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Detecting trace gases such as hydrogen chloride (HCl) in Mars' atmosphere is among the primary objectives of the ExoMars Trace Gas Orbiter (TGO) mission. Terrestrially, HCl is closely associated with active volcanic activity, so its detection on Mars was expected to point to some form of active magmatism/outgassing. However, after its discovery using the mid‐infrared channel of the TGO Atmospheric Chemistry Suite (ACS MIR), a clear seasonality was observed, beginning with a sudden increase in HCl abundance from below detection limits to 1–3 ppbv in both hemispheres coincident with the start of dust activity, followed by very sudden and rapid loss at the southern autumnal equinox. In this study, we have investigated the relationship between HCl and atmospheric dust by making comparisons in the vertical distribution of gases measured with ACS and aerosols measured co‐located with the Mars Climate Sounder (MCS). This study includes HCl, water vapor, and ozone measured using ACS MIR, water vapor and temperature measured with the near infrared channel of ACS, and temperature, dust opacity, and water ice opacity measured with MCS. In part 1, we show that dust loading has a strong impact in temperature, which controls the abundance of water ice and water vapor, and that HCl is very closely linked to water activity. In part 2, we investigate the quantitative correlations between each quantity and discuss the possible source and sinks of HCl, their likelihood given the correlations, and any issues arising from them. Plain Language Summary: After four full Martian years in orbit since 2018, the ExoMars Trace Gas Orbiter (TGO) has observed three Martian dusty seasons, which occur when it is spring and summer in the southern hemisphere. The first, starting in summer 2018, featured a global dust storm (GDS) after which we made the first detection of hydrogen chloride (HCl) in the Martian atmosphere using the Atmospheric Chemistry Suite (ACS) instrument. Finding this gas was a priority of ExoMars because its presence may indicate that the planet is volcanically active. Since then, we have observed two more dusty periods without a GDS and observed the reappearance of HCl each time. Here, we present the climatology of HCl in both hemispheres over these three dusty periods (in Mars years 34, 35, and 36) and investigate their relationships with temperature and water vapor measured by ACS, and with airborne dust and water ice measured with the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO). In this paper, we examine how the vertical structure of each quantity changes over time. We show that there is a close relationship between HCl and H2O, and that both are controlled by temperature, driven by dust loading. Key Points: Comparison of trace gas abundance and aerosol extinction between Atmospheric Chemistry Suite on ExoMars TGO and Mars Climate Sounder on Mars Reconnaissance OrbiterReveal the seasonal changes in hydrogen chloride on MarsShow that dust affects atmospheric temperature, which controls water vapor abundance and ice extinction, and thus impacts HCl abundance [ABSTRACT FROM AUTHOR]

The detection of hydrogen chloride (HCl) in the atmosphere of Mars was among the primary objectives of the ExoMars Trace Gas Orbiter (TGO) mission. Its discovery using the Atmospheric Chemistry Suite mid‐infrared channel (ACS MIR) showed a distinct seasonality and possible link to dust activity. This paper is part 2 of a study investigating the link between HCl and aerosols by comparing gas measurements made with TGO to dust and water ice opacities measured with the Mars Climate Sounder (MCS). In part 1, we showed, and compared, the seasonal evolution of vertical profiles of HCl, water vapor, temperature, dust opacity, and water ice opacity over the dusty periods around perihelion (solar longitudes 180°–360°) across Mars years 34–36. In part 2, we investigated the quantitative correlations in the vertical distribution between each quantity, as well as ozone. We show that there is a strong positive correlation between HCl and water vapor, which is expected due to fast photochemical production rates for HCl when reacting with water vapor photolysis products. We also show a strong positive correlation between water vapor and temperature, but are unable to show any correlation between temperature and HCl. There are weak correlations between the opacities of dust and water ice, and dust and water vapor, but only very low correlations between dust and HCl. We close with a discussion of possible sources and sinks and that interactions between HCl and water ice are the most likely for both, given the inter‐comparison. Plain Language Summary: The ExoMars Trace Gas Orbiter (TGO) has observed three Martian dusty seasons (summer in the southern hemisphere). In mid‐2018, we made the first detection of hydrogen chloride (HCl) in the Martian atmosphere using the Atmospheric Chemistry Suite (ACS). Finding this gas, among others, was a priority of ExoMars because its primary source may be volcanic. Since then, we have observed two more dusty periods with the reappearance of HCl each time. In part 1, we presented the climatology of HCl over these three dusty periods (in Mars years 34, 35, and 36) and investigate their relationships with temperature and water vapor measured by ACS, and with airborne dust and water ice measured with the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO). In this paper, part 2, we quantify the correlations between HCl, water vapor, ozone, dust, temperature, and water ice. We show that HCl is closely correlated to water vapor, which is, in turn, correlated to temperature. There is only a very low correlation between HCl and dust or water ice, which both impact water vapor. Possible mechanisms for seasonal HCl production and destruction are discussed, concluding that the freeze‐thaw cycle of atmospheric water is most likely. Key Points: Comparison of trace gases and aerosol opacity between ACS on ExoMars TGO and MCS on MROLow correlations between HCl and the opacities of dust or water ice, but very strong correlation with water vapor and the formation of icesHCl source and sink possibilities are discussed, concluding that frost activity may be the most likely possibility for both [ABSTRACT FROM AUTHOR]

