Sensitivity Analysis of Brown Carbon on Snow Albedo Using SNICAR Radiative Transfer Model

GANESH CHELLUBOYINA, Chenchong Zhang, Rajan K. Chakrabarty, Washington University in St. Louis

     Abstract Number: 533
     Working Group: Aerosols, Clouds and Climate

Abstract
Deposition of light absorbing particles (LAPs) on snow induces a reduced surface albedo compared to that of pristine snow. Brown carbon (BrC), in contrast to other LAPs, strongly absorbs solar radiation in the ultraviolet (UV) and short visible wavelengths, which encompasses the peak of solar spectral irradiance. The absorption due to BrC, and consequently the reduction in albedo, is heavily influenced by its imaginary refractive index (κ). Recent in situ studies of BrC in snow have retrieved κ and measured albedo, which agrees with model-based predictions. However, BrC relative abundance in snow and its optical properties remain poorly constrained, and the resulting snow albedo and radiative forcing are not fully resolved.

Here we show the response of snow albedo to a broad range of BrC optical properties. The sensitivity analysis is performed using the Snow, Ice, and Aerosol Radiative (SNICAR) model, a two-stream radiative transfer model that calculates the radiative fluxes and surface albedo based on downwelling solar irradiance and particle optical properties. In addition, we identify BrC size distribution and relative abundance as tunable parameters for this sensitivity analysis. Preliminary results using a Kramers-Kronig dispersion relation for κ indicate that an albedo reduction of up to 10% compared to pristine snow occurs in the UV-visible region of the spectrum for 10 ppm of BrC in snow. We anticipate the results from this study will better constrain the albedo reducing effect and surface radiative forcing due to BrC on snow. Furthermore, simulation results may be combined with satellite remote sensing data to estimate ground concentrations of BrC in remote locations.