Reassessing the atmospheric oxidation mechanism of toluene

Significance Aromatic hydrocarbons account for 20 to 30% of volatile organic compounds and contribute importantly to ozone and secondary organic aerosol (SOA) formation in urban environments. The oxidation of toluene, the most abundant aromatic compound, is believed to occur mainly via OH addition, primary organic peroxy radical (RO 2 ) formation, and ring cleavage, leading to ozone and SOA. From combined experimental and theoretical studies, we show that cresol formation is dominant, while primary RO 2 production is negligible. Our work reveals that the formation and subsequent reactions of cresols regulate the atmospheric impacts of toluene oxidation, suggesting that its representation in current atmospheric models should be reassessed for accurate determination of ozone and SOA formation. The results from our study provide important constraints and guidance for future modeling studies.