Source characterization for aerosol constituents and changing roles of calcium and ammonium aerosols in the neutralization of aerosol acidity at a semi-urban site in SW India

Atmospheric aerosols were collected at a semi-urban site in Pune city, located in the southwestern part of India, during the year 2007–08 covering different seasons. Anthropogenically derived particles (Non seasalt and non crustal fractions of SO4, Cl, K, Ca and Mg together with NO3, NH4, Cu, Zn and black carbon) contributed about 73% of the total measured TSP. Natural sources like sea (16%) and soil (11%) contributed about 27% to the total measured composition of TSP on annual basis. Surprisingly, Ca which is generally observed from crustal source, showed equal contribution from crustal and anthropogenic sources and was the major neutralizer of aerosol acidity in summer and monsoon seasons. NH4 was the most abundant component on annual average basis among the measured chemical components and also it was the leading neutralizer of aerosol acidity during post-monsoon and winter seasons. Aerosols showed alkaline nature (mean annual pH 6.51 and Neutralization Potential/Acidic Potential ratio 1.45) due to the neutralizing effect of Ca and NH4.