the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Mar 2024
The variations of VOCs based on the policy change of Omicron in polluted winter in traffic-hub city, China
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 PM2.5 and total VOCs (TVOCs) ranged from 54 to 239 µg/m3 and from 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 PM2.5 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/m3 and 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 PM2.5 pollution in winter.
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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 -
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 -
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
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