Service interruption on Monday 11 July from 12:30 to 13:00: all the sites of the CCSD (HAL, Epiciences, SciencesConf, AureHAL) will be inaccessible (network hardware connection).
Skip to Main content Skip to Navigation
Journal articles

Atmospheric Trends and Radiative Forcings of CF4 and C2F6 Inferred from Firn Air

Abstract : The atmospheric histories of two potent greenhouse gases, tetrafluoromethane (CF4) and hexafluoroethane (C2F6), have been reconstructed for the 20th century based on firn air measurements from both hemispheres. The reconstructed atmospheric trends show that the mixing ratios of both CF4 and C2F6 have increased during the 20th century by factors of 2 and 10, respectively. Initially, the increasing mixing ratios coincided with the rise in primary aluminum production. However, a slower atmospheric growth rate for CF4 appears to be evident during the 1990s, which supports recent aluminum industry reports of reduced CF4 emissions. This work illustrates the changing relationship between CF4 and C2F6 that is likely to be largely the result of both reduced emissions from the aluminum industry and faster growing emissions of C2F6 from the semiconductor industry. Measurements of C2F6 in the older firn air indicate a natural background mixing ratio of <0.3 parts per trillion (ppt), demonstrating that natural sources of this gas are negligible. However, CF4 was deduced to have a preindustrial mixing ratio of 34 ± 1 ppt (50% of contemporary levels). This is in good agreement with the previous work of Harnisch et al. (18) and provides independent confirmation of their results. As a result of the large global warming potentials of CF4 and C2F6, these results have important implications for radiative forcing calculations. The radiative forcings of CF4 and C2F6 are shown to have increased over the past 50 years to values in 2001 of 4.1 × 10-3 Wm-2 and 7.5 × 10-4 Wm-2, respectively, relative to preindustrial concentra tions. These forcings are small compared to present day forcings due to the major greenhouse gases but, if the current trends continue, they will continue to increase since both gases have essentially infinite lifetimes. There is, therefore, a large incentive to reduce perfluorocarbon emissions such that, through the implementation of the Kyoto Protocol, the atmospheric growth rates may decline in the future.
Document type :
Journal articles
Complete list of metadata
Contributor : Aurore Gayraud Connect in order to contact the contributor
Submitted on : Thursday, April 16, 2009 - 1:46:21 PM
Last modification on : Tuesday, October 19, 2021 - 6:58:04 PM

Links full text




David R. Worton, William T. Sturges, Laila K. Gohar, Keith P. Shine, Patricia Martinerie, et al.. Atmospheric Trends and Radiative Forcings of CF4 and C2F6 Inferred from Firn Air. Environmental Science and Technology, American Chemical Society, 2007, 41 (7), pp.2184 à 2189. ⟨10.1021/es061710t⟩. ⟨insu-00375935⟩



Record views