Annual Appearance of Hydrogen Chloride on Mars and a Striking Similarity With the Water Vapor Vertical Distribution Observed by TGO/NOMAD

Hydrogen chloride (HCl) was recently discovered in the atmosphere of Mars by two spectrometers onboard ExoMars Trace Gas Orbiter. The reported detection made Martian Year 34 transient, present several months after global dust storm during southern summer season. Here, we full data set vertically resolved HCl detections obtained NOMAD instrument, which covers also year 35. We show that particular increase abundances season is annually repeated, and formation independent from a event. find vertical distribution strikingly similar to water vapor, suggests uptake ice clouds plays an important role. observed rapid decrease at end would require strong sink photochemical loss.