The direct and indirect radiative effects of sea salt aerosols over the western Pacific using an online-coupled regional chemistry-climate model with a developed sea salt emission scheme

The direct and indirect radiative effects of sea salt aerosols (SSA) over the western Pacific Ocean of East Asia for the year 2014 are investigated by using an online-coupled regional chemistry-climate model (RIEMS-Chem) with a developed sea salt emission scheme (G03SSTRH) by considering the effects of sea surface temperature (SST) and relative humidity (RH) on sea salt generation. Model comparison with observations at coastal and island sites demonstrates the G03SSTRH scheme apparently improve model simulation for sea salt concentration, with the overall model-observation bias for PM10 concentration reduced from 29% to 16% and more evident improvement at northern sites of the western Pacific. It is noteworthy that compared to the experiment with the old SSA emission scheme (G03), the G03SSTRH experiment substantially alters the spatial distribution of mass concentration and radiative effects of sea salt, shifting the maximum value center from the ocean northeast of Japan to the southern parts of the western Pacific with the maximum value increasing to some extent. SSA exerts a negative radiative effect at the top of atmosphere (TOA), in which direct radiative effect (DRESSA) dominates over indirect radiative effect (IRESSA) in the western Pacific. The oceanic and annual mean DRESSA, IRESSA, and total radiative effect (TRESSA) are estimated to be -1.22 W/m2, -0.46 W/m2, and -1.65 W/m2, respectively, from the G03SSTRH experiment, which are 16%, 5%, and 12% stronger than those from the G03 experiment, and the seasonal mean DRESSA in G03SSTRH are approximately 45% and 32% higher than those in G03 in summer and autumn. Distinct seasonality of SSA radiative effects is revealed in the G03SSTRH experiment, showing stronger DRESSA and IRESSA in summer and autumn than those in spring and winter, in marked contrast to the little seasonality in the G03 experiment. This study provides a comprehensive regional estimation of radiative effects induced by SSA and reveals the significant effect of different SSA emission schemes on both mass concentration, radiative effects and seasonal variation of SSA over the western Pacific.