NO3 radical initiated oxidation products of Δ-3-carene: Characterization and mechanism of formation

A series of experiments of NO₃ radical initiated oxidation of monoterpenes (C₁₀H₁₆) were conducted using an oxidation flow reactor (Go:PAM) combined with an iodide high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). This study characterized the major organonitrate products from NO₃ radical initiated oxidation of Δ‑3-Carene with various levels of oxidation, i.e. by increasing the concentration of NO₃. C₁₀ monomers (products with 10 carbons) are generally the dominant products of Δ‑3-carene (e.g. C₁₀H₁₅NO₇ and C₁₀H₁₇NO₅); but where higher oxidant levels enhance fragmentation. In comparison to α-pinene, the  Δ‑3-carene oxidation has a higher propensity to create low volatile species, i.e. promote aerosol formation, mechanistically explained by difference in alkoxy radical (RO) bond scissions. A kinetic model (using FACSIMILE) was developed to simulate the formation of dominant products. The mechanism was based on analogue systems within the Master Chemical Mechanism (MCM) and recently available literature. The fate of RO₂ under different chemical regimes was also investigated by comparing model runs and the experimental results.