From the journal Environmental Science: Atmospheres Peer review history

01-Sep-2023

Dear Dr Hata:

Manuscript ID: EA-ART-07-2023-000105
TITLE: Urban-scale analysis of the seasonal trend of stabilized-Criegee intermediates and their effect on sulphate formation in the Greater Tokyo Area

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

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Associate Editor, Environmental Science: Atmospheres

************

Reviewer 1

This manuscript describes a chemical transport model of the greater Tokyo area, aimed at assessing the role of carbonyl oxides in the sulfate production in the region. The modeling incorporates the newest understanding about carbonyl oxide chemistry – the implementation is described clearly, and the conclusions are in line with modeling in other regions. The clear analysis of the seasonal variation in removal rates is useful. I have some suggestions (attached) that I believe would bring out the contributions of this study.

Reviewer 2

The manuscript EA-ART-07-2023-000105 written by Yuya Nakamura conducted an urban-scale analysis of the contribution of gas-phase sCIs to sulfate formation. Yes, as introduced by the authors, this study will promote our understanding of the role of sCIs. Especially, one of the conclusions of the comparable contribution of the unimolecular decomposition of sCIs and the reaction between sCIs and water is interesting, because these loss processes have not been considered in previous studies.

However, I have strong opposition to this analysis. Where can we see the evaluation of your modeling? Does this modeling have been well validating and used in this Tokyo domain? If this modeling is perfect, there is no need to introduce such additional reactions of sCIs. What are the difficulties in this modeling and why do the authors introduce sCIs reactions? In the current presentation, this is just a report of a modeling test, and the scientifical significance is less. The readers will not convince of this result without a clear introduction to this study. Therefore, I have judged this manuscript did not meet the four criteria required as a full paper in the journal of Environmental Science: Atmospheres.

Reviewer 3

The authors present a study of the impact of recent advances in understanding of stabilized Criegee intermediate (sCI) chemistry on model production of sulphate aerosol in the Greater Tokyo area using the Community Multiscale Air Quality (CMAQ) model. The chemical mechanism in the model has been updated to include outcomes of recent studies of sCI kinetics, with results indicating that the dominant reactions of sCIs are unimolecular decomposition and reaction with water/water dimers. As a consequence, the impact of sCIs is expected to be low, in contrast to suggestions from previous modelling studies which considered recent developments in understanding of Criegee + SO2 chemistry but, at the time, were not able to fully appreciate the effects of other reactions.

The study will be of interest to the atmospheric science community and is appropriate for publication once the comments below have been addressed.

Major comments:
It would be helpful to indicate the fraction of alkenes oxidised by ozone in the model to demonstrate the wider applicability of the results and to rule out the possibility that the impact of sCI chemistry on sulphate aerosol formation is low because sCI chemistry is not generally significant in this region.
What are the main fates of the C-containing products of sCI chemistry? Is there an impact on secondary organic aerosol?
What is the impact of updates to sCI decomposition kinetics on OH concentrations?

Minor comments on the manuscript are detailed below:
The abstract should mention the model used in the study.
In the abstract, ‘seasonal and timely’ would be better described as ‘seasonal and temporal’.
In the introduction, it should be noted that the production of OH from sCIs is dependent on structure of the sCI. Reaction with NO has been demonstrated to be slow, the comment on reaction with nitrogen oxides would be better described as reaction with NO2. The reactions of sCIs with NO2 listed in the supplementary information show NO3 as a reaction product, but several studies have demonstrated that NO3 is not produced (Lewis et al, 2015 doi: 10.1039/C4CP04750H, Caravan et al., 2017 doi: 10.1039/C7FD00007C).
The regional transport model used in previous studies should be named.
‘GTA area’ to ‘GTA’.
In the methodology section (or elsewhere) it would be helpful to detail why model calculations were performed for 2015 specifically, is 2015 a typical year? Are there measurements of sulphate aerosol in the region for this time period that can be compared with the model results?
When incorporating reaction rate coefficients, were experimental measurements for decomposition considered where available and compared to those suggested by Vereecken et al.? Experimental measurements of rate coefficients for CH2OO + H2O/(H2O)2 are mentioned, but there is no discussion of measurements for decomposition.

Answer to Referee 1:
This manuscript describes a chemical transport model of the greater Tokyo area, aimed at assessing the role of carbonyl oxides in the sulfate production in the region. The modeling incorporates the newest understanding about carbonyl oxide chemistry – the implementation is described clearly, and the conclusions are in line with modeling in other regions. The clear analysis of the seasonal variation in removal rates is useful. I have some suggestions that I believe would bring out the contributions of this study and some questions that I think the authors should address.
The authors are grateful to referee 1 to evaluate our study as useful and to give us informative suggestions. We improved several sentences in accordance with the suggestions carefully. The modified parts are highlighted in yellow.

