The impact of weather patterns and related transport processes on aviation's contribution to ozone and methane concentrations from NO<sub><i>x</i></sub> emissions

Rosanka, Simon; Frömming, Christine; Grewe, Volker

doi:https://doi.org/10.5194/acp-20-12347-2020

Articles | Volume 20, issue 20

Atmos. Chem. Phys., 20, 12347–12361, 2020

https://doi.org/10.5194/acp-20-12347-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

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

Atmos. Chem. Phys., 20, 12347–12361, 2020

https://doi.org/10.5194/acp-20-12347-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 20

Research article 29 Oct 2020

Research article | 29 Oct 2020

The impact of weather patterns and related transport processes on aviation's contribution to ozone and methane concentrations from NO_x emissions

Simon Rosanka et al.

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Final revised paper (published on 29 Oct 2020)
Preprint (discussion started on 31 Jan 2020)

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Status: closed

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

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RC1: 'Review of Rosanka et al.', William Collins, 26 Feb 2020
- AC1: 'Answer to referee comment by William Collins', Simon Rosanka, 18 Jun 2020
RC2: 'Review of “The impact of weather pattern and related transport processes on aviation’s contribution to ozone and methane concentrations from NOx emissions”', Anonymous Referee #2, 02 Mar 2020
- AC2: 'Answer to anonymous referee #2', Simon Rosanka, 18 Jun 2020

Peer-review completion

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

AR by Simon Rosanka on behalf of the Authors (18 Jun 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (03 Jul 2020) by Jason West

RR by William Collins (17 Jul 2020)

Suggestions for revision or reasons for rejection

This manuscript is substantially improved, but needs minor revisions still.

I think I understand from the author responses that the main theme of the study is that the time of ozone maximum is a useful diagnostic for the overall effects of aircraft NOx. This needs to be clarified in the text, as it is still not obvious. In particular there are still instances where the text refers to an early ozone maximum leading to or causing some effect. These all need to be more explicit that this is a correlation, not a causal link.

The text states that this diagnostic is computationally cheaper than running a full GCM, but doesn’t take this any further in explaining how the diagnostic could be used in practice.

Abstract, last sentence: This study doesn’t (but should) show how the findings can be used to towards a climate impact assessment.

Page 2, line 19: The discussion of the PMO needs to give a bit more detail.

Table 1: The caption should state where these regions are: ie. “in a ridge”, “to the west of a ridge”. PMO needs writing out in full in the caption.

Figure 1: The caption needs to state whether the time evolution of the chemical burdens in the lower plot is only along the parcel trajectories or a global change.

Page 3, line 10: The NOx cycling needs to be explained in a bit more detail. The lifetime of NOx is only around 2 days and is not washed out. Presumably the NOx cycles through NOy reservoirs (HNO3, PAN) and it is the HNO3 that is washed out.

Page 4, line 11: No, the earlier ozone does not cause a higher integrated O3, it is correlated with it.

Page 8, line 25: This wording needs to be more precise. Do these really have a “maximum at the end of the simulation” i.e. day 90? Or is it that they don’t have a maximum at all i.e. they are still increasing by day 90 – which is what you say a couple of sentences later.

Page 8, line 26: How high are these latitudes? Be specific.

Page 10, line 4: It may be better to be explicit “air parcels with an early O3 maximum are those that are transported to lower latitudes”. i.e. the early O3 maximum doesn’t cause the transport.

Page 10, line 6: better “air parcels with a late maximum are those that mostly stay …” i.e. the late maximum doesn’t cause them to stay.

Page 11, line 4: I don’t think (subgrid) deep convection affects the trajectories in your analysis.

Page 11, line10 – page 12, line 1: The thickness doesn’t determine a high pressure system as it is purely temperature. You need to use the geopotential heights to determine the synoptic conditions.

Figure 5, since thickness and temperature show more or less the same thing you don’t need both. I suggest using geopotential height instead for the top plot.

Page 18, line 22: DU refers to burden, not concentration.

Page 20, line 6: Better to say that high O3 maxima are only” found”, rather than “possible” You have shown a correlation, but not a causation.

