To assess individual direct radiative effects of diverse aerosol species on a regional scale, the air quality modeling system RAMS-CMAQ (Regional Atmospheric Modeling System and Community Multiscale Air Quality) coupled with an aerosol optical properties/radiative transfer module was used to simulate the temporal and spatial distributions of their optical and radiative properties over East Asia throughout 2005. Annual and seasonal averaged aerosol direct radiative forcing (ADRF) of all important aerosols and individual components, such as sulfate, nitrate, ammonium, black carbon (BC), organic carbon (OC), and dust at top-of-atmosphere (TOA) in clear sky are analyzed. Analysis of the model results shows that the annual average ADRF of all important aerosols was in the range of 0 to -18 W m(-2), with the maximum values mainly distributed over the Sichuan Basin. The direct radiative effects of sulfate, nitrate, and ammonium make up most of the total ADRF in East Asia, being concentrated mainly over North and Southeast China. The model domain is also divided into seven regions based on different administrative regions or countries to investigate detailed information about regional ADRF variations over East Asia. The model results show that the ADRFs of sulfate, ammonium, BC, and OC were stronger in summer and weaker in winter over most regions of East Asia, except over Southeast Asia. The seasonal variation in the ADRF of nitrate exhibited the opposite trend. A strong ADRF of dust mainly appeared in spring over Northwest China and Mongolia.

The air quality modeling system RAMS (Regional Atmospheric Modeling System)-CMAQ (Models-3 Community Multi-scale Air Quality) is developed to simulate the aerosol optical depth (AOD) and aerosol direct forcing (DF). The aerosol-specific extinction, single scattering albedo, and asymmetry factor are parameterized based on Mie theory taking into account the aerosol size distribution, composition, refractive index, and water uptake of solution particles. A two-stream solar radiative model considers all gaseous molecular absorption, Rayleigh scattering, and aerosols and clouds. RAMS-CMAQ is applied to simulate all major aerosol concentrations (e.g., sulfate, nitrate, ammonium, organic carbon, black carbon, fine soil, and sea salt) and AOD and DF over East Asia in 2005. To evaluate its performance, the simulated AOD values were compared with ground-based in situ measurements. The comparison shows that RAMS-CMAQ performed well in most of the model domain and generally captured the observed variations. High AOD values (0.2-1.0) mainly appear in the Sichuan Basin as well as in central and southeastern China The geographic distribution of DF generally follows the AOD distribution patterns, and the DF at the top-of-the-atmosphere is less than -25 and -20 W m(-2) in clear-sky and all-sky over the Sichuan Basin. Both AOD and DF exhibit seasonal variations with lower values in July and higher ones in January. The DF could obviously be impacted by high cloud fractions.