Reactivity of Benzoylperoxy Radicals with Monoterpenes: One-Step Reaction to Form Low-Volatility Organic Compounds

Oxidation of volatile organic compounds (VOCs) significantly impacts air quality and climate by contributing to ozone and secondary organic aerosol (SOA) formation. Accurate representation of VOC oxidation in atmospheric models is essential but challenging due to complex reaction mechanisms. Using high-level computational tools, we investigate oxidation reactions of α-pinene, β-pinene, limonene, and sabinene, initiated by benzoyl peroxy radical. The calculated total reaction rate coefficients are on the order of 10⁻¹⁴-10⁻¹⁵ cm³/s, which is fast enough to be competitive under clean, low-NOx atmospheric conditions. Further oxidation pathways of sabinene-derived RO₂ were studied. We identified an oxidation pathway that propagates the oxidative chain and may help explain the high SOA yields observed for sabinene. Moreover, saturation vapor pressures of benzoyl peroxy radical-initiated oxidation intermediates were estimated using the COSMOtherm program and a machine learning model (COSMO-ML). The results suggest that one of these intermediates is already a low-volatility organic compound (LVOC) with a saturation vapor pressure of 10⁻⁷ pascal. Furthermore, we find that later-generation oxidation products of sabinene have saturation vapor pressures low enough to classify them as extremely low-volatility organic compounds (ELVOC). These findings highlight a potentially important SOA formation route with significant atmospheric and environmental implications.