Biogenic sulfur compounds and their oxidation products in the spring-to-summer Arctic marine atmosphere

Gas-phase biogenic organosulfur compounds, and their oxidation products are important for the formation and growth of aerosol in the marine environment. During the spring-summer increase in marine biological activity in the northern hemisphere, dimethyl sulfide ((CH₃)₂S, DMS) and methanethiol (CH₃SH, MeSH) are emitted from ocean and sea-ice environments. The emission or transport, and following oxidation, of organosulfur compounds to the Arctic marine environment impacts the available aerosol number and cloud condensation nuclei. Here, we examine organosulfur compound composition, atmospheric fate, and relationships to the aerosol population at the onset of sea-ice melt.

We present shipborne gas-phase measurements of reduced and oxidized organosulfur compounds made with a H­₃O⁺/NH₄⁺ reagent ion switching chemical ionization time-of-flight mass spectrometer as part of the Atmospheric Rivers and the onseT of sea ice MELT (ARTofMELT) campaign on IB Oden. Our measurements during ARTofMELT spanned from May 7^th to June 15^th of 2023 and took place over pack ice and the marginal ice zone between 78 and 81°N between the east coast of Greenland and the Svalbard archipelago (the Fram Strait). Non-DMS organosulfur species made a significant contribution to atmospheric sulfur during the campaign. MeSH was present at concentrations ~10% of DMS (10’s of ppt_v) during periods of elevated organosulfur compounds (DMS exceeding ~100 ppt_v) and was correlated with DMS (R² > 0.8). Ambient temperatures ranged between -15 and 2°C, making the primary oxidation reaction between DMS and the hydroxyl radical the OH-addition pathway to produce dimethyl sulfoxide (DMSO). We observed DMSO in concentrations occasionally exceeding 150 ppt_v, and the chemical formula C₂H₆SO₂ (likely dimethyl sulfone) at similar concentrations to DMSO. During low ozone periods (< 10 ppb_v), the loss of DMS was potentially influenced by halogen chemistry resulting in an increased abundance of DMSO relative to DMS. We use our measurements to investigate organosulfur compound composition and loss pathways under a variety of atmospheric conditions.