Observations and source investigations of the boundary layer bromine monoxide (BrO) in the Ny-Ålesund Arctic

Luo, Yuhan; Si, Fuqi; Zhou, Haijin; Dou, Ke; Liu, Yi; Liu, Wenqing

doi:https://doi.org/10.5194/acp-18-9789-2018

Articles | Volume 18, issue 13

https://doi.org/10.5194/acp-18-9789-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-18-9789-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 13

Research article

|

11 Jul 2018

Research article |

| 11 Jul 2018

Observations and source investigations of the boundary layer bromine monoxide (BrO) in the Ny-Ålesund Arctic

Yuhan Luo, Fuqi Si, Haijin Zhou, Ke Dou, Yi Liu, and Wenqing Liu

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Final revised paper (published on 11 Jul 2018)
Supplement to the final revised paper
Preprint (discussion started on 23 Aug 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'referee comment', Anonymous Referee #1, 08 Sep 2017
- AC1: 'Response to Anonymous Referee #1', Yuhan Luo, 30 Nov 2017
RC2: 'Referee comment', Anonymous Referee #2, 20 Sep 2017
- AC2: 'Response to Anonymous Referee #2', Yuhan Luo, 30 Nov 2017

Peer-review completion

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

AR by Yuhan Luo on behalf of the Authors (30 Nov 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Dec 2017) by Anna Jones

RR by Anonymous Referee #1 (21 Dec 2017)

Suggestions for revision or reasons for rejection

The paper is much improved, and all my major points were addressed.

However, for two of the major points still some corrections are suggested, see details below.

After these points are addressed, I recommend this paper for publication.

1) Previous major point B:

I still think the possibility of long range transport can not be completely ruled out (but I agree with the authors that it very probably plays no important role for the observed event).

I suggest to change the logic of the discussion about the role of long range transport. In my view the following points are important:

a) In 2015 Spitsbergen is close to the sea ice edge; only in the South of Spitsbergen the sea is free of ice. This means that the sensitivity of satellite observations for the detection of enhanced BrO is high north of Spitsbergen.
b) In the GOME BrO maps enhanced BrO VCDs are observed north and east of Spitsbergen during the period of interest and the days before. However, directly north of Spitsbergen always an area with low BrO VCDs is observed from satellite.
c) Trajectory calculations show that transport from the north takes place. However, it is not very probable that the enhanced BrO over the Kings bay is caused by this long range transport because of the rather low BrO VCDs directly north of Spitsbergen. Also such long range transport would probably have led to a longer period of enhanced BrO.
d) Trajectory calculations show that transport from the east coast of Greenland is not probable. So transport from these areas of enhanced BrO VCDs can very porbably be ruled out.
e) In summary, long range transport as an explanation for the enhanced BrO at Spitsbergen can not be completely ruled out. But given the temporal coincidence of the enhamced BrO and the occurrence of the sea ice at Spitsbergen, it can be concluded that the local production of BrO is the most probable explanation.

In addition I have two suggestions:
-please add trajectory calculations also for 2 days before and 2 days after the event. In this way long range transport patterns could be compared with those on the day of the event.
-In the text you write: ‘BrO VCD maps from from GOMEGOME -2 measurement from 20 April to 13 May are shown in Fig. 10.’
But in Fig. 10 measurements start only on April 24. Please make the text and Fig. consistent.

2) Previous major point E:
In Fig. 5 you show DAMFs in the left (top) figure, but SCDs in the right (bottom) figure.
Please make both figures consistent. My suggestion would be to simply subtract the 90° values from the low elevation values in the right (bottom) figure (then the 90° values of the simulated and measured data should both be zero).
You might also use the same x-axes for both figures.

