C. He, RAL/NCAR

High-mountain Asia (HMA) (also known as the Third Pole) functions as a “water tower” of Asia, with its glacier and snowpack providing water resources for billions of people for drinking, irrigation, and other activities. The deposition of light-absorbing particles (LAPs), including black carbon (BC), dust, and brown carbon (BrC), has been known to significantly reduce snow albedo and hence accelerate snow melting and glacier retreat in this region. Particularly, most previous studies have focused on the radiative effects of BC and dust over HMA in the past decade, whereas much less is known for BrC climatic effects in the region partially due to the lack of modeling capabilities for BrC evolution during its lifecycle in terms of concentration and optical properties. Recent advances in the scientific understanding of BrC atmospheric evolution allow an improved representation of BrC aerosol in chemistry-climate models. In this study, we implement a series of BrC-relevant processes into the widely-used Weather Research and Forecasting (WRF) model coupled with chemistry (WRF-Chem) to represent the BrC atmospheric evolution. Specifically, we add representations of direct emissions, secondary formation, aerosol-radiation interaction, aerosol-cloud interaction, deposition (dry and wet), and aerosol-snow interaction for BrC in the model. We apply the enhanced WRF-Chem model to HMA to quantify the effects of BrC on aerosol concentrations and optical depths (AOD), atmospheric radiative impacts, and influences on snowpack albedo and melting in this region. We evaluate the model simulations against available satellite and ground-based observations over Asia in terms of chemistry (e.g., AOD, surface aerosol concentration, aerosol in snow) and meteorology (e.g., surface temperature and albedo, snow cover, precipitation).