• the impact of this particular study on the accuracy of model predictions is not stated as clearly as it could be. Take for example the comparison with reference 11, which also looked at carbonyl oxide effects on sulfates over Tokyo, and which predicted about an order of magnitude larger effect for a particular winter episode, saying that carbonyl oxide chemistry could help remedy sulfate underpredictions in winter. The present manuscript is a considerable improvement and correction to those earlier studies because of the inclusion of more accurate unimolecular removal kinetics for carbonyl oxides and kinetics of removal by water dimer. How well do models now capture sulfate concentrations and seasonal variability in the greater Tokyo area? Where is the need for further improvement?
Thank you for giving us suggestions to include the discussions of model performance with relating sCIs chemistry. The modeling performance was discussed based on three indicators: normalized mean bias (NMB), normalized mean error (NME), and correlation coefficient (R). Emery et al. (2017) proposed the values of the indicators which should be sufficient to replicate observed results. Overall, the values of NMB, NME, and R in the greater Tokyo area (GTA) suggested well modeling performance in this study, while the modeled SO42- relatively underestimated the observed results in winter and spring seasons. These discussions were added in the revised manuscript as follows.
Sect. Methodology: “The modelling performance for SO42−, the targeted component of this study, was evaluated using three indicators such as the normalized mean bias (NMB), normalized mean error (NME), and correlation coefficient (R), of which NMB and NME are defined in equations (1) and (2) as follows:

NMB=(∑_(i=1)^N▒(〖Mod〗_i-〖Obs〗_i ) )⁄(∑_(i=1)^N▒〖Obs〗_i .)　　　　　(1)

NME=(∑_(i=1)^N▒|〖Mod〗_i-〖Obs〗_i | )⁄(∑_(i=1)^N▒〖Obs〗_i .)　　　　　(2)


where subscript i is the pairing of N times observations (Obs) and calculations (Mod) from each site and time. Emery et al. proposed values of NMB, NME, and R that are required for the chemical transport modelling.27 In terms of SO42−, Emery et al. proposed that the required criteria of NMB, NME, and R are < ±0.30, < 0.50, and > 0.40, respectively while the required goal of NMB, NME, and R are < ±0.10, < 0.35, and > 0.70, respectively.”
Sect. Results: “Fig. 2 shows the comparison of observed and calculated results of SO42− at the three analysed sites: Tokyo Bay, Suburban, and Mountain in the four analysed seasons without incorporation of the chemistry of sCIs. Except for the value of NMB of Suburban, all the plots in the three analysed sites met the goal of modelling performance proposed by Emery et al.27 (the definitions of the indicators are described in the Methodology). The value of NMB for Suburban also met the criteria of modelling performance. For these reasons, the calculated SO42− concentration in the analysed domain reproduced the observed results well and can be applied for the kinetic analysis of sCIs-related chemistry. Despite these facts, the calculated SO42− concentration underestimated the observed results in winter and spring seasons for Tokyo Bay and Suburban area by ~50%.”
Meanwhile, the results of this study suggested that sCIs-chemistry are not critical to the formation of SO42- in GTA because of high-rate constants of sCIs loss reactions by unimolecular decay and water dimer. Thus, sCIs reactions are not important to improve modeled SO42- in the underestimated seasons. Nevertheless, this study clarified the basic atmospheric behavior of various types of sCIs in urban, suburban, and rural areas which will contribute to understand the fate of sCIs in the atmosphere. These discussions were added in the revised manuscript as follows.
Sect. Results: “As stated in the previous section, the calculated SO42− underestimated the observed results in winter and spring seasons for Tokyo Bay and Suburban regions by ~50%. Nevertheless, the contribution of sCIs to SO42− formation is at most ~0.3% according to Fig. 5(b), and we conclude that sCIs reactions are not the main reasons for the underestimation of SO42− in the calculated region.”

• (related to above) How might uncertainty in the source terms (e.g., VOC inventory) and in the assumptions that need to be made in the model (e.g., because of incomplete information about carbonyl oxide chemistry) affect the conclusions? Can the authors point to the most important uncertainties to address?
Thank you for the clarification. The results of this study suggest that gas-phase chemistry of sCIs is not the main contributor of the uncertainty of modeling performance. The performance of model is determined by several factors including emission inventory, chemical mechanism, atmospheric depositions, meteorology, etc., and modeling study should be tackled by the multiple aspects to enhance the performance of model. In terms of chemistry, there are three types of chemical processes divided by the phase: gas-phase, aqueous-phase (in-cloud and liquid phase of aerosol), and heterogeneous-phase chemical reactions. In this study, only gas-phase sCIs-chemistry was considered but several studies pointed out the importance of aqueous- and heterogeneous-chemistries of sCIs to SO42- and SOA formation. Despite this, the detailed kinetics of aqueous and heterogeneous sCIs reactions are still under construction, and the effect of those chemistries can be evaluated in the future works.

