Characterization of Key Intermediates and Products from the Ozonolysis of Styrene-Like Compounds

Stabilized Criegee intermediates (sCIs) are key reactive species in atmospheric chemistry. Styrene-like compounds are special aromatics, as they can react with the ozone to generate phenyl-substituted sCIs (C 6 H 5 CHOO), yet no prior study has directly characterized such sCIs. This study took styrene and trans-β-methylstyrene as proxies for styrene-like compounds. Matrix isolation combined with infrared spectroscopy technology was applied to capture anti- and syn-C 6 H 5 CHOO at 972 and 930 cm –1, respectively. Quantum chemical calculations enabled the identification of intermediates and verified the reactivity of sCIs’ unimolecular decomposition and bimolecular reactions with water vapor. Besides the reported organic peroxy radical (RO 2 ) + sCIs + hydroperoxy radical (HO 2 ) reactions, oligomers formed via RO 2 + sCIs + R′O 2, HO 2 + sCIs + HO 2 /R′O 2, and highly oxygenated RO 2 + sCIs + HO 2 /R′O 2 reactions were also proposed based on chamber experiments. At higher relative humidity, C 6 H 5 CHOO-related oligomers emerged as the most prominent aerosol components. The insertion of C 6 H 5 CHOO units was found to dramatically reduce oligomer volatility and enhance oligomer toxicity. The lower susceptibility to removal by water vapor suggests more competitive particle generation and even nucleation involving C 6 H 5 CHOO, providing insights into urban air pollution mechanisms and the identification of toxic compounds in particles.