Evaluation of reaction between SO₂ and CH₂OO in MCM mechanism against smog chamber data from ethylene ozonolysis

Rationale. The oxidation of SO2 by CH2OO radicals in the ethylene-O-3 system is one of the important pathways of sulfate aerosol formation, but the accuracy of Master Chemical Mechanism (MCM) simulation for this reaction was not evaluated, although the MCM has been widely used in previous studies. Methodology. The oxidation of SO2 in the ethylene-O-3 system was performed in detail under different conditions, which were used to evaluate the accuracy of MCM simulation for the reactions in this study. Results. The experimental conditions of low RH and high initial SO2 concentration favour the SO2 oxidation in the ethylene ozonolysis, and the yield of CH2OO in the ethylene ozonolysis without irradiations was determined to be 0.43. The n-hexane (C6H14) oxidation intermediates can promote the SO2 oxidation rate by generating sulfur- containing organics in the aerosol water. The original MCM simulated SO2 consumption after 4-h reaction was more than 70% smaller than the measured results. By adjusting the yield of CH2OO and updating the reaction rate constants of CH2OO-related reactions (e. g. with SO2, H2O and organic acid), the difference between experiments and simulations decreased from 70% to 6.6%. Discussion. The promotion effects of n-hexane on the oxidation of SO2 suggest that alkanes may be the precursors of sulfur- containing organics in the atmospheric environment. This study further confirms the effect of CH2OO on the oxidation of SO2 in the atmospheric environment and provides information on the performance of MCM simulation.