The variations of VOCs based on the policy change of Omicron in polluted winter in traffic-hub city, China

Zhang, Bowen; Zhang, Dong; Dong, Zhe; Song, Xinshuai; Zhang, Ruiqin; Li, Xiao

doi:https://doi.org/10.5194/egusphere-2024-575

Preprints

https://doi.org/10.5194/egusphere-2024-575

Preprints

08 Mar 2024

| 08 Mar 2024

The variations of VOCs based on the policy change of Omicron in polluted winter in traffic-hub city, China

Bowen Zhang, Dong Zhang, Zhe Dong, Xinshuai Song, Ruiqin Zhang, and Xiao Li

Abstract. Online volatile organic compounds (VOCs) were continuous monitored before and after the Omicron policy change at an urban site in polluted Zhengzhou from December 1, 2022, to January 31, 2023. The characteristics and sources of VOCs were explored. The daily average concentration of PM_2.5 and total VOCs (TVOCs) ranged from 54 to 239 µg/m³andfrom 15.6 to 57.1 ppbv with an average value of 112 ± 45 µg/m³ and 36.1 ± 21.0 ppbv, respectively during the entire period. The values of PM_2.5 and TVOCs in Case 3 (pollution episode after the abolishment of “Nucleic Acid Screening Measures for all staff” policy) were 1.3 and 1.8 times of the values in the Case 1 (pollution episode during “Nucleic Acid Screening Measures for all staff” policy). The concentration of TVOCs in Case 1 and Case 3 were 48.4 ± 20.4 and 67.6 ± 19.6 ppbv, respectively, increased by 63 % and 188 % compared with values during clean days. Alkanes were found to be the most abundant compounds during the entire period. Equivalent volume contribution of halogenated hydrocarbon and oxygenated VOCs (15 %) were found the most in Case 3, followed by alkenes (10 %). Though the volume contributions of aromatics were the lowest (6 % in Case 1 and 7 % in Case 3), the highest increasing ratio was found from clean days to polluted episodes. Positive Matrix Factor model results showed that the main source of VOCs during the observation period was industrial emissions, which accounted for 30 % of the TVOCs, followed by vehicular emission (24 %) and combustion (23 %). The vehicular emission became the largest source during Case 1 (40 %) and Case 3 (29 %), consisting of large numbers of people going out after the blockade. Secondary organic aerosol formation potential (SOAFP) values were 37 and 109 µg/m³, respectively with the highest SOAFP contribution (17–19 μg/m³and 31–51 %) from vehicular emission both in Case 1 and Case 3. Solvent usage sources had the second highest SOAFP value (9 and 16 μg/m³) with the contributions of 23 and 31 % in Case 1 and Case 3 respectively. The control of vehicular emission, and solvent usage should be focused in Zhengzhou, and combustion was also important for the control of PM_2.5 pollution in winter.

Received: 27 Feb 2024 – Discussion started: 08 Mar 2024

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Journal article(s) based on this preprint

10 Dec 2024

The variations in volatile organic compounds based on the policy change for Omicron in the traffic hub of Zhengzhou

Bowen Zhang, Dong Zhang, Zhe Dong, Xinshuai Song, Ruiqin Zhang, and Xiao Li

Atmos. Chem. Phys., 24, 13587–13601, https://doi.org/10.5194/acp-24-13587-2024,https://doi.org/10.5194/acp-24-13587-2024, 2024

Short summary

Bowen Zhang, Dong Zhang, Zhe Dong, Xinshuai Song, Ruiqin Zhang, and Xiao Li

Interactive discussion

Status: closed

CC1: 'Comment on egusphere-2024-575', Jingz Gao, 10 Mar 2024

Zhang等在COVID-19期间在郑州确定了100多种VOC物种。总的来说，这项研究很有趣，作者也获得了一些结果。不幸的是，手稿过于肤浅，缺乏明显的新颖性。此外，许多结论，例如不同情况下的来源贡献，都过于简单和没有深度。我建议作者应该在手稿中使用一些物理/化学模型来增加一些关于臭氧或SOA的预算机制的讨论。虽然我不是这份手稿的推荐人，但我觉得这份手稿不符合ACP的标准。

Citation: https://doi.org/10.5194/egusphere-2024-575-CC1
CC2: 'Comment on egusphere-2024-575', Jingz Gao, 10 Mar 2024

Zhang et al. determined more than 100 VOC species in Zhengzhou during the COVID-19 period. Overall, the study is interesting and the authors also obtain some results. Unfortunately, the manuscript is too superficial and lacks of significant novelty. Moreover, many conclusions such as the source contributions in different cases are too simple and depthless. I suggest the authors should add some discussions about budget mechanisms of ozone or SOAs in the manuscript using some physical/chemical models. Although I am not a referrer of this manuscript, I felt the manuscript cannot meet the standard of ACP.

Citation: https://doi.org/10.5194/egusphere-2024-575-CC2
CC3: 'Comment on egusphere-2024-575', Fengyi Wu, 11 Mar 2024

I read the manuscript written by Zhang et al. and the comment from Gao carefully. I completely agree with Gao's comment. The manuscript lacks of significant novelty and the quality was much below the average standard of ACP. I strongly recommend the editor to reject this manuscript.

