Reaction of Condensed-Phase Criegee Intermediates with Carboxylic Acids and Perfluoroalkyl Carboxylic Acids

This work presents evidence for the formation of alpha-acyloxyalkyl-1-hydroperoxides (AAHPs) from the reaction of carboxylic acids with Criegee intermediates formed by gas-phase ozone reacting heterogeneously with a condensed-phase alkene, squalene. With liquid chromatography-electrospray-tandem mass spectrometry, it is shown that a long-chain fatty acid, palmitic acid, is lost when squalene is exposed to ozone in the presence of palmitic acid. This is consistent with the formation of higher molecular weight products via Criegee intermediate reactions observed by direct analysis in real-time mass spectrometry. Confirmation of AAHP formation comes from application of a new atmospheric pressure chemical ionization-tandem mass spectrometry method that is specific to organic hydroperoxides. Experiments with perfluorotetradecanoic acid confirm that the perfluoroalkyl carboxylic acids, a class of compounds that was heretofore thought to be unreactive in the condensed phase, can also be lost via reactions with Criegee intermediates in this manner. Condensed-phase water competes with this reaction, likely leading to alpha-hydroxyhydroperoxides via the direct reaction of water with the Criegee intermediates. The potential environmental importance of this chemistry is discussed in terms of the fate of perfluoroalkyl carboxylic acids, secondary organic aerosol formation, and oxidation of organic films in indoor settings.