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

Water-soluble ionic species (WSIS) have been used as potential markers for different source(s) and underlining process(es) emitting and transforming atmospheric aerosols. PM 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, NO, PO and SO; cations: Na, NH, K, Ca and Mg) using the ion chromatography system. Results showed that WSIS constitutes around 15% of PM aerosol load in the region. SO contributes the maximum (~ 50%) followed by NO (~ 12.5%) and NH (~ 12.5%) to the total concentration of WSIS analysed. During all the seasons, average concentrations of PM 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 PM-associated WSIS viz. re-suspension of soil or local sediments; conversion of pollutant gases (SO, NO and NH) 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.