Revisiting the contribution of land transport and shipping emissions to tropospheric ozone

Mertens, Mariano; Grewe, Volker; Rieger, Vanessa S.; Jöckel, Patrick

doi:https://doi.org/10.5194/acp-18-5567-2018

Articles | Volume 18, issue 8

https://doi.org/10.5194/acp-18-5567-2018

© Author(s) 2018. 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-18-5567-2018

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

Articles | Volume 18, issue 8

Research article

|

24 Apr 2018

Research article |

| 24 Apr 2018

Revisiting the contribution of land transport and shipping emissions to tropospheric ozone

Mariano Mertens, Volker Grewe, Vanessa S. Rieger, and Patrick Jöckel

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Final revised paper (published on 24 Apr 2018)
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Preprint (discussion started on 12 Oct 2017)
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Interactive discussion

Status: closed

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

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RC1: 'response to methods, definitions, and assertions', Anonymous Referee #1, 09 Nov 2017
- AC1: 'Reply to referee#1', Mariano Mertens, 16 Feb 2018
RC2: 'Review: "Revisiting the contribution of land transport and shipping emissions to tropospheric ozone"', Anonymous Referee #2, 19 Dec 2017
- AC2: 'Reply to referee#2', Mariano Mertens, 16 Feb 2018

Peer-review completion

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

AR by Mariano Mertens on behalf of the Authors (16 Feb 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (19 Feb 2018) by Tim Butler

RR by Anonymous Referee #1 (06 Mar 2018)

Suggestions for revision or reasons for rejection

The authors have responded well to the reviewers' comments and recommendations. I recommend two final comments. The first should be quite easy. The second I offer for consideration.

The authors have added a good description of Grewe (2004) to justify NOy,i/NOy ~ NOx,i/NOx, but have not offered any such evidence for NMHC. The authors rightly point out that the MESSy solver diagnosed rates may implicitly account for much. That being said, the authors should acknowledge that the error associated with the NMHC has not been quantified. If it has been quantified, the authors should point the readers to it.

The authors response to NOy/NMHC needs to be enhanced for radiative forcing with respect to shipping. Radiative forcing is particularly sensitive to ozone in the upper troposphere. Grewe (2004) showed that shipping contributed ~1% (Fig 3) in the 300-100hPa range and that the Fa estimate was -1 to 1% (Fig 4). In this case, the difference for shipping in the free troposphere (where RF is sensitive) is on the same order as the contribution itself. The sensitivity of all small contributors (e.g., shipping) can be inferred to be the direct result of unstable systems associated with Lightning NOx (Fa=-10,-20%) and strat intrusions. Given that Grewe (2004) attributes large amounts of ozone to lightning, some ozone production in the free troposphere likely occurs following a lightning injection -- well within a few hours of the emission near the non-steady state period. Near the lightning NOx injection would be consistent with when Grewe (2004) showed highest sensitivity. However, the emissions in Grewe (2004) were continuous in both boxes. By contrast, lightning would be episodically fresh and shipping emissions would be consistently well oxidized by the time they reach the upper troposphere. The contrast between fresh lightning and oxidized shipping provides the exact conditions that this tagging methodology is sensitive to. The authors make a nod to this uncertainty by referencing Grewe (2004), but in this reviewers opinion the authors minimize the relevance. As the Grewe (2004) pointed out, the truth is elusive and the methodological comparison (Fa) does not necessarily identify a flaw in this tagging. However, the conceptual model of lightning in the upper troposphere provides a theoretical framework for questioning the tagged results in the region relevant to RF. I do not think this should stop the manuscript, but I also think the dismissal of the concern based on 10% from Grewe (2004) is overly simplistic.

Specific line edits:

pg 5,26 submodul should be submodule

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RR by Tim Butler (15 Mar 2018)

ED: Publish subject to minor revisions (review by editor) (15 Mar 2018) by Tim Butler

AR by Mariano Mertens on behalf of the Authors (22 Mar 2018) Author's response Manuscript

ED: Publish as is (23 Mar 2018) by Tim Butler

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Short summary

We quantified the contribution of land transport and shipping emissions to tropospheric ozone using a global chemistry–climate model. Our results indicate a contribution to ground-level ozone from land transport emissions of up to 18 % in North America and Southern Europe as well as a contribution from shipping emissions of up to 30 % in the Pacific. Our estimates of the radiative ozone forcing due to land transport and shipping emissions are 92 mW m⁻² and 62 mW m⁻², respectively.