Possible implications of enhanced chlorofluorocarbon-11 concentrations on ozone

Dameris, Martin; Jöckel, Patrick; Nützel, Matthias

doi:https://doi.org/10.5194/acp-19-13759-2019

Articles | Volume 19, issue 22

https://doi.org/10.5194/acp-19-13759-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

The Modular Earth Submodel System (MESSy) (ACP/GMD inter-journal...

https://doi.org/10.5194/acp-19-13759-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 22

Research article

|

15 Nov 2019

Research article |

| 15 Nov 2019

Possible implications of enhanced chlorofluorocarbon-11 concentrations on ozone

Martin Dameris, Patrick Jöckel, and Matthias Nützel

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Final revised paper (published on 15 Nov 2019)
Preprint (discussion started on 18 Mar 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'review of acp-2019-239', Anonymous Referee #1, 20 Mar 2019
- AC1: 'First reply to referee #1', Martin Dameris, 09 Apr 2019
RC2: 'Review of acp-2019-239', Anonymous Referee #2, 19 May 2019
- AC2: 'Reply to referee #2', Martin Dameris, 29 May 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Martin Dameris on behalf of the Authors (06 Sep 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Sep 2019) by Jens-Uwe Grooß

RR by Anonymous Referee #1 (23 Sep 2019)

Suggestions for revision or reasons for rejection

The manuscript has clearly improved compared to the previous version. The authors took most of my comments into account or provided reasonable explanations otherwise. I am still not fully convinced by the experimental set-up, but I appreciate that the framing and motivation of the paper have been clearly revised and that a second sensitivity simulation has been performed. In my view the argumentation in the paper is still a bit inconsistent from time to time. Below I made some suggestions for additional minor revisions.

- Constant 2002 vs constant 2017: In my first review I suggested to run a simulation with fixed 2017 CFC-11 levels. In their reply the authors provided a comprehensible justification of their approach. I could imagine that many readers will have similar problems as I had with understanding the set up of the CFC-11 scenario. Therefore, I would recommend to add a short version of this justification to the paper or an appendix.

- ozone budget analysis: At the moment this section is pretty much limited to the presentation of changes of the individual ozone production and loss cycles. I would prefer to see some more explanation of the underlying processes. For example, the decline of ozone loss by the NOx-cycle – is this due to enhanced ClONO2 formation or the cooling of the stratosphere? I guess due to the latter, but I assume the authors could easily check differences in ClONO2 in their simulations. The same holds for changes in the other cycles.

- “gap in our understanding of CFC-11 sources and sinks since the early 2000s”: I do not understand how this statement can be regarded as motivation for the present study, and how it can be used as argument for keeping mixing ratios constant at 2002 levels? It might well be that the observed CFC-11 concentrations do not match our current understanding of sources and sinks, but for stratospheric ozone atmospheric CFC-11 concentrations matter, and as correctly mentioned by the authors, constant emissions are not equal to constant mixing ratios. I think that authors should rethink their argumentation in this respect and rewrite their text where necessary.

- “worst case scenario”: The authors state that the goal of their study is to create an upper limit. They argue that their diagnosed CFC-11 emissions of ca. 90 Gg/yr required to maintain constant CFC-11 levels is higher than observed over the last years. At the same time the authors argue that future emissions and concentrations of CFC-11 are uncertain, and the studies of Montzka et al. (2018) and Rigby et al. (2019) indicate increasing emissions since 2016, getting close to 90 Gg/yr. In my view there is some contradiction in the presented argumentation. In essence, I would be a bit careful with statements like “upper limit” or “worst case scenario” as nobody can envisage how future atmospheric CFC-11 concentrations will look like.

- p5, l30/31: I do not understand this sentence. How does the reference ClOx profile in EMAC affect the changes in Cl mixing ratios at different altitudes?

- p6, l16: How is recovery defined here? Return to 1980 levels?

- p11, l16 onwards: In their reply the authors state that their study is not meant to provide a robust projection of future ozone changes, but in this section, they actually discuss return dates and the fate of the Antarctic ozone hole. To me this sounds pretty much like a projection.

- Fig. 1: Instead of “low” and “high” CFC-11 mixing ratios I would prefer to see actual numbers at the y-axis.

- Fig. 7: Headings for the individual panels would be helpful (e.g. “TCO (60N-60S)” for a)

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RR by Anonymous Referee #2 (03 Oct 2019)

ED: Publish subject to minor revisions (review by editor) (03 Oct 2019) by Jens-Uwe Grooß

AR by Martin Dameris on behalf of the Authors (09 Oct 2019) Author's response Manuscript

ED: Publish subject to technical corrections (11 Oct 2019) by Jens-Uwe Grooß

AR by Martin Dameris on behalf of the Authors (15 Oct 2019) Author's response Manuscript

Short summary

A chemistry–climate model (CCM) study is performed, investigating the consequences of a constant CFC-11 surface mixing ratio for stratospheric ozone in the future. The total column ozone is particularly affected in both polar regions in winter and spring. It turns out that the calculated ozone changes, especially in the upper stratosphere, are smaller than expected. In this attitudinal region the additional ozone depletion due to the catalysis by reactive chlorine is partly compensated for.