Constraints on the Loss of Hydroperoxymethyl Thioformate (HPMTF) to Marine Clouds Using Aircraft Observations

The photochemical oxidation of dimethyl sulfide (DMS) by the hydroxyl radical (OH) contributes to the production and growth of particles and cloud condensation nuclei in the marine boundary layer (MBL). DMS oxidized by OH can go on to form a stable intermediate, hydroperoxymethyl thioformate (HPMTF), which is both globally ubiquitous and efficiently lost to multiphase processes in the marine atmosphere. Recent work has shown that clouds act as a significant and irreversible loss path for HPMTF, sequestering sulfur and greatly reducing the production of long-lived, climate-relevant species (e.g., SO2 and OCS). Until recently, there have been few observational constraints on the role of clouds in the spatiotemporal distribution of HPMTF and other soluble molecules in the MBL. Using a steady-state approximation, we determine a reactive uptake and first-order aqueous loss rate constant of HPMTF to cloud droplets of 1.2 (0.9–1.9) × 10–2 and 1.4 (0.4–2.2) × 10–1 s–1, respectively. The results suggest that hydrolysis and ozonolysis are significant within cloud droplets, and their competition likely impacts the distribution of sulfate and organic acids in the marine environment.