Reactions of C₁₂–C₁₄ n‑Alkylcyclohexanes with Cl Atoms: Kinetics and Secondary Organic Aerosol Formation

Long-chain alkanes are a type of intermediate volatility organic compound (IVOC) in the atmosphere and a potential source of secondary organic aerosols (SOAs). C₁₂–C₁₄ n-alkylcyclohexanes are important compositions of IVOCs, with considerable concentrations and emission rates. The reaction rate constants and SOA formation of the reactions of C₁₂–C₁₄ n-alkylcyclohexanes with Cl atoms were investigated in the present study. The reaction rate constants of the long-chain alkanes obtained via the relative-rate method at 298 ± 0.2 K (in units of ×10^–10 cm³ molecule^–1 s^–1) were as follows: k_{hexylcyclohexane} = 5.11 ± 0.28, k_{heptylcyclohexane} = 5.56 ± 0.30, and k_{octylcyclohexane} = 5.74 ± 0.31. The gas-phase products of the reactions were identified as mainly small molecules of aldehydes, ketones, and acids. The particle-phase products were mostly monomers and oligomers, but there were still trimers even under high-NO_x conditions. Moreover, under high-NO_x conditions (urban atmosphere), the SOA yields of hexylcyclohexane are higher than that under low-NO_x conditions (remote atmosphere), indicating that more attention should be given to the SOA formation of Cl-initiated n-alkylcyclohexane oxidations in polluted regions. This research can further clarify the oxidation processes and SOA formation of n-alkylcyclohexanes in the atmosphere.