Climatology of the CO Vertical Distribution on Mars Based on ACS TGO Measurements

Carbon monoxide is a non-condensable gas in the Martian atmosphere produced by photolysis of CO2. Its abundance responds to condensation and sublimation CO2 from polar caps, resulting seasonal variations CO mixing ratio. ACS onboard ExoMars Trace Gas Orbiter have measured infrared bands solar occultation. Here we provide first long-term monitoring vertical distribution at altitude range 0 80 km for 1.5 years Ls = 163° MY34 end MY35. We obtained mean ratio ∼960 ppmv latitudes 45°S 45°N altitudes below 40 km, mostly consistent with previous observations. found strong enrichment near surface 100–200° high southern layer 3,000–4,000 ppmv, corresponding local depletion At equinoxes an increase above 50 both hemispheres explained downwelling flux Hadley circulation on Mars, which drags enriched air. General models tend overestimate intensity this process, bringing too much CO. The observed minimum mid-latitudes summer amounts 700–750 agreeing nadir measurements. During global dust storm MY34, when H2O peaks, see less than during calm MY35, suggesting impact HOx chemistry abundance.