The geographical and seasonal characteristics in nitrate aerosol and its direct radiative forcing over East Asia are analyzed by using the air quality modeling system RAMS-CMAQ coupled with an aerosol optical properties/radiative transfer module.For evaluating the model performance,nitrate ion concentration in precipitation,and mixing ratios of PM_(10),and some gas precursors of aerosol during the whole year of2007 are compared against surface observations at 17 stations located in Japan.Korea,and China,and the satellite retrieved NO_2 columns.The comparison shows that the simulated values are generally in good agreement with the observed ones.Simulated monthly averaged values are mostly within a factor of 2of the measurements at the observation stations.The distribution patterns of NO_2 from simulation and satellite measurement are also similar with each other.Analysis of the distribution features of monthly and yearly averaged mass concentration and direct radiative forcing(DRF) of nitrate indicates that the nitrate aerosol could reach about 25-30%of the total aerosol mass concentration and DRF in Sichuan Basin,Southeast China,and East China where the high mass burden of all major aerosols concentrated.The highest mass concentration and strongest DRF of nitrate could exceed 40μg/m~3 and-5W/m~2,respectively.It also indicates that other aerosol species,such as carbonaceous and mineral particles,could obviously influence the nitrate DRF for they are often internally mixed with each other. The geographical and seasonal characteristics in nitrate aerosol and its direct radiative forcing over East Asia are analyzed by using the air quality modeling system RAMS-CMAQ coupled with an aerosol optical properties / radiative transfer module. For evaluating the model performance, nitrate ion concentration in precipitation , and mixing ratios of PM_ (10), and some gas precursors of aerosol during the whole year of2007 are compared against surface observations at 17 stations located in Japan. Korea, and China, and the satellite retrieved NO_2 columns. the comparison shows that the simulated values ​​are generally in good agreement with the observed ones. Simulated monthly averaged values ​​are mostly within a factor of 2 of the measurements at the observation stations. The distribution patterns of NO_2 from simulation and satellite measurements are also similar to each other. Analysis of the distribution features of monthly and yearly averaged mass concentration and direct radiative forcing (DRF) of n itrate indicates that the nitrate aerosol could reach about 25-30% of the total aerosol mass concentration and DRF in Sichuan Basin, Southeast China, and East China where the high mass burden of all major aerosols concentrated. the highest mass concentration and strongest DRF of nitrate could exceed 40μg / m ~ 3 and-5W / m ~ 2, respectively. It also says that other aerosol species, such as carbonaceous and mineral particles, could obviously influence the nitrate DRF for they are often internally mixed with each other.