Atmospheric Chemistry of Hydroxypinonaldehydes: Their Reactions with Hydroperoxy Radicals in the Atmosphere

Carbonyl compounds are abundant and important in the atmosphere because their atmospheric oxidation processes significantly contribute to the formation of secondary organic aerosols and free radicals. Here, we have theoretically investigated the reactions of n-hydroxypinonaldehydes (n = 1, 7, and 10; n-HO-C₁₀H₁₅O₂) representing large-sized carbonyl compounds with HO₂ radical by using PNO-LCCSD(T)-F12a/cc-pVTZ-F12//M06-2X/MG3S method. Their kinetics are calculated by using the dual-level strategy. The calculated results reveal that all anharmonicity, multistructure torsional anharmonicity, tunneling, and recrossing effects cannot be neglected in kinetics calculations. Our calculated kinetics uncover that the rate constants are 1.26 × 10^-13, 1.52 × 10^-14, and 2.04 × 10^-14 cm³ molecule^-1 s^-1 for the reactions 1-HO-C₁₀H₁₅O₂, 7-HO-C₁₀H₁₅O₂, and 10-HO-C₁₀H₁₅O₂ with HO₂ at 298 K, respectively. Furthermore, the atmospheric lifetimes were calculated, and the results suggest that n-HO-C₁₀H₁₅O₂ + HO₂ may compete with n-HO-C₁₀H₁₅O₂ + OH in the areas with the highest concentration of HO₂. In addition, the present findings also suggest that while the reverse reaction back to n-HO-C₁₀H₁₅O₂ + HO₂ is likely to dominate, the forward reaction can still partially form the RO₂ radical at 200-230 K. Subsequently, the formed RO₂ radical finally leads to the formation of formic acid, acetic acid, and alkoxy radicals in the presence of the high concentration of NO in the atmosphere.