Field Observations of In-Cloud Nucleation and the Modification of Atmospheric Aerosol Size Distributions after Cloud Evaporation

The authors measured aerosol and droplet size distributions in the range from 0.1 to 50 µm, concentrations and sizes of precipitation particles, concentrations of condensation nuclei, and state parameters in and in the vicinity of a towering summer cumulus cloud. The measurements show that the liquid water content, droplet concentration, and vertical velocity all peaked in the upper half of the cloud, but the droplet mean diameter increased with altitude. A large fraction of the aerosols (0.1–3.0 µm) remains in the haze state. The vertical profiles of aerosols and condensation nuclei showed peaks between 5.0 and 7.0 km. The normalized aerosol size distribution shows a shift toward large aerosols. The peaks and the shift in the distribution were explained by chemical conversion of SO2 to sulfate in-cloud droplets.