Assessing London CO<sub>2</sub>, CH<sub>4</sub> and CO emissions using aircraft measurements and dispersion modelling

Pitt, Joseph R.; Allen, Grant; Bauguitte, Stéphane J.-B.; Gallagher, Martin W.; Lee, James D.; Drysdale, Will; Nelson, Beth; Manning, Alistair J.; Palmer, Paul I.

doi:https://doi.org/10.5194/acp-19-8931-2019

Articles | Volume 19, issue 13

https://doi.org/10.5194/acp-19-8931-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Greenhouse gAs Uk and Global Emissions (GAUGE) project (ACP/AMT...

https://doi.org/10.5194/acp-19-8931-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 13

Research article

|

12 Jul 2019

Research article |

| 12 Jul 2019

Assessing London CO₂, CH₄ and CO emissions using aircraft measurements and dispersion modelling

Joseph R. Pitt, Grant Allen, Stéphane J.-B. Bauguitte, Martin W. Gallagher, James D. Lee, Will Drysdale, Beth Nelson, Alistair J. Manning, and Paul I. Palmer

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Final revised paper (published on 12 Jul 2019)
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Preprint (discussion started on 15 Oct 2018)
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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: 'Review of Pitt et al', Jocelyn Turnbull, 18 Nov 2018
RC2: 'Review of the manuscript "Assessing London CO2, CH4 and CO emissions using aircraft measurements and dispersion modelling"', Anonymous Referee #2, 27 Nov 2018
AC1: 'Author response to referees', Joseph Pitt, 22 Feb 2019

Peer-review completion

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

AR by Joseph Pitt on behalf of the Authors (22 Feb 2019)

ED: Referee Nomination & Report Request started (26 Feb 2019) by Dominik Brunner

RR by Anonymous Referee #2 (29 Mar 2019)

Suggestions for revision or reasons for rejection

With the major revision of the discussions, the manuscript « Assessing London CO2, CH4 and CO emissions using aircraft measurements and dispersion modelling » by Pitt et al. is now much more cautious and balanced when assessing the results from their estimate of the CO2, CH4 and CO emissions from the Greater London area.

I am fully satisfied with the answers to my comments on its first version. The transcription of these answers in the manuscript is not always as convincing: in particular, I think that the abstract could be more significantly updated in line with the new major discussions. However, all the issues are now discussed somewhere and the authors made a clear point about the lack of confidence on the CO2 estimate.

My concern is now that the additions to the text often seem to have been written quite quickly. As a result, the paper has lost a bit of its quality and its structure has been a bit weakened. I recommend a new in depth proofreading to the authors and maybe a bit of re-ordering. Here is a list of minor comments, most of which relate to this:

- Some of the references to other sections are a bit cycling and there are now redundancies, because the discussions have been split and spread among several sections rather than addressed in depth at a relevant location. In particular:
-> regarding the influence of fluxes upwind and downwind the Greater London area: p13 l21 in Sect. 3.2.1 refers to Sect. 3.3 and p14 l9 in Sect. 3.3 refers to Sect 3.2.1 and both actually discuss the topic in the same way; this topic is also discussed in Sect 3.1.1 in which p8 l2 refers to Sect. 3.3. and in Sect. 3.1.2 (« It is worth stating again ») in which p10l18 refers to 3.1.1. Finally, the end of the introduction (p3 l26-28) surprisingly gives a first summary of the results and already starts to discuss this topic.
-> the strategy for measuring the background is discussed in details in Sect. 3.2.1 but not in Sect. 3.1.1 which just states « given the sampling strategy employed » on p7 l29-30
-> the topic of the influence of natural fluxes has been disconnected from that of the upwind and downwind fluxes (see Sect. 1 and Sect. 3.1.2) but they are strongly connected
-> regarding the temporal representativity of the estimates: p7 l4 in Sect. 3 refers to Sect. 3.1.2 but p7 l1-4 already give the main details of the discussion in Sect. 3.1.2, and Sect. 3.1.2 even says on p10 l27 « it is important to remember ». p11l3 seems to start the discussion once again, ignoring the beginning of the previous paragraph (these two parts should be merged).
-> discussions on p8 l17-28 and on p9l29 to p10l9 may work better merged together

- the comparison to the atmospheric inversion should be slightly revised:
-> p3 l10: « over constraining such that the results only reflect the choice of prior emissions »: if the atmospheric observations over constrain the problem, the weight of the prior should be low, did the authors mean « under constraining » ?
-> p3 l11-12: I am not sure to understand what it means, I think that it depends on the emission target in terms of spatial and temporal scales (and see what is said on p3 l8-9)
=> the lines p3 l9-12 are quite confusing and may need to be more practical (with practical considerations regarding the temporal and spatial representativity of the aircraft data ?)
-> p3 l17: « using a cost function » is a too vague and does not really reflect the difference between the two methods from my point of view (see the comment on this topic in my first review)
-> p3 l20-21: actually the new method does not « adjust » the budget of emissions (as would do a Bayesian approach which gives some statistical weight to the prior information on the targeted emission budget), it derives a new one that is independent of the « prior » budget
=> the lines p3 l17-21 could be improved for both clarity and simplification of the concepts

- p10 lines 29 to 31: the new « With this caveat » at the beginning, the « are consistent » and then the « For CH4 however » do not really fit well all together, or at least it now confuses me and it requires some thinking.

- p11 l9-15 this is confusing, because it addresses 3,4 general topics together in few lines; some of these topics could rather be discussed at the end of this section or in the last sections of the paper (they are not related to CH4 only)

- p11 l23: I think it’s more about the diff between the budget of NPP in the footprint of the measurements used to compute the London emissions (both outside and inside London) vs that in the footprint of the background concentrations than about the diff between the NPP in London and outside London

-p14l30 to p15 l7: this paragraph should be improved, its lack of structure and clarity makes it difficult to understand

- some examples of sentences that could be revised and better combined to sentences before and after: p2 l16-17, p2 l33 to p3 l2 (going around in circle), p6 l7 to 9 (going around in circle, and the grid is defined in the next sentence), p11 l9 (unclear), p11 l12 (wind bias) vs l13 (random error in dispersion modelling), p14l21-23 (« in that study … in that study »)

- the comparison between the modeled and measured wind directions is discussed in the answer to the reviews, but not in the text while I feel that it is an interesting analysis. The bias at the measurement locations may not reflect that on the average wind direction between London and this transect, but it is important to show that the author did not miss an easy explanation for the mismatch between the main patterns of the modeled and measured plumes or backgrounds.

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ED: Publish subject to minor revisions (review by editor) (09 Apr 2019) by Dominik Brunner

AR by Joseph Pitt on behalf of the Authors (03 May 2019) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (22 May 2019) by Dominik Brunner

AR by Joseph Pitt on behalf of the Authors (31 May 2019) Author's response Manuscript

ED: Publish as is (06 Jun 2019) by Dominik Brunner

AR by Joseph Pitt on behalf of the Authors (20 Jun 2019) Manuscript

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Short summary

This paper presents a new method to assess inventory estimates of greenhouse gas and air pollutant emissions for large cities and their surrounding regions. A case study using data sampled by a research aircraft around London was used to test the method. We found that the UK national inventory agrees with our observations for CO but needed lower emissions for CH₄ to agree with the measured data. Repeated studies could help determine how these emissions vary on different timescales.