Citation: https://doi.org/10.5194/egusphere-2024-575-CC3
RC1:
'Comment on egusphere-2024-575', Anonymous Referee #1, 28 Mar 2024

The article explored the relationship between VOCs and PM2.5 with abundant VOCs species observed in Zhengzhou during the COVID-19 and made recommendations for the control of VOCs source emissions.
The current discussion may not be sufficiently supportive, please add more details to each section to make the entire article more logical. Basic details regarding instrumentation and data collection are missing. The authors need to supplement materials related to the reliability of the PMF results. Furthermore, more work is needed to elucidate the relationship between VOCs and haze pollution, as well as the influencing factors. And it is suggested that model simulation on SOA formation potential be added to the manuscript.
While the theme and results of the study are interesting, I have provided a few suggestions for improvement.

Line 124-135: The authors lack more detailed descriptions of the instrumentation. What are the working procedures of the instruments? What is the time resolution of the samples? How long were the samples collected for? Where were they captured? It is recommended to include information about instrument quality control methods.
Section 2.2 PMF model
How did the authors conduct factor selection, and why did not choose the 5-factor solution, 6-factor solution, and 7-factor solution? The authors need to provide more explanations and justifications in the manuscript.

Section 3.1 Pollution characteristics
Line 194: Ensure that the font in the figures is consistently in Times New Roman. The y-axis labels do not match the legend (NO and NOx).
What does the shading in Figure 1 represent? What are Case 1, Case 2, Case 3, Case 4, and Case 5? Clear explanations need to be provided. If these cases represent haze pollution processes, how do you define your pollution processes? Please include the references you consulted.

Line 217-225: Why did you only discuss Case 1 and Case 3? Are these two periods particularly significant? Provide your reasoning.
In Figure 2, the font should be changed to Times New Roman.
In this section, you only analyzed the variations in pollutant concentrations and meteorological conditions. What is the relationship between them? Which factors are crucial causes of pollution? You have not provided analysis and explanations.
Line 222-223: “[…] Among them, Case 1 (from 222 December 5 to December 10 and […]” A closing bracket is missed.

Section 3.2 Source appointment
Line 272: ‘indicating that the measured air VOC content was influenced by both remote sources and urban area emissions’, Are you referring to all VOCs? Or specifically to m/p-xylene and ethylbenzene?

Line 271-273: Your conclusion indicates that VOCs are influenced by transport and emissions from distant regions. Can this be further substantiated through transport or other means?

Line 306: 'olefins' should be corrected to 'alkenes'.

Line 316-325: Have you performed PMF in Case 1, Case 3, and the clean days? It is recommended to check whether the results of factor analysis are consistent in different conditions (Case 1, Case 2, and clean days) and compare the results.

Section 3.2 SOAFP
In this part, only Case 1 and Case 2 processes were discussed, then leading to the conclusion that the control of PM2.5 pollution in winter should focus on controlling vehicle emissions, solvent use, and combustion. I am afraid it is not convincing enough. It is recommended to add analysis of clean days. Contrast the pollution process with the clean day.

Citation: https://doi.org/10.5194/egusphere-2024-575-RC1
- AC1: 'Reply on RC1', Bowen Zhang, 17 Jun 2024
  
  Thank you for your careful reading of our paper and valuable comments and suggestions. We believe that we have adequately addressed your comments. Please refer to the attached file for details.
  
  Citation: https://doi.org/10.5194/egusphere-2024-575-AC1
RC2:
'Comment on egusphere-2024-575', Anonymous Referee #2, 06 Apr 2024

Overall comment:
The COVID-19 lockdown measures provide a natural experiment for probing air quality changes under substantial emission reductions. Zhang et al. investigate the variations of VOCs in response to the policy-driven emission changes in Zhengzhou city of China by using online ambient measurements, and the PMF model. While this paper is within the scope of ACP, the present manuscript is limited to a cursory data analysis (simply reporting measurement results), without convincing evidence and in-depth discussion, which makes this paper unpublishable in the present form. Further, the innovation of this work is far below the standard required to be published on ACP, which is even not qualified as a measurement report. Though addressing the specific comments below may improve the paper, I don’t think these improvements could justify publication in a high-standard journal such as ACP. Concerning the major flaws and the lack of innovation, I think this paper should be rejected.
Major comments:
1) The major weakness of this work is the lack of innovation. The impacts of the Omicron outbreak on Chinese cities are already well-documented and extensive studies have been conducted to elucidate the role of the anthropogenic sector on air pollution during- and post-outbreak periods. The authors claimed that industrial and vehicular emissions are dominant sectors contributing to ambient VOC, which is quite clear in prior studies. Further, the changes in PM2.5 and VOCs in response to the lockdown are broadly consistent with previous findings in Zhengzhou (even in Chinese literature). What is the innovation of this work and what are the new findings from this work that contribute to the air quality community?
2) The usage of SOAP should be revisited. The authors should be aware that SOAP is a very simple metric that provides limited information on SOA formation potential because SOA yield for individual VOCs in China may vary significantly in other countries due to the different levels of NOx and other oxidants. SOAP is generally adopted to reflect the SOA production potential based on bottom-up emission inventory (see Wu & Xie, ES&T), rather than using short-time ambient measurements. Therefore, I doubt the conclusion driven by the simple SOAP calculation. The authors should consider using F0AM and PBM-MCM for examining SOA production changes rather than SOAP.
3) The captions of the results section are meaningless. "Pollution characteristics" and "Source appointment" is not clear to the readers and should be rewritten for clarification.
4) The writing of this paper is in need of much attention. Specifically, the writing suffers from a series of fundamental issues, including a lack of clear organization, pervasive grammatical, and stylistic errors. I suggest the authors carefully read through the manuscript and rephrase the results section. There is substantial awkward phrasing throughout the paper which is confusing and misleading to the readers.
Minor comments:
1) The SOA formation potential is called "SOAP" rather than "SOAFP". The author should correct this abbreviation.

