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In 2020, hydrogen chloride (HCl) in the gas phase was discovered in the atmosphere of Mars with the Atmospheric Chemistry Suite (ACS) onboard the Trace Gas Orbiter (TGO) mission (Korablev et al., 2021). Its volume mixing ratio (VMR) shows a seasonal increase of up to 5 ppbv during the perihelion season, followed by a sudden drop to undetectable levels, contradicting modelling estimates of the HCl lifetime of several months. In the Earth's stratosphere, heterogeneous uptake of HCl onto water ice is known to be a major sink for this species. This reaction is now also considered when modelling HCl abundances in the Martian atmosphere. In this work, we use simultaneous measurements of water ice and HCl obtained by the ACS instrument to find particular structures in the vertical profiles as detached gas layers at ice-free altitudes ("ice-holes"). From these particular examples we conclude that the heterogeneous uptake of HCl onto water ice operates on Mars and is a fast mechanism regulating the HCl abundance in the atmosphere of Mars. • Simultaneous vertical profiles of water ice and HCl analysed over 2.5 Martian years. • HCl gas layers at ice-free altitudes reveal local anticorrelation of HCl vs water ice. • Heterogeneous uptake of HCl onto water ice rapidly regulates HCl abundance. [ABSTRACT FROM AUTHOR]

Abstract: Using the SPICAV-UV spectrometer aboard Venus Express in nadir mode, we were able to derive spectral radiance factors in the middle atmosphere of Venus in the 170–320nm range at a spectral resolution of R ≃200 during 2006 and 2007 in the northern hemisphere. By comparison with a radiative transfer model of the upper atmosphere of Venus, we could derive column abundance above the visible cloud top for SO2 using its spectral absorption bands near 280 and 220nm. SO2 column densities show large temporal and spatial variations on a horizontal scale of a few hundred kilometers. Typical SO2 column densities at low latitudes (up to 50°N) were found between 5 and 50μm-atm, whereas in the northern polar region SO2 content was usually below 5μm-atm. The observed latitudinal variations follow closely the cloud top altitude derived by SPICAV-IR and are thought to be of dynamical origin. Also, a sudden increase of SO2 column density in the whole northern hemisphere has been observed in early 2007, possibly related to a convective episode advecting some deep SO2 into the upper atmosphere. [ABSTRACT FROM AUTHOR]

Highlights: [•] The key radical OH is detected for the first time in the Mars atmosphere. [•] The OH emission appears as near-infrared night glow in the polar winter atmosphere. [•] The OH Meinel band structure constrains formation and de-excitation pathways. [•] The observations support current models of Mars atmospheric transport and chemistry. [Copyright &y& Elsevier]