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. We present new observations of trace gases in the stratospherebased on a cost-effective sampling technique that can access much higheraltitudes than aircraft. The further development of this method now providesdetection of species with abundances in the parts per trillion (ppt) rangeand below. We obtain mixing ratios for six gases (CFC-11, CFC-12, HCFC-22,H-1211, H-1301, and SF 6 ), all of which are important for understandingstratospheric ozone depletion and circulation. After demonstrating thequality of the data through comparisons with ground-based records andaircraft-based observations, we combine them with the latter to demonstrateits potential. We first compare the data with results from a global model drivenby three widely used meteorological reanalyses. Secondly, we focus on CFC-11as recent evidence has indicated renewed atmospheric emissions of thatspecies relevant on a global scale. Because the stratosphere represents themain sink region for CFC-11, potential changes in stratospheric circulationand troposphere–stratosphere exchange fluxes have been identified as thelargest source of uncertainty for the accurate quantification of suchemissions. Our observations span over a decade (up until 2018) and thereforecover the period of the slowdown of CFC-11 global mixing ratio decreasesmeasured at the Earth's surface. The spatial and temporal coverage of theobservations is insufficient for a global quantitative analysis, but we dofind some trends that are in contrast with expectations, indicating that thestratosphere may have contributed to the slower concentration decline inrecent years. Further investigating the reanalysis-driven model data, we findthat the dynamical changes in the stratosphere required to explain theapparent change in tropospheric CFC-11 emissions after 2013 are possiblebut with a very high uncertainty range. This is partly caused by the highvariability of mass flux from the stratosphere to the troposphere,especially at timescales of a few years, and partly by large differencesbetween runs driven by different reanalysis products, none of which agreewith our observations well enough for such a quantitative analysis.

atmospheric chemistry and physics

Investigating stratospheric changes between 2009 and 2018 with halogenated trace gas data from aircraft, AirCores, and a global model focusing on CFC-11