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Trifluoromethyl Sulfur Pentafluoride (SF5CF3) and Sulfur Hexafluoride (SF6) from Dome Concordia

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Investigators

W. T. Sturges,1 T. J. Wallington,2 M. D. Hurley,2 K. P. Shine,3 K. Sihra,3 A. Engel,4 D. E. Oram,1 S. A. Penkett,1 R. Mulvaney,5 and C. A. M. Brenninkmeijer6

1School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
2Ford Motor Company, Mail Drop SRL-3083, Dearborn, Michigan 48121-2053, U.S.A.
3Department of Meteorology, University of Reading, Reading RG6 6BB, United Kingdom
4Institute for Meteorology and Geophysics, Johann Wolfgang Goethe University of Frankfurt, D-60325 Frankfurt, Germany
5British Antarctic Survey, Natural Environmental Research Council, Cambridge CB3 0ET, United Kingdom
6Atmospheric Chemistry Division, Max Planck Institute for Chemistry, D-55060 Mainz, Germany

Period of Record

1965-1999

Methods

The sampling and analytical methods are described more fully in Sturges et al. (2000). In summary, air samples were pumped from consolidated deep snow (firn) at Dome Concordia (eastern Antarctica) in December 1998 and January 1999, from the surface to a depth of approximately 100 m. Air samples were analyzed with a gas chromatograph - mass spectrometer, with a detection limit of about 0.001 parts per trillion (ppt). A diffusive transport model was used to calculate the age of samples as a function of depth. Measurements of SF6 were used to determine the mean age of the firn air by comparison with extrapolated measurements from Cape Grim, Tasmania combined with estimates from industrial emissions (Maiss and Brenninkmeijer 1998, adapted by Sturges et al. 2000). Dates for SF5CF3 are different than for SF6 due to the lower diffusivity of SF5CF3: the SF6 ages were multiplied by the ratio of the free-air diffusion coefficient of SF5CF3 to that of SF6 (1.18). Free-air diffusion coefficients were determined by a semi-empirical formula based on molecular volumes (Fuller et al. 1966). Note that mean ages represent a very wide distribution of probable ages spanning many years, with an increasing spread of ages at increasing depth.

Trends

The measured concentration of SF5CF3 increased from zero in 1965-1966 to about 0.12 ppt in 1999, with a current growth rate of about 0.008 ppt per year (about 6% per year). Given the similarity of the growth curves of SF5CF3 and SF6 (which increased from 0.18 ppt in 1970 to 4.0 ppt in 1999), Sturges et al. (2000) speculate that the former may originate as a breakdown product of the latter in high-voltage equipment. While the current radiative forcing of SF5CF3 may be minor, the high growth rate and long atmospheric residence time suggest that the greenhouse significance of this gas could increase markedly in the future. Conversely, SF5CF3 appears not to have any natural sources, so control might be feasible, once the sources are identified.

References

  • Fuller, E.N., P.D. Schettler, and J.C. Giddings. 1966. A new method for prediction of binary gas-phase diffusion coefficients. Industrial Engineering and Chemistry 58:19- 27.
  • Maiss, M., and C.A.M. Brenninkmeijer. 1998. Atmospheric SF6: Trends, sources, and prospects. Environmental Sciences and Technology 32:3077-3086.
  • Sturges, W.T., T.J. Wallington, M.D. Hurley, K.P. Shine, K. Sihra, A. Engel, D.E. Oram, S.A. Penkett, R. Mulvaney, and C.A.M. Brenninkmeijer 2000. A potent greenhouse gas identified in the atmosphere: SF5CF3. Science 289:611-613.

CITE AS: Sturges, W.T., T. J. Wallington, M. D. Hurley, K. P. Shine, K. Sihra, A. Engel, D. E. Oram, S. A. Penkett, R. Mulvaney, and C. A. M. Brenninkmeijer. 2000. Trifluoromethyl Sulfur Pentafluoride (SF5CF3) and Sulfur Hexafluoride (SF6) from Dome Concordia. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.