AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Kinetics and Products of Multiphase Ozonolysis of Unsaturated Lipids
ZILIN ZHOU, Shouming Zhou, Jonathan Abbatt, University of Toronto, Canada
Abstract Number: 143 Working Group: Aerosol Chemistry
Abstract The heterogeneous ozonolysis reactions of multiple unsaturated lipids present in atmospheric aerosol and on household or human surfaces were studied. By using a new high-performance liquid chromatography/electrospray ionization mass spectrometry (LC-ESI-MS) method, the rapid decay of triolein (an unsaturated triglyceride in cooking oil arising from glycerol and oleic acid) in a thin surface film was observed. The reactive uptake coefficients (γ) were determined to be between (4.2 ± 0.8) × 10-6 to (1.5 ± 0.3) × 10-5 for films with average thicknesses between 4 and 40 nm. Stable secondary ozonides were observed to be the major condensed-phase products, along with a series of oxygenated compounds (acids and aldehydes) whose abundance exhibited a strong dependence on relative humidity (RH). Due to the unavailability of pure high-molecular weight secondary ozonides as internal standards, an 1H NMR method was developed for the quantification of ozonolysis products, which involved the use of methyl sulfone as a universal reference. Results indicate that, under dry air, 65-80% of the ozonolysis products in triolein and methyl oleate are secondary ozonides that accumulate on the surface, whereas the remaining 20-35% of the reaction presumably yields volatile products (e.g. 1-nonanal) that are released into the air. Elevated relative humidity significantly suppresses the formation of ozonides in both lipids, making gas-phase products more favorable. In contrast, the yield of secondary ozonides and volatile products from ozonated oleic acid were (16 ± 2)% and (44 ± 5)% respectively, along with an insignificant dependence on relative humidity. The formation of high-molecular weight hydroperoxides were also observed. The environmental implications of this chemistry will be discussed from the perspectives of oxidative aging of lipids in atmospheric aerosol and volatile species affecting indoor air quality.