Experimental Kinetic Study of the Reactions Between NO3 Radicals and α- and β-Phellandrenes

Abstract

Nighttime NO₃-initiated oxidation of biogenic volatile organic compounds (BVOCs), such as monoterpenes, plays a crucial role as sources of organic nitrates (ONs) and secondary organic aerosols (SOA), which are known to have significant impacts on climate, air quality, and human health. Nevertheless, these reactions are still poorly understood. Therefore, the primary objective of this study is to provide new kinetic data for two monoterpenes, α-phellandrene and β-phellandrene through experiments in simulation chambers. The rate constants have been determined using an absolute kinetic method and found to be (3.9 ± 0.6) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for α-phellandrene and (6.6 ± 1.0) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for β-phellandrene. These rate constants have been compared to data from the literature. For α-phellandrene, previous studies were scattered, and this new determination allows us to confirm the lowest value provided by the other absolute rate determination. For β-phellandrene, our study provides the first absolute rate determination which is in good agreement with the unique value from the literature obtained by the relative rate technique. Rate constants of α- and β-phellandrene are also compared to those of other monoterpenes having similar chemical structures. These kinetic results show that the oxidation by NO₃ is a significant sink of α- and β-phellandrene during nighttime.