Anthropogenic Effects on Cloud Condensation Nuclei Distribution and Rain Initiation in East Asia

The recently developed method for retrieving cloud drop concentrations (N_d), cloud base updraft, and supersaturation made it possible to map these properties over East Asia. It was done for the summers of 2013 to 2019, in conjunction to low level wind direction. The background CCN concentrations were nearly equally low (<300 cm⁻³) over minimally perturbed air masses to the south and east of the densely populated areas of China, over ocean, and to the north over northern China, Mongolia, and southern Siberia. This stood in large contrast to large concentrations of activated CCN into cloud droplets reaching up to 2,000 cm⁻³ over and downwind of the densely populated regions over East Asia. Because cloud depth for rain initiation (D_c) increased linearly with CCN concentrations, the enhanced CCN increased D_c from a background of <1 km over ocean and ~2 km to the north of China to D_c > 4 km over the most polluted regions.