. When considering marine contribution, SO₄^2-/Na⁺, Ca²⁺/Na⁺ and Mg²⁺/Na⁺ ratios are higher than the reference value suggesting contribution of sources other than marine. Depositions of both Districts show that the concentration of Al is the highest while that of Mn is the lowest. Principal component analysis suggests that influencing human activities on chemical composition of rain water depends on thermal power plant, oil refinery, heavy traffic and waste incineration in the study area.