Atmospheric Chemistry and Physics, vol. 12, issue 17 (2012) pp. 8205-8222
Photochemical reactions represent the main pathway for the removal
of non-methane volatile organic compounds (VOCs) in the atmosphere.
VOCs may react with hydroxyl radical (OH), the most important atmospheric
oxidant, or they can be photolyzed by actinic radiation. In the presence
of clouds and fog, VOCs may partition into the aqueous phase where
they can undergo aqueous photolysis and/or reaction with dissolved
OH. The significance of direct aqueous photolysis is largely uncertain
due to the lack of published absorption cross sections and photolysis
quantum yields. In light of this, we strive to identify atmospherically
relevant VOCs where removal by aqueous photolysis may be a significant
sink. The relative importance of different photochemical sinks is
assessed by calculating the ratios of the removal rates inside air
parcels containing cloud and fog droplets. This relative approach
provides useful information in spite of the limited aqueous photolysis
data. Results of this work should help guide researchers in identifying
molecules that are the most likely to undergo aqueous OH oxidation
and photolysis. For example, we find that out of the 27 atmospherically
relevant species investigated, the removal of glyceraldehyde and
pyruvic acid by aqueous photolysis is potentially an important sink.
We also determine the relative magnitudes of these four chemical
sinks for the set of relevant organic compounds.
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