Atmospheric Histories and Emissions of Chlorofluorocarbons CFC-13(CClF[subscript 3]), ΣCFC-114 (C[subscript 2]Cl[subscript 2]F[subscript 4]), and CFC-115 (C[subscript 2]ClF[subscript 5]
Author(s)
Ivy, Diane J
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Based on observations of the chlorofluorocarbons CFC-13 (chlorotrifluoromethane), 6CFC-114 (combined measurement of both isomers of dichlorotetrafluoroethane), and CFC-115 (chloropentafluoroethane) in atmospheric and firn samples, we reconstruct records of their tropospheric histories spanning nearly 8 decades. These compounds were measured in polar firn air samples, in ambient air archived in canisters, and in situ at the AGAGE (Advanced Global Atmospheric Gases Experiment) network and affiliated sites. Global emissions to the atmosphere are derived from these observations using an inversion based on a 12-box atmospheric transport model. For CFC-13, we provide the first comprehensive global analysis. This compound increased monotonically from its first appearance in the atmosphere in the late 1950s to a mean global abundance of 3.18 ppt (dry-air mole fraction in parts per trillion,
pmolmol[superscript −1]) in 2016. Its growth rate has decreased since
the mid-1980s but has remained at a surprisingly high mean
level of 0.02 ppt yr[superscript −1] since 2000, resulting in a continuing
growth of CFC-13 in the atmosphere. 6CFC-114 increased from its appearance in the 1950s to a maximum of 16.6 ppt in the early 2000s and has since slightly declined to 16.3 ppt in 2016. CFC-115 increased monotonically from its first appearance in the 1960s and reached a global mean mole fraction of 8.49 ppt in 2016. Growth rates of all three compounds
over the past years are significantly larger than would be expected
from zero emissions. Under the assumption of unchanging lifetimes and atmospheric transport patterns, we derive global emissions from our measurements, which have remained unexpectedly high in recent years: mean yearly emissions for the last decade (2007–2016) of CFC-13 are
at 0.48 ± 0.15 kt yr[superscript −1] (> 15 % of past peak emissions), of
6CFC-114 at 1.90 ± 0.84 kt yr[superscript −1] (∼ 10 % of peak emissions),
and of CFC-115 at 0.80±0.50 kt yr[superscript −1] (> 5 % of peak
emissions). Mean yearly emissions of CFC-115 for 2015–2016 are 1.14 ± 0.50 kt yr[superscript −1] and have doubled compared to the 2007–2010 minimum. We find CFC-13 emissions from aluminum smelters but if extrapolated to global emissions, they cannot account for the lingering global emissions determined from the atmospheric observations. We find impurities
of CFC-115 in the refrigerant HFC-125 (CHF2CF3) but if extrapolated
to global emissions, they can neither account for the lingering global CFC-115 emissions determined from the atmospheric observations nor for their recent increases. We also conduct regional inversions for the years 2012–2016 for the northeastern Asian area using observations from the Korean
AGAGE site at Gosan and find significant emissions for 6CFC-114 and CFC-115, suggesting that a large fraction of their global emissions currently occur in northeastern Asia and more specifically on the Chinese mainland.
Date issued
2018-01Department
Massachusetts Institute of Technology. Center for Global Change Science; Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary SciencesJournal
Atmospheric Chemistry and Physics Discussions
Publisher
Copernicus GmbH
Citation
Vollmer, Martin K., et al. “Atmospheric Histories and Emissions of Chlorofluorocarbons CFC-13(CClF[subscript 3]), ΣCFC-114 (C[subscript 2]Cl{subscript 2]F[subscript 4}), and CFC-115 (C[subscript 2]ClF[subscript 5]” Atmospheric Chemistry and Physics Discussions, Oct. 2017, pp. 1–39. Crossref, doi:10.5194/acp-2017-935. © 2018 Authors
Version: Final published version
ISSN
1680-7375