(611b) Evaluating the Significance of Direct Photolysis of Organic Compounds Dissolved in Cloud and Fog Waters

In the atmosphere, organic compounds may partition into cloud and fog droplets and undergo transformations by dissolved oxidants and actinic radiation.  It is well established that aqueous phase reactions can transform atmospheric gases and particulate matter; however, the significance of direct aqueous photolysis is uncertain due to the lack of experimental data.  We present a frame-work to evaluate the relative rates of aqueous and gaseous photolysis for several series of compounds containing various chemical functionalities and carbon numbers.  Structure activity predictions of Henry’s Law constants and hydration equilibrium permit for the identification of chemical families for which direct aqueous photolysis may be important in the atmosphere.  Using this frame-work, we pick glyceraldehyde (2,3-dihydroxypropanal), a highly water soluble triose, to serve as a surrogate for oxidized organic material for which direct aqueous photolysis will be a significant sink.  We present photolysis experiments designed to determine the extinction coefficient and quantum yield of glyceraldehyde in water.  These parameters allow us to calculate the rate of removal of direct aqueous photolysis as a function of solar zenith angle and temperature.  Results of this analysis will guide researchers in the identification of compounds that are likely to be destroyed by aqueous photolysis and will aid in our understanding of the ultimate chemical fate of relevant atmospheric organics.