Citation: https://doi.org/10.5194/egusphere-2024-575-RC2
- AC2: 'Reply on RC2', Bowen Zhang, 17 Jun 2024
  
  Thank you for your careful reading of our paper and valuable comments and suggestions. We believe that we have adequately addressed your comments. Please refer to the attached file for details.
  
  Citation: https://doi.org/10.5194/egusphere-2024-575-AC2
RC3:
'Comment on egusphere-2024-575', Anonymous Referee #3, 06 Apr 2024
To provide a fair assessment, I refrained from reading previous reviews of the manuscript. Zhang et al. investigated VOC emissions during winter in Zhengzhou, China, likely aiming to understand the impact of the Omicron lockdown on city pollutants. However, given the extensive documentation of air quality studies during COVID pandemic and its variants, including Omicron, the manuscript lacks novelty in this context. The discussion on source apportionment also falls short, lacking depth and quantitative analysis. Overall, the manuscript does not meet the standards for publication in ACP. I recommend the authors revise the manuscript, enhance data analysis and interpretation, present their findings in a more scientifically rigorous manner, and plan to resubmit as a new submission.
Some of my major concerns are as below:
The manuscript lacks analysis of measurements during or post-Omicron period to provide relevant insights for policy and management. Authors have broadly compared two pollution cases with a clean day during the sampling period. Even in this regard, the poor labeling technique of Figure 1, makes it very confusing what are Cases 1 through 5. Discussions for Cases 2 and 4 are missing. I feel that the title is misleading as the data has not been leveraged to present relevant results related to the Omicron period and policy relevance.

In the source apportionment section, the authors seem to have limited knowledge of using the VOC ratios. The results presented are very vague and do not seem to add any quantitative information.

The PMF source apportionment is weak, lacking statistical analysis and error estimation. There is no statistical analysis that supports why 5 factor was the best solution. The use of median value to replace missing values is not a justifiable way to treat the data, if the authors think so then needs to be discussed. Authors should examine at least 100 base runs with different seed numbers to find the best solution. Authors should discuss uncertainty and error estimations, and rotation ambiguity analysis.

While analyzing PMF factors, authors should use the time series trend, diurnal variations, use of wind speed and direction for identifying possible source sectors, and comparison with other inorganic tracers like trace gases to parameterize the PMF factors. Without some of these analyses, naming the factors just using the VOC profile may be inaccurate as there can be several sources for an individual VOC.

The authors should analyze differences in PMF factors/source profiles during and post-Omicron lockdown days and between high pollution and clean days.

The use of short-term measurements for SOA formation potential may not provide quantitative results. Authors should acknowledge such limitations. The comparison between Case 1 and 2 SOA formation potential is unclear regarding what information provided by the authors is useful.

Minor comment:
Methodology details for VOC, trace gas, PM, and meteorological measurements, including instrumentation techniques, calibration methods, data curation, and validation, should be provided.

English editing is necessary to improve the manuscript's readability and clarity.
Citation: https://doi.org/10.5194/egusphere-2024-575-RC3
- AC3: 'Reply on RC3', Bowen Zhang, 17 Jun 2024
  
  Thank you for your careful reading of our paper and valuable comments and suggestions. We believe that we have adequately addressed your comments. Please refer to the attached file for details.
  
  Citation: https://doi.org/10.5194/egusphere-2024-575-AC3

Interactive discussion

Status: closed

CC1: 'Comment on egusphere-2024-575', Jingz Gao, 10 Mar 2024

Zhang等在COVID-19期间在郑州确定了100多种VOC物种。总的来说，这项研究很有趣，作者也获得了一些结果。不幸的是，手稿过于肤浅，缺乏明显的新颖性。此外，许多结论，例如不同情况下的来源贡献，都过于简单和没有深度。我建议作者应该在手稿中使用一些物理/化学模型来增加一些关于臭氧或SOA的预算机制的讨论。虽然我不是这份手稿的推荐人，但我觉得这份手稿不符合ACP的标准。

Citation: https://doi.org/10.5194/egusphere-2024-575-CC1
CC2: 'Comment on egusphere-2024-575', Jingz Gao, 10 Mar 2024

Zhang et al. determined more than 100 VOC species in Zhengzhou during the COVID-19 period. Overall, the study is interesting and the authors also obtain some results. Unfortunately, the manuscript is too superficial and lacks of significant novelty. Moreover, many conclusions such as the source contributions in different cases are too simple and depthless. I suggest the authors should add some discussions about budget mechanisms of ozone or SOAs in the manuscript using some physical/chemical models. Although I am not a referrer of this manuscript, I felt the manuscript cannot meet the standard of ACP.

