Unsaturated triglycerides are commonly found on indoor surfaces contaminated by cooking oils and human skin lipids. It is well known in laboratory reactor studies that these lipids decay rapidly under ozone, following the Criegee mechanism. However, such reactions between ozone and triglycerides have not been monitored and characterized in real indoor environments. Here, we studied the heterogeneous ozonolysis reactions of oils on genuine surfaces near cooking areas. Our results indicate that, under typical indoor ozone (5 – 20 ppb) and RH (30% - 80%) conditions, the oils deposited on surfaces decomposed substantially within 24 hours. Both mass spectral and NMR spectroscopy analyses confirm that the secondary ozonides are the major condensed-phase products remaining on the surface, whose formation is significantly affected by the changing relative humidity (RH) in the air. These secondary ozonide coatings on surface exhibit high stability in the ambient air, with an average thickness on the order of 10 nm after 16 days of growth in a university cafeteria kitchen with routine cooking activities. In addition, other stable oxygenated products such as aldehydes are also observed, accompanied with volatile organic compounds like nonanal that leads to carbon loss of the acyl chains. Overall, the oils on surfaces contribute to the indoor ozone sink, with a large formation of secondary ozonides that require further studies for their toxicological properties.

Characterization of multiphase ozonolysis of unsaturated oils on indoor surfaces

ACS Spring 2022

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