Atmospheric Implications of Aqueous Solvation on the Photochemistry of Pyruvic Acid

Formation of aerosol from organic compounds is under investigation in order to better predict the overall radiative forcing from atmospheric aerosols and their influence on global climate. One possible formation pathway for secondary organic aerosol (SOA), which is now becoming more widely accepted, is from bulk aqueous photoreactions in atmospheric particles that create low volatility compounds. These products may remain particulate upon droplet evaporation, increasing SOA mass in the atmosphere. SOA formed in this manner may account for some of the discrepancy between measured and predicted amounts of SOA.

This presentation will describe the photochemistry of pyruvic acid, an α-keto acid found in the atmosphere, in aqueous solutions representative of solutes in fogs, clouds, and wet aerosols. Solvation of pyruvic acid in water changes the photodissociation mechanism and products from that of the gas phase. The photoproducts from the aqueous phase are higher in molecular weight and therefore possible SOA precursors. Further, these polymers partition to the surface of water and are expected to modify the the surface properties of atmospheric aerosols that determine the kinetics of water uptake. The reaction mechanism of pyruvic acid as a function of its environment and concentration will be presented along with the kinetics obtained for the photochemistry in aqueous solution. These results are used as input in an atmospheric model to evaluate the atmospheric consequences of solvation of pyruvic acid on its atmospheric reactivity and its role as a global sink.