The heterogeneous ozonolysis reactions of multiple unsaturated lipids present on household surfaces and in atmospheric aerosol were studied. By using a new high-performance liquid chromatography/electrospray ionization mass spectrometry (LC-ESI-MS) method, the rapid decay of a thin film of triolein (an unsaturated triglyceride arising from glycerol and oleic acid) on surfaces was observed. With little dependence on the ozone mixing ratio, the reactive uptake coefficients (?) 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. The reacto-diffusive depth was estimated to be above 10 nm, indicating reactions at both the interface and in the bulk. Stable secondary ozonides were observed to be major condensed-phase products, along with a series of oxygenated compounds (acids and aldehydes) whose abundance exhibited a strong dependence on the relative humidity (RH) in the experiment. 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 that are released into the air. In contrast, the yield of secondary ozonides and volatile products from ozonated oleic acid were (14 ± 2) % and (48 ± 5) %, respectively. Some high-molecular weight hydroperoxides were also observed. The environmental implications of this chemistry will be discussed from the perspectives of indoor air quality and the oxidative aging of lipids in atmospheric aerosol.

Kinetics and products of multiphase ozonolysis of unsaturated lipids

2019 Fall National Meeting

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