Atmospheric Fate of the CH₃SOO Radical from the CH₃S + O₂ Equilibrium

Abstract

The atmospheric oxidation mechanisms of reduced sulfur compounds are of great importance in the biogeochemical sulfur cycle. The CH 3 S radical represents an important intermediate in these oxidation processes. Under atmospheric conditions, CH 3 S will predominantly react with O 2 to form the peroxy radical CH 3 SOO. The formed CH 3 SOO has two competing unimolecular reaction pathways: isomerization to CH 3 SO 2 , which further decomposes into CH 3 and SO 2 , or a hydrogen shift followed by HO 2 loss, leading to CH 2 S. Previous theoretical calculations have suggested that CH 2 S formation should be the dominant pathway, in disagreement with existing experimental results. Our large active space multireference configuration interaction calculations agree with the experimental results that the formation of CH 3 and SO 2 is the dominant route and the formation of CH 2 S and HO 2 can, at most, be a minor pathway. We support the calculations with new experiments starting from the OH + CH 3 SH reaction for CH 3 S formation under low NO x conditions and find a SO 2 yield of 0.86 ± 0.18 within our reaction time of 7.9 s. Model simulations of our experiments show that the SO 2 yield converges to 0.98. This combined theoretical and experimental study thus furthers the understanding of the general oxidation mechanisms of sulfur compounds in the atmosphere.

Efficient Production of Carbonyl Sulfide in the Low‐NOx Oxidation of Dimethyl Sulfide

“…This is supported by the work of Chen et al. (2021), who also found that CH 3 S∙ oxidizes to SO 2 in near unit yield and not H 2 CS, a potential precursor to OCS.…”

Oceanic emissions of dimethyl sulfide and methanethiol and their contribution to sulfur dioxide production in the marine atmosphere

“…The atmospheric yield of SO 2 from the oxidation of MeSH by OH under low NO x was recently reported as 0.98 based on modeling results constrained by a laboratory oxidation study, which is in good agreement with the efficient production of SO 2 from MeSH proposed in our reaction scheme (Chen et al, 2021). We exploit this link between MeSH oxidation by OH and known DMS oxidation chemistry to develop a MeSH oxidation mechanism for implementation in a 0-D chemical box model as described further in the subsequent text.…”

Oceanic emissions of dimethyl sulfide and methanethiol and their contribution to sulfur dioxide production in the marine atmosphere

“…The atmospheric yield of SO2 from the oxidation of MeSH by OH under low NOx was recently reported as 0.98 based on 135 modeling results constrained by a laboratory oxidation study, which is in good agreement with the efficient production of SO2 from MeSH proposed in our reaction scheme (Chen et al, 2021). We exploit this link between MeSH oxidation by OH and known DMS oxidation chemistry to develop a MeSH oxidation mechanism for implementation into a 0-D chemical box model as described further in the subsequent text.…”

“…Model diel profiles of SO2 mixing ratios and PSO2 with and without MeSH emissions are shown in Fig 7 . In the campaign mean case MeSH emissions contribute 30% of the overall SO2 production (or a 43% increase in total SO2 production compared to the FDMS only case). The model yield of SO2 from MeSH oxidation was 0.99 which is comparable to an experimentally constrained model determination of the atmospheric yield of 0.98 (Chen et al, 2021). We include the full MeSH oxidation mechanism for 400 completeness due to its overlap with known DMS chemistry and ease of implementation in the box model.…”

“…CC BY 4.0 License. determined model yield of SO2 from MeSH of 0.99, and a recently determined yield of 0.98 constrained by laboratory oxidation studies (Chen et al, 2021), future modeling efforts may be justified in simplifying this mechanism by including only a direct MeSH + OH → SO2 reaction at a yield of 1. Prior efforts to constrain the total SO2 budget in the marine boundary layer required a unit yield of SO2 from DMS (Faloona et al, 2009) which stands in contrast to the 40-80% range typically determined in 405 laboratory and modeling studies (Faloona, 2009;Gray et al, 2011).…”