Low Cloud Dispersion Effects by Anthropogenic Aerosols in Polluted Air

Abstract Aerosol–cloud interactions (ACI) are a major source of uncertainty in anthropogenic climate forcing. Anthropogenic aerosols modulate the cloud albedo by impacting the relative dispersion ( ε ) of cloud droplet size distributions (CDSDs), known as the dispersion effect. This effect can be either suppressive or enhancing, introducing considerable uncertainties in polluted continental clouds. Here, we developed in situ measurements in polluted East China and simultaneously measured the CDSDs and aerosol properties. A wide range of ε from 0.20 to 0.78 with a mean value of 0.43 was observed. Machine learning analysis shows that aerosol number concentration and hygroscopicity dominate the changes of ε in polluted continental stratiform clouds under weak vertical velocities (<0.5 m s −1 ) and low liquid water content (∼0.1 g m −3 ) conditions. Overall, the dispersion effect enhances the aerosol indirect effect by ∼11%. These results highlight the importance of aerosol properties in evaluating ACI in polluted environments.