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Titel |
Trend and lifetime of sulfur hexafluoride at mid-latitudes deduced from ACE-FTS occultation measurements |
VerfasserIn |
Emmanuel Mahieu, Pierre Duchatelet, Rodolphe Zander, Peter F. Bernath, Alex Brown, Chris D. Boone, Kaley A. Walker |
Konferenz |
EGU General Assembly 2011
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 13 (2011) |
Datensatznummer |
250048743
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Zusammenfassung |
Sulfur hexafluoride (SF6) is one of the strongest greenhouse gases on a per molecule basis,
with a global warming potential of 22800 (100-yr horizon). This is an extremely stable gas in
the atmosphere, which results in a very long lifetime, with large uncertainties. The value
adopted by IPCC is 3200 years, but some studies suggest shorter lifetimes, as low as 800
years. Surface concentrations are now about 7 ppt, with reported trends indicating a steady
and strong increase of 0.3 ppt/yr. Most emissions are of anthropogenic origin, related to its
use as an insulator in high-voltage electrical installations. Secondary contributions
result from magnesium and aluminum production as well as from the manufacturing
of semiconductors (see e.g. Levin et al., 2010; Rigby et al., 2010 and references
therein).
In this contribution, we use occultation measurements performed by the ACE-FTS
(Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument, launched
in August 2003 onboard the Canadian SCISAT satellite (Bernath et al., 2005). ACE-FTS is
still in operation to date, with no significant degradation in its performance. This
spectrometer achieves a spectral resolution of 0.02 cm-1 in the broad 750-4400 cm-1 range
which covers the unresolved ν3 band Q branch of SF6 centered at 947.9 cm-1.
Signal-to-noise ratios of 200-300 are typically obtained in the spectral region of
interest.
Version 3 retrievals performed by University of Waterloo give volume mixing ratio
profiles of SF6 in the 11-32 km altitude range. We consider all available sunrise and sunset
occultation measurements obtained at mid-latitudes in both hemispheres to derive the trend of
SF6 in the lower stratosphere, from late February 2004 onwards. Consistency between both
hemispheres will be investigated. In addition, concurrent N2O measurements are used to
evaluate the atmospheric lifetime of SF6, following a method used previously for other
long-lived gases (e.g. Zander et al, 1996).
Comparisons with trends derived from in situ surface measurements or from
ground-based remote-sensing observations (e.g. at the Jungfraujoch station, 46.5ºN) are also
included.
Acknowledgments
The University of Liège contribution to the present work has primarily been supported by
the PRODEX program funded by the Belgian Federal Science Policy Office, Brussels. The
Atmospheric Chemistry Experiment (ACE) is a Canadian-led mission mainly supported by
the Canadian Space Agency (CSA) and the Natural Sciences and Engineering Research
Council (NSERC) of Canada.
References
Bernath, P. F., McElroy, C. T., Abrams, M. C. et al., Atmospheric Chemistry Experiment
(ACE): mission overview, Geophys. Res. Lett., 32, L15S01, doi:10.1029/2005GL022386,
2005.
Levin, I., Naegler, T., Heinz, R., Osusko, D., Cuevas, E., Engel, A., Ilmberger, J.,
Langenfelds, R. L., Neininger, B., Rohden, C. V., Steele, L. P., Weller, R.,
Worthy, D. E., and Zimov, S. A.: The global SF6 source inferred from long-term high
precision atmospheric measurements and its comparison with emission inventories, Atmos.
Chem. Phys., 10, 2655-2662, doi:10.5194/acp-10-2655-2010, 2010.
Rigby, M., Mühle, J., Miller, B. R., Prinn, R. G., Krummel, P. B., Steele, L. P.,
Fraser, P. J., Salameh, P. K., Harth, C. M., Weiss, R. F., Greally, B. R., O’Doherty, S.,
Simmonds, P. G., Vollmer, M. K., Reimann, S., Kim, J., Kim, K.-R., Wang, H. J.,
Olivier, J. G. J., Dlugokencky, E. J., Dutton, G. S., Hall, B. D., and Elkins, J. W.:
History of atmospheric SF6 from 1973 to 2008, Atmos. Chem. Phys., 10, 10305-10320,
doi:10.5194/acp-10-10305-2010, 2010.
Zander, R., Solomon, S., Mahieu, E., Goldman, A., Rinsland, C. P., Gunson, M.
R., Abrams, M. C., Chang, A. Y., Salawitch, R. J., Michelsen, H. A., Newchurch,
M. J., and Stiller, G. P., Increase of stratospheric carbon tetrafluoride (CF4) based
on ATMOS observations from space, Geophys. Res. Lett., 23, 2353-2356, 1996. |
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