A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase
Photochemical reactions represent the main pathway for the removal\nof non-methane volatile organic compounds (VOCs) in the atmosphere.\nVOCs may react with hydroxyl radical (OH), the most important atmospheric\noxidant, or they can be photolyzed by actinic radiation. In the presence\nof clouds and fog, VOCs may partition into the aqueous phase where\nthey can undergo aqueous photolysis and/or reaction with dissolved\nOH. The significance of direct aqueous photolysis is largely uncertain\ndue to the lack of published absorption cross sections and photolysis\nquantum yields. In light of this, we strive to identify atmospherically\nrelevant VOCs where removal by aqueous photolysis may be a significant\nsink. The relative importance of different photochemical sinks is\nassessed by calculating the ratios of the removal rates inside air\nparcels containing cloud and fog droplets. This relative approach\nprovides useful information in spite of the limited aqueous photolysis\ndata. Results of this work should help guide researchers in identifying\nmolecules that are the most likely to undergo aqueous OH oxidation\nand photolysis. For example, we find that out of the 27 atmospherically\nrelevant species investigated, the removal of glyceraldehyde and\npyruvic acid by aqueous photolysis is potentially an important sink.\nWe also determine the relative magnitudes of these four chemical\nsinks for the set of relevant organic compounds.