Oxidation Mechanism and Kinetics of γ‑Terpinene in the Indoor Atmosphere

γ-terpinene is widely used in personal care and household cleaning products. The gas-phase oxidation mechanism of γ-terpinene is essential for understanding its influence on atmospheric chemistry and its implications for human health. Utilizing quantum chemical calculations and computational toxicology simulations, we examined the •OH-mediated atmospheric transformation and toxicological progression of γ-terpinene in the indoor environment. The results indicate that •OH additions are the dominant pathways for the reaction of •OH + γ-terpinene. The most favorable reactive intermediates formed from the •OH-addition reactions subsequently react with O₂ to form hydroxy γ-terpinene peroxy radicals (OH-γ-terp-RO₂•). The formed OH-γ-terp-RO₂• follows concerted peroxy radical (RO₂•) and alkoxy radical (RO•) modulated autoxidation, providing a new case for such a mechanism beyond the well-known only RO₂-driven autoxidation mechanism. Our findings also reveal that the transformation of OH-γ-terp-RO₂• demonstrates the competitive nature of the cyclization pathway indoors, with dicarbonyl formation, a rarely observed process in hydroxy terpene RO₂ reaction systems. Toxicological evaluations further indicate that a significant proportion of transformation products (TPs) display higher mutagenicity, carcinogenicity, skin sensitization, and irritation to eyes compared to γ-terpinene. The detailed mechanism for •OH-initiated γ-terpinene advances our understanding of RO₂• and RO• chemistry while also emphasizing the potential adverse effects that arise from the interaction of these chemicals in indoor environments.