Fast Peroxy Radical Isomerization and OH Recycling in the Reaction of OH Radicals with Dimethyl Sulfide

Abstract

Dimethyl sulfide (DMS), produced by marine organisms, represents the most abundant, biogenic sulfur emission into the Earth's atmosphere. The gas-phase degradation of DMS is mainly initiated by the reaction with the OH radical forming first CH₃SCH₂O₂ radicals from the dominant H-abstraction channel. It is experimentally shown that these peroxy radicals undergo a two-step isomerization process finally forming a product consistent with the formula HOOCH₂SCHO. The isomerization process is accompanied by OH recycling. The rate-limiting first isomerization step, CH₃SCH₂O₂ → CH₂SCH₂OOH, followed by O₂ addition, proceeds with <i>k</i> = (0.23 ± 0.12) s^-1 at 295 ± 2 K. Competing bimolecular CH₃SCH₂O₂ reactions with NO, HO₂, or RO₂ radicals are less important for trace-gas conditions over the oceans. Results of atmospheric chemistry simulations demonstrate the predominance (≥95%) of CH₃SCH₂O₂ isomerization. The rapid peroxy radical isomerization, not yet considered in models, substantially changes the understanding of DMS's degradation processes in the atmosphere.