Criegee Intermediate as a Major Atmospheric Sink for Methane Sulfonamide: A Pathway to Functionalized Hydroperoxides

Atmospheric organosulfur compounds play critical roles in marine chemistry and climate processes. Methane sulfonamide (MSAM), a recently detected organosulfur species in the Arabian Sea, is estimated to have a a short atmospheric lifetime (∼2 days) that is inconsistent with laboratory-measured OH radical reaction rates, suggesting the existence of alternative removal pathways. The identification of all major sinks is crucial for accurately predicting atmospheric lifetimes, sulfur cycling, and related climate effects. Herein, we identified the reaction with Criegee intermediates (CIs), formed from alkene ozonolysis, as a previously unrecognized major sink for MSAM. Using Density Functional Theory and master-equation kinetic modeling studies, we show that CH₂OO and anti-CH₃CHOO react with MSAM at rates ∼10-fold higher than those of the hydroxyl radicals, corresponding to atmospheric lifetimes of ∼3.5 and ∼6.8 days at 298 K and 1 atm pressure. The reaction of MSAM with larger CIs, including anti-methacrolein oxide, is significantly dependent on the structure and temperature. Our estimates show that the lifetime of MSAM with respect to the reactions of anti-methacrolein oxide reduces from an upper bound of ∼19 days at 298 K to ∼1 day at 200 K, implying that the lifetime decreases under colder tropospheric conditions. The lifetimes of MSAM with respect to the reactions with most CIs considered here surpass those of OH reactions (∼80 days). CI-mediated reactions, thus, emerge as a key process controlling MSAM fate, with implications for marine aerosol composition and climate-relevant processes.