Observations of speciated isoprene nitrates in Beijing: implications for isoprene chemistry

Reeves, Claire E.; Mills, Graham P.; Whalley, Lisa K.; Acton, W. Joe F.; Bloss, William J.; Crilley, Leigh R.; Grimmond, Sue; Heard, Dwayne E.; Hewitt, C. Nicholas; Hopkins, James R.; Kotthaus, Simone; Kramer, Louisa J.; Jones, Roderic L.; Lee, James D.; Liu, Yanhui; Ouyang, Bin; Slater, Eloise; Squires, Freya; Wang, Xinming; Woodward-Massey, Robert; Ye, Chunxiang

doi:https://doi.org/10.5194/acp-21-6315-2021

Articles | Volume 21, issue 8

https://doi.org/10.5194/acp-21-6315-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

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https://doi.org/10.5194/acp-21-6315-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 8

Research article

|

27 Apr 2021

Research article |

| 27 Apr 2021

Observations of speciated isoprene nitrates in Beijing: implications for isoprene chemistry

Claire E. Reeves, Graham P. Mills, Lisa K. Whalley, W. Joe F. Acton, William J. Bloss, Leigh R. Crilley, Sue Grimmond, Dwayne E. Heard, C. Nicholas Hewitt, James R. Hopkins, Simone Kotthaus, Louisa J. Kramer, Roderic L. Jones, James D. Lee, Yanhui Liu, Bin Ouyang, Eloise Slater, Freya Squires, Xinming Wang, Robert Woodward-Massey, and Chunxiang Ye

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Interactive discussion

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

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RC1: 'Isoprene nitrates', Anonymous Referee #1, 09 Feb 2020
RC2: 'Reeves et al', Anonymous Referee #3, 18 Feb 2020
AC1: 'Author response to both reviewers', Claire Reeves, 20 Aug 2020

Peer-review completion

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

AR by Claire Reeves on behalf of the Authors (20 Aug 2020) Manuscript

ED: Referee Nomination & Report Request started (26 Aug 2020) by Frank Keutsch

RR by Anonymous Referee #3 (07 Sep 2020)

Suggestions for revision or reasons for rejection

The paper by Reeves et al. has been significantly improved. The authors have carefully addressed the main issues raised, in my judgement. I feel that the revised paper is a significant contribution to the literature, given the speciated organic nitrate measurements reported here, from isoprene chemistry. The measurements made were difficult, and, with the uncertainties added in the revision, represent useful ambient data.
The paper could be further improved, if there is one more round of edits by again paying less attention to the tedious details (e.g. telling the reader about all the information that is in W2018) and focusing on what is new. In particular, the Conclusions just repeat what is said in the paper, implying that it wasn’t said well enough in the paper. The Conclusions section is an opportunity to paint the big picture as to – what did we learn that is new? A list of the points made in the paper is relatively dull. It would be better to focus on what new understanding was obtained, and at least equally importantly, what needs to be done next (which is there to some extent). Are there suggestions for improved measurements? Better time resolution? Are there laboratory studies that need to be done? What could be done to better understand the fate of nitrooxy-peroxy radicals, etc. I note that with all those standards, it would be trivial to measure all the hydrolysis rates, and information about hydrolysis lifetimes vs aerosol pH and structure are badly needed. Minor edits I would recommend are listed below, in the order they arose in the paper.

