Effects of shipping emissions on cloud physical properties over coastal areas near Shanghai

Abstract To investigate the effects of shipping aerosols on radiation, cloud physical properties, and near-surface PM2.5, four sensitive experiments with the WRF-Chem model were performed over coastal areas near Shanghai for July 2014. In general, the direct effect of shipping aerosols resulted in negative shortwave (SW) radiation forcing at the land surface. However, when considering the indirect effect, the downward SW radiation at the sea surface declined significantly. By the direct effect, shipping aerosols could modify cloud structure, resulting in a higher cloud base, lower cloud top, and shallower cloud depth. With the indirect effect included, both the cloud base and cloud top showed a declining trend over sea areas. The indirect effect of shipping aerosols was relatively more significant in influencing clouds. For example, the results revealed a 1.2% change of low cloud coverage from the indirect effect but only a 0.1% change due to the direct effect. Through their direct and indirect effects, shipping aerosols cause non-negligible impacts on precipitation, which are concentrated within light precipitation (