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EXploring Chemistry, Composition and Circulation in the stratosphere with Innovative TEchnologies

Periodic Reporting for period 4 - EXC3ITE (EXploring Chemistry, Composition and Circulation in the stratosphere with InnovativeTEchnologies)

Okres sprawozdawczy: 2020-06-01 do 2022-03-31

It is ozone that primarily heats and therefore creates the stratosphere. Human emissions of ozone-depleting substances (ODSs) have however led to dramatic stratospheric ozone losses for decades. This global problem is ongoing and of renewed concern due to recent unexpected changes. It is also likely affecting the nature of the stratosphere itself, with implications for global health and economy. In addition, emissions of greenhouse gases have been proposed to lead to a long-term acceleration of the stratospheric overturning circulation. In summary, significant stratospheric changes are to be expected from both, ozone losses and global warming.
Indications for such changes have been reported, but there are substantial uncertainties and limitations connected with these studies. In addition, current technologies to explore stratospheric composition and chemistry are very expensive and often offer only infrequent data. There was clearly a need for new and improved tools to correctly detect and quantify changes from observations.
The EXC3ITE project has been investigating 3 novel avenues to explore stratospheric chemistry, composition and circulation:

1) A newly developed low-cost technology to retrieve and analyse air from the stratosphere. These AirCores are a new way to derive budgets of all important and newly emerging ODSs directly in the stratosphere; while at the same time it provides observations of many strong greenhouse gases. At the beginning of the project only a handful of atmospherically important gases such as carbon dioxide and methane had been measured using AirCores. The aim of the EXC3ITE project was to increase that number to >30.

2) New evidence for substantial past changes in stratospheric chemistry and circulation. An unprecedented investigation of stratospheric air archives spanning 40 years and >50 trace gases is allowing new insights into these changes and

3) New diagnosis tools and a detailed comparison with state-of-the-art models are identifying the implications for future climate.

The EXC3ITE project has allowed for a breakthrough in the understanding of stratospheric changes which are of high importance for society through their impact on climate prediction and ozone recovery.
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).
As a result of the many interesting and partly unexpected findings as well as the newly forged collaborations, the host institution is supporting the continuation of all three research avenues beyond the end of the project.

We here highlight that

a) We have carried out the first ever ODS measurements on air retrieved from the stratosphere via an AirCore, which confirms the suitability of this technique as a cost-effective way to investigate the composition, chemistry and circulation of the stratosphere. In total, we have gathered data from 37 balloon flights during the EXC3ITE project.

b) We have expanded the number of trace gases suitable for directly tracking the stratospheric circulation from two to seven, all of which will be valuable tools for the investigation of long-term changes in the stratosphere.

c) We have identified several new threats to the ozone layer as well as alternative possibilities to improve the diagnosis of stratospheric circulation and chemistry changes.