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Abstract:
Wet and dry deposition of black carbon (BC) aerosol in the Arctic lowers snow albedo, thus contributing to warming in the Arctic. However, the processes and impacts associated with BC deposition in the Arctic are poorly understood because of the scarcity and uncertainties of measurements of BC in snow with adequate spatiotemporal resolution. We sampled snowpack at two sites (11 m and 300 m above sea level) at Ny-Alesund, Spitsbergen, in April 2013. We also collected falling snow near the surface with a windsock from September 2012 to April 2013. The size distribution of BC in snowpack and falling snow was measured using a single-particle soot photometer combined with a nebulizer. The BC size distributions did not show significant variations with depth in the snowpack, suggesting stable size distributions in falling snow. The BC number and mass concentrations (CNBC and CMBC) at these sites agreed to within 19% and 10%, respectively, despite the sites difference in snow water equivalent (SWE). This indicates the small influence of the amount of SWE (or precipitation) on these quantities. Average CNBC and CMBC in snowpack and falling snow at nearly the same locations agreed to within 5% and 16%, after small corrections for artifacts associated with the sampling of the falling snow. This comparison shows that the relative contribution of dry deposition to total deposition to be smaller than the uncertainty of their measurements. CNBC and CMBC in falling snow and BC concentrations in ambient air were highest in winter.