Hydrogen peroxide in the marine boundary layer over the South Atlantic during the OOMPH cruise in March 2007

Fischer, H.; Pozzer, A.; Schmitt, T.; Jöckel, P.; Klippel, T.; Taraborrelli, D.; Lelieveld, J.

doi:https://doi.org/10.5194/acp-15-6971-2015

Volume 15, issue 12

Atmos. Chem. Phys., 15, 6971–6980, 2015
https://doi.org/10.5194/acp-15-6971-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

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

Atmos. Chem. Phys., 15, 6971–6980, 2015
https://doi.org/10.5194/acp-15-6971-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Volume 15, issue 12

Research article 29 Jun 2015

Research article | 29 Jun 2015

Hydrogen peroxide in the marine boundary layer over the South Atlantic during the OOMPH cruise in March 2007

H. Fischer et al.

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Final revised paper (published on 29 Jun 2015)
Discussion paper (discussion started on 02 Dec 2014)

Interactive discussion

Status: closed

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

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- Supplement

SC C9793: 'Ozone over the South Atlantic', Hans-Werner Jacobi, 04 Dec 2014
- AC C12751: 'Reply to the comment by HAns-Werner Jacobi', Horst Fischer, 24 Mar 2015
RC C10637: 'Review of Fischer et al.', Anonymous Referee #1, 01 Jan 2015
- AC C12744: 'Reply to anonymous referee #1', Horst Fischer, 24 Mar 2015
RC C11619: 'Review of paper acp-2014-30547: Hydrogen peroxide in the marine boundary layer over the southern Atlantic during the OOMPH cruise in March 2007 by Fischer et al.', Laurens Ganzeveld, 27 Jan 2015
- AC C12748: 'Reply to Laurens Ganzeveld (Referee)', Horst Fischer, 24 Mar 2015

Peer review completion

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

AR by Horst Fischer on behalf of the Authors (20 Apr 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (28 Apr 2015) by Rupert Holzinger

RR by Anonymous Referee #2 (10 May 2015)

Suggestions for revision or reasons for rejection

Dear editor, author, co-authors;
Overall most of my specific comments have been well addressed but there are still two issues that I would like to raise.

1) Regarding the issue on the too large H2O2 dry deposition velocities; this appears to be mainly a unit/conversion issue and where the maximum H2O2 dry deposition velocities are 1.8 cm s-1. The sensitivity analysis that has been done has been based on reducing the maximum wind speed use for the calculation of dry deposition to 5 m s-1 (by the way, I assume that EMAC reproduced quite well the actually observed meteorological conditions during the measurement campaign). I guess that this does not only apply to the H2O2 dry deposition rate but to all dry deposition velocities which implies that also the chemical regime, affecting the H2O2 chemical production might have substantially changed. The maximum VdH2O2 is then 0.6 cm s-1 but it raises the question why the VdH2O2 would be that small when wind speeds in those regions can be large as 10-20 m s-1. Recognizing the fact that calculation of the turbulent transport term is pretty straightforward, it implies that there should be a substantial surface resistance against H2O2 uptake by the oceanic surface layer and wonder what this could be where the solubility cannot be the limiting factor or? Consequently, although the conducted sensitivity analysis suggests that a strongly reduced VdH2O2 results in a much better agreement between the model and the observations, there is no viable explanation why VdH2O2 should be that small. There is an extensive discussion about the dry deposition process in the discussion section but think that this “finding” on requiring a substantially smaller VdH2O2 to explain discrepancies between model and observations is conflicting with common-sense estimates of VdH2O2 for the conditions encountered in the region of interest. This really requires an effort to measure in-situ H2O2 dry deposition fluxes. This could be further addressed in the discussion.

2) I raised the comment on the potential role of entrainment of FT air masses in explaining both the underestimation of O3 and H2O2. In the response it is then referred to the fact that MHP is also affected by entrainment and where a potential enhanced role of FT entrainment would make the comparison worse for MHP which is already largely overstimated. But further reading about some of the potential issues on the MHP measurements and also recognizing the fact that the deposition process for MHP is really poorly constrained by measurements, I am not convinced that MHP is the proper tracer to exclude a potential explanation of the discrepancies associated with the entrainment process. Here it might be more optimal to rely directly on analysis of some of the physical properties that can indicate about the role of entrainment, e.g., moisture.

Some remaining minor comment: In the revised version the following statement has been included also in response to the comments I raised.

“The deposition velocity calculated by the model for O3 does not depend on the wind speed and is about 0.05 cm/s, indicating that the deposition loss is limited by the ocean uptake resistance.”

The O3 dry deposition over the ocean still depends on wind speed (actually as it appears now it depends stronger on it than previously known due to the role of waterside turbulent transport) but its effect is minor. Consequently, I suggest to rephrase to:

“The deposition velocity calculated by the model for O3 hardly depends on the wind speed being small as ~0.05 cm/s, indicating that the deposition loss is limited by the ocean uptake resistance.”

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RR by Anonymous Referee #1 (11 May 2015)

ED: Reconsider after minor revisions (Editor review) (29 May 2015) by Rupert Holzinger

AR by Horst Fischer on behalf of the Authors (03 Jun 2015) Author's response Manuscript

ED: Publish as is (03 Jun 2015) by Rupert Holzinger

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Hydrogen peroxide in the marine boundary layer over the South Atlantic during the OOMPH cruise in March 2007