SGER: Investigations of Cloud Condensation Nuclei

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This is a Small Grant for Exploratory Research (SGER) to support research on the physical and chemical properties of cloud condensation nuclei. The experiments will be conducted in the winter of 2001-02 at two, or possibly three, mountaintop observatories in the southwestern United States. Central to the experiment is a novel instrument called the Cloud Condensation Nuclei Remover (CCNR). It is a thermal gradient diffusion chamber through which an air sample is slowly drawn. It flows as a thin, laminar ribbon between two saturated plates having different temperatures. The supersaturation at the center of the chamber is regulated by adjusting the temperatures of the plates. Depending on the supersaturation, some of the aerosols in the sample are activated, grow, and settle out as droplets on the bottom of the chamber as the air moves through. The size distribution of the surviving particles is compared with that of the particles entering the chamber to determine the sizes of the particles that served as centers for cloud condensation. By comparing electron microscope images and the chemical composition of the particles before and after exposure to the supersaturation it may be possible to learn more about the aerosol particles that are active in cloud formation. The project is designed to resolve the discrepancies that currently exist between observations of the physical and chemical properties of aerosol particles and their cloud-forming ability.