High resolution vertical information of halogenated trace gas abundances in the polar stratosphere: First flight of the „MegaAirCore“ in summer 2021

Measurements of halogenated trace gases such as CFCs, halons, HCFCs, HFCs, and PFCs are highly relevant due to their impact on the stratospheric ozone layer as well as their high Global Warming Potentials. Yet in situ profiles of the abundances of many of these species in the stratosphere have been increasingly rare in the last two decades, especially above the altitude range accessible by aircraft (i.e. up to 20 km). More recently, the AirCore technique, which was initially utilized for measurements of more abundant trace gases such as carbon dioxide and methane (Karion et al., 2010), has been demonstrated to also enable stratospheric mixing ratio determination for six halogenated species (Laube et al., 2020). However, a direct measurement comparison of AirCore-based air samples with those collected via a more established technique has been missing so far for such low-abundant species. We here present results from a large balloon flight in Esrange, Sweden (67.8877°N, 21.0838°E) in August 2021. An established cryogenic whole-air sampler (Engel et al., 2009) was flown on the same gondola as a so-called “MegaAirCore”, which has, at ~15 liters, a much larger internal volume than common AirCores (~1-1.5 liters). The air collected between ~32 km and ~5 km by this “MegaAirCore”  was transferred into 51 sub-samples immediately after the flight, and these were subsequently analysed for their content of >30 halogenated trace gases. The 13 larger air samples collected by the cryosampler were also measured on the same mass spectrometry-based instrument.Results compare well for many species, which represents an independent verification of AirCore-based measurements of halogenated trace gases at mixing ratios of parts per trillion levels or below – while at the same time demonstrating the viability of stratospheric air sampling at a much higher vertical resolution than previously possible. This opens up new possibilities for studying stratospheric chemistry and dynamics as well as for improvements of the independent validation of remote sensing-based observations. 

 

References

Engel et al., Nat. Geosci., 2, 28–31, 2009

Karion et al., J. Atmos. Ocean. Technol., 27(11), 1839–1853, 2010

Laube, et al., Atmos. Chem. Phys., 20, 9771–9782, 2020, https://doi.org/10.5194/acp-20-9771-2020