Experimental and Theoretical Studies of Fundamental and Photochemical Processes in Aqueous Environments

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The Environmental Chemical Sciences Program in the Chemistry Division at the National Science Foundation supports the research of Professors Veronica Vaida and Rex T. Skodje both at the University Colorado at Boulder in a collaborative experimental/theoretical effort by their groups that is focused on the study the photochemical reactions of organic molecules occurring at air/water interfaces and in small hydrated clusters in the gas phase. These photochemical reactions can play an important role in the formation and chemical evolution of atmospheric aerosols with potential important consequences to human health and climate change. The intellectual merit in the proposed investigation stems from addressing the basic scientific aspects of sunlight-initiated, water-mediated chemistry of organic molecules. Using a combination of laboratory and theoretical studies, the outcome of the work will be an improved understanding of the mechanisms, dynamics, and rates of photochemical reactions occurring in clusters and on aerosol surfaces that are of importance in the atmosphere. What distinguishes this work from other efforts is the emphasis on deriving molecular-level mechanisms and quantitative models for atmospheric photochemistry in aqueous environments. It is anticipated that greater understanding of the fundamental chemistry involved in the photochemistry occurring in aerosols and more general aqueous environments. An important part of the proposed work is the direct observation of the photochemistry of air/water/organic gas phase mixtures using the French CESAM instrument (Experimental Multiphasic Atmospheric Simulation Chamber). Experiments conducted in this chamber permit the direct observation of aerosol formation and the chemical evolution of the mixture under the influence of intense UV/visible radiation.In terms of broader impacts, improving the ability to model atmospheric processes involved in climate change is an important goal for society and can impact public policy. The treatment of aerosols in current models is a "weak link" and requires significant attention. The proposed study of photochemical mechanisms involved in aerosol nucleation and chemical evolution has the potential to provide improved performance of these models by incorporating a more correct treatment of the chemistry of secondary organic aerosols. In addition, the interdisciplinary, international collaborations proposed will lead to the exchange of students and postdoctoral fellows, and promote cross-fertilization of ideas between different institutions in the basic science of atmospheric photochemistry. The proposed research program contributes to the recruitment, retention and educational development of graduate and undergraduate students, especially from under-represented groups, by exposure to a collaborative and interdisciplinary research environment.