Formation of highly oxygenated organic molecules  from the oxidation of limonene by OH radical:  significant contribution of H-abstraction pathway

Luo, Hao; Vereecken, Luc; Shen, Hongru; Kang, Sungah; Pullinen, Iida; Hallquist, Mattias; Fuchs, Hendrik; Wahner, Andreas; Kiendler-Scharr, Astrid; Mentel, Thomas F.; Zhao, Defeng

doi:https://doi.org/10.5194/acp-23-7297-2023

Articles | Volume 23, issue 13

https://doi.org/10.5194/acp-23-7297-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-23-7297-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 23, issue 13

Research article

|

04 Jul 2023

Research article |

| 04 Jul 2023

Formation of highly oxygenated organic molecules from the oxidation of limonene by OH radical: significant contribution of H-abstraction pathway

Hao Luo, Luc Vereecken, Hongru Shen, Sungah Kang, Iida Pullinen, Mattias Hallquist, Hendrik Fuchs, Andreas Wahner, Astrid Kiendler-Scharr, Thomas F. Mentel, and Defeng Zhao

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Final revised paper (published on 04 Jul 2023)
Supplement to the final revised paper
Preprint (discussion started on 09 Dec 2022)
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Interactive discussion

Status: closed

RC1:
'Comment on acp-2022-803', Anonymous Referee #1, 05 Jan 2023

The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-803/acp-2022-803-RC1-supplement.pdf

Citation: https://doi.org/10.5194/acp-2022-803-RC1
- AC1: 'Reply on RC1', Hao Luo, 04 Apr 2023
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-803/acp-2022-803-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2022-803-AC1
RC2:
'Comment on acp-2022-803', Anonymous Referee #2, 17 Jan 2023

The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-803/acp-2022-803-RC2-supplement.pdf

Citation: https://doi.org/10.5194/acp-2022-803-RC2
- AC2: 'Reply on RC2', Hao Luo, 04 Apr 2023
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-803/acp-2022-803-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2022-803-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Hao Luo on behalf of the Authors (04 Apr 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (18 Apr 2023) by Nga Lee Ng

RR by Anonymous Referee #1 (01 May 2023)

RR by Anonymous Referee #2 (03 May 2023)

Suggestions for revision or reasons for rejection

Revision comment:
In the revision, the authors have addressed some of my comments and improved the manuscript quality overall. However, there are a few remaining issues that were insufficiently explained or discussed, as detailed below.

Initial comment #1:
The Hyttinen et al. (2017) study was to explain why less oxidized HOMs are not well detected with NO3- ionization. Thus, it is inappropriate to use this study to debate whether underestimation of HOM yields is possible. HOMs with high oxygen numbers from both alpha-pinene ozonolysis and alpha-pinene + OH oxidation have more than two hydrogen bond donor functional groups. Though, the sensitivities are dramatically different.
The author further argued that the underestimation of HOMs from alpha-pinene + OH was mainly attributed to the steric hinderance in forming HOM-nitrate cluster for HOM with bicyclic structures and thus not common for all HOMs. First of all, is there a reference study for this point? Why is there a steric hinderance for nitrate ionization, but not acetate ionization? More importantly, the authors stated that bicyclic structures are not common for all HOMs. But in Schemes 1 and 2 in this manuscript, I see a lot of bicyclic structures.

Initial comment #2:
With the amended chemical reactions, it should be realized that the yields of different functional groups (ROH, R=O, and ROOH) are highly structure dependent. Carbonyl yield + alcohol yield does not necessarily equal to 1; the values of alpha and beta largely vary with structure; alkoxy radical fate also largely affects the yields. My whole point is, with such complexity, deriving these equations (Eq. 2-8) is not very meaningful.

Initial comment #4:
Part of the response is confusing. I thought that the authors suggested that the HOMs from the OH abstraction channel is through RO isomerization, not RO2. Then, “Y1 is the fraction of primary RO2 undergoing autoxidation to form highly oxygenated C10H15Ox” means that Y1 is nearly zero? Considering the additional step to form RO from RO2+RO2, Eq, R1 is wrong. What are the ranges of kuni_1, kuni_2, and k[NO] anyway?
“From this, we infer that the average reactive rate of C10H17Ox• at high NO is higher than that at low NO, which finally result in the increases of C10H17Ox• consumption. This inference is supported by the higher relative contribution of C10H17NOx at high NO (36.3%) than at low NO (16.1%) in Fig. 2.”
Wouldn’t this statement work the same way for C10H15Ox?

Initial comment #5:
Thanks for the analysis regarding secondary chemistry. It appears that secondary chemistry has increased significantly after ~ 5 min. I wonder if the same analysis is performed comparing first 5-min vs. 15-min, what contributions would be for the OH-abstraction chemistry in limonene+OH oxidation. With the 15-min analysis, the authors suggest that C10H15Ox-derived HOMs contribute 41-42% of total C10-HOMs. Would this number be lower within the first 5 min?

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ED: Publish subject to minor revisions (review by editor) (04 May 2023) by Ivan Kourtchev

AR by Hao Luo on behalf of the Authors (23 May 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (01 Jun 2023) by Ivan Kourtchev

AR by Hao Luo on behalf of the Authors (03 Jun 2023) Manuscript

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Short summary

Oxidation of limonene, an element emitted by trees and chemical products, by OH, a daytime oxidant, forms many highly oxygenated organic molecules (HOMs), including C_10-20 compounds. HOMs play an important role in new particle formation and growth. HOM formation can be explained by the chemistry of peroxy radicals. We found that a minor branching ratio initial pathway plays an unexpected, significant role. Considering this pathway enables accurate simulations of HOMs and other concentrations.