Page 20, line 18-19: “allows” is too strong. You have shown that they are correlated, but not that one causes the other.

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RR by Anonymous Referee #2 (20 Jul 2020)

Suggestions for revision or reasons for rejection

I thank the authors for the depth of work they have performed in responding to the reviews. The majority of my concerns have been addressed. The new analysis of HOx cycling in particular is a significant improvement over the analysis that was previously present.

However, I do still have one significant concern, which remains from my previous review. The paper’s focus is on the time and magnitude of the maximum in excess ozone due to an aviation NOx emission. In the abstract, introduction, and conclusions, the authors use these metrics as a proxy for climate impact. In the response to the review, they state that the introduction now explains why these metrics are chosen and why they are appropriate. The authors also stated that “[i]dentifying the resulting climate impact is not the objective of this paper”, which is fair. If indeed the manuscript can be modified to very clearly limit the scope to investigating the influence of weather on only the magnitude and timing of the ozone maximum, then my concerns would be fully addressed.

However, the abstract still states the “the controlling factor to identify the climate impact from aviation NOx emissions are transport processes”, which I do not think is supported. The finding that the timing and magnitude of the ozone peak will both change in response to weather patterns is interesting indeed. However I do not think that the paper yet provides sufficient evidence that a larger, earlier peak in the ozone perturbation inevitably means a larger long-term ozone perturbation, and therefore a larger climate impact. In particular I do not agree with the statement on page 4, line 11 that “It becomes obvious that an earlier and larger O3 change leads to a higher integrated O3 and a higher climate impact”. This statement seems to be contradicted by Figure 3, which shows that a delayed ozone maximum (the "late" case) could result in a significant integrated impact, depending on the evolution after the 90 day point. The authors direct the reader to Frömming et al 2020 and Grewe et al 2014 in defense of their point. However, the former was only submitted to ACPD and as such not yet peer-reviewed, and does not (as of the time of this review) appear to be available as a preprint. The latter paper is a model development paper and does not quantify the relationship between the ozone peak and the long-term climate impact. As such I could not verify these claims.

I recommend that the authors either: 1) quantitatively and rigorously demonstrate that the timing and magnitude of the ozone maximum correlates with a more conventional metric of impact, such as integrated ozone perturbation; or 2) remove claims that aviation’s climate impacts are predicted by these metrics. In the latter case I believe that only minor changes would be needed, specifically to moderate some of the impact claims or to make clear the limitations of this approach.

Minor comments

There is a contradiction on page 2. On line 25, it is stated that a larger climate impact occurs at low altitudes, but then on line 31 it is stated that climate impacts are generally larger for emissions at high altitudes.

It also appears that the revisions have introduced a number of new grammatical errors (e.g. the very first line of the introduction: “…climate change has been well established since years and it is well know…”; page 2, line 31 of the marked-up manuscript reads “…by O3 out weights the cooling…”; page 3, line 21 reads “In exact, one emission region is within…”; page 4, line 1 stats “only little O3 is produced”, etc). I recommend that authors make a few iterations to clean these up, and thus maximize the impact of what I believe to be an important paper.

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ED: Publish subject to minor revisions (review by editor) (25 Jul 2020) by Jason West

AR by Simon Rosanka on behalf of the Authors (18 Aug 2020) Author's response Manuscript

ED: Publish as is (20 Aug 2020) by Jason West

Short summary

Aviation-attributed nitrogen oxide (NO_x) emissions lead to an increase in ozone and a depletion of methane. We investigate the impact of weather-related transport processes on these induced composition changes. Subsidence in high-pressure systems leads to earlier ozone maxima due to an enhanced chemical activity. Background NO_x and hydroperoxyl radicals limit the total ozone change during summer and winter, respectively. High water vapour concentrations lead to a high methane depletion.

The impact of weather patterns and related transport processes on aviation's contribution to ozone and methane concentrations from NOx emissions

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The impact of weather patterns and related transport processes on aviation's contribution to ozone and methane concentrations from NO_x emissions