Effects of Shipping-originated Aerosols on Physical Cloud Properties over Marine Areas near East China

Shipping emissions have received increasing attention due to their influence on regional climate, and air quality at ports and in coastal areas around the world. In the context of climatology, the effects of shipping-originated aerosols (using the aerosol optical depth, AODship, as a proxy) on clouds in marine areas near East China were examined based on multi-satellite datasets. On average, AODship is approximately 0.17, 0.20, 0.15 and 0.13 in the different seasons, contributing 23%, 30%, 36% and 25% of the total AOD, respectively. In remote sea areas, AODship is generally higher in spring and summer and lower in autumn. Statistical analysis shows that it is strongly related to the cloud parameters, such as the cloud fraction (CF), cloud optical thickness (COT) and cloud effective radius (CER) in the liquid phase. In particular, CER and AODship exhibit a positive correlation in winter but a weakly negative correlation in summer over the northern East China Sea and a positive correlation in spring and summer over the Yellow Sea. In all four seasons, COT and CF decrease as AODship increases. The correlations between AODship and the cloud properties are stronger (R > 0.3) when the aerosol-cloud layers are well mixed than when they are separated, indicating that shipping-originated aerosols drawn into the cloud body can directly affect the microphysical properties of cloud droplets during cloud formation. The water vapor content and upward air motion are key thermodynamic conditions within the low atmospheric layers under the cloud bottom that play an important role in cloud formation and development. Our results provide new insight into the influence of shipping emissions on clouds in Asian marine areas.