Yak-dung burning influences refractory black carbon concentrations in seasonal snow at lower elevations of the Dudh Koshi River Basin of Nepal

When deposited on snow and ice, light absorbing impurities (LAIs) such as dust and black carbon (BC) reduce surface albedo and enhance melt. BC comes from the incomplete combustion of fossil fuels and biomass. Local and regional sources of BC exist in High Mountain Asia, such as dry-dung burning for heat and fuel, which occurs in close proximity of snow and glaciers. Local dust or dust transported from the Indo-Gangetic Plain is also present. In the Ganges River Basin, meltwater is dominated by seasonal snow, yet relatively few observations of impurities in seasonal snow exist. We present results of refractory black carbon (rBC) measured by Single Particle Soot Photometer (SP2), total organic carbon and trace elements in seasonal snow on land in the Dudh Koshi River Basin of the Khumbu Region of Nepal. We collected snow samples, mostly in the Gokyo Valley, at varying distances from local tea houses along a 2000 m elevation transect from 3250 m to 5299 m. rBC concentrations ranged from 3.69 to 68.9 μg-rBC/L-H₂O and are similar to previously reported results in the nearby Khumbu Valley. In general, rBC concentrations were higher in aged snow than fresh snow. In aged snow samples, rBC decreased with elevation. Moderate Imaging Spectroradiometer (MODIS) satellite observations concurrent with rBC samples also show smaller impacts to snow albedo in visible wavelengths from LAIs in fresh snow than aged snow. Results from the Navy Aerosol Analysis Prediction System (NAAPS) global aerosol model indicate anthropogenic and biogenic fine (ABF) aerosols are the primary aerosol species in the atmosphere for the study period, 2016-01-20 to 2016-02-07 at approximately twice the concentration of dust and smoke. The ABF aerosols are a mixture of sulfate and black/organic carbon from biofuel (dry-dung burning) in the region.