Concentrations and Size Distributions of Black Carbon in the Surface Snow of Eastern Antarctica in 2011

Knowledge of black carbon (BC) concentrations and size distributions within surface snow in Antarctica is limited. However, these measurements are important to understanding global aerosol transport from combustion sources, and BC contributes to positive radiative forcing. This study analyzed the concentrations and size distributions of BC and inorganic ions in snow samples collected at the Syowa station in Antarctica from April to December 2011 and along a traverse route to an inland (Mizuho) station. The BC size distributions in snow were bimodal with mass median diameters of similar to 140 and similar to 690 nm. We also estimated the mass median diameter from unimodal distributions and found smaller diameters than were reported by other studies. The mass concentrations of BC in snow were higher in inland samples than in Syowa samples. Among Syowa samples, the BC concentrations in December (2117.3 ng L-1 on average) were higher than in other periods (288.2 ng L-1 on average). The December samples experienced ambient temperatures above 0 degrees C, and the atmospheric BC concentrations did not increase simultaneously. Inorganic ions originated from the ocean and decreased with increasing distance from the coastal area. We conclude that the BC concentrations in surface snow increased mainly by postdeposition processes through the loss of water mass due to melting, evaporation, and sublimation. Our study is the first to report detailed BC concentrations and size distributions in eastern Antarctica, and the results will help to evaluate BC global transport, the snow albedo estimations in this region, and the climate impacts of BC.