Carbon monoxide (CO) is the main product of CO₂ photolysis in the Martian atmosphere. Production of CO is balanced by its loss reaction with OH, which recycles CO into CO₂. CO is therefore a sensitive tracer of the OH-catalysed chemistry that contributes to the stability of CO₂ in the atmosphere of Mars. To date, CO has been measured only in terms of vertically integrated column abundances, and the upper atmosphere, where CO is produced, is largely unconstrained by observations. Here we report vertical profiles of CO from 10 to 120 km, and from a broad range of latitudes, inferred from the Atmospheric Chemistry Suite on board the ExoMars Trace Gas Orbiter. At solar longitudes 164–190°, we observe an equatorial CO mixing ratio of ~1,000 ppmv (10–80 km), increasing towards the polar regions to more than 3,000 ppmv under the influence of downward transport of CO from the upper atmosphere, providing a view of the Hadley cell circulation at Mars’s equinox. Observations also cover the 2018 global dust storm, during which we observe a prominent depletion in the CO mixing ratio up to 100 km. This is indicative of increased CO oxidation in a context of unusually large high-altitude water vapour, boosting OH abundance.

一氧化碳（CO）是CO ₂在火星大气中光解的主要产物。CO 的产生通过其与 OH 的损失反应来平衡，OH 将 CO 再循环为 CO ₂。因此，CO 是 OH 催化化学的敏感示踪剂，有助于 CO _{2的稳定性}在火星大气层中。迄今为止，CO 仅根据垂直积分柱丰度来测量，而产生 CO 的高层大气在很大程度上不受观测的限制。在这里，我们报告了从 ExoMars 微量气体轨道器上的大气化学套件推断出的 10 到 120 公里的 CO 垂直剖面，并且来自广泛的纬度。在太阳经度 164-190°，我们观察到赤道 CO 混合比约为 1,000 ppmv（10-80 公里），在 CO 从高层大气向下传输的影响下，向极地地区增加到超过 3,000 ppmv，提供火星春分时哈德利细胞循环的视图。观测还涵盖了 2018 年全球沙尘暴，在此期间，我们观察到高达 100 公里的 CO 混合比显着减少。