Here we present water vapor vertical profiles observed with the ExoMars Trace Gas Orbiter/Nadir and Occultation for MArs Discovery instrument during the perihelion and Southern summer solstice season (LS = 240°–300°) in three consecutive Martian Years 34, 35, and 36. We show the detailed latitudinal distribution of H2O at tangent altitudes from 10 to 120 km, revealing a vertical plume at 60°S–50°S injecting H2O upward, reaching abundance of about 50 ppmv at 100 km. We have observed this event repeatedly in the three Martian years analyzed, appearing at LS = 260°–280° and showing inter‐annual variations in the magnitude and timing due to long term effects of the Martian Year 34 Global Dust Storm. We provide a rough estimate of projected hydrogen escape of 3.2 × 109 cm−2 s−1 associated to these plumes, adding further evidence of the key role played by the perihelion season in the long term evolution of the planet's climate. Plain Language Summary: Studying the vertical distribution of the Martian atmosphere is crucial to understand what happened to the water presumably present in larger abundance on ancient Mars. We have analyzed the vertical profiles of three Martian Years during the Southern summer, revealing a strong vertical transport of water vapor to the upper atmosphere. This seasonal phenomenon seems to be repeated annually, although with variations in the location and time of the year. Our estimation of the associated upward hydrogen flux represents an important loss which could have contributed to the escape of water to space for at least the period in which Mars had its present orbital inclination. Key Points: Latitudinal distributions of water vapor up to 120 km are analyzed in detail using Nadir and Occultation for MArs Discovery (NOMAD) observations with an improved retrieval schemeWater vapor injection during the perihelion localized around 50°–60°S in three consecutive Martian yearsMartian year 34 Global Dust Storm may have affected the driving mechanisms of the plume, delaying its appearance and reducing its magnitude [ABSTRACT FROM AUTHOR]

The paper provides information on the index of fluctuating asymmetry of the Pitsunda pine in industrial and recreational areas in the city of Tuapse (the Russian Black Sea coast of the Caucasus). It is shown that pollution is localized in the port area, and in the city center, the fluctuating asymmetry index is comparable to that for resort areas at a considerable distance from the Tuapse port. The necessity of taking into account the climate when using the coefficient of fluctuating asymmetry of the needles of the Mediterranean (Pitsunda) pine in assessing the degree of ecological well-being of various areas is shown.

Temperature and density in the upper Martian atmosphere, above ∼100 km, are key diagnostic parameters to study processes of the species' escape, investigate the impact of solar activity, model the atmospheric circulation, and plan spacecraft descent or aerobraking maneuvers. In this paper, we report vertical profiling of carbon dioxide (CO2) density and temperature from the Atmospheric Chemistry Suite (ACS) solar occultations onboard the ExoMars Trace Gas Orbiter. A strong CO2 absorption band near 2.7 μm observed by the middle infrared spectrometric channel (ACS MIR) allows the retrieval of the atmospheric thermal structure in an unprecedentedly large altitude range, from 20 to 180 km. We present the latitudinal and seasonal climatology of the thermal structure for 1.5 Martian years (MYs), from the middle of MY 34 to the end of MY 35. The results show the variability of distinct atmospheric layers, such as a mesopause (derived from 70 to 145 km) and homopause, changing from 90 to 100 km at aphelion to 120–130 km at perihelion. Some short‐term homopause fluctuations are also observed depending on the dust activity. Plain Language Summary: We report vertical distributions of the density and temperature in the Martian atmosphere in the altitude range from 20 to 180 km. This broad interval of heights embraces regions of the troposphere (<50 km), the mesosphere (50–100 km), and the thermosphere (>100 km). Knowledge of thermal structure in the middle and upper atmosphere (above 50 km) is unique for the Martian climate modeling, studying the atmospheric escape and the impact of solar activity, as well as planning spacecraft maneuvers. Our data are based on remote measurements of the carbon dioxide (CO2) absorption in the atmosphere at very high altitude resolution of one kilometer. Sensing this major component, 95% of the total density, in the infrared wavelength range allows us to derive the atmospheric temperature as well. We observe the climatology of different atmospheric layers depending on latitude and seasons for 1.5 Martian years, from May 2018 to January 2021. For example, we reveal extremely high variability of the coldest layer, mesopause, from 70 km in the southern winter to 150 km in the southern summer. Key Points: Seasonal variability of the Martian atmospheric thermal structure at altitudes 20–180 km is reported from CO2 infrared spectroscopyThe mesopause altitude rises from 70 to 90 km in the high‐winter latitudes to 130–150 km in the summer season for both hemispheresThe homopause altitude varies from 90 km at aphelion to 130 km at perihelion in the Martian years 34 and 35, and it depends on dust activity [ABSTRACT FROM AUTHOR]