Polar boundary layer bromine explosion and ozone depletion events in the chemistry–climate model EMAC v2.52: implementation and evaluation of AirSnow algorithm

Falk, Stefanie; Sinnhuber, Björn-Martin

doi:https://doi.org/10.5194/gmd-11-1115-2018

Articles | Volume 11, issue 3

https://doi.org/10.5194/gmd-11-1115-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

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

https://doi.org/10.5194/gmd-11-1115-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 11, issue 3

Development and technical paper

|

28 Mar 2018

Development and technical paper |

| 28 Mar 2018

Polar boundary layer bromine explosion and ozone depletion events in the chemistry–climate model EMAC v2.52: implementation and evaluation of AirSnow algorithm

Stefanie Falk and Björn-Martin Sinnhuber

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Final revised paper (published on 28 Mar 2018)
Supplement to the final revised paper
Preprint (discussion started on 06 Jul 2017)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Comments on Falk and Sinnhuber manuscript on polar boundary layer bromine explosion and ozone depletion events', Anonymous Referee #1, 02 Aug 2017
RC2: 'Review of "Polar boundary layer bromine explosion and ozone depletion events in the chemistry-climate model EMAC v2.52: Implementation and evaluation of AirSnow algorithm"', Anonymous Referee #2, 04 Aug 2017
AC1: 'Final authors response to reviewer comments', Stefanie Falk, 11 Oct 2017
EC1: 'Reminder of the aims and scope of GMD', Slimane Bekki, 19 Oct 2017
- AC2: 'Reminder of the aims and scope of GMD', Stefanie Falk, 08 Nov 2017

Peer-review completion

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

AR by Stefanie Falk on behalf of the Authors (19 Nov 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Nov 2017) by Slimane Bekki

RR by Anonymous Referee #1 (28 Nov 2017)

RR by Anonymous Referee #2 (04 Jan 2018)

Suggestions for revision or reasons for rejection

The authors have sufficiently addressed the reviewer and editor comments; therefore, this paper should be accepted after the authors address the following issues:

Note – line and figure numbering refers to the track changes version of the paper. There is a problem with the figure numbering in this version as the first figure given is Figure 2.

- Page 1, Line 3 – In the abstract & elsewhere in the paper. The authors seem to think the main evidence for boundary layer bromine in the polar regions is from satellites. This is not the case. The main evidence for boundary layer bromine is from in-situ and ground based remote sensing data. In addition, aircraft data in the troposphere provides direct evidence of the presence of bromine (e.g. during POLARCAT, ARCTAS). Then, satellites have been used the provide the spatial scale of such enhancements, but are relatively insensitive to boundary layer enhancements of bromine. The authors should clarify their discussion of measurements to more accurately reflect the knowledge of bromine enhancements and why they use satellite data to validate their model. I am not asking the authors to use other data in the present study, but to recognize that other data exists and should be used in a 2nd step to evaluate and further improve the model.

- Page 1, Line 19 – bromine explosion events “may” play an important role in mercury deposition. It is not 100% clear this is the case, so insert the word may here. Additional up to date references are needed for this sentence.

Page 2, Line 3 – Custard et al is not a review paper.

Page 2, Lines 17-25 – This paragraph shows the authors have not thought about the difference between the stratosphere and knowledge of chemistry on ice surfaces at temperatures relevant to conditions in the lower troposphere. Specifically:
- Ice above -40 C has a liquid like layer, which does not behave as a gas-solid reactive surface.
- Multi-year ice has not been 100% discarded as a source of bromine and/or a surface on which bromine can be recycled once activated
- It is not true that acidity is not important on ice surfaces. The study used as an example here is for HOBr uptake onto frozen NaBr/NaCl solutions. However, other studies for other surface reactions have shown a dependence on the pH of the solution before freezing (e.g. Oldridge and Abbatt, JCP A, 2011, DOI: 10.1021/jp200074u). In addition, this reference should be included at the end of line 25.
- The sentence on lines 23-25 has no clear meaning.

Page 2, Lines 29-30 – A more accurate and clear sentence is needed here.

Page 3, Line 5 – annual cycle “in” both hemispheres. Fix on -> in

Page 3, line 21 – Should cite Toyota’s paper here, since this is where the mechanism came from

Page 5 – Note that in the track changes version, the first figure is Figure 2. This should be fixed in the final version.

Page 5, Line 21 – Standard PSC chemistry is likely not sufficient for aerosols in the troposphere. This does not need to be fixed for this study, but it should be noted and mentioned as an area to work on later during the future work/conclusions/perspectives.

Page 6, Lines 26-27 – Please spell out units of the deposition velocity so there is no confusion

Page 6, Line 32 – This is one of the areas where my first comment is important, see above.

Section 3.1 – the writing/figures in this section need some work. Here are some specific suggestions:
- Move Figure 1 from the response to reviewers into the paper, this is additional info that can be discussed in relationship to the ozone time series presented.
- I find the authors are discussing the figures in the supplement more than the figures in the paper, the authors should consider moving the more detailed supplement figures with BrO VCD from EMAC and GOME into the paper so the discussion is clearer. Both the VCD maps and the anomalies (shown now) should be in the paper.
- Figure 4 (anomalies of VCD for BrO – the months should be labeled on both the right and left panels.

Conclusions – a comparison/discussion of results from other bromine activation mechanisms is needed. Specifically, a discussion of mechanism from X. Yang and its prior evaluation compared to GOME-2 is needed (e.g. Theys et al., ACP, 2011, DOI: 10.5194/acp-11-1791-2011 and prior work). Where are the two different mechanisms working best, where are they failing? Is it necessary to use both mechanisms in a future study to evaluate them further?

General comment – the authors should re-edit the paper for clarity as some of the writing is still quite unclear as to the meaning of the sentences.

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ED: Reconsider after major revisions (12 Jan 2018) by Slimane Bekki

AR by Stefanie Falk on behalf of the Authors (23 Feb 2018) Author's response Manuscript

ED: Publish as is (06 Mar 2018) by Slimane Bekki

AR by Stefanie Falk on behalf of the Authors (06 Mar 2018)

Short summary

Ozone depletion events (ODEs) in the polar boundary layer are observed frequently in spring. ODEs serve as a source of tropospheric BrO at high latitudes. A treatment of bromine release and recycling on sea-ice- and snow-covered surfaces is implemented in global chemistry–climate model EMAC based on a scheme of Toyota et al. (2011). Many aspects of bromine enhancement and associated ODEs are reproduced in both polar regions. Further bromine release mechanisms can now be tested in a global model.