• How do other fates of the carbonyl oxide (besides direct reaction with SO2) affect sulfate formation? Does the fraction that eventually forms OH make any difference for sulfate concentrations or is that small enough to be irrelevant?
Thank you for the important indication. The authors had not evaluated the effect of OH derived from sCIs, and we analyzed the difference of OH contribution before and after the incorporation of sCIs chemistry. The change of OH concentration derived from sCIs was clarified to be important. The concentration of OH increased by 4% or more before and after the incorporation of sCIs-chemistry to the chemical mechanism of CMAQ. The increase of OH also affects the formation of SO42- through direct oxidation of SO2. We added this discussion to the revised manuscript by adding new section “Effect of sCIs on OH formation” in discussion as follows.
Sect. Discussion: “Anglada et al. suggested the potential impact of sCIs on OH formation and its influence on atmospheric oxidation.46 Fig. S12 shows the difference (%) in OH concentration before and after introducing sCIs-chemistry into the chemical mechanism of SAPRC-07 in the four seasons of the targeted domain. It is estimated that the OH concentrations increase by at least approximately 4% in all the seasons, and by up to 8% in winter. The OH is directly produced by the unimolecular decomposition of sCIs, bimolecular reactions of sCIs + HNO3, etc., and these reactions occur not only during the daytime but also at night, when the total OH concentration is low. These factors eventually increased the contribution of sCI on OH formation in the GTA. The increase in OH also contributes to the increase in SO42− formation through the direct oxidation of SO2 by OH. Fig. S13 shows the ratio of the SO42− formation rate between the increase in OH (Δ[OH]) and the increase in sCIs (Δ[CI]). In the winter season, the formation of SO42− is governed by the oxidation of SO2 by increasing OH, whereas in spring and summer seasons the formation of SO42− is contributed by both sCIs and the increase of OH. In autumn, most of the SO42− is increased by increasing OH. The contribution of OH increase is related to Tokyo Bay. Suburban and Mountain areas hold forests and trees that emit BVOCs contributing to a high production of OH, whereas Tokyo Bay is an urban area that has less BVOC emission. Therefore, the impact of the increase of OH through sCIs chemistry is more sensitive in Tokyo Bay than those in Suburban and Mountain areas, showing the relevant contribution of the increase of OH to the formation of SO42−. In conclusion, the enhancement of the formation of SO42− after the incorporation of sCIs chemistry is resulted from the oxidation reaction of SO2 by sCIs and the increased OH. In addition, the oxidation of SO2 by the increased OH contributes much more to the formation of SO42− than the direct sCIs oxidation of SO2.”

• The relative role of unimolecular decomposition and water reaction seems to be stated inconsistently within the paper. On the top of page three it says that water reaction is known as the main contributor, responsible for more than 70% of removal, but in the conclusions section we see that uniformly removal by water reaction is about the same as unimolecular decay. This should be described more consistently.
Thank you for the clarification. The descriptions were modified as follows to be consistent with between introduction and conclusion by modifying the description of “Loss of sCIs via reaction with water monomer and water dimer” in page 3 as follows.
“Water is known as the main contributor to the loss of sCIs from the atmosphere, which accounts for more than half of the total sCI consumption.”

Finally, there seems to be something wrong in the references — on first page Mauldin et al. is called reference 5 (I think this might be intended as Mauldin et al., A new atmospherically relevant oxidant of sulphur dioxide, Nature, 488, 193-196, 2012), but ref. 5 is something else, and no Mauldin et al. paper appears in the references.
Thank you for pointing out inconsistency of reference. We carefully checked and modified the references, added Mauldin et al (2012).
 
Answer to Referee 2:
The manuscript EA-ART-07-2023-000105 written by Yuya Nakamura conducted an urban-scale analysis of the contribution of gas-phase sCIs to sulfate formation. Yes, as introduced by the authors, this study will promote our understanding of the role of sCIs. Especially, one of the conclusions of the comparable contribution of the unimolecular decomposition of sCIs and the reaction between sCIs and water is interesting, because these loss processes have not been considered in previous studies.
However, I have strong opposition to this analysis. Where can we see the evaluation of your modeling? Does this modeling have been well validating and used in this Tokyo domain? If this modeling is perfect, there is no need to introduce such additional reactions of sCIs. What are the difficulties in this modeling and why do the authors introduce sCIs reactions? In the current presentation, this is just a report of a modeling test, and the scientifical significance is less. The readers will not convince of this result without a clear introduction to this study. Therefore, I have judged this manuscript did not meet the four criteria required as a full paper in the journal of Environmental Science: Atmospheres.
The authors are grateful to Referee 2 to read and evaluate our manuscript. The validation of modeling to the observed results were added to the revised manuscript. The contribution of sCIs-chemistry to the model validation was also evaluated. All the revised sentences were highlighted in yellow. The added sentences are as follows.
Sect. Methodology: “The modelling performance for SO42−, the targeted component of this study, was evaluated using three indicators such as the normalized mean bias (NMB), normalized mean error (NME), and correlation coefficient (R), of which NMB and NME are defined in equations (1) and (2) as follows:

NMB=(∑_(i=1)^N▒(〖Mod〗_i-〖Obs〗_i ) )⁄(∑_(i=1)^N▒〖Obs〗_i .)　　　　　(1)

