Dark Brown Carbon Snow Darkening Effect: An Experimental Validation

GANESH CHELLUBOYINA, Taveen Kapoor, Rajan K. Chakrabarty, Washington University in St. Louis

     Abstract Number: 258
     Working Group: Aerosol Physics

Abstract
Smoke from frequent wildfire events continues to pose serious climatic challenges. One of these challenges is the eventual settling of some wildfire smoke particles in the cryosphere, causing the snow darkening effect and contributing to the albedo climate feedback. Of all the light absorbing constituents of wildfire smoke, strongly absorbing dark brown carbon (d–BrC) has been the least studied, as it only has recently been identified in laboratory studies and observed in a field campaign. Most studies prior to this one have focused on snow albedo reduction and radiative forcing impacts due to black carbon (BC) or water-soluble organic carbon originating from smoldering combustion. Our work aims to bridge the gap in the understanding of d–BrC induced snow radiative forcing through aerosol deposition experiments. Through a purpose-built chamber cooled by liquid nitrogen, we rapidly froze a mist spray and accumulated ice grains to create artificial snow. D–BrC particles generated through the dry distillation of wood were deposited on this snow. Reflectances of the snow samples were measured using an integrating sphere. Aerosol optical properties and concentrations, and the snow grain size were key tunable parameters, and we observed their impact on the snow albedo. Using this experimental data, we compared and validated our Snow, Ice, and Aerosol Radiative (SNICAR) model-based albedo predictions. We also present measurements related to the evolution of the aerosol size distribution in snow. Finally, we examine the influence of the aerosol deposition mode, whether wet deposited (along with precipitation) or dry deposited (continuous deposition flux from the atmosphere), on aerosol-snow mixing state and thereby albedo by varying the experimental conditions. These results will amplify our understanding of the wildfire snow darkening effect and the aftereffects thereof.