Enhancement of snow albedo reduction and radiative forcing due to coated black carbon in snow

Abstract. When black carbon (BC) is internally mixed with other atmospheric particles, BC light absorption is effectively enhanced. This study is the first to explicitly resolve the optical properties of coated BC in snow, based on core/shell Mie theory and a snow, ice, and aerosol radiative model (SNICAR). Our results indicate that a "BC coating effect" enhances the reduction of snow albedo by a factor of 1.1–1.8 for a non-absorbing shell and 1.1–1.3 for an absorbing shell, depending on BC concentration, snow grain radius, and core/shell ratio. We develop parameterizations of the BC coating effect for application to climate models, which provides a convenient way to accurately estimate the climate impact of BC in snow. Finally, based on a comprehensive set of in situ measurements across the Northern Hemisphere, we find that the contribution of the BC coating effect to snow light absorption has exceeded that of dust over northern China. Notably, the high enhancements of snow albedo reductions by BC coating effect were found in the Arctic and Tibetan Plateau, suggesting a greater contribution of BC to the retreat of Arctic sea ice and Tibetan glaciers.