NME=(∑_(i=1)^N▒|〖Mod〗_i-〖Obs〗_i | )⁄(∑_(i=1)^N▒〖Obs〗_i .)　　　　　(2)


where subscript i is the pairing of N times observations (Obs) and calculations (Mod) from each site and time. Emery et al. proposed values of NMB, NME, and R that are required for the chemical transport modelling.27 In terms of SO42−, Emery et al. proposed that the required criteria of NMB, NME, and R are < ±0.30, < 0.50, and > 0.40, respectively while the required goal of NMB, NME, and R are < ±0.10, < 0.35, and > 0.70, respectively.”
Sect. Results: “Fig. 2 shows the comparison of observed and calculated results of SO42− at the three analysed sites: Tokyo Bay, Suburban, and Mountain in the four analysed seasons without incorporation of the chemistry of sCIs. Except for the value of NMB of Suburban, all the plots in the three analysed sites met the goal of modelling performance proposed by Emery et al.27 (the definitions of the indicators are described in the Methodology). The value of NMB for Suburban also met the criteria of modelling performance. For these reasons, the calculated SO42− concentration in the analysed domain reproduced the observed results well and can be applied for the kinetic analysis of sCIs-related chemistry. Despite these facts, the calculated SO42− concentration underestimated the observed results in winter and spring seasons for Tokyo Bay and Suburban area by ~50%.”
One of our conclusions of this study is that sCIs are not critical to SO42- formation in the calculated region. Thus we also added following sentences to explain sCIs reactions are not the main issue to improve modelling performance of SO42-.
Sect. Results: “As stated in the previous section, the calculated SO42− underestimated the observed results in winter and spring seasons for Tokyo Bay and Suburban regions by ~50%. Nevertheless, the contribution of sCIs to SO42− formation is at most ~0.3% according to Fig. 5(b), and we conclude that sCIs reactions are not the main reasons for the underestimation of SO42− in the calculated region.”
 
Answer to Referee 3:
The authors present a study of the impact of recent advances in understanding of stabilized Criegee intermediate (sCI) chemistry on model production of sulphate aerosol in the Greater Tokyo area using the Community Multiscale Air Quality (CMAQ) model. The chemical mechanism in the model has been updated to include outcomes of recent studies of sCI kinetics, with results indicating that the dominant reactions of sCIs are unimolecular decomposition and reaction with water/water dimers. As a consequence, the impact of sCIs is expected to be low, in contrast to suggestions from previous modelling studies which considered recent developments in understanding of Criegee + SO2 chemistry but, at the time, were not able to fully appreciate the effects of other reactions.
The study will be of interest to the atmospheric science community and is appropriate for publication once the comments below have been addressed.
The authors are grateful to Referee 3 to evaluate and to make several suggestions and clarifications. We carefully improved the manuscript based on the comments. All the revised parts are highlighted in yellow.

Major comments:
It would be helpful to indicate the fraction of alkenes oxidised by ozone in the model to demonstrate the wider applicability of the results and to rule out the possibility that the impact of sCI chemistry on sulphate aerosol formation is low because sCI chemistry is not generally significant in this region.
What are the main fates of the C-containing products of sCI chemistry? Is there an impact on secondary organic aerosol?
The fate of organic compounds derived from sCIs are listed in Tables S3 to S9 of the supplementary information. The sCIs are converted to aldehydes and ketones, organic peroxides, organic acids, etc. of which all of them could contribute to atmospheric chemical cycle (HOx cycle). We analyzed the change of SOA before and after the incorporation of sCIs chemistry to the chemical mechanism of CMAQ, but the contributions were quite low (only ~0.01%).

What is the impact of updates to sCI decomposition kinetics on OH concentrations?
Thank you for the important question. The authors had not analyzed the effect of sCIs to OH. We analyzed the effect and obtained the important fact that OH concentration increase more than 4% through sCIs chemistry added in the chemical mechanism used in this study. At the beginning of this study, we thought that SO42- may increase only by the enhancement of SO2 + sCIs reactions, but the increase of OH is also important by the oxidation reaction off SO2 + OH. We added following sentences to discuss this issue.
Sect. Discussion: “Anglada et al. suggested the potential impact of sCIs on OH formation and its influence on atmospheric oxidation.46 Fig. S12 shows the difference (%) in OH concentration before and after introducing sCIs-chemistry into the chemical mechanism of SAPRC-07 in the four seasons of the targeted domain. It is estimated that the OH concentrations increase by at least approximately 4% in all the seasons, and by up to 8% in winter. The OH is directly produced by the unimolecular decomposition of sCIs, bimolecular reactions of sCIs + HNO3, etc., and these reactions occur not only during the daytime but also at night, when the total OH concentration is low. These factors eventually increased the contribution of sCI on OH formation in the GTA. The increase in OH also contributes to the increase in SO42− formation through the direct oxidation of SO2 by OH. Fig. S13 shows the ratio of the SO42− formation rate between the increase in OH (Δ[OH]) and the increase in sCIs (Δ[CI]). In the winter season, the formation of SO42− is governed by the oxidation of SO2 by increasing OH, whereas in spring and summer seasons the formation of SO42− is contributed by both sCIs and the increase of OH. In autumn, most of the SO42− is increased by increasing OH. The contribution of OH increase is related to Tokyo Bay. Suburban and Mountain areas hold forests and trees that emit BVOCs contributing to a high production of OH, whereas Tokyo Bay is an urban area that has less BVOC emission. Therefore, the impact of the increase of OH through sCIs chemistry is more sensitive in Tokyo Bay than those in Suburban and Mountain areas, showing the relevant contribution of the increase of OH to the formation of SO42−. In conclusion, the enhancement of the formation of SO42− after the incorporation of sCIs chemistry is resulted from the oxidation reaction of SO2 by sCIs and the increased OH. In addition, the oxidation of SO2 by the increased OH contributes much more to the formation of SO42− than the direct sCIs oxidation of SO2.”

