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Gas-phase Hydrogen Peroxide from Multiphase Ozonolysis of Unsaturated Lipids
ZILIN ZHOU, Jonathan Abbatt, University of Toronto, Canada
Abstract Number: 545
Working Group: Aerosol Chemistry
Abstract
Gas-phase hydrogen peroxide (H2O2) is an oxidant in the atmosphere and an indoor air pollutant that is an irritant to the respiratory system at high concentrations. It is well known that the gas-phase ozone oxidation of gas-phase alkenes, such as limonene, leads to the formation H2O2 through the reaction between Criegee intermediates (CI) and water. However, the degree of H2O2 formation from multiphase ozonolysis on surfaces has not been reported. Here, we studied the heterogeneous ozonolysis reactions of multiple unsaturated lipids present in natural environments and on household surfaces. H2O2 formation and ozone consumption were simultaneously monitored online by a Picarro H2O2 analyzer and an ozone monitor during the reaction. Upon exposure to ozone, gas-phase H2O2 was only observed under high relative humidity, as a result of the decomposition of hydroxyhydroperoxides (α‑HHP) that are generated through water reaction with CI. In addition, α‑HHP can be stable over a few hours under dry conditions and their decomposition is facilitated by water vapor. The H2O2 yields vary, ranging from 7-35% for triolein, methyl oleate and squalene, with insignificant dependence on relative humidity between 50% and 80%. In contrast, the H2O2 yield in ozonolysis of oleic acid was negligible, presumably due to the rapid scavenging of CI by the acid head group of the fatty acid. The environmental implications of this chemistry will be discussed from the perspectives of the oxidizing ability in the atmosphere and indoor air quality.