Atmospheric Temperature Dependence of β-Caryophyllene Ozonolysis Kinetics Is Governed by Stabilized Prereactive Complexes.

Atmospheric lifetime of volatile organic compounds (VOCs) is determined by oxidation kinetics, which is potentially sensitive to the change of temperature. However, the influence of temperature on the oxidation kinetics of large VOCs, such as sesquiterpenes, remains inadequately explored due to limited experimental data and insufficient accuracy of computations. In this study, we accurately simulate the temperature dependence (243-313 K) of ozonolysis kinetics of β-caryophyllene, a representative sesquiterpene in the atmosphere, by explicitly incorporating stabilized prereactive complexes (SPCs). Our results reveal that SPCs formed at the endocyclic C═C double bond primarily drive the temperature-dependent ozonolysis kinetics owing to their low energy barriers for forming primary ozonides (POZs). These endocyclic SPCs also exhibit a balance between the forward reaction and backward dissociation. In contrast, exocyclic SPCs, while more thermodynamically stable, are less reactive and tend to dissociate back into β-caryophyllene and ozone (O₃). This mechanistic difference may explain why O₃ cycloaddition at the endocyclic C═C double bond dominates the ozonolysis kinetics of β-caryophyllene, despite the lower relative abundance of endocyclic SPCs compared to the exocyclic SPCs. The computed kinetics exhibits a pre-exponential factor of 2.0 × 10^-15 cm³ molecule^-1 s^-1 and a negative activation energy of -4.4 kJ mol^-1. Our computed temperature dependence factor is 529.8 K^-1, which agrees with the experimental value (559 ± 97 K^-1) in previous measurements. The SPC-incorporated computation further supports the accurate prediction of the pseudo-first-order atmospheric lifetime at different temperatures. Overall, this study demonstrates that incorporating SPCs into computational models can provide an effective framework for simulating VOC oxidation kinetics and thus atmospheric lifetimes at the extreme temperatures in climate change.