International Collaboration in Chemistry: Measuring the effects of surfactants on cloud microphysics

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The Environmental Chemical Sciences Program supports Professor Ronald C. Cohen of the University of California, Berkeley, in collaboration with the research group of Barbara Noziere of the University of Lyon, France to advance understanding of cloud droplets by studying whether surfactants affect droplet growth rates. In the Earth's atmosphere, cloud droplets are formed exclusively by the condensation of water vapor onto micron-size aerosol particles. The research will develop new ideas and approaches to understanding cloud droplet growth especially with respect to the key question of how mixtures of organic chemicals in aerosol and on water droplets affect droplet growth rates. In Lyon, the focus of the research will be on the characterization of surfactants found in ambient aerosol. At Berkeley the focus will be on determining parameters that affect droplet growth and evaporation and understanding how model surfactants as well as the surfactants extracted from ambient aerosol by the Lyon group affect the evaporation and growth. To accomplish these goals, novel analytical and spectroscopic methods will be developed, including optical traps, fluorescence anisotropy decay, Raman thermometry and cavity enhanced Raman scattering, to investigate the effect of atmospheric surfactants on cloud droplet formation and growth.This project will develop and apply the next generation of laboratory experiments to study the fundamental chemistry of cloud droplet growth. In the Earth's atmosphere, cloud droplets are formed exclusively by the condensation of water vapor onto micron-size aerosol particles. The Cohen group at Berkeley and the Noziere group at Lyon have separately pioneered new approaches to studying droplet growth over the last few years. Fusion of the experimental skills and knowledge of the two teams, a goal of this project, is expected to lead to unique advances in our understanding of the chemical link between aerosol and clouds, especially at the crucial step of cloud droplet growth. This project is expected to result in significant advances in our understanding of the scientific basis for policy decisions regarding air quality and climate. The results will be communicated both in the scientific literature, to a more general audience through various media and directly to regulators and policy makers in California with whom the PI meets informally at meetings aimed at planning for climate change in the local region