ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-5563-2012 Aerosol direct radiative forcing based on GEOS-Chem-APM and uncertainties Ma X. 1 Yu F. 1 Luo G. 1 Atmospheric Sciences Research Center, State University of New York, 251 Fuller Road, Albany, New York 12203, USA 26 06 2012 12 12 5563 5581 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/5563/2012/acp-12-5563-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/5563/2012/acp-12-5563-2012.pdf

Aerosol direct radiative forcing (DRF) plays an important role in global climate change but has a large uncertainty. Here we investigate aerosol DRF with GEOS-Chem-APM, a recently developed global aerosol microphysical model that is designed to capture key particle properties (size, composition, coating of primary particles by volatile species, etc.). The model, with comprehensive chemistry, microphysics and up-to-date emission inventories, is driven by assimilated meteorology, which is presumably more realistic compared to the model-predicted meteorology. For this study, the model is extended by incorporating a radiation transfer model. Optical properties are calculated using Mie theory, where the core-shell configuration could be treated with the refractive indices from the recently updated values available in the literature. The surface albedo is taken from MODIS satellite retrievals for the simulation year, in which the data set for the 8-day mean at 0.05° (5600 m) resolution for 7 wavebands is provided. We derive the total and anthropogenic aerosol DRF, mainly focus on the results of anthropogenic aerosols, and then compare with those values reported in previous studies. In addition, we examine the anthropogenic aerosol DRF's dependence on several key factors, including the particle size of black carbon (BC) and primary organic carbon (POC), the density of BC and the mixing state. Our studies show that the anthropogenic aerosol DRF at top of atmosphere (TOA) for all sky is −0.41 W m<sup>−2</sup>. However, the sensitivity experiments suggest that the magnitude could vary from −0.08 W m<sup>−2</sup> to −0.61 W m<sup>−2</sup>, depending on assumptions regarding the mixing state, size and density of particles.

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