Sunlight Initiated Photochemical Reactions: Relevance to Atmospheric Chemistry and Climate

Despite the importance of organics in the chemistry of the atmosphere, their chemical composition and atmospheric transformation remain uncertain. This presentation targets a novel photoprocessing mechanism for oxygenated and low-volatility organic acids and alcohols whose overall budgets are poorly constrained, as are the processes governing their concentrations. Most atmospheric photochemical reactions are initiated through electronic transitions of molecules in the UV spectral region. Results of an investigation of sunlight initiated chemical reactions occurring at low energy by overtone induced chemistry of oxygenated organics will be presented. The targets for this study are atmospherically relevant acids and alcohols where excitation of OH vibrational overtones in the near-IR and visible, near the solar maximum photon output leads to dehydration, decaboxylation or decarbonylation. Relatively low energy concerted photochemical reactions produce high-energy intermediates and products. These photochemical reactions are in some cases water catalyzed and expected to occur on atmospheric aerosols. This new chemistry opens the possibility of photochemical processing for acids and alcohols in the atmosphere, in or on aerosols. This chemistry affects atmospheric aerosol processing and is therefore important in climate.