Budget and export of anthropogenic SOx from East Asia during continental outflow conditions -: art. no. 4167

[1] We examine the budget and export of anthropogenic SOx (SO2 and sulfate aerosol) emitted from East Asia during the late winter/early spring when continental outflow conditions dominate. Our study is based on simulations using a modified version of the China-MAP coupled regional climate/ chemical transport model of Qian and Giorgi [1999]. The modification involves the addition of algorithms to treat the vertical transport and removal of SOx by convective clouds. Model-calculated anthropogenic SO2 concentrations peaked at values greater than 20 ppbv at the surface in the urban source regions of China and Korea, but averaged only about 5 pbbv in the rural areas. Midtropospheric SO2 concentrations were more than an order of magnitude less, with peak values of around 0.1-0.15 ppbv overlying the urban source regions. The model-calculated sulfate aerosol distribution is more disperse, with peak surface concentrations of 5-10 ppbv in urban source regions, and concentrations of about 3 ppbv or less in rural areas and 1 ppbv or less in the midtroposphere. The model-calculated SOx concentrations are generally within a factor of 2 of the relevant observed concentrations at nonurban sites. The calculations indicate that during the late winter/early spring period, about 50% of the anthropogenic SOx emitted over East Asia is removed from the continental source regions. Roughly 30% is wet and dry deposited onto the neighboring oceans, and the remaining 20% is exported out of the model domain. The vast majority of the exported SOx is in the form of sulfate aerosol and is transported into the midtroposphere overlying the North Pacific Ocean. The rate of SOx export, about 0.2 Tg S per month, is significant when compared to natural S sources to the North Pacific Ocean, suggesting that the export of anthropogenic SOx from East Asia is perturbing sulfate aerosol concentrations over the North Pacific Ocean during the late winter and early spring. On an intraregional basis we find that China is the largest contributor to the emission and export of SOx from East Asia. However, all the nations/ continental subregions of East Asia appear to be net exporters of SOx, even those downwind of China.