Manuscript to be Submitted to Geophys. Res. Lett. Albedo Reduction by Black Carbon in Snow: Measurements and Implications

• Main Authors: Charles S. Zender, Jean-charles Gallet, Florent Dominé, Ghislain Picard, Mark G
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; albedo; black carbon
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.418.9242; http://dust.ess.uci.edu/ppr/ppr_ZGD08.pdf

Industrial and biomass burning emissions of black carbon (BC) from low- and mid-latitudes dominate the radiative forcing by absorbing impurities trapped in snow and ice at mid- and high- northern latitudes. Correct model representation of albedo reduction by BC-contaminated snow is crucial because our GCM simulations show that dirty snow can explain about 30 % of the observed 20th century Arctic warming. Until now, measurements of actual snow darkening by BC have been attempted only in the field, under non-reproducible conditions, and limited by the BC concentration that happens to be present. We have conducted the first measurements of the direct effect of BC-contamination on snow albedo by in a controlled environment. We doped natural snow with a commercially available BC-analogue and measured the resulting albedo change at visible and near-infrared wavelengths. Snow albedo was measured in a (portable) integrating sphere system. Snow grain size is estimated from the near-infrared albedo. Snow density, temperature, and BC properties were known a priori. The albedo measurement reproducibility is about 1 % for natural snow. Our measurements agree with model predictions that BC concentrations from 250 ppbmto