Meteorological Conditions Favorable for Strong Anthropogenic Aerosol Impacts on Clouds

Ship-track-like polluted cloud tracks provide a direct way to study aerosol-cloud interactions. Here, we study environmental conditions favorable for pollution tracks' formation. We study polluted cloud tracks forming downwind of localized anthropogenic air pollution hot spots of Norilsk and Cherepovets in Russia and Thompson in Canada. Polluted cloud tracks form on 20%-37% of days with liquid-phase clouds. The large-scale atmospheric circulation largely determines the occurrence of track-favoring conditions. Tracks tend to form in clean and thin clouds under stable and dry conditions that are more often associated with anticyclonic large-scale flow in the studied locations. Plain Language Summary Tiny solid and liquid air pollution particles called aerosols offset an unknown fraction of the greenhouse gas warming. Here, we study under which conditions aerosols have strong impacts on clouds leading to a cooling effect on Earth's climate. We study clouds downwind of anthropogenic air pollution hot spots. We compare the conditions where air pollution changes the properties of clouds to the conditions where the influence of air pollution is not seen. Anthropogenic air pollution particles more readily lead to changes in the properties of clean and thin clouds under stable and dry conditions that are more often associated with anticyclonic large-scale airflow in the studied locations. Our results help reduce the uncertainty related to the anthropogenic aerosol impacts on clouds and Earth's climate.