Citation: https://doi.org/10.5194/egusphere-2024-575-CC2
CC3: 'Comment on egusphere-2024-575', Fengyi Wu, 11 Mar 2024

I read the manuscript written by Zhang et al. and the comment from Gao carefully. I completely agree with Gao's comment. The manuscript lacks of significant novelty and the quality was much below the average standard of ACP. I strongly recommend the editor to reject this manuscript.

Citation: https://doi.org/10.5194/egusphere-2024-575-CC3
RC1:
'Comment on egusphere-2024-575', Anonymous Referee #1, 28 Mar 2024

The article explored the relationship between VOCs and PM2.5 with abundant VOCs species observed in Zhengzhou during the COVID-19 and made recommendations for the control of VOCs source emissions.
The current discussion may not be sufficiently supportive, please add more details to each section to make the entire article more logical. Basic details regarding instrumentation and data collection are missing. The authors need to supplement materials related to the reliability of the PMF results. Furthermore, more work is needed to elucidate the relationship between VOCs and haze pollution, as well as the influencing factors. And it is suggested that model simulation on SOA formation potential be added to the manuscript.
While the theme and results of the study are interesting, I have provided a few suggestions for improvement.

Line 124-135: The authors lack more detailed descriptions of the instrumentation. What are the working procedures of the instruments? What is the time resolution of the samples? How long were the samples collected for? Where were they captured? It is recommended to include information about instrument quality control methods.
Section 2.2 PMF model
How did the authors conduct factor selection, and why did not choose the 5-factor solution, 6-factor solution, and 7-factor solution? The authors need to provide more explanations and justifications in the manuscript.

Section 3.1 Pollution characteristics
Line 194: Ensure that the font in the figures is consistently in Times New Roman. The y-axis labels do not match the legend (NO and NOx).
What does the shading in Figure 1 represent? What are Case 1, Case 2, Case 3, Case 4, and Case 5? Clear explanations need to be provided. If these cases represent haze pollution processes, how do you define your pollution processes? Please include the references you consulted.

Line 217-225: Why did you only discuss Case 1 and Case 3? Are these two periods particularly significant? Provide your reasoning.
In Figure 2, the font should be changed to Times New Roman.
In this section, you only analyzed the variations in pollutant concentrations and meteorological conditions. What is the relationship between them? Which factors are crucial causes of pollution? You have not provided analysis and explanations.
Line 222-223: “[…] Among them, Case 1 (from 222 December 5 to December 10 and […]” A closing bracket is missed.

Section 3.2 Source appointment
Line 272: ‘indicating that the measured air VOC content was influenced by both remote sources and urban area emissions’, Are you referring to all VOCs? Or specifically to m/p-xylene and ethylbenzene?

Line 271-273: Your conclusion indicates that VOCs are influenced by transport and emissions from distant regions. Can this be further substantiated through transport or other means?

Line 306: 'olefins' should be corrected to 'alkenes'.

Line 316-325: Have you performed PMF in Case 1, Case 3, and the clean days? It is recommended to check whether the results of factor analysis are consistent in different conditions (Case 1, Case 2, and clean days) and compare the results.

Section 3.2 SOAFP
In this part, only Case 1 and Case 2 processes were discussed, then leading to the conclusion that the control of PM2.5 pollution in winter should focus on controlling vehicle emissions, solvent use, and combustion. I am afraid it is not convincing enough. It is recommended to add analysis of clean days. Contrast the pollution process with the clean day.

Citation: https://doi.org/10.5194/egusphere-2024-575-RC1
- AC1: 'Reply on RC1', Bowen Zhang, 17 Jun 2024
  
  Thank you for your careful reading of our paper and valuable comments and suggestions. We believe that we have adequately addressed your comments. Please refer to the attached file for details.
  
  Citation: https://doi.org/10.5194/egusphere-2024-575-AC1
RC2:
'Comment on egusphere-2024-575', Anonymous Referee #2, 06 Apr 2024

