the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Oct 2025
Observationally-derived Fractional Release Factors, Ozone Depletion Potentials, and Stratospheric Lifetimes of Four Long-Lived CFCs: CFC-13 (CClF3), CFC-114 (C2Cl2F4), CFC-114a (CF3CCl2F), and CFC-115 (C2ClF5)
Abstract. The longer an Ozone Depleting Substance (ODS) remains in the stratosphere, the longer it will be available for the process of ozone depletion. We present improved policy-relevant parameters: Fractional Release Factors (FRFs), Ozone Depletion Potentials (ODPs), and stratospheric lifetimes, for four understudied long-lived chlorofluorocarbons (CFCs): CFC-13 (CClF3), CFC-114 (CClF2CCClF2), CFC-114a (CCl2FCF3), and CFC-115 (C2ClF5). Previous estimates for the stratospheric lifetimes of these compounds were derived using model and laboratory-based kinetic studies. This study instead uses stratospheric observational data, and correlations between FRFs and lifetimes, to semi-empirically and independently determine the steady-state stratospheric lifetimes of these compounds.
Our newly derived stratospheric lifetime estimates are 315 (287–331) yr for CFC-13 (300+ years shorter than previous estimates), 190 (176–201) yr for CFC-114 (1 year shorter than previous estimates), 81 (7687) yr for CFC-114a (25.7 years shorter), and 369 (328–435) yr for CFC-115 (295 years shorter). For CFC-13 and CFC-115 this is outside the uncertainty ranges of previously published estimates. This suggests that these two compounds may have had greater emissions than previously thought, in order to account for their abundance. We calculated FRFs and ODSs for the four CFCs of interest: CFC-13 (FRF = 0.07, ODP = 0.4), CFC-114 (FRF = 0.12, ODP = 0.5), CFC-114a (FRF = 0.31, ODP = 0.52), and CFC-115 (FRF = 0.06, ODP = 0.27). Providing new and updated lifetimes, FRFs and ODPs for these compounds, will help improve future estimates of their tropospheric emissions and their potential resulting damage to the stratospheric ozone layer.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-4941', Anonymous Referee #1, 04 Nov 2025
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AC1: 'Reply on RC1', Elinor Tuffnell, 05 Nov 2025
RC “This manuscript presents new estimates for the stratospheric lifetimes, fractional release factors (FRFs) and ozone depletion potentials (ODPs) for CFC-13, CFC-114, CFC-114a and CFC-115. The new estimates are based on stratospheric measurements rather than a combination of modelling and laboratory studies. They thus provide valuable complementary evidence regarding the current measurements and would be of direct interest for use in the Scientific Assessment of Ozone Depletion.
The analysis is good and the uncertainties are described so that it is certainly publishable material.”
Author Reply:
We thank the reviewer for this positive assessment of our work and its relevance to the Scientific Assessment of Ozone Depletion.
RC: “However the structure of the manuscript makes it hard to read and understand. More thought on how the material is ordered and presented would make the paper stronger as well as more accessible. I do not think that more analysis is required.
The main problem is that there is no description on how the manuscript is structured as part of the introduction. Rather, it ends with a somewhat technical discussion of the difficulties of getting separate measurements of the two isomers CFC-114 and CFC-114a. Previous estimates of lifetimes, ODPs and FRFs are presented in Table 1. This could be presented more as a state of knowledge, a description of what new information this manuscript will provide (perhaps the current discussion section) and end with a summary of the sections that will follow. A clear discussion of the broader significance of the work is also lacking. Why should I care about FLFs, etc?
The manuscript would also benefit from similar ‘heads up’ material at the beginning of each main section (Methods, Results, etc.).”
Author reply:
We thank the reviewer for these helpful suggestions to improve the structure and readability of the manuscript. We have added the suggested ‘heads-up’ material to better sign-post the content for the reader.
