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 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 to 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. To understand sources of impurities and their concentrations for seasonal snow on land, we evaluated multiple lines of evidence to scale up from ground-based measurements in the Dudh Koshi River Basin, a remote headwater basin within the Khumbu Region of Nepal. We obtained ground-based in-situ observations of refractory black carbon (rBC) measured by Single Particle Soot Photometer (SP2), including size distributions in snow on land. We interpreted these results in the context of concurrent Moderate Imaging Spectroradiometer (MODIS) satellite observations and speciated aerosol optical depth derived from reanalysis products modeled with the Navy Aerosol Analysis Prediction System global aerosol model. We collected snow samples, mostly in the Gokyo Valley, at varying distances from local tea houses along a 2000 meters above sea level (m a.s.l.) elevation transect from 3250 to 5299 m a.s.l. rBC concentrations ranged from 3.9 to 76.8 μg-rBC/L-H₂O. Although previous data do not exist at these lower elevations, our findings are higher than previous surface snow results at higher elevations in the nearby Khumbu Valley. In general, rBC concentrations were lower in fresh snow than aged snow; concurrent MODIS satellite observations of snow albedo also show smaller impacts from LAIs in visible wavelengths in fresh snow. In aged snow samples, rBC decreased with elevation, as did concurrent MODIS albedo observations. rBC-particle size distributions also shifted to a larger mode for aged snow samples. Results from the Navy Aerosol Analysis Prediction System model indicate anthropogenic and biogenic fine aerosols from biofuel (dry-dung burning) are the primary aerosol species in the atmosphere for the study period, at ∼thrice the concentration of dust and smoke.

当沉积在雪和冰上时，诸如灰尘和黑碳（BC）的吸光杂质（LAI）会减少表面反照率并增强融化。BC来自化石燃料和生物质的不完全燃烧。不列颠哥伦比亚省的本地和区域性资源存在于亚洲高山地区，例如干粪燃烧产生的热量和燃料，这种燃烧非常靠近雪和冰川。也存在局部灰尘或从印度恒河平原运来的灰尘。在恒河流域，融雪水主要受季节性降雪的影响，但相对较少观察到季节性降雪中存在杂质。为了了解陆地上季节性降雪的杂质来源及其浓度，我们评估了多条证据，以扩大在尼泊尔昆布地区偏远水源盆地达德·科希河盆地的地面测量范围。原位单颗粒煤烟光度计（SP2）测量的难熔黑碳（rBC）的观测结果，包括陆地上雪中的粒度分布。我们在同时进行中度成像光谱仪（MODIS）卫星观测和从以海军气溶胶分析预测系统全球气溶胶模型建模的再分析产品中得出的气溶胶光学深度的背景下解释了这些结果。我们收集了大部分位于Gokyo谷地的雪样，这些雪样与当地茶馆的海拔高度在3250至5299 m asl之间，距海拔2000米（m asl）的横断面不同，rBC浓度范围从3.9到76.8μg-rBC/ LH ₂O.尽管在这些较低的海拔高度上不存在先前的数据，但我们的发现要比附近的昆布谷地较高海拔的先前地面降雪结果更高。通常，新鲜雪中的红细胞浓度低于老雪。同时进行的MODIS卫星对雪反照率的观测还表明，在新鲜雪中可见光波长内LAI的影响较小。在老年雪样品中，rBC随着海拔的升高而下降，同时进行的MODIS反照率观测也是如此。对于老化的雪样，rBC粒度分布也转移到较大模式。海军气溶胶分析预测系统模型的结果表明，在研究期内，由生物燃料（干粪燃烧）产生的人为和生物成因的精细气溶胶是大气中的主要气溶胶种类，其尘埃和烟气浓度约为其三倍。