Overall comment:
The COVID-19 lockdown measures provide a natural experiment for probing air quality changes under substantial emission reductions. Zhang et al. investigate the variations of VOCs in response to the policy-driven emission changes in Zhengzhou city of China by using online ambient measurements, and the PMF model. While this paper is within the scope of ACP, the present manuscript is limited to a cursory data analysis (simply reporting measurement results), without convincing evidence and in-depth discussion, which makes this paper unpublishable in the present form. Further, the innovation of this work is far below the standard required to be published on ACP, which is even not qualified as a measurement report. Though addressing the specific comments below may improve the paper, I don’t think these improvements could justify publication in a high-standard journal such as ACP. Concerning the major flaws and the lack of innovation, I think this paper should be rejected.
Major comments:
1) The major weakness of this work is the lack of innovation. The impacts of the Omicron outbreak on Chinese cities are already well-documented and extensive studies have been conducted to elucidate the role of the anthropogenic sector on air pollution during- and post-outbreak periods. The authors claimed that industrial and vehicular emissions are dominant sectors contributing to ambient VOC, which is quite clear in prior studies. Further, the changes in PM2.5 and VOCs in response to the lockdown are broadly consistent with previous findings in Zhengzhou (even in Chinese literature). What is the innovation of this work and what are the new findings from this work that contribute to the air quality community?
2) The usage of SOAP should be revisited. The authors should be aware that SOAP is a very simple metric that provides limited information on SOA formation potential because SOA yield for individual VOCs in China may vary significantly in other countries due to the different levels of NOx and other oxidants. SOAP is generally adopted to reflect the SOA production potential based on bottom-up emission inventory (see Wu & Xie, ES&T), rather than using short-time ambient measurements. Therefore, I doubt the conclusion driven by the simple SOAP calculation. The authors should consider using F0AM and PBM-MCM for examining SOA production changes rather than SOAP.
3) The captions of the results section are meaningless. "Pollution characteristics" and "Source appointment" is not clear to the readers and should be rewritten for clarification.
4) The writing of this paper is in need of much attention. Specifically, the writing suffers from a series of fundamental issues, including a lack of clear organization, pervasive grammatical, and stylistic errors. I suggest the authors carefully read through the manuscript and rephrase the results section. There is substantial awkward phrasing throughout the paper which is confusing and misleading to the readers.
Minor comments:
1) The SOA formation potential is called "SOAP" rather than "SOAFP". The author should correct this abbreviation.

Citation: https://doi.org/10.5194/egusphere-2024-575-RC2
- AC2: 'Reply on RC2', Bowen Zhang, 17 Jun 2024
  
  Thank you for your careful reading of our paper and valuable comments and suggestions. We believe that we have adequately addressed your comments. Please refer to the attached file for details.
  
  Citation: https://doi.org/10.5194/egusphere-2024-575-AC2
RC3:
'Comment on egusphere-2024-575', Anonymous Referee #3, 06 Apr 2024
To provide a fair assessment, I refrained from reading previous reviews of the manuscript. Zhang et al. investigated VOC emissions during winter in Zhengzhou, China, likely aiming to understand the impact of the Omicron lockdown on city pollutants. However, given the extensive documentation of air quality studies during COVID pandemic and its variants, including Omicron, the manuscript lacks novelty in this context. The discussion on source apportionment also falls short, lacking depth and quantitative analysis. Overall, the manuscript does not meet the standards for publication in ACP. I recommend the authors revise the manuscript, enhance data analysis and interpretation, present their findings in a more scientifically rigorous manner, and plan to resubmit as a new submission.
Some of my major concerns are as below:
The manuscript lacks analysis of measurements during or post-Omicron period to provide relevant insights for policy and management. Authors have broadly compared two pollution cases with a clean day during the sampling period. Even in this regard, the poor labeling technique of Figure 1, makes it very confusing what are Cases 1 through 5. Discussions for Cases 2 and 4 are missing. I feel that the title is misleading as the data has not been leveraged to present relevant results related to the Omicron period and policy relevance.

In the source apportionment section, the authors seem to have limited knowledge of using the VOC ratios. The results presented are very vague and do not seem to add any quantitative information.

The PMF source apportionment is weak, lacking statistical analysis and error estimation. There is no statistical analysis that supports why 5 factor was the best solution. The use of median value to replace missing values is not a justifiable way to treat the data, if the authors think so then needs to be discussed. Authors should examine at least 100 base runs with different seed numbers to find the best solution. Authors should discuss uncertainty and error estimations, and rotation ambiguity analysis.

While analyzing PMF factors, authors should use the time series trend, diurnal variations, use of wind speed and direction for identifying possible source sectors, and comparison with other inorganic tracers like trace gases to parameterize the PMF factors. Without some of these analyses, naming the factors just using the VOC profile may be inaccurate as there can be several sources for an individual VOC.

The authors should analyze differences in PMF factors/source profiles during and post-Omicron lockdown days and between high pollution and clean days.

The use of short-term measurements for SOA formation potential may not provide quantitative results. Authors should acknowledge such limitations. The comparison between Case 1 and 2 SOA formation potential is unclear regarding what information provided by the authors is useful.

Minor comment:
Methodology details for VOC, trace gas, PM, and meteorological measurements, including instrumentation techniques, calibration methods, data curation, and validation, should be provided.

English editing is necessary to improve the manuscript's readability and clarity.
Citation: https://doi.org/10.5194/egusphere-2024-575-RC3
- AC3: 'Reply on RC3', Bowen Zhang, 17 Jun 2024
  
  Thank you for your careful reading of our paper and valuable comments and suggestions. We believe that we have adequately addressed your comments. Please refer to the attached file for details.
  