RC: “It is important to make clear the distinction between what information or data already exists in the literature and what new information is presented. For example, it was not clear to me on first reading that all the material in Table 1 is published and that it represents the current knowledge on which this manuscript builds. It is important that this is made clear in the accompanying text and in the caption.”
Author reply:
Thank you for catching this oversight, we have now added the necessary clarification to the text and caption.
RC: “The Discussion and Conclusion sections are both on the short side. Most of the material in the Discussion section could go in the Introduction as it is not really discussing the implications of the results. Can the paper do without a Discussion section by bolstering the material about implications in the Results section and ending with a stronger summary? “
Author reply:
There was a lively discussion amongst the co-authors of this paper regarding the discussion section of the manuscript; what should go there, what should be removed, and whether a discussion section was necessary in this case. In light of this and your comment, some restructuring along the lines you suggest, has been completed.
Citation: https://doi.org/10.5194/egusphere-2025-4941-AC1
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AC1: 'Reply on RC1', Elinor Tuffnell, 05 Nov 2025
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RC2: 'Comment on egusphere-2025-4941', Anonymous Referee #2, 05 Dec 2025
This study uses stratospheric observational data and correlations between FRFs and lifetimes of well-studied ozone depleting substances to determine the steady-state stratopsheric lifetimes of minor CFCs. The work in this paper provides a valuable contribution to our understanding of the lifetimes and emissions of these CFCs. Most of my comments are on clarity and framing with one major point about proper accounting of uncertainties.
The largest concern I have with this paper is with regards to the following:
uncertainties in lifetimes of well-studied compounds are largely due to uncertainty in upwelling rates. That would imply that the bias in lifetimes estimates would be correlated to bias in assumed age of air – if upwelling is faster than believed, then AoA would be younger than believed and lifetimes shorter. I may have missed this but I believe this study glosses over this relationship and assumes AoA is well constrained and that biases in AoA are independent of those in atmospheric lifetimes. How would accounting for this correlated bias change the results here? Do the uncertainties noted here account for that? Further, are the uncertainties in the atmospheric lifetimes used to fit your curve shown in Fig 3 assumed to be independent or correlated with one another? For example, how would it impact your reported uncertainties if they were perfectly correlated?
Minor comments:
Line 84 – suggestion to add uncertainties to CFC-115 lifetimes.
Line 93 – an impurity in the production of CFC-12 (Western et al, 2023). I didn’t see that in the referenced paper,instead Ifound: “CFC-13 may be a by-product during the production of CFC-11” referencing [Vollmer, M. K. et al. Atmospheric histories and emissions ofvchlorofluorocarbons CFC-13 (CClF3), ΣCFC-114 (C2Cl2F4), andCFC-115 (C2ClF5). Atmos. Chem. Phys. 18, 979–1002 (2018)]. Alternatively, Western references the potential for CFC-13 emissions during the plasma arc destruction of CFC-12, but references: [Murphy, A. B., Farmer, A. J. D., Horrigan, E. C. & McAllister, T. Plasma destruction of ozone depleting substances. Plasma Chem. Plasma Process. 22, 371–385 (2002)]. I suggest referencing the original source rather than the Western paper, as Western’s paper was not directly studying the production/manufacturing processes.
I’m having a hard time interpreting the method presented to deal with the separation of CFC114 from 114a. For example, can you explain what is being correlated with what here:
A simple linear correlation (without offset) was calculated for both the Vollmer et al., (2018) and the UEA CGO data, and comparison of these linear correlations was used to derive a conversion factor “x” with thelowest residual sum of squares (RSS) (which were CFC-13=0.11, CFC-115=0.11, and ΣCFC-114=0.81), to attempt to make UEA measurements compatible with Vollmer et al., (2018).”
I also do not follow why the authors take the sum of CFC-114 and CFC-114a data “in order to be compare to Vollmer et al., (2018)” even though “Vollmer et al. did not distinguish between CFC-114 and CFC-114a, and so the data for these two compounds are combined to give ‘ΣCFC-114’ which not a mathematical sum of the two, rather a weighted sum.”
