Organic matter contributes 20% to 90% of PM2.5 mass concentrations in the troposphere. Unsaturated carboxylic acids are widespread in organic aerosols. Double bonds (C=C) in unsaturated species are generally oxidized by electrophilic ozone. In contrast with the ozonation of unsaturated species in the gas phase, the mechanism and products of their ozonation on the surface of aqueous organic aerosols are unknown. In the gas-phase, O3 adds to olefinic double bonds generating chemically activated ozonides, which rapidly decompose into carbonyl oxide Criegee (CIs) intermediates. The fate of gas-phase Criegee intermediates (CIs) in the troposphere is determined by their reactions with water and water clusters. Our recent studies on the CIs produced on air-water interfaces (AWIs) by the in situ ozonation of sesquiterpenes have showed that millimolar n-alkyl-COOH acids are able to compete for CIs with water. In this work, we investigate the ozonation of unsaturated carboxylic acids at air-water interface. Our work focuses on the impacts of molecular structure on the products of the interfacial ozonation of unsaturated carboxylic acid by O3(g). Our studies were conducted by means of our online electrospray mass spectrometry (o-ESI-MS), which probes the composition of reactive interfacial layers within 1 ms. We have used o-ESI-MS to investigate for the first time the ozonation of various aerosol components at the AWIs, such as phenol, α-humulene and β-caryophyllene. In this study, we explore the intramolecular and intermolecular products from reactions of the CIs derived from the interfacial ozonation of various unsaturated carboxylic acids. We present results on how products depend on the alkene structure (cyclic or linear) and the separation of olefinic double bonds from the –COOH functionality. The competition between intramolecular and intermolecular addition of –COOH and the reaction of CIs with H2O is discussed. This work evaluates the contribution of different unsaturated carboxylic acids to aerosol aging and the potential pathways to extremely low volatility organic compounds (ELVOCs) through multiphase reactions.

Processing of unsaturated carboxylic acids by ozone at the air-water interface: Implications for aerosol aging

254th National Meeting (2017)

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