  Citation: https://doi.org/10.5194/egusphere-2024-575-AC3

Peer review completion

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

AR by Bowen Zhang on behalf of the Authors (09 Jul 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (15 Jul 2024) by Kelvin Bates

RR by Anonymous Referee #1 (26 Jul 2024)

Suggestions for revision or reasons for rejection

The authors have made significant efforts to address the comments and suggestions from the previous review. The revisions have improved the manuscript, but there are still some issues that need to be addressed before it can be considered for publication.
Detailed comments:
Line 42: The current list of keywords is quite limited. I recommend including additional relevant terms that reflect the core topics and methodologies discussed in the manuscript.
Section 3.1 Overview of variation in pollutants and meteorological parameters
While the correlations between PM2.5, TVOCs, NOx, and relative humidity are mentioned, a more detailed analysis of these correlations is needed. Explain the nature of these relationships and their impact on understanding pollution formation, and compare these correlations with previous research results. Although the influence of meteorological conditions on pollution formation is noted, further elaboration on how specific meteorological factors (such as low wind speed and temperature) affect pollutant concentrations is necessary. Discuss why these conditions might lead to higher or lower pollutant levels. Additionally, while the comparison of pollutant concentrations between different periods is addressed, a detailed analysis of the observed trends, such as the increase in PM2.5 and TVOCs during the recovery period, should be provided. Analyze the possible reasons for these trends and their relationship with the resumption of production activities.
Section 3.2 SOAFP
The analysis of SOAP contributions across different pollution processes provides an overview but lacks in-depth explanations. It would be beneficial to include more detailed analysis on why the industrial source is dominant in Case 1 and why solvent usage and fuel evaporation sources are more evenly distributed in Case 2. Additionally, analyze whether the observed trends in SOAP values and source contributions are related to other environmental factors or changes over time. Explain how these trends impact air quality and PM2.5 pollution.
Section 4 Conclusions
The conclusions provided primarily summarize the results without offering detailed explanations for the observed changes or the influence of different sources on VOCs and PM2.5 pollution. To strengthen the conclusions, it would be beneficial to include more in-depth analysis and discussion regarding why certain changes were observed and how they relate to the influence of specific sources on VOCs and PM2.5 formation, how different sources contribute to changes in TVOCs and PM2.5 levels across different periods, and potential driving factors behind the presence and variation of these sources during different pollution episodes. Incorporating such explanations will provide a clearer understanding of the underlying mechanisms driving the observed results and enhance the overall impact of the conclusions.

Hide

RR by Anonymous Referee #3 (30 Jul 2024)

Suggestions for revision or reasons for rejection

I would like to thank the authors for submitting the review of your manuscript. However, I regret to recommend not publishing the manuscript in its current form as it still lacks clarity and scientific significance on how the results have been presented. Below, I have outlined only some of my specific concerns.
Abstract:
1. Line 16: The abrupt mention of Case 2 is confusing. How many cases were analyzed, and based on what factors were these cases chosen?
2. Lines 23-25: The significance of this section is unclear. Please clarify what you mean and what you are trying to signify.
3. The abstract needs a more cohesive approach to presenting the results.
Introduction:
1. Line 97: The term "human factor" is vague and hard to understand. Please specify what you mean.
2. Lines 120-125: The phrase "See what results show later on..." is unclear. What results are you referring to, and how do they relate to the study's objectives?
3. Line 110: The rationale for choosing this sampling duration is unclear. Was the Omicron lockdown a significant interruption compared to earlier variants? Providing a timeline of Omicron detection, lockdown periods, and sampling coverage would help clarify this. Additionally, what is meant by "nuclei acid screening measure for all staff," and how does it relate to your study? Clarify whether "all staff" refers to government staff or the general population.
4. The introduction should clearly explain Cases 1 and 2, as well as the clean period, to clarify the study's objectives. Although some of this information will appear in the methods section, the introduction and abstract should provide a clear understanding of the study's purpose.
Methods:
1. Line 140: The claim that the sampling period covered the entire infection period of Omicron is questionable. According to your introduction, Omicron started on October 8th and lasted until early December, while your sampling is from December 1st to January 31st. Your sampling period appears to coincide with the post-Omicron period.
2. Line 145: Please provide references to other literature discussing the TH-PKU 300b instrument and its methodology.
3. Line 160: Was the instrument calibrated for all 160 compounds?
4. Line 252: Jan 1 as an absolute cutoff of "infection period" and "recovery period" needs proper debate.
Results and Discussion:
1. Figure 2: The composition pie chart does not show a discernible difference between the two cases. Surprisingly, the recovery period had even lower NOx and aromatics than the infection period. Please clarify.
2. Line 286: What do you mean by "highest increase ratio"?
3. Tables 1 and 2: The criteria for dividing the infection period vs. the recovery period are unclear. In several instances, the terms Cases 1 and 2 are used interchangeably with infection and recovery periods, which is confusing.
4. Line 303: The use of VOC ratios possesses uncertainty. If you reference values of 0.13-0.7 for combustion, how does an average value of 1 align with combustion? Similarly, how do you reconcile the isopentane/n-pentane ratio with liquid petrol if the average does not fall within the referenced range? The same question applies to the isobutane/n-butane ratio for natural gas. The current explanation suggests a limited understanding of VOC ratios.
5. Figure 5: The figure caption is awkwardly written. Combine the note into the caption itself. Generally, wind speeds below 1 m/s indicate local emissions and are not suitable for CPF analysis. Apply a filter of <1 m/s for CPF. Despite CPF indicating local sources, you also mention long-range transport as the most influential source in other instance, which is contradictory.
6. The study's main aim seems to be comparing infection vs. recovery cases and/or pollution Cases 1 and 2 vs clean period, yet the overall PMF for entire sampling is discussed in the main text, while PMFs differences for the periods of interest are in the supplementary section. This does not align with the study's objectives.
7. Line 374: Clarify what is meant by "peak of Omicron infection period." The terminology used is confusing, making it difficult to follow the results.

