Transport of black carbon to polar regions: Sensitivity and forcing by black carbon

Abstract

The transport of black carbon (BC) to polar regions is studied using the University of Michigan IMPACT aerosol model driven by two sets of meteorological fields from the NCAR CAM5 and GFDL AM3 models. The sensitivity of the transport of BC to wet deposition processes is tested by varying the wet deposition in large-scale precipitation. BC concentrations and deposition in polar regions are shown to be sensitive to both the meteorological fields and the wet deposition treatment. Using the default wet deposition, both IMPACT-CAM5 and IMPACT-AM3 simulate an appropriate amount of BC deposition in polar regions as compared to ice core observations. Although the seasonal cycle of BC surface air concentrations is reasonable, the concentrations are about 1~2 orders of magnitude smaller than observations. With reduced wet deposition efficiency, the total deposition of BC increases by a factor of ~2 to ~3 due to more transport to the poles. The near surface BC concentrations increase even more (by a factor of ~3 to ~10) but are still largely underestimated especially in the north polar region. The radiative forcing from the BC deposited on snow and sea ice is also sensitive to the wet deposition treatment and the different meteorological fields. The global (Arctic) annual mean forcing is about +0.020 W m−2 (+0.11 W m−2) for IMPACT-CAM5 and +0.022 W m−2 (+0.13W m−2) for IMPACT-AM3.