Atmospheric Fate of Hydrofluoroethers: Degradation of Parent Compounds and Primary Products by Multiple Oxidants

Abstract

Hydrofluoroethers (HFEs) are widely used as substitutes for ozone-depleting substances, yet their atmospheric fate remains poorly understood. We investigated the gas-phase degradation of HFE-7100 (C4F9OCH3) and HFE-7200 (C4F9OC2H5) by OH, Cl, and NO3 at 298 K. The measured OH and Cl rate coefficients were consistent with previous studies, while the first constraints on reactions with NO3 were obtained as upper-limit values of 7.92 × 10–18 and 9.67 × 10–18 cm3 molecule–1 s–1, respectively. Their estimated overall atmospheric lifetimes were 2.32 and 0.34 years, with OH oxidation as the dominant loss pathway. We systematically established the kinetics and structure–reactivity relationships of approximately 40 HFEs toward OH radicals and Cl atoms, revealing α-hydrogen abstraction as the dominant oxidation pathway and, importantly, identifying through product analysis a previously unrecognized alkoxy-radical decomposition pathway leading to HCHO formation. We further determined the OH and Cl reaction kinetics and near-UV photolysis rates of the two primary carbonyl products. Their photolysis lifetimes were several days, indicating rapid atmospheric removal, and their photolysis generated COF2, CF3C(O)F, HCHO, and CO2. These results refine the atmospheric degradation mechanisms of HFEs and suggest that their oxidation may contribute to trifluoroacetic acid (TFA) formation and inorganic fluorine accumulation.