Aerosol Optical Depth（AOD） is a key factor that reflects the impact of atmospheric aerosol on the climate. The accurate simulation of AOD is the basis for a climatic model in modeling the aerosol climate effects. In this study, an online-coupled three-dimensional regional climate–atmospheric chemistry–aerosol model was used to investigate the AOD over eastern China in 2010 to understand the spatial and seasonal behavior of AOD and the role aerosol plays over this region.The Regional Integrated Environmental Modeling System online-coupled with atmospheric chemistry and aerosol processes（RIEMS-Chem） was used in this study.This model contains sophisticated atmospheric dynamic, atmospheric chemical, and aerosol chemical processes. The onlinecoupled system facilitates the model to simulate the impact of aerosol on climatic factors and the feedback of climate on aerosol distribution.Simulated AOD was verified by satellite retrieval of the Moderate-Resolution Imaging Spectroradiometer（MODIS） and insitu measurements from the Aerosol Robotic Network（AERONET） in four seasons.The comparison of the AOD simulation result with the corresponding MODIS retrieval indicated the capability of the model to reproduce the seasonal variation and spatial distribution of AOD over eastern China, although the model somewhat underestimated the magnitude in summer.The comparison of AOD measurements from the six AERONET sites also showed that the model was able to simulate the spatial and seasonal variation of AOD, but underestimated the magnitude over north China, with an overall correlation coefficient of 0.6 compared with all AERONET measurements. The MODIS retrieval and corresponding simulation result showed that, over eastern China, the AOD was generally higher in summer,followed by spring, and lower in autumn and winter. However, the daytime seasonal mean AOD showed different seasonal distribution patterns:For areas around the North China Plain, the daytime seasonal mean AOD reached its highest level in summer with values ranging from 1.1 to 1.5, but lowest in other seasons. By contrast, over areas of the middle and lower reaches of the Yangtze River, the daytime seasonal mean AOD was reached its highest level in spring with values ranging from 1.1 to 1.7, followed by autumn and winter, but lowest in summer. For the region of eastern China,the daytime seasonal mean AOD reach edits highest level over areas north of the Yangtze River in summer, over areas south of the Yangtze River in winter, and over areas along the middle and lower reaches of the Yangtze River in spring and autumn.Model verification indicated that RIEMS-Chem was able to reflect the characteristics of AOD distribution and its seasonal variation, but under predicted the observation by approximately 20% in terms of the annual mean. According to the model result, the daytime AOD distribution exhibited distinct subregional and seasonal characteristics over eastern China, implying that, over this region, aerosol optical and climatic effects could be subregional and seasonal dependent.

regional online-coupled model;Aerosol Optical Depth（AOD）;seasonal variation;eastern China;MODIS;AERONET