Characteristics of Atmospheric Pollution in a Chinese Megacity: Insights from Three Different Functional Areas

Round 1

Reviewer 1 Report

The authors Yang et al., summarized the impact of atmospheric ambient air pollution in the megacity of China. The overall quality of the present article is good and presented well. The major atmospheric pollutants, i.e., PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃. The authors assessed the characteristics of atmospheric ambient pollution by analyzing daily and hourly levels in three different functional sites in Shanghai (2019-2021).

 I made some suggestions/ comments that need to be addressed by minor revision. Below are some specific comments to be taken into consideration by the authors:

-     Abstract is fine but requires language improvement.

-          Line 50-61: Please improve sentence errors

-          Plz revise the Keywords

-          Please avoid the I, We, our….  entire MS.

-          Figures quality is good

-          Please revise the Conclusion section and mention future perspectives

-          The manuscript abounds with grammatical errors, which should be attended to.

Author Response

The authors Yang et al., summarized the impact of atmospheric ambient air pollution in the megacity of China. The overall quality of the present article is good and presented well. The major atmospheric pollutants, i.e., PM2.5, PM10, SO2, NO2, CO, and O3. The authors assessed the characteristics of atmospheric ambient pollution by analyzing daily and hourly levels in three different functional sites in Shanghai (2019-2021).

 

 I made some suggestions/ comments that need to be addressed by minor revision. Below are some specific comments to be taken into consideration by the authors:

 

-     Abstract is fine but requires language improvement.

Response：We revised the abstract as follows:

Line 14-28:

Abstract: The most important atmospheric pollutants include PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃. Characteristics of atmospheric pollution were investigated by analyzing daily and hourly concentrations of the six key pollutants in three different functional areas (urban, suburban, and rural) of Shanghai during 2019-2021. Results show that O₃, exceeding PM_2.5, has become primary pollutant determining air quality in Shanghai. The frequency of O₃ as primary pollutant ranged from 40% in urban area to 71% in rural area, which was much higher than that of PM_2.5 (14-21%). NO₂ and SO₂, precursors of PM_2.5, presented clear weekend effect, whereas PM_2.5 on weekends seems higher than that on weekdays. In the warm season, O₃ on weekends was higher than that on weekdays in the three different functional areas, whereas no significant difference was observed between O₃ on weekdays and weekends in the cold season. Potential source contribution function analysis indicated air pollution in Shanghai was impacted by inter-regional and intra-regional transport. The potential source areas of PM_2.5 and O₃ were different, which brought challenges to the coordinated control of PM_2.5 and O₃ in Shanghai. This study emphasizes the prominent O₃ pollution in Shanghai and the prevention and control of O₃ pollution requires regional joint prevention and control strategy.

 

-          Line 50-61: Please improve sentence errors

Response：we revised the text as follows:

Line 68-83：

In China, PM_2.5 was incorporated into the national ambient air quality standard (GB 3095-2012) for the first time in 2012. Then the Chinese government implemented the Air Pollution Prevention and Control Action Plan from 2013 to 2017, followed by Three-year Action Plan for the Blue Sky Protection Campaign during 2018-2020. Annual average PM_2.5 concentration of 337 Chinese cities decreased to 33 μg/m³ in 2020 (Data source: China National Environmental Monitoring Centre, http://www.cnemc.cn/jcbg/zghjzkgb/(accessed on 1 January 2022)), which satisfied the national ambient air quality standard of PM_2.5 (35 μg/m³) for the first time. However, the average annual concentration of PM_2.5 in urban areas of China has heavy disparity from the 2021 guidance value of WHO (5 μg/m³), which implied urban residents still suffered potential health risks caused by air pollution. To keep the trend of continuous improvement of air quality in long term is still a challenge for China, especially in densely populated urban areas.

 

-          Plz revise the Keywords

Response：We revised the keywords as follows:

Air quality; Different functional areas; Weekday-weekend effect; Potential source contribution function; Shanghai.

 

-          Please avoid the I, We, our….  entire MS.

Response：Done. “We” are used in three places in the text and we have revised all.

 

-          Figures quality is good

Response：We appreciate the reviewer’s positive comment.

-          Please revise the Conclusion section and mention future perspectives

Response： We have revised the Conclusion section and mention future perspectives in the Discussion section. Please see the revised text, as follows:

Line 475-495:

5. Conclusions

In the study, characteristics of atmospheric pollution were discussed by analyzing daily and hourly concentrations of PM2.5, PM10, SO2, NO2, CO, and O3 in three different functional areas, which is representative of urban, suburban, and rural areas in Shanghai from 2019 to 2021. The frequency of O3 identified as primary pollutant was 40% in the urban site, 51% in the suburban site, and 71% in the rural site in Shanghai, far higher than that of PM2.5 (14-21%). The frequency of NO2 as primary pollutant was 41% in the urban site and 23% in the suburban site. NO2 and SO2 presented clear weekend effect, whereas PM2.5 on weekends seems higher than that on weekdays in urban and suburban areas. In the warm season, O3 on weekends was higher than that on weekdays in the three sites. However, no significant difference was observed between O3 on weekdays and weekends in the cold season. Different temporal variations of O3 in the warm and the cold season were not only resulted from the weakened NO titration effect, but also were related to meteorological conditions. Comparison of variations of pollutants on weekdays and weekends indicated complex nonlinear relationship between primary pollutants and secondary pollutants. Inter-regional and intra-regional transport played an important role in the pollution process in Shanghai. Potential source areas of PM2.5 in Shanghai mainly included the Yangtze River Delta region and its surrounding areas, whereas Bohai Sea Economic Region in China, North and South Korea were identified as mainly potential source areas of O3 during all seasons. Different source areas of PM2.5 and O3 brought challenges to the coordinated control of PM2.5 and O3 in Shanghai.

