Chemical Characteristics of Atmospheric Aerosol at Alaknanda Valley (Srinagar) in the Central Himalaya Region, India

Abstract

Measurements of fine (PM2.5) and inhalable (PM10) particles were collected at the Alaknanda Valley in the heart of Garhwal region during December 2015–December 2016. Collected samples of PMs were analyzed for major chemical species as anions (F−, Cl−, SO42−, NO2− and NO3−) and cations (Na+, NH4+, K+, Ca2+ and Mg2+) by ion chromatography. During the study period, the concentrations of PM2.5 and PM10 were 78.7 ± 25.1 and 111.8 ± 23.4 μg m−3, respectively. The measured chemical species were found a large variability in different seasons due to the impact of emissions and meteorological parameters. The measured water-soluble (WS) chemical species of PM2.5 and PM10 were 43% (33.7 μg m−3) and 57% (64.2 μg m−3), respectively, with the highest concentrations during the winter season followed by summer, monsoon and post-monsoon seasons. A significant positive correlation was observed between NH4+ and other species (Cl−, SO42− and NO3−) in both PM2.5 and PM10, which indicates its presence in the atmosphere as ammonium salts. As a result, NH4+ play a crucial role in neutralization of acidic species in the winter season; however, the contrary feature was observed in the summer season where Ca2+ was responsible for the main neutralizing species, mainly transported from the inland region during the summer. Principal component analysis shows that secondary aerosol, biomass burning, and soil-driven dust were the possible sources of the measured species over the station. Further, air mass back trajectory analyses indicate that the highest mass concentrations of PMs and WS chemical species were in the post-monsoon season when the air masses pass from eastern Pakistan and western part of India over receptor site. In the winter season, the concentrations of PMs and WS species were highest (second) when the air masses transported from a long distance up to Southern Afghanistan covering with Pakistan and western part of India. In overall, the study suggests the long-range transport of pollutants plays a crucial role in the enhancement of PMs over Alaknanda valley region.