In the winter and spring of 2019/2020, the unusually cold, strong, and stable polar vortex created favorable conditions for ozone depletion in the Arctic. Chemical ozone loss started earlier than in any previous year in the satellite era, and continued until the end of March, resulting in the unprecedented reduction of the ozone column. The vortex was located above the Polar Environment Atmospheric Research Laboratory in Eureka, Canada (80 °N, 86 °W) from late February to the end of April, presenting an excellent opportunity to examine ozone loss from a single ground station. Measurements from a suite of instruments show that total column ozone in 2020 was at an all-time low in the 20-year dataset, 22 to 102 DU below previous records set in 2011. Ozone minima (<200 DU), enhanced OClO and BrO slant columns, and unusually low HCl, ClONO2 , and HNO3 columns were observed in March. Polar stratospheric clouds were present as late as 20 March, and ozonesondes show unprecedented depletion in the March and April ozone profiles (to <0.2 ppmv). While both chemical and dynamical factors lead to reduced ozone when the vortex is cold, the contribution of chemical depletion was exceptional in spring 2020 when compared to typical Arctic winters. The mean chemical ozone loss over Eureka was estimated to be 111-127 DU (27-31%) using April measurements and passive ozone from the SLIMCAT chemical transport model. While absolute ozone loss was generally smaller in 2020 than in 2011, percentage ozone loss was greater in 2020.

Carbonyl sulfide (OCS) is a non-hygroscopic trace species in the free troposphere and the primary sulfur reservoir maintained by direct oceanic, geologic, biogenic and anthropogenic emissions and the oxidation of other sulfur-containing source species. It’s the largest source of sulfur transported to the stratosphere during volcanically quiescent periods. Data from 22 ground-based globally dispersed stations are used to derive trends in total and partial column OCS. Middle infrared spectral data are recorded by solar-viewing Fourier transform interferometers that are operated as part of the Network for the Detection of Atmospheric Composition Change between 1986 and 2020. Vertical information in the retrieved profiles provides analysis of discreet altitudinal regions. Trends are found to have well-defined inflection points. In two linear trend time periods ~2002 - 2008 and ~2008 - 2016, tropospheric trends range from ~0.0 to (1.55 ± 0.30 %/y) in contrast to the prior period where all tropospheric trends are negative. Regression analyses show strongest correlation in the free troposphere with anthropogenic emissions. Stratospheric trends in the period ~2008 - 2016 are positive up to (1.93 ± 0.26 %/y) except notably low latitude stations that have negative stratospheric trends. Since ~2016, all stations show a free tropospheric decrease to 2020. Stratospheric OCS is regressed with simultaneously measured N$_2$O to derive a trend accounting for dynamical variability. Stratospheric lifetimes are derived and range from (54.1 ± 9.7)y in the sub-tropics to (103.4 ± 18.3)y in Antarctica. These unique long-term measurements provide new and critical constraints on the global OCS budget.

Experimental measurements of collision-induced absorption (CIA) cross-sections for CO2-H2 and CO2-CH4 complexes were performed using Fourier transform spectroscopy over a spectral range of 100-500 cm and a temperature range of 200-300 K. These experimentally derived CIA cross-sections agree with the spectral range and temperature dependence of the calculation by \citeA{Robin}, however the amplitude is half of what was predicted. Furthermore, the CIA cross-sections reported here agree with those measured by \citeA{Turbet}. The CIA cross-sections can be applied to planetary systems with CO$_{2}$-rich atmospheres, such as Mars and Venus, and will be useful to terrestrial spectroscopists. Additionally, radiative transfer calculations of the early Mars atmosphere were performed and showed that CO2$-CH4 CIA would require surface pressure greater than 3 bar for a 10% methane atmosphere to achieve 273 K at the surface. CO2-H2, however, liquid water is possible with 5% hydrogen and less than 2 bar of surface pressure.

Experimental measurements of collision-induced absorption (CIA) cross-sections for CO-H2 and CO2-CH4 complexes were performed using Fourier transform spectroscopy over a spectral range of 100-500 cm and a temperature range of 200-300 K. These experimentally derived CIA cross-sections agree with the spectral range and temperature dependence of the calculation by Wordsworth (2017), however the amplitude is half of what was predicted. Furthermore, the CIA cross-sections reported here agree with those measured by Turbet (2019). The CIA cross-sections can be applied to planetary systems with CO2-rich atmospheres, such as Mars and Venus, and will be useful to terrestrial spectroscopists. Additionally, radiative transfer calculations of the early Mars atmosphere were performed and showed that CO2-CH4 CIA would require surface pressure greater than 3 bar for a 10% methane atmosphere to achieve 273 K at the surface. CO2-H2, however, liquid water is possible with 5\% hydrogen and less than 2 bar of surface pressure.

An unanswered question in planetary science is how could the early Martian atmosphere have maintained a greenhouse effect sufficient to allow for liquid water on the surface? A recent study by Wordsworth et al. (DOI:10.1002/2016GL071766) suggested that previously unaccounted-for collision-induced absorption (CIA) by carbon dioxide (CO2) and hydrogen gas (H2), and by CO2 and methane (CH4) could provide the additional atmospheric absorption needed to trap enough radiation to raise the Martian surface temperature above freezing. However, as CIA cross-sections for CO2-H2 and CO2-CH4 complexes do not exist in the literature, the authors could only use computational methods to simulate the CIA absorption cross-sections that they themselves identify in the study as needing experimental validation. Preliminary results will be presented from experimental measurements of the CIA cross-sections for CO2-H2 and CO2-CH4 complexes performed using Fourier Transform Spectroscopy. We have obtained Beam-time at the Canadian Light Source Far-IR beamline in late October and early November which will allow us to derive Cross-sections over a spectral range of 0-3000 cm-1 and a temperature range of 200-350 K. In addition to allowing us to experimentally validate the hypothesis of Wordsworth, the cross-sections so obtained can also be applied to other planetary systems with CO2-rich atmospheres, such as Venus, and will be useful to terrestrial spectroscopists.