AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Criegee Intermediate Driven Autooxidation of Lipid Aerosol Surfaces
MEIRONG ZENG, Nadja Heine, Kevin Wilson, Lawrence Berkeley National Laboratory
Abstract Number: 93 Working Group: Indoor Aerosols
Abstract Lipids are the essential nutrients for humans and are important structural components in cell membranes. Lipid oxidation, which plays a central role in aging-related diseases and food systems, have long been thought to be a solely driven by the formation and decomposition of hydroperoxides, a process known as lipid autooxidation. Recently, we found evidences for an alternative mechanism involving the formation and subsequent chemistry of Criegee intermediates (CI) produced when unsaturated lipids are exposed to hydroxyl radicals (OH). A series of model compounds, with different numbers and substituents of C=C bonds: squalene (Sqe), 9-tricosene, oleic acid, linoleic acid, and arachidonic acid, were investigated in a continuous flow stirred tank reactor. For Sqe, aldehydes and secondary ozonides (SOZs) are detected as major products using a vacuum ultraviolet aerosol mass spectrometer. The detection of SOZs, generally observed only in ozonolysis experiments, provides a distinctive signature of Criegee intermediate reaction pathways. To further confirm this, 2-decyl-1-tetradecanol, a Criegee scavenger, was added to the lipids + OH experiments. The detection of α-alkoxylalkyl hydroperoxides, produced from the Criegee and scavenger reactions, further confirms the importance of CI in the heterogeneous lipids and OH oxidation. Effective uptake coefficients of Sqe increase from 1 to 70 upon decreasing [OH] from 2 x 108 to 6 x105 molecules/cm3, which clearly indicate the importance role that CI play in the autooxidation chemistry of Sqe under typical indoor OH concentrations. A kinetic model, built with Criegees based pathways, can reasonably reproduce these experimental results. This work provides potential link typing present Criegee-driven autooxidation mechanism to the OH involved dehydration of human and food lipids, as well as evolution of atmospheric unsaturated aerosols.