Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air

S. J. Allin*, J. C. Laube, E. Witrant, J. Kaiser, E. McKenna, P. Dennis, R. Mulvaney, E. Capron, P. Martinerie, Thomas Roeckmann, T. Blunier, J. Schwander, P. J. Fraser, R. L. Langenfelds, W. T. Sturges

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The stratospheric degradation of chlorofluorocarbons (CFCs) releases chlorine, which is a major contributor to the destruction of stratospheric ozone (O-3). A recent study reported strong chlorine isotope fractionation during the breakdown of the most abundant CFC (CFC-12, CCl2F2, Laube et al., 2010a), similar to effects seen in nitrous oxide (N2O). Using air archives to obtain a long-term record of chlorine isotope ratios in CFCs could help to identify and quantify their sources and sinks. We analyse the three most abundant CFCs and show that CFC-11 (CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant stratospheric chlorine isotope fractionation, in common with CFC-12. The apparent isotope fractionation (epsilon(app)) for mid- and high-latitude stratospheric samples are respectively -2.4 (0.5) and -2.3 (0.4) parts per thousand for CFC-11, -12.2 (1.6) and -6.8 (0.8) parts per thousand for CFC-12 and -3.5 (1.5) and -3.3 (1.2) parts per thousand for CFC-113, where the number in parentheses is the numerical value of the standard uncertainty expressed in per mil. Assuming a constant isotope composition of emissions, we calculate the expected trends in the tropospheric isotope signature of these gases based on their stratospheric Cl-37 enrichment and stratosphere-troposphere exchange. We compare these projections to the long-term delta (Cl-37) trends of all three CFCs, measured on background tropospheric samples from the Cape Grim air archive (Tasmania, 1978-2010) and tropospheric firn air samples from Greenland (North Greenland Eemian Ice Drilling (NEEM) site) and Antarctica (Fletcher Promontory site). From 1970 to the present day, projected trends agree with tropospheric measurements, suggesting that within analytical uncertainties, a constant average emission isotope delta (delta) is a compatible scenario. The measurement uncertainty is too high to determine whether the average emission isotope delta has been affected by changes in CFC manufacturing processes or not. Our study increases the suite of trace gases amenable to direct isotope ratio measurements in small air volumes (approximately 200 mL), using a single-detector gas chromatography-mass spectrometry (GC-MS) system.

Original languageEnglish
Pages (from-to)6867-6877
Number of pages11
JournalAtmospheric chemistry and physics
Volume15
Issue number12
DOIs
Publication statusPublished - 2015

Funding

We thank the UK Natural Environment Research Council (grant nos. NE/K500896/1, NE/F015585/1 & NE/I021918/1, the National Centre for Atmospheric Science) and the European Commission (INFRA-2011-1.1.11-284274) for funding. We thank the staff at the Cape Grim station and at CSIRO GASLAB Aspendale for collecting and maintaining the Cape Grim air archive and preparing the UEA flasks and sub-samples. We also acknowledge CSIRO and the Bureau of Meteorology for funding these activities. NEEM is directed and organised by the Centre for Ice and Climate at the Niels Bohr Institute and US NSF, Office of Polar Programs. It is supported by funding agencies and institutions in Belgium (FNRS-CFB and FWO), Canada (GSC), China (CAS), Denmark (FIST), France (IPEV, CNRS/INSU, CEA and ANR), Germany (AWI), Iceland (RannIs), Japan (NIPR), Korea (KOPRI), the Netherlands (NWO/ALW), Sweden (VR), Switzerland (SNF), United Kingdom (NERC) and the USA (US NSF, Office of Polar Programs). The Geophysica flights from Oberpfaffenhofen were funded by ESA under the PremieEx project and by Forschungszentrum Julich. The Fletcher air pumping campaign was made possible with the support of BAS operations and logistics and funded by the Natural Environment Research Council. The Geophysica flights from Kiruna were funded by the European Commission as part of the FP7 project RECONCILE (grant no. RECONCILE-226365-FP7-ENV-2008-1). Air sampling during these campaigns was funded by the Dutch Science Foundation (NWO, grant no. 865.07.001). In addition we are grateful for contributions from Michel Bolder and the Geophysica team (sample collection and campaign organisation).

Keywords

  • OZONE-DEPLETING SUBSTANCES
  • ATMOSPHERIC N2O
  • NITROUS-OXIDE
  • ICE-CORE
  • SEASONAL CYCLES
  • POLAR FIRN
  • SOUTH-POLE
  • GREENLAND
  • CHEMISTRY
  • TRANSPORT

Fingerprint

Dive into the research topics of 'Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air'. Together they form a unique fingerprint.

Cite this