The ESA-Roscosmos ExoMars Trace Gas Orbiter is investigating the martian atmosphere. Discovering new gases related to active process and looking for their sources is a key goal of the mission. ExoMars has discovered hydrogen chloride for the first time. It appeared during a global dust storm in 2018 and disappeared again afterwards.
Source:
https://phys.org/news/2021-02-gases-mars.html