We participated in four international field campaigns in 2017, 2018 and 2019 and also developed our own launch capability in parallel and were able to launch 19 AirCores by the end of the project in March 2022. We can now measure a range of over 20 gases via the AirCore technique, including some that pose an emerging threat to the ozone layer. Results for six gases were published in Laube et al. (2020).
A major change to the project was the move to Germany at the end of 2018, which required the reestablishing of the entire lab. There were, however, many positive effects as a result of this move, including synergistic balloon and modelling activities.
In 2021 we participated in a large balloon campaign in Sweden co-funded by the EU project Hemera. Especially for this, we built and certified the largest AirCore ever made, which allowed measurements of a wider range of trace gases at better vertical resolution, and the first direct validation of the AirCore technique. We also flew a normal-sized AirCore at the same time as a potential future satellite instrument. A comparison of the data is in progress and showcases the future potential of the AirCore technique to validate data products derived via remote sensing techniques.
The reanalysis of the air archives had been delayed repeatedly due to a) technical challenges during the construction of an improved analytical system, b) the project move, and c) limited lab access and repair/maintenance problems due to the Covid-19 pandemic. However, in summer 2020 measurements using a new, semi-automated inlet finally enabled the high-precision analysis of stratospheric air samples collected in 1976, 1977, 1981, 1982, 1993, 1999, and 2015. A comparison of this unique data set with stratospheric model runs is in progress.
Moreover, existing data was utilised to investigate novel ways to detect changes in stratospheric circulation. We have been able to identify 5 more gases that provide additional direct constraints on stratospheric transport times. Leedham Elvidge et al. (2018) also included an analysis of the knock-on consequences for policy-relevant parameters that affect predictions of the recovery of the ozone layer. Contributions were made to a publication on the atmospheric distributions of CFC-113a, an emerging threat to the ozone layer with strong growth rates in the atmosphere (Adcock et al., 2018).
Another publication investigated recent global trends of PFCs, which are powerful greenhouse gases with Global Warming Potentials 1000s of times higher than that of CO2. All of the six gases examined are still increasing in abundance, and one could be used as a tracer of stratospheric circulation (Droste et al., 2020). Furthermore, Thomas et al. (2021) published the first ever stratospheric isotope footprints of carbon in CFCs, which could also help to constrain estimates of circulation changes. Contributions were made to two more publications, one on the atmospheric sources of CFC-11. Global CFC-11 emissions had been found to be increasing again and our analysis confirmed that major sources existed in East Asia (Adcock et al., 2020). The other publication contributed to investigate, for the first time, ozone-depleting substances (ODSs) above the Asian Monsoon, which is a large source of air entering the northern hemispheric stratosphere. We found that concentrations of many ODSs were significantly enhanced in this region. This has negative implications for the recovery of the ozone layer (Adcock et al., 2021).
The quality of the new AirCore data was evaluated, in combination with an investigation of stratospheric circulation changes over the decade from 2009 to 2018 (using also aircraft-based data), and a comparison of the results to those from a global model driven by three widely used meteorological reanalysis packages (Laube et al., 2020). Two further studies expanded this research by a) assessing the comparability of the stratospheric circulation strength in the new ERA-5 meteorological reanalysis with observations (Ploeger et al., 2021), and b) examining the validity of an alternative method to quantify stratospheric circulation trends in a model framework (Poshyvailo-Strube et al., 2022).
