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Molly Larsen
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Project Title: Photochemistry of Atmospherically Relevant Small Organic MoleculesMolly Larsen is a visiting postdoctoral fellow working in Veronica Vaida’s lab. Molly’s research examines the photochemistry with red sunlight of atmospherically relevant organic molecules, such as small organic acids and alcohols. Molecular oxygen and ozone in the upper-mid stratosphere absorb most of the ultraviolet light in the solar spectrum so it is the lower energy visible photons that are available for most of the photochemical processes in the Earth’s lower atmosphere. The question under study is if visible light exciting vibrational overtone transitions of acids and alcohols could play an important role in the chemistry of these organic molecules which would lead to secondary organic aerosol (SOA) formation. While the oxidation of these small molecules by O3 and OH are known to be important in the degradation of SOA precursors, current aerosol models ignore the photochemistry on particles and underestimate the secondary organic aerosol mass by two orders of magnitude. The research Molly is doing to study the low energy photochemistry of small organic molecules will be used as input to atmospheric models. A related aspect to Molly’s research focuses on how interactions with water can enhance the photochemical reactions described above. Theoretical results show that water can catalyze these photoreactions by lowering the energy of the transition state in the reaction. Interactions with water can also shift and broaden the absorption spectra of these molecules, greatly affecting their interactions with the solar spectrum. Since these small organic molecules are taken into aerosols in the atmosphere, understanding their photochemistry in the liquid phase, in the ice phase, and at the liquid/water interface is necessary for understanding their atmospheric relevance. Molly’s research will focus on examining the visible light initiated photochemistry in these three atmospherically important phases and on how water can influence atmospheric reactions.
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