Minor comments on the manuscript are detailed below:
The abstract should mention the model used in the study.
The model used in this study was added in the abstract as follows.
“…, the community multiscale air quality modelling (CMAQ) system.”

In the abstract, ‘seasonal and timely’ would be better described as ‘seasonal and temporal’.
Thank you for the suggestion. The word ‘timely’ was substituted by ‘temporal’ in the revised manuscript.

In the introduction, it should be noted that the production of OH from sCIs is dependent on structure of the sCI.
Thank you for the suggestion. We added the following words in introduction regarding structure dependence of OH production.
“… depending on their structure,”

Reaction with NO has been demonstrated to be slow, the comment on reaction with nitrogen oxides would be better described as reaction with NO2. The reactions of sCIs with NO2 listed in the supplementary information show NO3 as a reaction product, but several studies have demonstrated that NO3 is not produced (Lewis et al, 2015 doi: 10.1039/C4CP04750H, Caravan et al., 2017 doi: 10.1039/C7FD00007C).
Thank you for the clarifications. Nitrogen oxides (NOx) was changed to nitrogen dioxide (NO2) in the introduction. There were several studies which focused on the reaction of CI + NO2. Traditionally, NO3 was expected as the product of CI + NO2 reactions, which was expected to contribute to nighttime NO3 formation (Ouyang et al. Phys. Chem. Chem. Phys. 2013, 15, 17070-17075; Presto and Donahue. J. Phys. Chem. A 2004, 108, 9096-9104). Recently, direct measurements of CI + NO2 were conducted and NO3 is obtained maximally 30% from CI + NO2 reactions and remained products are organic nitrate (Meidan et al. ACS Earth Space Chem. 2017, 1, 288-298; Caravan et al. Faraday Discuss. 2017, 200, 313-330). The main focus of this study is SO42- induced by sCIs and for simplicity of other reactions, we assumed NO2 is directly oxidized to be NO3. Following sentences were added to the methodology section of revised manuscript.
Sect. Methodology: “Notably, several studies have concluded that the product of sCIs + NO2 is NO3,37-38 and hence, we assumed that all the products from sCIs + NO2 reactions were NO3. Nevertheless, it should be noted that Caravan et al. found that main product of sCIs + NO2 could be organic nitrate and maximally ~30% decompose to NO3 and ketone (aldehyde);39 however, this finding was not considered in this study.”

The regional transport model used in previous studies should be named.
Thank you for the suggestion. The model used in the previous studies were added in the revised manuscript.

‘GTA area’ to ‘GTA’.
Thank you for the clarification. The word ‘area’ was deleted.

In the methodology section (or elsewhere) it would be helpful to detail why model calculations were performed for 2015 specifically, is 2015 a typical year? Are there measurements of sulphate aerosol in the region for this time period that can be compared with the model results?
Thank you for the suggestion. Honestly, the reason why we performed CTM calculations for 2015 was that the latest year of validated emission inventory we possessed was for 2015 when this study has been conducted since 2019. Therefore, there were less meaning to mention the reason of choosing 2015, we did not include it to the revised manuscript. In terms of the observations, Japanese government monitors atmospheric pollutants including SO42- in particle every year in the four seasons. In the revised manuscript, the validation of calculated results comparing with the observational data was added.

When incorporating reaction rate coefficients, were experimental measurements for decomposition considered where available and compared to those suggested by Vereecken et al.? Experimental measurements of rate coefficients for CH2OO + H2O/(H2O)2 are mentioned, but there is no discussion of measurements for decomposition.
The measurements of the rate coefficients of unimolecular decomposition of sCIs were conducted by several previous studies. The reason we used the rate coefficients suggested by Vereecken et al. is that Vereecken et al. estimated the rate coefficients for almost all the structures of sCIs exist in the atmosphere. Despite this, we added the citations related to the experiments to show that there were several studies of the unimolecular decomposition of sCIs conducted by both experimental and theoretical methods in the methodology section as follows.
Sect. Methodology: The unimolecular decomposition mechanism of sCIs was investigated by several studies using both experimental and theoretical methods.18,30-32 In this study, we applied the rate constants for unimolecular decomposition proposed by Vereecken et al.18

13-Oct-2023

Dear Dr Hata:

Manuscript ID: EA-ART-07-2023-000105.R1
TITLE: Urban-scale analysis of the seasonal trend of stabilized-Criegee intermediates and their effect on sulphate formation in the Greater Tokyo Area

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

After careful evaluation of your manuscript and the reviewers’ reports, I will be pleased to accept your manuscript for publication after revisions.

