Modeling Study of the Impact of Heterogeneous Reactions on Dust Surfaces on Aerosol Optical Depth and Direct Radiative Forcing over East Asia in Springtime

Abstract

The spatial distributions and interannual variations of aerosol concentrations, aerosol optical depth (AOD), aerosol direct radiative forcings, and their responses to heterogeneous reactions on dust surfaces over East Asia in March 2006–10 were investigated by utilizing a regional coupled climate-chemistry/aerosol model. Anthropogenic aerosol concentrations (inorganic + carbonaceous) were higher in March 2006 and 2008, whereas soil dust reached its highest levels in March 2006 and 2010, resulting in stronger aerosol radiative forcings in these periods. The domain and five-year (2006–10) monthly mean concentrations of anthropogenic and dust aerosols, AOD, and radiative forcings at the surface (SURF) and at the top of the atmosphere (TOA) in March were 2.4 μg m-3, 13.1 μg m-3, 0.18, −19.0 W m–2, and −7.4 W m-2, respectively. Heterogeneous reactions led to an increase of total inorganic aerosol concentration; however, the ambient inorganic aerosol concentration decreased, resulting in a smaller AOD and weaker aerosol radiative forcings. In March 2006 and 2010, the changes in ambient inorganic aerosols, AOD, and aerosol radiative forcings were more evident. In terms of the domain and five-year averages, the total inorganic aerosol concentrations increased by 13.7% (0.17 μg m-3) due to heterogeneous reactions, but the ambient inorganic aerosol concentrations were reduced by 10.5% (0.13 μg m-3). As a result, the changes in AOD, SURF and TOA radiative forcings were estimated to be −3.9% (−0.007), −1.7% (0.34 W m-2), and −4.3% (0.34 W m-2), respectively, in March over East Asia.