Kinetics and Photochemistry of Atmospheric Aldehyde Reactions

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9610285 Zhu The primary objective of this project is to determine the kinetics of atmospheric aldehyde reactions and their photochemistry. Aldehydes are key participants in photochemical reactions affecting smog processes; their photodissociation represents a major source of free radicals and organic aerosols for tropospheric photochemistry. Despite the importance of aldehyde photolysis in the chemistry of the troposphere, few studies of aldehyde photolysis product channels and quantum yields have been carried out either under atmospheric conditions or under conditions that can be readily extrapolated to those of the atmosphere. Free radicals, such as formyl radicals, are readily converted in the atmosphere to hydroperoxyl and hydroxyl radicals, which participate in photochemical oxidation processes. In this project, studies of the photolysis of aldehydes with five carbon atoms or more, aromatic aldehydes, and dicarbonyls, will be carried out. The photolysis product channels and quantum yields will be characterized, as well as their dependence on photodissociation wavelengths. The relationship between the structure of alkyl side chains and photolysis quantum yields will be extracted for homologous series of aldehydes. The experimental studies will be carried out using pulsed laser photolysis coupled with a sensitive optical absorption technique, cavity ring-down spectroscopy. In addition to the photolysis studies, the kinetics and mechanisms of aldehyde formation reactions, such as the reaction of the methoxy radical with molecular oxygen, will be elucidated.