Measurements of atmospheric parameters during Indian Space Research Organization Geosphere Biosphere Program Land Campaign II at a typical location in the Ganga Basin: 2. Chemical properties

Abstract

This paper attempts to analyze the chemical compositions of the near surface aerosols at a typical location in the Ganga basin with an emphasis on delineating the source of aerosols in foggy/hazy conditions. Collocated measurements of a number of atmospheric and aerosol parameters along with simultaneous sampling of near surface aerosols of size less than 10 μm (PM10) were made as part of an intense field campaign launched under the Indian Space Research Organization Geosphere Biosphere Program (ISRO‐GBP) in December 2004. PM10 and black carbon (BC) mass concentration was found to be significantly higher during the foggy/hazy period. Much of the PM10 mass (∼81%) was due to fine/accumulation mode particles (0.1–0.95 μm). Significant proportions of water soluble ions such as NH4+, K+, Na+, Cl−, NO3− and SO42− were present in the fine mode particles while considerable amounts of Ca2+ and Mg2+ along with NH4+, K+, Na+, Cl−, NO3− and SO42− were found in the coarse mode particles. Also, water soluble ions NH4+ and NO3− were significantly higher; however, Na+, K+, SO42− and Cl− did not show significant difference between foggy/hazy and clear days. In contrast, Ca2+, Mg2+ and acid soluble metals were significantly lower during foggy/hazy days as compared to the clear days. Presence of higher amounts of NH4+, K+, NO3− and SO42− associated with very low values (<5 ppmv) of SO2 despite considerable plausible emissions due to fossil fuel and biomass burning in the region suggests that loading of fine mode aerosols in the region could have been enhanced through reactions of gaseous pollutants on the solid surfaces. These results along with the findings presented in the companion paper indicate that prolonged foggy/hazy conditions in the region may be due to the increased anthropogenic emissions.