Reaction between perfluoroaldehydes and hydroperoxy radical in the atmosphere: Reaction mechanisms, reaction kinetics modelling, and atmospheric implications

Abstract. Linear perfluoroaldehydes are important products formed in the atmospheric oxidation of industrial fluorinated compounds. However, their atmospheric lifetimes are incompletely known. Here, we employ high level quantum chemistry methods and a dual-level strategy for kinetics to probe the reactions of C₂F₅CHO and C₃F₇CHO with HO₂. Our calculated results unveil almost equal activation enthalpies at 0 K for perfluoroaldehyde reaction with HO₂, indicating that the carbon chain length minimally influences reaction thermodynamics. Interestingly, the present findings reveal that anharmonicity remarkably enhances the reaction rate constant, whereas multi-structural anharmonicity, recrossing, and tunnelling effects exhibit lesser impacts in the C₂F₅CHO/C₃F₇CHO + HO₂ reaction. In particular, the atmospheric lifetimes for C₂F₅CHO and C₃F₇CHO, approximately 14.4–31.3 hours and 21.6–51.8 hours by HO₂ are much shorter than those via OH radical, underscoring the dominant removal role of HO₂ toward C₂F₅CHO and C₃F₇CHO in the atmosphere. Since GEOS-Chem simulation shows that the concentration of HO₂ is at least 10² times higher than that of OH radical in Russia, Malaysia, and parts of Africa, the reactions of C₂F₅CHO and C₃F₇CHO with HO₂ radicals dominate over those with OH radicals and play more vital role in the atmospheric chemical processes of these regions. This study enhances our understanding of the chemical transformations of linear perfluoroaldehydes and provides a scientific foundation for strategies aimed at mitigating their emissions.