Comment on egusphere-2026-119

Abstract. Carbonyl oxide (CH2OO) is paramount in atmospheric oxidation chemistry, yet quantitative kinetics data for its bimolecular reactions are very limited and even unknown. Here we establish a computational framework to obtain quantitative kinetics from small to large reaction systems. For CH2OO + HCHO, we develop electronic structure methods to reach CCSDTQ/CBS accuracy for its activation enthalpies at 0 K. For CH2OO + aldehydes (RCHO; R = CH3-C5H11, CH2F, CHF2, CF3), we introduce two strategies that recover CCSDTQ/CBS-quality activation enthalpies at 0 K. A dual-level strategy has been used to calculate their kinetics. The calculated rate constants show excellent agreement with available experimental data for CH₂OO + RCHO (R = CH3–C3H7), which validates the designed computational framework. We find that fluorination leads to exceptional rate enhancement, with reactions of CHF2CHO and CF3CHO exceeding 10⁻10 cm3 molecule⁻1 s⁻1 over 200–320 K, approaching the collision limit. We also find that fluorination-driven reactivity enhancement originates predominantly from lower-level electronic effects than that of post-CCSD(T). Incorporation of the kinetics into a global chemical transport model uncovers previously unrecognized atmospheric impacts, with CH2OO + HCHO reducing nighttime CH2OO and gas-phase sulfate concentrations by 25.3 % in Antarctica and 12.2 % over Canada, respectively. The present findings address a long-term challenge in how to obtain quantitative kinetics for large molecular systems, where post-CCSD(T) calculations are prohibitive and provide new insights into the chemical transformation of CH2OO and fluorinated aldehydes in the atmosphere.