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ED: Reconsider after major revisions (31 Jul 2024) by Kelvin Bates

AR by Bowen Zhang on behalf of the Authors (27 Aug 2024) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (03 Sep 2024) by Kelvin Bates

I would like to thank the authors for responding to this latest round of reviewer comments, which I believe have substantially improved the manuscript. The reviewers both still had misgivings about the manuscript, stating that it was not ready for publication in its previous iteration and may require additional rounds of review. I do think the manuscript is approaching a state in which it is ready for publication, and that the most recent round of revisions should preclude the need for additional reviews, but I worry that some of the responses to the current round of reviews were not satisfactorily detailed. I'm therefore asking the authors to reconsider these latest reviews in greater detail by responding to the points I've outlined below with a new revision of the manuscript. Once these points are addressed I hope we will be ready to publish the manuscript.

First, please make sure all statements not derived from data shown here are properly sourced. This applies especially to some of the sections detailed below (i.e., descriptions of the impacts of meteorology and the behaviors of residents during and after lockdown), but also throughout the introduction (e.g., L152, "always the most polluted period in the entire year").

Rev1 Sec 3.1: your answer begins by implying that meteorology is most important since "emissions from pollutant sources usually change very little over a period of time" while meteorology does change, but later in the same paragraph you state that meteorological differences between the two periods are "minor" (though the reader does not know what level of difference "minor" entails) and, without any evident justification, say that meteorology is not responsible for any differences between the pollution periods. It's also not clear what the sentence "when comparing the meteorological conditions of the two pollution processes, none of the processes showed a tendency to be more prone to pollution" means; what are the two "processes"? Overall, this section requires a more quantitative approach; by how much should temperature, wind speed, and humidity affect pollution levels (based either on theory or prior research in this area), and therefore, why can we be sure that the differences are not meteorological? It could be that the conclusion remains there's "no discernible trend towards greater susceptibility to pollution" (L280-281) in period 2, but that needs quantitative justification.

Reviewer 2, Line 110: This added text is extremely confusing and difficult to read. The tenses switch between present and past, and most of the sentences are run-ons with many connected clauses. It's not clear why details of the city's screening processes are needed for this manuscript. Ideally this paragraph could be clarified, substantially shortened, and boiled down to only the most salient aspects for the present analysis. It would also be helpful if statements about human behavior during the various periods (e.g. "the number of people moving around Zhengzhou has increased", "people basically rested at home", etc.) could be supported by citations to sources that corroborate this.

Reviewer 2 Results & Discussion question 1: your response does not address the reviewer's point that the NOx decreased in the recovery period.

Reviewer 2 Results & Discussion question 4: on VOC ratios -- my interpretation is that the reviewer was not implying that the isomer ratio method has limitations, but that its application is incorrect here, and that hasn't been fixed in your revisions. For example, your measured ratio of isobutane to n-butane is squarely within the range for LPG, above the range for vehicle emissions, and below the range for natural gas emissions (L338-340). Possible interpretations of your measured value of 0.5 imply (a) a mix between all three sources, (b) a mix between vehicle and natural gas sources, or (c) emissions dominated by LPG. However, you conclude on L342 that your measured value implies a contribution from natural gas, without explaining how you got there, even though that doesn't line up with the range in which the measured value falls. The analysis of isopentane/n-pentane ratios seems similarly problematic (L332-337); the measured ratio of 1.4 doesn't necessarily mean that pentane is "mainly" derived from liquid petrol and fuel evaporation, since the same ratio could be achieved by mixing sources from coal and vehicle exhaust in the proper ratio. The analysis in this section needs reworking.

While I don't foresee this needing to go to reviewers again, that may depend on the degree to which these subsequent revisions fully address the reviewer comments. Thank you for taking the time to address these outstanding issues, and hopefully we can proceed to publication soon.

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AR by Bowen Zhang on behalf of the Authors (09 Sep 2024) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (11 Sep 2024) by Kelvin Bates

Thanks to the authors for substantially revising the language in the added sections -- all are much clearer than they were in the previous revision. However, two of the reviewers' comments remain unaddressed.

First, while the section describing the influence of meteorology (3.1) is easier to read, the analysis was not made more quantitative in this revision as requested. I believe the fundamental concern here is that no effort has been made to calculate, quantitatively, how much the higher pollution in Case 2 could be due to meteorology rather than increased emissions. The current analysis brushes off any meteorological differences as minor, even though the higher wind speed and temperature and lower humidity might all contribute to a buildup of gas phase pollutants. For example, given that the wind speed in Case 2 is 25% lower than in Case 1, in a simple box model the pollutants could be expected to build up to levels [1/(1-.25)-1] = 33% higher just due to the lower ventilation, which is enough to account for much of the concentration differences of some pollutants between the periods. The influences of temperature and humidity may be more complex, but still, a quantitative estimate of their impact would be useful, or at least an acknowledgment of their potential importance. In cases where this fundamentally changes the conclusions that can be drawn from the analysis -- for example, if the difference in wind speed is indeed sufficient to explain some appreciable portion of the difference in pollutant concentrations -- that should also be noted in the conclusions and abstract.

