Investigating the Kinetics of Heterogeneous Lipid Ozonolysis by an Online Photoionization High-Resolution Mass Spectrometry Technique.

Lipid oxidation-induced imbalance in the redox system is one of the key causative factors leading to accelerated aging in living organisms and related diseases. Online sampling and analysis of the heterogeneous ozonolysis kinetics of lipid aerosols are highly important in revealing the oxidation-driven aging process of lipids. In this paper, an online detection method based on atmospheric pressure photoionization combined with ultrahigh resolution mass spectrometry (APPI-HRMS) is developed for real-time analysis of the heterogeneous reactions between lipid particles (oleic acid and squalene) and ozone. The online APPI-HRMS technique serves as an ideal platform for analyzing the heterogeneous oxidation of particles, exhibiting remarkable stability, sensitivity, and responsiveness across a wide range of particle concentrations. Owing to the distinctive characteristics of soft ionization, the heterogeneous effective oxidation rate of lipid aerosols was quantitatively measured. This has facilitated the detection of a series of fingerprint particle-phase products, including aldehydes, secondary ozonides, and hydroperoxides. Additionally, the kinetics evolution of these products with the ozone concentration was captured. Consequently, the ability of this online APPI-HRMS technique in assessing the multiphase oxidation of organic particles has been demonstrated, positioning it as a promising and feasible tool for revealing the heterogeneous reactions of particles.