Investigations of multi-phase chemistry in levitated surrogate cloud droplets

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The Environmental Chemical Sciences Program in the Chemistry Division at the National Science Foundation supports the research of Professor Frank N. Keutsch at the University of Wisconsin- Madison who proposes a novel experimental approach that will simulate cloud-processing of reactive hydrocarbons, which is an important pathway for the formation and transformation of ambient fine particulate matter (aerosol). Cloud processing influences aerosol concentrations and physicochemical properties, which in turn regulate aerosol optical and cloud-nucleating properties. Cloud processing thus represents a paradigm for chemistry-climate coupling. The proposed approach combines optical tweezers with a suite of analytical instrumentation to transcend existing experimental limitations, allowing exploration of the critical competition of gas/condensed phase exchange, chemical reactions and cloud droplet drying/growth cycles. The research will provide important mechanistic parameters of aerosol formation and properties, which are currently lacking in models of climate and air quality. The proposed work is ultimately designed to aid prediction of aerosol properties, thereby enhancing the mitigation of anthropogenic effects on human health, the environment and the climate. This project will also provide education of scientists and develop undergraduate laboratory experiments that consider not only individual processes, but also the coupled chemical/physical feedbacks, such as those between the gas and condensed phases. The work will also expand the scope of analytical experimental methodology available to other fields of research.