Dissolved Organic Matter and Inorganic Ions in a Central Himalayan Glacier—Insights into Chemical Composition and Atmospheric Sources

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Abstract

Melting of Himalayan glaciers can be accelerated by the deposition of airborne black carbon and mineral dust as it leads to significant reductions of the surface albedo of snow and ice. Whereas South Asia has been shown a primary source region to these particles, detailed sources of these aerosol pollutants remain poorly understood. In this study, the chemical compositions of snow pit samples collected from Jima Yangzong glacier in the central Himalayas were analyzed to obtain information of atmospheric aerosols deposited from summer 2009 to spring 2010. Especially, an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was used for the first time to chemically characterize the dissolved organic and inorganic matter (DOM and DIM) in snow samples. The concentrations of these species varied seasonally, with high levels observed during the winter-spring period and low levels during the summer monsoon period. On average, the dissolved substances was dominated by organics (58%) with important contributions from inorganic species, NO3(-) (12.5%), Ca(2+) (9.1%), NH4(+) (8.7%), and SO(4)(2-) (8.1%). DOM was found more oxidized with an average (± 1σ) atomic oxygen-to-carbon ratio (nO/nC) of 0.64 (± 0.14) and organic mass-to-carbon ratio (OM/OC) of 2.01 (± 0.19) during the winter-spring periods compared to the summer season (nO/nC = 0.31 ± 0.09 and OM/OC = 1.58 ± 0.12). In addition, biomass burning particles were found significantly enhanced in snow during the winter-spring periods, consistent with HYSPLIT back trajectory analysis of air mass history, which indicates prevailing atmospheric transport from northwest India and Nepal.

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