No detection of SO₂, H₂S, or OCS in the atmosphere of Mars from the first two Martian years of observations from TGO/ACS

International audienceThe detection of sulphur species in the Martian atmosphere would be a strong indicator of volcanic outgassing from the surface of Mars.We wish to establish the presence of SO2, H2S, or OCS in the Martian atmosphere or determine upper limits on their concen- tration in the absence of a detection.Weperformacomprehensiveanalysisofsolaroccultationdatafromthemid-infraredchanneloftheAtmosphericChemistry Suite instrument, on board the ExoMars Trace Gas Orbiter, obtained during Martian years 34 and 35.For the most optimal sensitivity conditions, we determine 1σ upper limits of SO2 at 20ppbv, H2S at 15ppbv, and OCS at 0.4 ppbv; the last value is lower than any previous upper limits imposed on OCS in the literature. We find no evidence of any of these species above a 3σ confidence threshold. We therefore infer that passive volcanic outgassing of SO2 must be below 2 ktons day−1