Black Carbon in Eastern Sierra Nevada Snow Pack

Abstract

The majority of surface water resources in semi-arid regions originates as mountain snow in higher elevations so detailed understanding of the drivers of snow melt is critical to water management in a changing climate. Black carbon (BC) aerosols emitted during combustion and deposited on permanent and seasonal snow covers decrease reflectance, leading to enhanced snow pack warming, sublimation and melt, but the concentrations, sources, and fate of BC particles in seasonal snow packs are highly uncertain. Measurements of BC, soluble ions, and physical properties in a sequence of snow pits and surface snow samples in the eastern Sierra Nevada mountains excavated during the snow accumulation and melt seasons in 2009 show average concentrations between 1-11 ppb, with surface concentrations as high as 429 ppb. Data analyses and interpretation of results suggests that deposition of BC remains stable as the snow accumulates, but during the melt season, the properties of BC (hydrophilic vs. hydrophobic) influence the fate and transport through the snow pack. The key finding of this study confirmed that BC in melting snow pack behaved independently of soluble impurities, and suggests that radiative forcing at mid-latitudes is significant.