Influence of aerosol hygroscopic growth parameterization on aerosol optical depth and direct radiative forcing over East Asia

The influence of aerosol hygroscopic growth parameterization on aerosol optical depth (AOD) and aerosol direct radiative forcing (ADRF) over East Asia is investigated by using an online coupled regional climate-chemistry/aerosol model (RIEMS-Chemaero) focusing on the period of summer 2006. Three aerosol hygroscopic growth schemes are tested in this study. Model performances are evaluated with ground observations and satellite retrievals. Comparison with observations of aerosol concentration demonstrates that the model is able to reproduce the spatial and temporal variations of aerosol components over East Asia. Model comparison with AOD measurements shows that AOD is best predicted by the aerosol hygroscopic growth scheme developed based on observations in China (Case B), and the aerosol hygroscopic growth affects AOD simulation significantly. In this study, the domain and seasonal mean AOD, ADRF at the top of the atmosphere, and ADRF at the surface over East Asia are estimated to be 0.31, − 9 W/m2, and − 29 W/m2 by Case B, respectively. Compared with Case B, the estimations from Case A (scheme from CCM3 radiation package) differ by + 71%, + 100%, and + 17%, respectively, while those from Case C (κ parameterization) differ by − 16%, + 11%, and − 17%. The large differences in AOD and ADRF among cases suggest the necessity to develop appropriate hygroscopic growth parameterization with geographical characteristics in climate model for estimating regional aerosol optical properties and radiative effects.