(Invited Speaker) Effects of particle composition on cloud droplet nucleation

The role of organic aerosol species in contributing to the activity and number concentrations of atmospheric cloud condensation nuclei has been a topic of interest for a number of years. Recent advances in measurement techniques have made possible many new field and laboratory observations of the hygroscopicity of organic aerosol species. This presentation will review the range of behaviors expected and compare with observations. In particular, observations suggest a rather narrow range of hygroscopicities, even for complex organic mixtures. Although somewhat lower than those for inorganic salts, these hygroscopicities are nevertheless large enough to allow organic-dominated aerosols to readily serve as cloud condensation nuclei in many cloud types.