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RR by Anonymous Referee #2 (09 Jan 2018)

Suggestions for revision or reasons for rejection

The authors put effort into a better interpretation of the MAX-DOAS data concerning the horizontal distribution of BrO. They added the new figure 5 including the results for some radiation transfer calculations and a comparison between observed BrO slant columns as a function of the viewing angle of the instrument and simulated slant columns for different layers of enhanced BRO also as a function of the viewing angle. This corresponds to the additional information requested by both reviewers. Unfortunately, the presentation of these results and the derived conclusions are rather confusing and in my opinion counteract the conclusion of a local ozone depletion event:
The authors present the observed BrO slant columns with at least three different color codes, but refer in the title two only two categories (4 hours before or after midnight). Why is that? Why not using only two colors?
What is the reason for using 4-hr averages, although according to figure 13 the entire depletion happened within less than 6 hours with potentially highly variable Br and BrO concentrations?
With the current figure it is difficult to identify, however, it seems to me that the observations before and after midnight are rather different. Why do the authors then claim that one profile with BrO in the 0-1 km range can explain all observations? Why don’t the authors use the highest temporal resolution possible for the observations, which is probably below 30 min for a full scan of all viewing angles?
Why do the authors only show results for this specific period? It would be interesting to see the results also for low BrO slant columns.
The authors claim that the observations shown in figure 5 are best reproduced by the BrO profile with a homogeneous layer between 0 and 1 km altitude. Why is that? Fig. 5b actually shows only two simulations with slant columns at 2° outside the observed range: BrO in a layer from 0 to 0.5 km and BrO in a layer from 0 to 1 km. The authors do not provide any quantitative information regarding the comparison of the simulations and the results. I find that the best agreement for the period before midnight (blue points) is obtained with the profile with BrO in the layer from 0 to 2 km and for the period after midnight with the profile with BrO in the layer from 0.5 to 1 km. However, this is only based on the visual inspection of the figure.
In my opinion, the comparison does not support the claim of the authors that the observed event corresponds to a local BrO formation caused by processes at the surface since the simulated slant columns for a BrO layer from 0 to 0.5 km are far from all observations at low elevation angles.
In summary, the analysis of the presented simulations and observations are to superficial to support the claim of the authors that (1) the simulation with BrO confined to 0 to 1 km corresponds best to the observations and (2) that the BrO increase is a local event. In my opinion, many other scenarios seem equally possible or correspond even better to the presented data.
Regarding the other points raised in my previous report (trajectory analysis, analysis of the mesoscale situation, transport of BrO from the Arctic Ocean, analysis of the boundary layer and impact on the observations, timing of the increase in BrO and decrease of ozone and mercury, sea ice conditions, impact of temperature, significance of calcium carbonate precipitation, measured BrO versus estimated Br) the revised manuscript does not provide a lot of additional information. The authors provide some arguments in the “Author’s Response”, but most of them are not included in the revised manuscript. Overall, the tone of the manuscript is still the same of the original version, since the authors claim throughout the manuscript that the depletion was a local process without providing a balanced analysis of other possibilities.

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RR by Anonymous Referee #3 (12 Feb 2018)

ED: Reconsider after major revisions (12 Feb 2018) by Anna Jones

AR by Yuhan Luo on behalf of the Authors (26 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Apr 2018) by Anna Jones

RR by Anonymous Referee #3 (17 Apr 2018)

ED: Reconsider after major revisions (17 Apr 2018) by Anna Jones

AR by Yuhan Luo on behalf of the Authors (23 May 2018) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (15 Jun 2018) by Anna Jones

AR by Yuhan Luo on behalf of the Authors (19 Jun 2018) Author's response Manuscript

ED: Publish as is (26 Jun 2018) by Anna Jones

AR by Yuhan Luo on behalf of the Authors (29 Jun 2018)

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Short summary

During polar spring, the presence of reactive bromine in the polar boundary layer is considered to be the main cause of ozone depletion and mercury deposition. In this study, a typical process of enhanced bromine, which distributed at 0–1 km above the sea surface in the Ny-Alesund boundary layer in late April 2015, was observed by applying a ground-based MAX-DOAS technique. Major contributions to this bromine enhancement are discussed in detail based on air mass history and sea ice distributions.