Articles | Volume 25, issue 18
https://doi.org/10.5194/acp-25-11247-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.Formation of chlorinated organic compounds from Cl atom-initiated reactions of aromatics and their detection in suburban Shanghai
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- Final revised paper (published on 25 Sep 2025)
- Supplement to the final revised paper
- Preprint (discussion started on 28 Feb 2025)
- Supplement to the preprint
Interactive discussion
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
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RC1: 'Comment on egusphere-2025-607', Anonymous Referee #1, 31 Mar 2025
- AC2: 'Reply on RC1', Lei Yao, 21 Jun 2025
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RC2: 'Comment on egusphere-2025-607', Anonymous Referee #2, 30 Apr 2025
- AC1: 'Reply on RC2', Lei Yao, 21 Jun 2025
Peer review completion
AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Lei Yao on behalf of the Authors (21 Jun 2025)
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ED: Referee Nomination & Report Request started (27 Jun 2025) by Tao Wang
RR by Anonymous Referee #2 (12 Jul 2025)

RR by Anonymous Referee #1 (13 Jul 2025)

ED: Publish subject to minor revisions (review by editor) (22 Jul 2025) by Tao Wang

AR by Lei Yao on behalf of the Authors (31 Jul 2025)
Author's response
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ED: Publish as is (09 Aug 2025) by Tao Wang
AR by Lei Yao on behalf of the Authors (11 Aug 2025)
Manuscript
The authors Li et al describe a series of laboratory flow tube studies and ambient urban measurements focused on Cl-radical initiated chemistry and resulting product Cl-OOMs. The results of the flow tube studies are potentially interesting and the ambient measurements are novel. However, I have major questions about the chemistry proposed within this work and how it may lead to the observed products. I believe the manuscript will only be suitable for publication with the addition of direct evidence in support of the proposed mechanisms.
My major issue is with the proposed mechanism for Cl addition to the aromatic rings. To my knowledge, this chemistry has not been directly supported through laboratory measurements, and in support of this mechanism the authors cite a lone theoretical paper. While theory is undeniably useful in guiding mechanism development, I am hesitant to accept the Cl addition mechanism at the stated probability (14%) without direct measurements. Does the Cl-aromatic product analogous to the first-generation phenolic product from OH addition form? Are any other first-generation products observed that are analogous to those from established OH chemistry? Formation of smaller molecular fragmentation products should be common, given the high level of RO2-RO2 chemistry (Figure S10) and the expected fragmentation of ensuing RO radicals formed during some RO2-RO2 reactions. The Vocus-PTR should be well-suited to measuring at least some of these molecules. The authors do note indirect evidence for initial Cl addition in the lack of observation of potential second-generation radicals in the family C8H12ClOx (Line 345). However, the authors also note that the detection of intermediate radicals is difficult (Line 285), and on its own this indirect evidence is not sufficiently convincing. I would suggest substantially deeper analysis of the data from the present experiments and ideally further experiments more tailored specifically to detecting first-generation products of the Cl-aromatic reaction and constraining these reaction pathways.
Relatedly, I do not believe the mechanism illustrated in the upper half of scheme 1 describing OOM formation following H-abstraction by Cl is reasonable. H-abstraction is expected to occur on the methyl substituents, and the internal RO2-H migrations described following initial H-abstraction are not supported by prior literature. To my knowledge, internal H-migration of an aromatic H is not expected to be a reasonable pathway. Additionally, though internal H-migration across an aromatic ring hasn't been studied (to my knowledge), a 1,7-migration between primary carbons is predicted to be slow (Vereecken and Noziere, 2020). If this were to occur, the second H-migration to form the radical C8H9O4 would be expected to immediately collapse to form an aldehyde in the closed shell molecule C8H8O3 and an OH radical (Bianchi et al., 2019). This suggests other formation pathways for the observed non-Cl containing radicals and closed-shell products. The simplest explanation would be OH addition chemistry, with OH forming from HO2 through H-abstraction at the methyl groups (see, e.g., the already cited Bhattacharyya et al., 2023). These observations call into question the authors' statements on a lack of OH chemistry in NOx-free experiments (line 360-361), with further implications for the potential mechanisms by which Cl-OOMs may form.
Minor comments
Line 365: more reduced molecules could also form through multi-generation chemistry when H-abstraction occurs from a carbon with an OH or OOH substituent, leading to the formation of a carbonyl.
Lin 443, Figure 4: I would like to see more discussion on some of the higher-concentration compounds, specifically C2O2, C6O3/4, C8O5, and C9O1. Even if these compounds were not observed in the flow tube studies, the observation is both novel and useful and can provide further insight on ambient Cl chemistry and/or primary Cl-OVOC/Cl-OOM emissions.
Line 459: fix citation.
Line 474: label concluding section
References not already within text