Equation 2 must assume there’s no trend in entry mixing ratios? Or is a time lag of the approximate age of air accounted for in this equation?
Line 270: Which compounds are the “well-studied” ones used here? How do you account for the uncertainties of the lifetimes of these compounds?
Line 287: I don’t think CFC-12 uncertainties are symmetric. I believe the uncertainties around the inverse of lifetimes are symmetric. Also – I would add the reference to the CFC-12 estimate provided here
Line 325 – CFC-114 is the exception because its lifetime was not updated, correct? This could be explained “, with the exception of CFC-114 (Fig. 5), whose lifetime estimate did not change significantly.”
I suggest reworking the framing of last paragraph a bit as follows: Edit the first sentence to something like:
“While this study suggests that emissions of CFC-113 and 115 are likely higher than previously estimated, it remains unclear whether additional emissions are released from long-term banks or new production.” And then the last sentence should be edited to something like: “This study does not attribute the source of emissions, but our shorter estimated lifetimes are consistent with higher inferred emissions, leaving the question of unaccounted
Citation: https://doi.org/10.5194/egusphere-2025-4941-RC2
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- 1
This manuscript presents new estimates for the stratospheric lifetimes, fractional release factors (FRFs) and ozone depletion potentials (ODPs) for CFC-13, CFC-114, CFC-114a and CFC-115. The new estimates are based on stratospheric measurements rather than a combination of modelling and laboratory studies. They thus provide valuable complementary evidence regarding the current measurements and would be of direct interest for use in the Scientific Assessment of Ozone Depletion.
The analysis is good and the uncertainties are described so that it is certainly publishable material. However the structure of the manuscript makes it hard to read and understand. More thought on how the material is ordered and presented would make the paper stronger as well as more accessible. I do not think that more analysis is required.
The main problem is that there is no description on how the manuscript is structured as part of the introduction. Rather, it ends with a somewhat technical discussion of the difficulties of getting separate measurements of the two isomers CFC-114 and CFC-114a. Previous estimates of lifetimes, ODPs and FRFs are presented in Table 1. This could be presented more as a state of knowledge, a description of what new information this manuscript will provide (perhaps the current discussion section) and end with a summary of the sections that will follow. A clear discussion of the broader significance of the work is also lacking. Why should I care about FLFs, etc?
The manuscript would also benefit from similar ‘heads up’ material at the beginning of each main section (Methods, Results, etc.).
It is important to make clear the distinction between what information or data already exists in the literature and what new information is presented. For example, it was not clear to me on first reading that all the material in Table 1 is published and that it represents the current knowledge on which this manuscript builds. It is important that this is made clear in the accompanying text and in the caption.
The Discussion and Conclusion sections are both on the short side. Most of the material in the Discussion section could go in the Introduction as it is not really discussing the implications of the results. Can the paper do without a Discussion section by bolstering the material about implications in the Results section and ending with a stronger summary?
Minor comments
50/51 ‘…respectively, while the…’
Tab 1 caption Something wrong with formatting. More importantly, I think there should be a clear statement that these values are published elsewhere.
Introduction I don’t think it is enough to
174/175 something gone wrong here – ‘..which is not a mathematical..’?
176 ‘..showed that the atmospheric ratio..’
208 ‘independent’
213 ‘dissociated’ more common
232 ‘..because of the non-linearities…’
243 ‘estimate’ rather than ‘prediction’
331 State what the Lickley simulation period is
364 How will the new metrics help understand the sources of these compounds?
365on This is the first time that this material has been presented. It should also be covered in the Introduction and the Discussion (if the authors decide to keep one). It is the type of broader discussion which I find lacking in the rest of the paper.
General Check correct format for references with date in brackets - ‘Laube et al, (2016)’. Is the comma needed?