Bromine atom production and chain propagation during springtime Arctic ozone depletion events in Barrow, Alaska

Thompson, Chelsea R.; Shepson, Paul B.; Liao, Jin; Huey, L. Greg; Cantrell, Chris; Flocke, Frank; Orlando, John

doi:https://doi.org/10.5194/acp-17-3401-2017

Articles | Volume 17, issue 5

https://doi.org/10.5194/acp-17-3401-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-17-3401-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 5

Research article

|

09 Mar 2017

Research article |

| 09 Mar 2017

Bromine atom production and chain propagation during springtime Arctic ozone depletion events in Barrow, Alaska

Chelsea R. Thompson, Paul B. Shepson, Jin Liao, L. Greg Huey, Chris Cantrell, Frank Flocke, and John Orlando

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Final revised paper (published on 09 Mar 2017)
Preprint (discussion started on 18 Jan 2016)

Interactive discussion

Status: closed

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

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RC1: 'Thompson et al. review', Anonymous Referee #1, 09 Jul 2016
RC2: '"Bromine atom production and chain propagation during springtime Arctic ozone depletion events in Barrow, Alaska" review', Anonymous Referee #2, 23 Jul 2016
AC1: 'Author Response', Chelsea Thompson, 15 Oct 2016

Peer-review completion

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

AR by Chelsea Thompson on behalf of the Authors (01 Nov 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Jan 2017) by Paul Monks

RR by Anonymous Referee #1 (09 Feb 2017)

Suggestions for revision or reasons for rejection

1. I feel that the wording rule with regard to what the authors call the “surface deposition umbrella” (referring to the collective contributions from the surface snowpack and the aerosol particles, Line 310) should be more strictly followed throughout the manuscript. For example, the authors should say “surface emissions/release” or something similar instead of “surface emissions” on Line 710, 736, 737, 752-753 and 762.

2. On Lines 284-288, the authors should comment that ozone mixing ratios are in fact adjusted in their model to observed ones. A similar problem exists for HOBr on Line 290, although I understand that HOBr is allowed to evolve freely in the model in some model runs.

3. In the paragraph between Lines 355 and 371, it seems appropriate and informative to refer to the range of the values for the HOBr deposition rate used to fit the simulated mixing ratios of HOBr in Figure 2c.

4. On Lines 376-377, the authors state “our model captures the diurnal cycle of HO2 and the daily fluctuations observed”. But I don’t agree that the daily fluctuations are captured very well. It should be rephrased to something like “the range of daytime mixing ratios is reproduced reasonably well.”

5. On Lines 670-671, the authors state “this is also supported by our results discussed previously that show that only 19% of HOBr is lost to photolysis”. I think this sentence should be simply removed. I believe BrO + HO2 leads to the ozone loss anyway whether HOBr is photolyzed or is deposited/taken up by the surfaces.

6. If I understand the message of the authors correctly, it is appropriate to state more clearly, in Section 3.4 as well as in Abstract and/or Conclusions, that the reproduction of Br2 via “reactive” deposition/uptake of HOBr and BrONO2 onto the surfaces followed by their gas-phase production via BrO + HO2 and BrO + NO2, respectively, plays a significant role in the catalytic ozone loss involving Br-atoms in the Arctic boundary layer.

[Technical suggestions]

L31: However -> On the other hand

L109-110: It is important to note that the chain length … -> It is important to note that, in our definition, the chain length …

L117-118: Equations I and II -> Equations 1 and 2

L137-142: It is evident that the reactions occurring on snow and aerosol surfaces are likely the initial source of halogen species to the polar boundary layer and that heterogeneous bromine recycling on these surfaces must be considered for HOBr and HBr (as well as BrNO2 and BrONO2 in higher NOx environments). However, the relative importance of gas-phase recycling of bromine atoms is uncertain, even though it is often assumed that the ozone depletion rate can be estimated reasonably well by the catalytic gas-phase radical reaction rates.

L144-145: …, which are predominantly produced directly from surface emissions and/or aerosol release

L167: …; however, …

L199: mole ratios -> mixing ratios

L217: that -> which

L218: lasting FOR ~3 days

L236: as a scaling factor -> as a basis of the scaling

L261: Delete “to state”.

L278: mole ratios -> mixing ratios

L305: …; however, …

L306: deposition -> uptake

L307-310: Given the highly simplified nature of the surface deposition/uptake in our model, we do not attempt to differentiate between aerosol uptake and deposition to the snow surface, and …

L316 & 318: Is Br2 “simulated” at all? I thought it mixing ratios were simply adjusted to the observed values.

L327: mole ratios -> mixing ratios

L331: … the instrument using an aircraft inlet.

L343: the majority of the Br2 present at the surface -> a significant fraction of the Br2 present at the snow surface

L378: Delete “also”.

L379: …; however, …

L384: can be can be -> can be

L442-443: Method 1 gives generally higher chain lengths than Method 2

L459: …; however, …

L446 & 552: I wonder if the authors actually meant “15:00 AKST” instead of “18:00 AKST” here.

L469: On 29 March, there is an early morning enhancement

L478: SEE below

L479: SEE below

L500-501: …, it is IMPLICITLY sensitive to them, …

L505: However -> On the other hand

L536: than OFTEN expected

L542: …, AS shown in Figure 4, …

L563-564: contributing TO the chain reactionS

L580: BrO + HOBr -> BrO + HO2

L588: I don’t quite get how “this corroborates the work of Zeng et al. (2006).” I would rather remove this sentence.

L599: 84-91% -> 88-91% (?)

L608: …, the BrO + IO reaction accounts for 4% of the propagation, …

L630: Delete “seem to”.

L660: HO -> HO2

L768: emissions -> release

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ED: Publish subject to technical corrections (09 Feb 2017) by Paul Monks

Short summary

The generally accepted mechanism leading to ozone depletion events in the Arctic assumes efficient gas-phase recycling of bromine atoms, such that the rate of ozone depletion has often been estimated as the rate that Br atoms regenerate through gas-phase BrO + BrO and BrO + ClO reactions. Using a large suite of data from the OASIS2009 campaign, our modeling results show that the gas-phase regeneration of Br is less efficient than expected and that heterogeneous recycling on surfaces is critical.