Preprints
https://doi.org/10.5194/acp-2021-176
https://doi.org/10.5194/acp-2021-176

  08 Mar 2021

08 Mar 2021

Review status: this preprint is currently under review for the journal ACP.

Towards a Chemical Mechanism of the Oxidation of Aqueous Sulfur Dioxide via Isoprene Hydroxyl Hydroperoxides (ISOPOOH)

Eleni Dovrou1,a, Kelvin H. Bates2, Jean C. Rivera-Rios3,b, Joshua L. Cox3, Joshua D. Shutter3, and Frank N. Keutsch1,3,4 Eleni Dovrou et al.
  • 1John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
  • 2Harvard University Center for the Environment, Cambridge, MA 02138, USA
  • 3Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
  • 4Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
  • anow at: Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany
  • bnow at: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA

Abstract. In-cloud chemistry has important ramifications for atmospheric particulate matter formation and gas-phase chemistry. Recent work has shown that, like hydrogen peroxide (H2O2), the two main isomers of isoprene hydroxyl hydroperoxide (ISOPOOH) oxidize sulfur dioxide dissolved in cloud droplets (SO2,aq) to sulfate. The work revealed that the pathway of SO2,aq oxidation with ISOPOOH differs from that of H2O2. We investigate the chemical mechanisms of oxidation of SO2,aq with ISOPOOH in the cloud-relevant pH range of 3–6 and compare them with the previously reported mechanisms of oxidation of SO2,aq with H2O2, 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 SO2,aq is present. A lower yield non-fragmentation oxygen addition pathway is proposed that results in 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.

Eleni Dovrou et al.

Status: open (until 03 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on Dovrou et al', Becky Alexander, 26 Mar 2021 reply
    • AC1: 'Reply on RC1', Eleni Dovrou, 16 Apr 2021 reply
  • RC2: 'Comment on acp-2021-176', Anonymous Referee #2, 29 Mar 2021 reply
    • AC2: 'Reply on RC2', Eleni Dovrou, 16 Apr 2021 reply

Eleni Dovrou et al.

Eleni Dovrou et al.

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Short summary
We examined the mechanism and products of oxidation of dissolved sulfur dioxide with the main isomers of isoprene hydroxyl hydroperoxides, via laboratory and model analysis. Two chemical mechanism pathways are proposed and the results provide an improved understanding of the broader atmospheric chemistry and role of multifunctional organic hydroperoxides, which should be the dominant VOC oxidation products under low-NO conditions, highlighting their significant contribution to sulfate formation.
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