This title appears in the Scientific Report :
2021
Please use the identifier:
http://hdl.handle.net/2128/27764 in citations.
Please use the identifier: http://dx.doi.org/10.5194/acp-2020-843 in citations.
Stratospheric carbon isotope fractionation and tropospheric histories of CFC-11, CFC-12 and CFC-113 isotopologues
Stratospheric carbon isotope fractionation and tropospheric histories of CFC-11, CFC-12 and CFC-113 isotopologues
We present novel measurements of the carbon isotope composition of CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CF2ClCFCl2), three atmospheric trace gases that are important for both stratospheric ozone depletion and global warming. These measurements were carried out on air samples collected in th...
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Personal Name(s): | Thomas, Max |
---|---|
Laube, Johannes C. (Corresponding author) / Kaiser, Jan / Allin, Samuel / Martinerie, Patricia / Mulvaney, Robert / Ridley, Anna / Röckmann, Thomas / Sturges, William T. / Witrant, Emmanuel | |
Contributing Institute: |
Stratosphäre; IEK-7 |
Published in: | Atmospheric chemistry and physics / Discussions, 2020 (2020) S. 843 |
Imprint: |
Katlenburg-Lindau
EGU
2020
|
DOI: |
10.5194/acp-2020-843 |
Document Type: |
Journal Article |
Research Program: |
EXploring Chemistry, Composition and Circulation in the stratosphere with InnovativeTEchnologies Composition and dynamics of the upper troposphere and middle atmosphere |
Link: |
OpenAccess |
Publikationsportal JuSER |
Please use the identifier: http://dx.doi.org/10.5194/acp-2020-843 in citations.
We present novel measurements of the carbon isotope composition of CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CF2ClCFCl2), three atmospheric trace gases that are important for both stratospheric ozone depletion and global warming. These measurements were carried out on air samples collected in the stratosphere – the main sink region for these gases – and on air extracted from deep polar firn snow. We quantify, for the first time, the apparent isotopic fractionation, εapp(13C), for these gases as they are destroyed in the high- and mid-latitude stratosphere: εapp(CFC-12, high-lat) = (−20.2 ± 4.4) ‰ and εapp(CFC-113, high-lat) = (−9.4 ± 4.4) ‰, εapp(CFC-12, mid-lat) = (−30.3 ± 10.7) ‰, and εapp(CFC-113, mid-lat) = (−34.4 ± 9.8) ‰. Our CFC-11 measurements were not sufficient to calculate εapp(CFC-11) so we instead used previously reported photolytic fractionation for CFC-11 and CFC-12 to scale our εapp(CFC-12), resulting in εapp(CFC-11, high-lat) = (−7.8 ± 1.7) ‰ and εapp(CFC-11, mid-lat) = (−11.7 ± 4.2) ‰. Measurements of firn air were used to construct histories of the tropospheric isotopic composition, δT(13C), for CFC-11 (1950s to 2009), CFC-12 (1950s to 2009), and CFC-113 (1970s to 2009) – with δT(13C) increasing for each gas. We used εapp(high-lat), which were derived from more data, and a constant isotopic composition of emissions, δE(13C), to model δT(13C, CFC-11), δT(13C, CFC-12), and δT(13C, CFC-113). For CFC-11 and CFC-12, modelled δT(13C) was consistent with measured δT(13C) for the entire period covered by the measurements, suggesting no dramatic change in δE(13C, CFC-11) or δE(13C, CFC-12) has occurred since the 1950s. For CFC-113, our modelled δT(13C, CFC-113) did not agree with our measurements earlier than 1980. While this discrepancy may be indicative of a change in δE(13C, CFC-113), it is premature to assign one. Our modelling predicts increasing δT(13C, CFC-11), δT(13C, CFC-12), and δT(13C, CFC-113) into the future. We investigated the effect of recently reported new CFC-11 emissions on background δT(13C, CFC-11) by fixing model emissions after 2012, and comparing δT(13C, CFC-11) in this scenario to the model base case. The difference in δT(13C, CFC-11) between these scenarios was 1.4 ‰ in 2050. This difference is smaller than our model uncertainty envelope and would therefore require improved modelling and measurement precision, as well as better quantified isotopic source compositions, to detect. |