| Issue |
A&A
Volume 687, July 2024
|
|
|---|---|---|
| Article Number | A191 | |
| Number of page(s) | 29 | |
| Section | Planets and planetary systems | |
| DOI | https://doi.org/10.1051/0004-6361/202449546 | |
| Published online | 12 July 2024 | |
Observed seasonal changes in Martian hydrogen chloride explained by heterogeneous chemistry★
1
School of GeoSciences, University of Edinburgh,
Edinburgh,
UK
e-mail: benjamin.taysum@dlr.de
2
Centre for Exoplanet Science, University of Edinburgh,
Edinburgh,
UK
e-mail: pip@ed.ac.uk
3
Department of Physics, University of Oxford,
Oxford,
UK
4
Space Research Institute (IKI),
Moscow,
Russia
5
Research School of Astronomy and Astrophysics, Australian National University,
Canberra,
ACT 2611,
Australia
6
LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS,
Guyancourt,
France
Received:
8
February
2024
Accepted:
3
May
2024
Aims. The aim of this work is to show that the seasonal changes and vertical distribution profiles of hydrogen chloride (HCl) on Mars, as observed by the ExoMars Trace Gas Orbiter, are consistent with the production of gas-phase chlorine atoms from airborne dust and a subsequent rapid uptake of HCl onto water ice particles.
Methods. A 1D photochemistry model was equipped with a chlorine reaction network and driven by dust, water ice, and water vapour profiles measured by the ExoMars Trace Gas Orbiter instrumentation in Mars year 34. The release of Cl and O atoms from airborne dust via the hydration and photolysis of perchlorate within dust grains was parameterised using prior laboratory studies, and the heterogeneous uptake of chlorine species onto dust and water ice was included for processes known to occur in Earth’s atmosphere.
Results. Observed seasonal variations in Martian HCl are reproduced by the model, which yielded low HCl abundances (<1 ppbv) prior to the dust season that rise to 2–6 ppbv in southern latitudes during the dust season. Structured atmospheric layers that coincide with locations where water ice is absent are also produced. As a consequence of the Cl atoms released via our proposed mechanism, the atmospheric lifetime of methane is shortened by two orders of magnitude. This suggests that the production of Cl induced by the breakdown of hydrated perchlorate via UV radiation (or another electromagnetic radiation) in airborne Martian dust, consistent with observed profiles of HCl, could help reconcile reported variations in methane with photochemical models.
Key words: planets and satellites: atmospheres / planets and satellites: terrestrial planets
1D model files used to produce the results of this paper can be found on the Zenodo data repository at https://zenodo.org/records/10955516. Aerosol profiles used in this paper, retrieved by the ACS TIRVIM-NIR spectrometer channels, can be found on the Mendeley Data repository at http://dx.doi.org/10.17632/9yrrw4t9gw.1, and are published here for the first time.
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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