Advertisement

Study of the Decomposition of Traces of SF6 in the Lower Atmosphere: The Kinetic Results

  • Jacques Castonguay
  • Jean-Marc Gauthier

Abstract

For the last three decades, sulfurhexafluoride has accumulated into the atmosphere to a concentration of ≈4 pptv, due mostly to leaks and releases from electrical equipment. Recognized as a very persistent gas, with lifetime exceeding three millennium, and as the molecule having the largest global warming potential, it was included as the sixth gas in the Kyoto Protocol. Since 95% of all the SF6 mass is contained in the troposphere, a test program was conducted to study the chemical stability and reactivity of the inert SF6 molecule in the typical conditions of the lower atmosphere (< I5 km). It was focused on the almost exclusive decomposition path resulting from the dissociative capture of an electron. Chemical kinetics of SF6 in SF6/air mixtures (1-1000 ppmv) were studied using reaction cells and setups favoring the interaction of SF6 with low energy electrons (≈0,2 eV). These were generated in-situ by photo-emission from the UV-irradiated inner Al cell walls. The following experimental conditions were chosen to simulate those of the lower atmosphere: pressure (25-100 kPa), temperature (-40 to +25°C), humidity (0.05-3.5%). The O2 concentration was also varied between 2-21%. In all cases, the decomposition of SF6 was observed to proceed at very low rates to form exclusively SO2F2, the only byproduct observed. A simple reaction mechanism is derived from the ion-molecule reaction of SF6 with O2, the typical negative ion formed by electron capture in air at atmospheric pressure. In our experimental conditions as in the atmosphere, this reaction must compete with many other neutralization paths of the O2, but the SF6 destruction certainly occurs, due to its large electron affinity. Indeed, the dissociation of SF6 into SF5 is certainly irreversible in those situations. The decomposition kinetics of SF6 measured in tropospheric air in this study can certainly improve the chemical reaction model used to estimate its persistence lifetime.

Keywords

Dissociative Electron Capture Lower Atmosphere Atmospheric Electric Field Simple Reaction Mechanism Tropospheric Condition 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    J. Butler, J.W. Elkins, S.A. Montzka, T.M. Thompson, et all, “Nitrous Oxide and Halocompounds”(Chap. 5), Climate Monitoring and Diagnostics Laboratory, Summary Report No. 24 , NOAA Environmental Research Laboratory, Dec. 1998, pp. 99–119.Google Scholar
  2. 2.
    A.R. Ravishankara, S. Solomon, A.A. Turnipseed, and R.F. Warren, “Atmospheric Lifetimes of Long-lived Species”, Science, Vol. 259, (1993), pp. 194–199.CrossRefGoogle Scholar
  3. 3.
    J.M. Gauthier and J. Castonguay, “Study of the Decomposition of SF6 in the Lower atmosphere: the Experimental Approach”, Gaseous Dielectric VIII: Proceedings of the 8th symposium on gaseous dielectrics (June 2-5, 1998), Plenum, NY, 1998, pp. 443–450.Google Scholar
  4. 4.
    D. Smith, P. Spanel, S. Matejcik, A. Stamatovic, T.D. Märk, T. Jaffke and E Illenberger, “Formation of SF5 in Electron Attachment to SF6, Swarm and Beam Results Reconciled”, Chem. Phys. Letters, Vol. 240, pp. 481–488, (1995).CrossRefGoogle Scholar
  5. 5.
    A.A. Viggiano, R.A. Morris and J.F. Paulson, “Effects of O2 and SF6 Vibrational Energy on the Rate Constant for Charge Transfer between O2 and SF6”, Int, J. Mass Spectrom., Vol. 135, pp. 31–37, (1994).CrossRefGoogle Scholar
  6. 6.
    W. Pong, “Photoemission from A1-A12O3 Films in the Vacuum Ultraviolet Region”, J. Applied Physics, Vol. 40, No. 4,1969, pp. 1733–1739.CrossRefGoogle Scholar
  7. 7.
    A. Buzulutskov, A. Breskin, R. Chechik and J. Va’vra, “Study of Photocathode Protection with Thin Dielectric Films”, Nucl. Instr. and Meth. in Phys. Res., Vol. A 371,1996, pp. 147–150.Google Scholar

Copyright information

© Springer Science+Business Media New York 2001

Authors and Affiliations

  • Jacques Castonguay
    • 1
  • Jean-Marc Gauthier
    • 1
  1. 1.Institut de recherche d’Hydro-QuebécVarennesCANADA

Personalised recommendations