A coupled regional climate and aerosol-chemistry model, RIEMS 2.0 (Regional Integrated Environmental Model System for Asia), in which anthropogenic sulfate, black carbon, and organic carbon were assumed to be externally mixed (EM), internally mixed (IM) or partially internally mixed (IEM), was used to simulate the impacts of these anthropogenic aerosols on East Asian climate for the entire year of 2006. The distributions of aerosol mass concentration, radiative forcing and hence the surface air temperature and precipitation variations under three mixing assumptions of aerosols were analyzed. The results indicated that the mass concentration of sulfate was sensitive to mixing assumptions, but carbonaceous aerosols were much less sensitive to the mixing types. Modeled results were compared with observations in a variety of sites in East Asia. It was found that the simulated concentrations of sulfate and carbonaceous aerosols were in accord with the observations in terms of magnitude. The simulated aerosol concentrations in IM case were closest to observation results. The regional average column burdens of sulfate, black carbon, and organic carbon, if internally mixed, were 11.49, 0.47, and 2.17 mg m 2 , respectively. The radiative forcing of anthropogenic aerosols at the top of the atmosphere increased from -1.27 (EM) to -1.97 W m 2 (IM) while the normalized radiative forcing (NRF) decreased from -0.145 (EM) to -0.139 W mg 1 (IM). The radiative forcing and NRF were -1.82 W m 2 and -0.141 W mg 1 for IEM, respectively. The surface air temperature changes over the domain due to the anthropogenic sulfate and carbonaceous aerosols were -0.067, -0.078, and -0.072 K, with maxima of -0.47, -0.50, and -0.49 K, for EM, IM, and IEM, respectively. Meanwhile, the annual precipitation variations were -8.0 (EM), -20.6 (IM), and -21.9 mm (IEM), with maxima of 148, 122, and 102 mm, respectively, indicating that the climate effects were stronger if the sulfate and carbonaceous aerosols were internally mixed.
In this paper, the RIEMS 2.0 model is used to simulate the distribution of sulfate, black carbon, and organic carbon aerosols over China (16.2°-44.1°N, 93.4°-132.4°E) in 1998. The climate effects of these three anthropogenic aerosols are also simulated. The results are summarized as follows: (1) The regional average column burdens of sulfate, BC, OC, and SOC were 5.9, 0.24, 2.4, and 0.49 mg m-2, with maxima of 33.9, 1.48, 7.3, and 1.1 mg m-2, respectively. The column burden and surface concentration of secondary organic carbon accounted for about 20% and 7%, respectively, of the total organic carbon in eastern China. (2) The radiative forcings of sulfate, organic carbon, and black carbon at the top of the atmosphere were -1.24, -0.6, and 0.16 W m-2, respectively, with extremes of -5.25, -2.6, and 0.91 W m-2. (3) The surface air temperature changes caused by sulfate, organic carbon, and black carbon were -0.07, -0.04, and 0.01 K, respectively. The air temperature increase caused by black carbon at 850 hPa was higher than that at the surface. The net effect of the three kinds of anthropogenic aerosols together decreased the annual average temperature by -0.075 K; the maximum value was -0.3 K. (4) Black carbon can reduce the precipitation in arid and semi-arid areas of northern China and increase the precipitation in wet and semi-wet areas of southern China. The average precipitation increase caused by black carbon in China was 0.003 mm d-1. The net effect of the three kinds of anthropogenic aerosols was to decrease the precipitation over China by 0.008 mm d-1.