Please revise your manuscript to fully address the reviewers’ comments. When you submit your revised manuscript please include a point by point response to the reviewers’ comments and highlight the changes you have made. Full details of the files you need to submit are listed at the end of this email.

Please submit your revised manuscript as soon as possible using this link :

*** PLEASE NOTE: This is a two-step process. After clicking on the link, you will be directed to a webpage to confirm. ***

https://mc.manuscriptcentral.com/esatmos?link_removed

(This link goes straight to your account, without the need to log in to the system. For your account security you should not share this link with others.)

Alternatively, you can login to your account (https://mc.manuscriptcentral.com/esatmos) where you will need your case-sensitive USER ID and password.

You should submit your revised manuscript as soon as possible; please note you will receive a series of automatic reminders. If your revisions will take a significant length of time, please contact me. If I do not hear from you, I may withdraw your manuscript from consideration and you will have to resubmit. Any resubmission will receive a new submission date.

The Royal Society of Chemistry requires all submitting authors to provide their ORCID iD when they submit a revised manuscript. This is quick and easy to do as part of the revised manuscript submission process. We will publish this information with the article, and you may choose to have your ORCID record updated automatically with details of the publication.

Please also encourage your co-authors to sign up for their own ORCID account and associate it with their account on our manuscript submission system. For further information see: https://www.rsc.org/journals-books-databases/journal-authors-reviewers/processes-policies/#attribution-id

Environmental Science: Atmospheres strongly encourages authors of research articles to include an ‘Author contributions’ section in their manuscript, for publication in the final article. This should appear immediately above the ‘Conflict of interest’ and ‘Acknowledgement’ sections. I strongly recommend you use CRediT (the Contributor Roles Taxonomy, https://credit.niso.org/) for standardised contribution descriptions. All authors should have agreed to their individual contributions ahead of submission and these should accurately reflect contributions to the work. Please refer to our general author guidelines https://www.rsc.org/journals-books-databases/author-and-reviewer-hub/authors-information/responsibilities/ for more information.

I look forward to receiving your revised manuscript.

Yours sincerely,
Dr. Stephen Klippenstein
Associate Editor, Environmental Science: Atmospheres

************

Reviewer 1

The authors have addressed my comments and suggestions satisfactorily and the work will be a valuable contribution to the understanding of the effects of carbonyl oxide Criegee intermediates on sulfate formation.

Reviewer 3

The authors have addressed the major concerns raised in the previous review and have improved the quality of the manuscript. However, there is a minor issue outstanding that should be addressed. The authors have added a comment on the potential products of SCI + NO2 reactions which states that several studies have concluded that NO3 is a product. Direct experimental studies have shown that this is not the case, and studies that have concluded that NO3 is a product have been shown to be influenced by secondary chemistry. While I agree that this is not the focus of the paper here, the authors should not indicate that there is support for NO3 being the main product. I suggest re-wording to acknowledge that the products are uncertain.

Reviewer 2 has commented on model validation and questioned whether there is a need for a study such as that described in this work if the model works well. I disagree with these comments. Our understanding of Criegee intermediate chemistry has improved significantly in recent years, and we now know that several reactions are more rapid than previously thought. It is perfectly possible that models which do not incorporate this chemistry may be correct but for the wrong reasons. It is only through studies such as the work presented here that we can determine the atmospheric impacts of new findings in Criegee intermediate chemistry.

Reviewer 2

The manuscript EA-ART-07-2023-000105.R1 written by Yuya Nakamura is the revised version of the previously submitted manuscript. By including the model evaluation, some points have been improved. I appreciate the authors for their revisions, and now I can review this manuscript. I still have major concerns about this study. The following points should be clarified to meet the four criteria required for a full paper in the journal of Environmental Science: Atmospheres.

Major points:
- Ambiguous expressions: By introducing previous studies of 11-16 (Page 14 of 50 (right column)), the authors expressed the sCI reactions as “impact”, “affected”, and “significantly impact”. However, on Page 15 of 50 (left column), it was expressed as “negligible” for 5% or less contributions. I do not fully catch up with such expressions based on the previous study itself or the authors’ judgment; however, these ambiguous expressions will mislead the readers. Actually, a previous study of 11 reported 0.5-3% contribution as stated on Page 18 of 50 (right column), but introduced as “impact”. Therefore, I do not fully figure out what percentage of contribution can be judged as “impact” or “no impact”. I would like to strongly ask for the quantitative discussion throughout the manuscript, and please avoid the subjective and vague discussion.
- The new finding in this study: One of the important findings drawn in this study will be the importance of the unimolecular decomposition of sCIs and less importance of sCI reactions for SO42- formation compared to the previous study. This is an interesting topic; however, in my understanding, this mechanism and approach taken in this study will be mostly similar to Vereecken et al. (2017) as introduced, and hence I do not follow what is newly found throughout this study. The limitation of the atmospheric impact of sCI has been already reported by Vereecken et al. (2017). Is this just an application to Japan? I am still not sure about the motivation for this study.
- Figures intention: “Page 23 of 50” and “Page 25 of 50” (same figure) seem to present the concept of sulfate production. However, the authors' conclusion is “less of an impact on sCIs to SO42– formation compared with that of previous studies”. I am impressed that this figure indicates the production of sulfate from sCI, and I think this figure will mislead the authors. It is required to totally change this figure to clear the authors’ intention.