Second, the interpretations about source apportionment in the VOC ratio analysis section (3.2) remain more conclusive than the data allow. I think the edits to Figure 3 have improved its usefulness. However, it is not true that the measured ratio, for example, of isopentane to n pentane "indicates that pentane is influenced by a combination of emissions from LPG and fuel evaporation". The same mean ratio could be reached through a linear combination of emissions from coal combustion and vehicle exhaust, for example. The statements attributing emissions to particular sources in this section should be hedged accordingly, acknowledging that other interpretations of these data can't be ruled out.

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AR by Bowen Zhang on behalf of the Authors (21 Sep 2024) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (24 Sep 2024) by Kelvin Bates

We thank the authors for their rapid resubmission and point-by-point response to the editorial comments. Unfortunately, the latest revision does not fundamentally address the concerns previously pointed out by the reviewers and editor. We apologize if the reviewers' and editor's comments have not been entirely clear, and will endeavor to reiterate them more clearly below. As reviewers have pointed out, previous iterations of this manuscript were not up to the standards of ACP, and while substantial improvements have been made, these repeated rounds of revisions are an effort to ensure that all the concerns of the reviewers are addressed in order to meet ACP standards.

On the influence of meteorology: the fundamental concern was that the impacts of meteorology on the analyzed pollution events have not been quantified, and therefore it cannot be ruled out that meteorology plays a major role (potentially as strong as or stronger than emissions changes) in the differences in pollution seen in the two analyzed events. The way this is currently addressed in the manuscript is by ignoring the meteorological differences without giving valid reasoning: e.g. "However, the discrepancy in wind speed (0.3 m/s) between Case 1 and Case 2 is deemed to be of negligible magnitude during the observation periods, and the actual impact is inconsequential." How is 0.3 m/s determined to be "negligible" and its impacts "inconsequential"? As was highlighted in a previous round of reviewer and editor comments, this 0.3 m/s represents a 25% decrease, which could be responsible for a non-negligible 33% increase in pollution levels based on a simple box model framework.

Required edits:
EITHER: quantify the potential effects of wind speed and other variables with, for example, a simple box model framework, and incorporate this into the analysis; in cases where this fundamentally changes the conclusions that can be drawn from the analysis -- for example, if the difference in wind speed is indeed sufficient to explain some appreciable portion of the difference in pollutant concentrations -- that should also be noted in the conclusions and abstract.
OR: remove unsupported statements such as the sentence quoted above about the magnitude of meteorological effects, and acknowledge -- here in the meteorology section, but also in the abstract and conclusions -- that meteorology may also play a role in differences between pollution events, and the importance of that role was not determined here.

On the VOC ratio analysis: the added lines (334-339) do not clarify this analysis. Instead they further obfuscate it, since not *two* sentences in close proximity both state that pentane is coming from a combination of LPG emissions and fuel evaporation, without acknowledging that coal combustion and vehicle exhaust may also contribute. Further, the X/E ratio looks suspiciously uniform -- was it really perfectly on the 2.01 : 1 line for almost all observations? Or are the observations clustered in the lower-left of graph 3d (near the origin) more scattered? If so, it would be more helpful to zoom in there.

Required edits:
EITHER: remove the paragraphs about the VOC ratios, as this analysis does not seem central to your conclusions (which are largely based on the PMF analysis instead).
OR: explicitly acknowledge in each of the paragraphs about a different pair of species that the observed ratio does not rule out linear combinations of other sources. In particular, in the paragraph about isopentane/n-pentane, it should be noted that the observed ratio does not rule out contribution from coal combustion and vehicle exhaust, and in the paragraph about isobutane/n-butane, it should be noted that the observed ratio, while consistent with LPG usage, could also be achieved by a combination of vehicular and natural gas emissions.

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AR by Bowen Zhang on behalf of the Authors (02 Oct 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (15 Oct 2024) by Kelvin Bates

AR by Bowen Zhang on behalf of the Authors (21 Oct 2024) Author's response Manuscript

Journal article(s) based on this preprint

10 Dec 2024

The variations in volatile organic compounds based on the policy change for Omicron in the traffic hub of Zhengzhou

Bowen Zhang, Dong Zhang, Zhe Dong, Xinshuai Song, Ruiqin Zhang, and Xiao Li

Atmos. Chem. Phys., 24, 13587–13601, https://doi.org/10.5194/acp-24-13587-2024,https://doi.org/10.5194/acp-24-13587-2024, 2024

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Bowen Zhang, Dong Zhang, Zhe Dong, Xinshuai Song, Ruiqin Zhang, and Xiao Li

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https://doi.org/10.5194/egusphere-2024-575-supplement

Bowen Zhang, Dong Zhang, Zhe Dong, Xinshuai Song, Ruiqin Zhang, and Xiao Li

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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Short summary

Continuous online VOCs monitoring was carried out at an urban site in a traffic-hub city for two months during the Omicron-infected stage. The characteristics and variations of VOCs in different periods were studied, and their impact on the formation of SOA were evaluated. The work in this manuscript evaluated the influence of the policy variation on VOCs pollution, which will provide some basis for VOCs pollution research and control of pollution sources.


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