Studies of aerosol scavenging and precipitation rates and efficiencies in snowing clouds at a mountaintop site in northwestern Colorado will continue. In-cloud measurements of aerosol particles, cloud droplets and ice particles as a function of size, and cloud condensation nuclei (CCN) spectra previously made will be analyzed to determine the distribution of chemical species among the three water components of a precipitating cloud: ice, water and vapor. From these measurements, the effect of varying populations of natural and anthropogenic aerosol particles on aerosol particle scavenging and precipitation processes will be assessed. Variations in the cloud droplet size distribution as a result of changes in the dominant atmospheric aerosol CCN particle source (natural versus anthropogenic) will be related to the two primary ice particle growth processes: accretion of droplets versus diffusion of water vapor. These variations in the in-cloud aerosol and water mass removal mechanisms and rates will be used to determine how changes in atmospheric aerosol concentrations effect cloud microstructure, pollutant scavenging and snowfall rates.