Specific points:
- Page 14 of 50 (right column): What is the “source-oriented” model?
- Page 14 of 50 (right column): Cox et al. include sCI + water reactions, and what is the result from this study? Does this reaction lead to the suppression of sulfate production via sCI? Compared to the introduction of other previous studies, this sentence is just the method of their study and there is no result. Please reorganize.
- Page 14 of 50 (right column): “GTA” needs to be defined here. In addition, this paragraph will be redundant to the last paragraph of the introduction section. Please reconsider.
- Page 17 of 50 (left column): I do not fully follow the meaning of the last sentence “Despite these facts, …”. Please confirm a connection to the prior sentence.

Technical points:
- “SO42-” or “sulfate aerosol” should be unified throughout this manuscript.

Answer to Referee 1
Comments to the Author
The authors have addressed my comments and suggestions satisfactorily and the work will be a valuable contribution to the understanding of the effects of carbonyl oxide Criegee intermediates on sulfate formation.
The authors are grateful to reviewer 1 to take time to sophisticate our manuscript.

Answer to Referee 3
Comments to the Author
The authors have addressed the major concerns raised in the previous review and have improved the quality of the manuscript. However, there is a minor issue outstanding that should be addressed. The authors have added a comment on the potential products of SCI + NO2 reactions which states that several studies have concluded that NO3 is a product. Direct experimental studies have shown that this is not the case, and studies that have concluded that NO3 is a product have been shown to be influenced by secondary chemistry. While I agree that this is not the focus of the paper here, the authors should not indicate that there is support for NO3 being the main product. I suggest re-wording to acknowledge that the products are uncertain.
The authors are grateful to reviewer 3 to reevaluate our manuscript and giving us important proposal. All the revised sentences are highlighted in yellow. Based on the suggestion, we modified the explanation of the products of sCI+NO2 as follows which indicating the uncertainty of the product of sCIs + NO2.
“Notably, while several studies have assumed that the product of sCIs + NO2 is NO3,37-38 Caravan et al. found that main product of sCIs + NO2 could be sCI-NO2 adduct with an upper limit of about ~30% decompose to NO3 and ketones (aldehyde).39 Therefore, the actual products are uncertain. However, because of this uncertainty and the emphasis of this study on SO2 products, we assumed that all the products from sCIs + NO2 reactions were NO3.”

Reviewer 2 has commented on model validation and questioned whether there is a need for a study such as that described in this work if the model works well. I disagree with these comments. Our understanding of Criegee intermediate chemistry has improved significantly in recent years, and we now know that several reactions are more rapid than previously thought. It is perfectly possible that models which do not incorporate this chemistry may be correct but for the wrong reasons. It is only through studies such as the work presented here that we can determine the atmospheric impacts of new findings in Criegee intermediate chemistry.
The accuracy of emission inventories applied in this study has already been proven by the previous studies from Chatani et al. (2018) and related articles, and that was why in the previous manuscript, the authors omitted to show the validation of modeled results to observational data. While our focus of this study was the importance of sCIs to SO42- formation in the high polluted regions of Japan, in the modeling aspect, we were convinced that it is necessary to show the modeling performance even in the future work.

Answer to Referee 2
Comments to the Author
The manuscript EA-ART-07-2023-000105.R1 written by Yuya Nakamura is the revised version of the previously submitted manuscript. By including the model evaluation, some points have been improved. I appreciate the authors for their revisions, and now I can review this manuscript. I still have major concerns about this study. The following points should be clarified to meet the four criteria required for a full paper in the journal of Environmental Science: Atmospheres.
The authors are grateful to reviewer 2 to reevaluate our manuscript and proposing several suggestions and clarifications. We modified the manuscript carefully based on the comments from reviewer 2. All the revised sentences are highlighted in yellow.

Major points:
- Ambiguous expressions: By introducing previous studies of 11-16 (Page 14 of 50 (right column)), the authors expressed the sCI reactions as “impact”, “affected”, and “significantly impact”. However, on Page 15 of 50 (left column), it was expressed as “negligible” for 5% or less contributions. I do not fully catch up with such expressions based on the previous study itself or the authors’ judgment; however, these ambiguous expressions will mislead the readers. Actually, a previous study of 11 reported 0.5-3% contribution as stated on Page 18 of 50 (right column), but introduced as “impact”. Therefore, I do not fully figure out what percentage of contribution can be judged as “impact” or “no impact”. I would like to strongly ask for the quantitative discussion throughout the manuscript, and please avoid the subjective and vague discussion.
Thank you for the important clarifications. We are convinced of the opinions and changed the words “impact” to “effect” or “contribution” because the word “impact” includes the ambiguous meaning. The expression “negligible” in page 15 of 50 was deleted. We added following sentence to the right side of page 14/50.
“Several studies suggested that the reaction of sCIs with water would significantly affect SO42– formation via the oxidation of SO2 by sCIs by 1 to 10% depends on which value is used for the rate constant of H2O reaction.14-16”

