Peroxy radicals are key intermediates in the oxidation chemistry of both anthropogenic and biogenic Volatile Organic Compounds(VOCs) in the troposphere. These species are central in the formation of photochemical smog and organic aerosols, and can be formed from abstraction reactions or from addition reactions with unsaturated hydrocarbons. Laboratory studies of the kinetics of peroxy radical reactions are complicated by the many competing self- and cross-reactions that typically occur. The large number of possible products, especially chain-propagating radical channels, further complicates the chemistry. Here we describe recent experiments using time-resolved photoionization mass spectrometry (PIMS) with ionization by VUV synchrotron radiation. This method provides a powerful, highly sensitive technique for studying the product branching ratios and reaction rates, by selective time-resolved detection of many of the reactants, intermediates, and primary products. We report investigations of peroxy radical reactions in a laser-photolysis low-pressure flow cell experiment that utilizes tunable VUV radiation generated at the Advanced Light Source synchrotron at the Lawrence Berkeley Laboratory, coupled to the Sandia multiplexed PIMS apparatus. We have performed experiments on the reactions of the acetyl peroxy radicals,  as well as the self-reaction of the ethyl peroxy radical. We are able to determine relative product yields based on measurements of absolute radical concentrations, new absolute photoionization cross sections, with the aid of kinetic modeling.

Reactions of atmospheric peroxy radicals studied by synchrotron VUV multiplexed photoionization mass spectrometry

249th National Meeting (2015)

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