1. Line 123 – We used a chemical…
2. Section 4.1 is not needed, it can be incorporated into the results and discussion, as needed.
3. Line 244 – during the Southern Oxidant…
4. Line 261 – why would that be? Please speculate. Is O3 highest in the high NO2/NO condition, and is OH highest at that time? Perhaps you can examine the product [OH][isoprene]xGamma.
5. Line 402 – are you assuming that all species are mixing with clean air? This is an assumption that cannot be justified for all species equivalently. Some longer-lived species such as propanone nitrate will likely have significant concentrations in the residual layer, and mix down as the BL height grows, leading to overestimation of the dilution in such a case, if you are treating all species the same. This should be discussed wherever you discuss the mixing issue (e.g. line 579, 592).
6. Lines 424 and 425 – this implies that for some days, model and data compare better? If so, say so.
7. Lines 426 and 427 – could there be greater evening production or slower loss?
8. Line 432 – than observed…
9. Line 434 – delete comma after that
10. Line 485- this assumes that transport to the surface is not the rate limiting step for deposition of “sticky” species. If you have reason to believe that, say why.
11. Line 525 (paragraph) – I think it would help the discussion to plot the average measured [NO3][isoprene] in Figure 8.
12. Line 624 – specify the ratio being discussed.
13. Line 638 – comma after 7
14. Line 665 – “Our interpretation is limited by the uncertainties in our measurements” – how so?
15. Figure 3 – The two colors in panel c are hard to distinguish. Could you plot radiation on those plots? It would help the reader with the discussion of daytime v. nighttime sources of propanone nitrate.
16. Figure 4 – I think you need legends in the figure – the colors won’t work well in the published version.
17. Figure 6 – use a color other than yellow?
18. Figure 7 – Why not add a line to panel F that represents the best fit to the data in panel E, for ease of comparison of measured and modelled data (esp. since the scales are different)?
19. S1.1 – state which values for the branching ratio you used for each ISOPOO.
20. S1.2 – first line – it should be nitrooxy, I think.
21. S1.3.1 line 6 and line 13 – you should mention production of the organic hydroperoxides when you mention HO2 as a reactant.
22. In this section you refer to “reaction rates” throughout, when it should say rate constants.

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RR by Anonymous Referee #1 (24 Sep 2020)

Suggestions for revision or reasons for rejection

This paper remains a rambling unfocussed document. As I said in my previous review it lacks the organization that would let any but the most determined reader identify what, if anything has been learned. I recommend it be rejected. It started too far from acceptable to have had a proper open review. I don’t see how it could become acceptable in one or two more revisions.

I recommend the paper create a new figure or figures with the specific set of rate constants (or ratios of rate constants) the paper is testing. That the figure should guide the reader to thinking about what is already known and what is new in this paper.

Some other specific comments follow. I have not taken the time to be complete in my suggestions. There are just too many places where this paper is in need of editing and focus.

1) The abstract is 4 paragraphs. The last one is inappropriate in an abstract. One in the middle includes the phrase, “although the correlation is weak due to their being only a few data points.” That paragraph should be removed. It sets the tome for the rest of the paper as a rambling collection of facts and not an attempt to distill what has been learned into some key conclusions.

2) All of the discussion in the paper that refers to their being too few data points to draw a strong conclusion should be deleted.

3) The introduction reads like it was written years ago. I recommend it start with W2018 and articulate key current uncertainties. Going back to papers that quote 4%IN yields that no one following the literature believes any more is not helpful to the reader.

4) The paper would be better if it started with the model predictions and then articulated which aspects of the model predictions the observations are able to test.

5) If the winter data is unusable, remove discussion of that from the paper.

6) Section 4.2.1 mixes up a description of what was measured with a comparison to models and other locations. The paper would be clearer if these were completely separated.

7) Line 243. The opposite of not surprising, is expected. I recommend the authors describe their results as what was expected.

8) Line 251, starting the discussion with non-detection of chemicals (and reporting that non-detection is expected) is not a good beginning. The discussion should start with observations that can teach us something.

9) Lines 260-270 there are so many differences in chemical concentrations between these observations and those of SOAS that a direct comparison is not meaningful.

10) Line 311-313. In what way do these comments about OH advance the theme of this paper.

11) Line 315-325 I recommend moving all of the comparison to SOAS to a single location in the paper.

12) Lines 429-435 and similar paragraphs should be deleted.

13) Line 490-496 lacks a clear focus

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ED: Reconsider after major revisions (24 Sep 2020) by Frank Keutsch

AR by Claire Reeves on behalf of the Authors (08 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (05 Mar 2021) by Frank Keutsch

AR by Claire Reeves on behalf of the Authors (10 Mar 2021) Author's response Manuscript

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Short summary

The impact of isoprene on atmospheric chemistry is dependent on how its oxidation products interact with other pollutants, specifically nitrogen oxides. Such interactions can lead to isoprene nitrates. We made measurements of the concentrations of individual isoprene nitrate isomers in Beijing and used a model to test current understanding of their chemistry. We highlight areas of uncertainty in understanding, in particular the chemistry following oxidation of isoprene by the nitrate radical.