https://doi.org/10.1029/2021GL092506  https://orfeo.kbr.be/bitstream/handle/internal/7865/Aoki%282021a%29.pdf

S. Aoki, F. Daerden, S. Viscardy, I. R. Thomas, J. T. Erwin, S. Robert, L. Trompet, L. Neary, G. L. Villanueva, G. Liuzzi, M. M. J. Crismani, R. T. Clancy, J. Whiteway, F. Schmidt, M. A. Lopez-Valverde, B. Ristic, M. R. Patel, G. Bellucci, J.-J. Lopez-Moreno, K. S. Olsen, F. Lefèvre, F. Montmessin, A. Trokhimovskiy, A. A. Fedorova, O. Korablev, A. C. Vandaele

 

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

 

aoki hcl h20

(a–c) Solar longitude—Latitude map of the maximum HCl mixing ratio (ppbv) below 30 km in (a) MY 34, (b) MY 35, and (c) MY34-35 plotted together. Only 3-σ detections are shown here. The gray points show observations corresponding to dust top altitude greater than 25 km, for which it is generally difficult to perform robust retrievals. The background color maps show the column-integrated water vapor density (pr-µm) obtained by MGS/TES for Mars year 26 (Smith, 2002, 2006) and the column-integrated dust opacity at 9.3 µm normalized for 610 Pa for MY 31 (b) and MY 34 (a) (Montabone et al., 2020). (d) Geographical distribution of HCl below 30 km in the seasonal range between Ls = 240° and 320°.