Methanethiol Abundance and Oxidation in a Polluted Marine Atmosphere

Abstract Biological activity in the surface ocean leads to emissions of methanethiol (MeSH) and dimethyl sulfide (DMS). Measurements of MeSH in the marine atmosphere are sparse and the impact of NO x pollution on MeSH oxidation remains unexplored. We present measurements of MeSH and DMS at a coastal site with NO x up to 24.3 ppb in the United Kingdom during May and June. Winds coming from the seaward (northerly) direction showed a median (25th quantiles) MeSH mixing ratio of 15.7 (7.9–26.9) ppt. The measurements reveal significantly lower MeSH during daytime. Atmospheric box model calculations suggest that ∼25% of the MeSH oxidation is initiated by NO 3 at this site and that NO x pollution can reduce the SO 2 yield from MeSH. This work is further evidence for the prevalence of MeSH and illustrates the impact of NO x pollution on MeSH oxidation with associated implications for its role in aerosol‐cloud processes, and climate.