Water-soluble ionic species in atmospheric aerosols over Dhauladhar region of North-Western Himalaya.

Abstract

Water-soluble ionic species (WSIS) have been used as potential markers for different source(s) and underlining process(es) emitting and transforming atmospheric aerosols. PM10 aerosol sampling was performed once in a week for a complete one year, at a mid-altitude urban and a low-altitude rural location simultaneously in the Dhauladhar region of the North-Western Himalaya. Aerosol samples were analysed for major WSIS (anions: F-, Cl-, NO3-, PO43- and SO42-; cations: Na+, NH4+, K+, Ca2+ and Mg2+) using the ion chromatography system. Results showed that WSIS constitutes around 15% of PM10 aerosol load in the region. SO42- contributes the maximum (~ 50%) followed by NO3- (~ 12.5%) and NH4+ (~ 12.5%) to the total concentration of WSIS analysed. During all the seasons, average concentrations of PM10 and associated WSIS were observed to be higher over the rural location in comparison to the urban location. The total concentration of WSIS was found to be maximum during the winter season. Principal component analysis performed on the WSIS concentration dataset revealed four major sources of PM10-associated WSIS viz. re-suspension of soil or local sediments; conversion of pollutant gases (SOx, NOx and NH3) to particles, i.e., secondary inorganic aerosol formation; evaporative loss or re-suspension of inorganic (NPK) fertilizers' residues and biomass/crop-residue burning emissions in the Dhauladhar region of the North-Western Himalaya.