Abstract
In a changing climate, potential stratospheric circulation changes require long-Term monitoring. Stratospheric trace gas measurements are often used as a proxy for stratospheric circulation changes via the <q>mean age of air</q> values derived from them. In this study, we investigated five potential age of air tracers-the perfluorocarbons CF4, C2F6 and C3F8 and the hydrofluorocarbons CHF3 (HFC-23) and HFC-125-and compare them to the traditional tracer SF6 and a (relatively) shorter-lived species, HFC-227ea. A detailed uncertainty analysis was performed on mean ages derived from these <q>new</q> tracers to allow us to confidently compare their efficacy as age tracers to the existing tracer, SF6. Our results showed that uncertainties associated with the mean age derived from these new age tracers are similar to those derived from SF6, suggesting that these alternative compounds are suitable in this respect for use as age tracers. Independent verification of the suitability of these age tracers is provided by a comparison between samples analysed at the University of East Anglia and the Scripps Institution of Oceanography. All five tracers give younger mean ages than SF6, a discrepancy that increases with increasing mean age. Our findings qualitatively support recent work that suggests that the stratospheric lifetime of SF6 is significantly less than the previous estimate of 3200 years. The impact of these younger mean ages on three policy-relevant parameters-stratospheric lifetimes, fractional release factors (FRFs) and ozone depletion potentials-is investigated in combination with a recently improved methodology to calculate FRFs. Updates to previous estimations for these parameters are provided.
| Original language | English |
|---|---|
| Pages (from-to) | 3369-3385 |
| Number of pages | 17 |
| Journal | Atmospheric Chemistry and Physics |
| Volume | 18 |
| Issue number | 5 |
| DOIs | |
| Publication status | Published - 8 Mar 2018 |
Funding
Acknowledgements. Johannes Laube received funding from the UK Natural Environment Research Council (Research Fellowship NE/I021918/1) and David E. Oram from the National Centre for Atmospheric Science. Part of this work was funded by the ERC project EXC3ITE (EXC3ITE-678904-ERC-2015-STG). We acknowledge the Cape Grim staff over many years for the collection of the Cape Grim air archive and for collecting air samples for UEA. Funding for the Cape Grim air archive is from CSIRO, the Bureau of Meteorology and Refrigerant Reclaim Australia. We thank Michel Bolder for collecting the Geophysica air samples and acknowledge the work of the Geophysica aircraft and CNES balloon teams as well as related funding from ESA (PremierEx project), the Forschungszentrum Jülich, the European Commission (FP7 projects RECONCILE-226365-FP7-ENV-2008-1 and StratoClim-603557-FP7-ENV-2013-two-stage) and the Dutch Science Foundation (NWO; grant number 865.07.001). The operation of the AGAGE instruments at SIO is supported by the National Aeronautics and Space Administration (NASA; grants NAG5-12669, NNX07AE89G and NNX11AF17G to MIT and grants NNX07AE87G, NNX07AF09G, NNX11AF15G and NNX11AF16G to SIO).
