Darkening of Soot-doped Natural Snow: Measurements and Model

We conducted the first measurements of the direct effect of laboratory controlled BCcontamination on snow albedo in a laboratory environment. Optical measurements of natural snow intentionally doped with industrial grade BC were conducted at visible and near-infrared wavelengths. Snow albedo was measured in a (portable) integrating sphere system. The absolute spectral albedos are less than expected at visible wavelengths due to absorption by the sample holder which is too shallow to present a semi-infinite sample surface. Hence we focus on the albedo change by BC doping, rather than on the absolute snow albedo itself. Using preliminary calibrations, our measurements agree well with model predictions that BC concentrations from 1–200 ppmm reduce albedo by 5–70%. A key uncertainty is assessing how much BC mass was “lost” during the doping process and thus did not fully contribute to snow darkening.