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In this study, we evaluate the ability of the latest NASA GISS composition-climate model, GISS-E2-PUCCINI, to simulate the spatial distribution of snow BC (sBC) in the Arctic relative to present-day observations. Radiative forcing due to BC deposition onto Arctic snow and sea ice is also estimated. Two sets of model simulations are analyzed, where meteorology is linearly relaxed towards National Centers for Environmental Prediction (NCEP) and towards NASA Modern Era Reanalysis for Research and Applications (MERRA) reanalyses. Results indicate that the modeled concentrations of sBC are comparable with present-day observations in and around the Arctic Ocean, except for apparent underestimation at a few sites in the Russian Arctic. That said, the model has some biases in its simulated spatial distribution of BC deposition to the Arctic. The simulations from the two model runs are roughly equal, indicating that discrepancies between model and observations come from other sources. Underestimation of biomass burning emissions in Northern Eurasia may be the main cause of the low biases in the Russian Arctic. Comparisons of modeled aerosol BC (aBC) with long-term surface observations at Barrow, Alert, Zeppelin and Nord stations show significant underestimation in winter and spring concentrations in the Arctic (most significant in Alaska), although the simulated seasonality of aBC has been greatly improved relative to earlier model versions. This is consistent with simulated biases in vertical profiles of aBC, with underestimation in the lower and middle troposphere but overestimation in the upper troposphere and lower stratosphere, suggesting that the wet removal processes in the current model may be too weak or that vertical transport is too rapid, although the simulated BC lifetime seems reasonable. The combination of observations and modeling provides a comprehensive distribution of sBC over the Arctic. On the basis of this distribution, we estimate the decrease in snow and sea ice albedo and the resulting radiative forcing. We suggest that the albedo reduction due to BC deposition presents significant space-time variations, with highest mean reductions of 1.25% in the Russian Arctic, which are much larger than those in other Arctic regions (0.39% to 0.64%). The averaged value over the Arctic north of 66° N is 0.4-0.6% during spring, leading to regional surface radiative forcings of 0.7, 1.1 and 1.0 Wm-2 in spring 2007, 2008 and 2009, respectively. [ABSTRACT FROM AUTHOR]

There has been increasing recognition of the important role that aerosols such as black carbon (BC) play in influencing net climate forcing, in particular the high rates of warming in the Arctic, and there is significant interest in reducing BC emissions. In order to assess mitigation options, there is a need for a better understanding of how current air quality policies designed for particulate matter reductions affect BC emissions and for the development of improved BC specific marginal abatement cost (MAC) curves. Using data from the United States (US), we assess the effects of existing air quality regulations on projected BC emissions (diesel fuel regulations in particular are already having significant effects). We also identify key US-specific abatement strategies and present MAC curves for further reducing BC emissions from two key US sources. This analysis may serve to inform similar research on BC mitigation in other regions and sectors. [ABSTRACT FROM AUTHOR]