Water Soluble Ionic Species in Atmospheric Aerosols: Concentrations and Sources at Agra in the Indo-Gangetic Plain (IGP)

This study presents a comprehensive set of 2 years of data (January 2009-December 2010) on the chemical composition of ambient aerosols collected at a university campus in Agra, which lies on the Indo-Gangetic Plain (IGP). The average concentration of total suspended particles (TSP) was 213.2 +/- 91.4 mu g/m(3). The most abundant ions in TSP were Ca2+, NO3 and SO42- , which contributed about 3.2%, 3.1% and 2.7%, respectively. TSP and most of the ions, such as F-, Cl-, NO3-, SO42- , NH4+ and K+, had the highest mass concentrations in winter, while higher mass concentrations of Ca2+ and Mg2+ were found in summer. Higher ionic concentrations during the winter season may be attributed to a combined effect of biomass burning and meteorological conditions (low temperature, wind speed and mixing height). The [NO3-]/[SO42-] ratio at the present sampling site was 1.1 +/- 0.4, which indicates that there were equal contributions from both stationary sources and vehicles. In winter, high [NO3-]/[SO42- ] ratios (1.7 +/- 0.4) could be due to the extensive use of fuelwood and cowdung cakes to combat the cold. The acidity in aerosols is neutralized by the alkaline species, as indicated by the correlation between NO3(-) and SO42- and sum of (Ca2+, Mg2+ and NH4+). Ca2+ is the major acid neutralizing cation in the aerosols, followed by Mg2+ and NH4+. The crustal source contribution was observed based on the ratios of various ions with respect to Ca in soil and aerosol. On the basis of backward trajectories and the associated concentrations of the ions, the aerosol samples were classified into sectors in relation to their origin to determine the related sources. The major sources of water soluble ions identified at Agra are biomass combustion and local soil.