- The new finding in this study: One of the important findings drawn in this study will be the importance of the unimolecular decomposition of sCIs and less importance of sCI reactions for SO42- formation compared to the previous study. This is an interesting topic; however, in my understanding, this mechanism and approach taken in this study will be mostly similar to Vereecken et al. (2017) as introduced, and hence I do not follow what is newly found throughout this study. The limitation of the atmospheric impact of sCI has been already reported by Vereecken et al. (2017). Is this just an application to Japan? I am still not sure about the motivation for this study.
The main purpose of our study is to update the understanding of the contribution of sCIs to SO42- formation in the greater Tokyo area (GTA) in Japan. Similar study was conducted by Itahashi et al. Atmosphere 2019, 10(9), 544, but this study did not take detailed chemistry of stabilized-Criegee intermediates (including unimolecular decomposition of CIs) into account. We applied detailed chemistry for several sCIs as well as detailing (H2O)2/H2O ratio to reevaluate the importance of sCIs to form SO42- in GTA. Our results showed that the contribution of sCIs to SO42- formation in GTA is ~10 times lower than previously predicted by Itahashi et al. which is a new finding and update from the previous study. Aside from this, this study shows seasonal trend of the concentration of sCIs in GTA and compared with that of U.K (alongside London which is as large city as Tokyo). evaluated by Cox et al. Atmos. Chem. Phys. 2020, 20(21), 13497-13519. Similar trend was obtained between this study and Cox et al. Cox et al. evaluated sCIs concentration by box modeling, while this study used chemical transport model, and the similarity of this study and Cox et al. indicates the universal trend of sCIs concentration close to high-urbanized area.

- Figures intention: “Page 23 of 50” and “Page 25 of 50” (same figure) seem to present the concept of sulfate production. However, the authors' conclusion is “less of an impact on sCIs to SO42– formation compared with that of previous studies”. I am impressed that this figure indicates the production of sulfate from sCI, and I think this figure will mislead the authors. It is required to totally change this figure to clear the authors’ intention.
Thank you for the clarification. The Graphical Abstract (GA) shown in page 23/50 and 25/50 is intending to show the general scheme of SO42- generation induced by sCIs to express that this study holds the topic of sCIs with SO2 reaction. While the conclusion of this study is, as indicated by reviewer 2, the contribution of sCIs to SO42- formation in GTA is lower than previously indicated, manuscript holds whole insight of sCIs including seasonal and daily series of sCIs conc., ratio of composition of each sCIs etc., and thus, the GA is representing the scope of this study, and if possible, we want to remain GA in the current form.

Specific points:
- Page 14 of 50 (right column): What is the “source-oriented” model?
We deleted the words “source-oriented” because this term is redundant. Source-oriented model means the kind of air quality model that simulate the concentration of air pollutants based on emission inventory and meteorological inputs; this definition is also applicable to CMAQ.

- Page 14 of 50 (right column): Cox et al. include sCI + water reactions, and what is the result from this study? Does this reaction lead to the suppression of sulfate production via sCI? Compared to the introduction of other previous studies, this sentence is just the method of their study and there is no result. Please reorganize.
According to the suggestion, we added following sentence to recognize part of the results of Cox et al.
“Cox et al. summarized the estimated atmospheric concentration of sCIs in the U.K. from kinetic analysis studies including sCI + water reactions and the unimolecular decomposition of sCIs,17 showing that most of the sCIs are scavenged by water reactions or unimolecular decompositions in urban, suburban, and rural areas of the U.K.”

- Page 14 of 50 (right column): “GTA” needs to be defined here. In addition, this paragraph will be redundant to the last paragraph of the introduction section. Please reconsider.
Thank you for the clarification. We added the definition of GTA in the description of Itahashi et al, and deleted the definition from the last paragraph.

- Page 17 of 50 (left column): I do not fully follow the meaning of the last sentence “Despite these facts, …”. Please confirm a connection to the prior sentence.
Thank you for the clarification. According to the suggestion, we modified the sentences as follows to make connection to the prior sentences.
“Despite the facts of well modelling performance, the calculated SO42− concentration underestimated the observed results in winter and spring seasons for Tokyo Bay and Suburban area by ~50%. The fact of underestimation should be considered when analysing the effect of sCIs to SO42- formation in winter and spring seasons.”

Technical points:
- “SO42-” or “sulfate aerosol” should be unified throughout this manuscript.
Thank you for the clarification. We unified most of the words “sulphate aerosol” or “sulphate” to be “SO42-“.

20-Oct-2023

Dear Dr Hata:

Manuscript ID: EA-ART-07-2023-000105.R2
TITLE: Urban-scale analysis of the seasonal trend of stabilized-Criegee intermediates and their effect on sulphate formation in the Greater Tokyo Area

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