Dovrou, Eleni; Bates, Kelvin H.; Rivera-Rios, Jean C.; Cox, Joshua L.; Shutter, Joshua D.; Keutsch, Frank N.

In-cloud chemistry has important ramifications for atmospheric particulate matter formation and gas-phase chemistry. Recent work has shown that, like hydrogen peroxide (inline-formulaH2O2), the two main isomers of isoprene hydroxyl hydroperoxide (ISOPOOH) oxidize sulfur dioxide dissolved in cloud droplets (inline-formulaSO2,aq) to sulfate. The work revealed that the pathway of inline-formulaSO2,aq oxidation with ISOPOOH differs from that of inline-formulaH2O2. We investigate the chemical mechanisms of oxidation of inline-formulaSO2,aq with ISOPOOH in the cloud-relevant pH range of 3–6 and compare them with the previously reported mechanisms of oxidation of inline-formulaSO2,aq with inline-formulaH2O2, methyl hydroperoxide and peroxyacetic acid. The organic products of the reaction are identified, and two pathways are proposed. For 1,2-ISOPOOH, a higher yield pathway via proposed radical intermediates yields methyl vinyl ketone (MVK) and formaldehyde, which can react to hydroxymethanesulfonate (HMS) when inline-formulaSO2,aq is present. A lower yield non-fragmentation oxygen addition pathway is proposed that results in the formation of isoprene-derived diols (ISOPOH). Based on global simulations, this mechanism is not a significant pathway for formation of MVK and formaldehyde relative to their gas-phase formation but, as previously reported, it can be regionally important for sulfate production. The study adds to previous work that highlights similarities and differences between gas-phase and cloud-droplet processing of reactive organic carbon.

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Dovrou, Eleni / Bates, Kelvin H. / Rivera-Rios, Jean C. / et al: Towards a chemical mechanism of the oxidation of aqueous sulfur dioxide via isoprene hydroxyl hydroperoxides (ISOPOOH). 2021. Copernicus Publications.

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