Line 470-474:

The present study has some limitations. Despite long-term analysis of NO₂ and O₃, the study failed to proceed in-depth analysis of ozone formation mechanism due to a lack of data on the concentrations and composition of VOCs. Data on long-term ambient VOC compositions in different functional areas in Shanghai and other megacities is recommended for future studies.

 

-          The manuscript abounds with grammatical errors, which should be attended to.

Response：In the revised manuscript, we carefully checked spelling mistakes and grammatical errors repeatedly, with the help of translation tools. Please see the revised manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

The article discusses atmospheric pollution in a Chinese megacity. It makes several valid points about research methodology and results. I would recommend some major revisions to this study to make it better.

1- The abstract needs to be rewritten to reflect the research challenge, the research methods, and finally the findings and conclusions. Here, I see that the abstract extends beyond explaining the research problem and in the final paragraph (Lines 25-27), the author recommends not only considering regional joint measures, but also adapting them to local conditions. ' This recommendation is very generic and not clear in what context it will be used.

2- The introduction needs to be revised and rewritten to discuss the gap in literature, research aims, argument and contribution to knowledge. In some places of the introduction the authors mention facts without any supportive references. The example here is given to 'Air pollution ranks fourth among health risk factors in China' on Page 1 Line 37–38.

 

3- The results section is well written and well explained. I did not recognize basic information in the discussion section, however. Here, the authors should link to the results of prior studies. In this case, I would recommend linking the results to studies that tackle other cities in China or around the world. The limitations need to also be discussed in this section.

 

4- The conclusion section needs rewriting in order to discuss in depth the main findings of this study in more detail. The conclusion should also be revised since some sentences are too generic. In Page 12 Line 318–321, the example given is 'The implication of this study is that the characteristics of air pollution in Chinese megacities are more complicated.' Using the results of the present study, describe in what manner such a complication was recognised. Discuss future research based on research limitations. 

Author Response

The article discusses atmospheric pollution in a Chinese megacity. It makes several valid points about research methodology and results. I would recommend some major revisions to this study to make it better.

• The abstract needs to be rewritten to reflect the research challenge, the research methods, and finally the findings and conclusions. Here, I see that the abstract extends beyond explaining the research problem and in the final paragraph (Lines 25-27), the author recommends not only considering regional joint measures, but also adapting them to local conditions. ' This recommendation is very generic and not clear in what context it will be used.

Response：We rewrote the abstract as suggested, as follows:

Line 13-27:

Abstract: The most important atmospheric pollutants include PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃. Characteristics of atmospheric pollution were investigated by analyzing daily and hourly concentrations of the six key pollutants in three different functional areas (urban, suburban, and rural) of Shanghai during 2019-2021. Results show that O₃, exceeding PM_2.5, has become primary pollutant determining air quality in Shanghai. The frequency of O₃ as primary pollutant ranged from 40% in urban area to 71% in rural area, which was much higher than that of PM_2.5 (14-21%). NO₂ and SO₂, precursors of PM_2.5, presented clear weekend effect, whereas PM_2.5 on weekends seems higher than that on weekdays. In the warm season, O₃ on weekends was higher than that on weekdays in the three different functional areas, whereas no significant difference was observed between O₃ on weekdays and weekends in the cold season. Potential source contribution function analysis indicated air pollution in Shanghai was impacted by inter-regional and intra-regional transport. The potential source areas of PM_2.5 and O₃ were different, which brought challenges to the coordinated control of PM_2.5 and O₃ in Shanghai. This study emphasizes the prominent O₃ pollution in Shanghai and the prevention and control of O₃ pollution requires regional joint prevention and control strategy.

2- The introduction needs to be revised and rewritten to discuss the gap in literature, research aims, argument and contribution to knowledge. In some places of the introduction the authors mention facts without any supportive references. The example here is given to 'Air pollution ranks fourth among health risk factors in China' on Page 1 Line 37–38.

 Response：We made some revision in the introduction and the reference is cited (Line 54). Please see the revised introduction, from Line 47 to Line 102.

 

3- The results section is well written and well explained. I did not recognize basic information in the discussion section, however. Here, the authors should link to the results of prior studies. In this case, I would recommend linking the results to studies that tackle other cities in China or around the world. The limitations need to also be discussed in this section.

 Response：We revised the Results Section and added a Discussion Section, in which results were linked to prior studies that tackle other cities in China, as follows:

Line 435-473:

4. Discussion

O₃ was identified as the most important pollutant determining air quality in Shanghai, which was consistent with the increasing trend of O₃ in other Chinese mega cities. In a previous study conducted at the Pearl River Delta (PRD) region in southern China, surface ozone shows upward trends at the rate of 0.28–1.02 ppb yr⁻¹ at urban sites from 2006 to 2019, which was attributed to the reduced NO titration effect [57]. Similarly, O₃ concentrations exhibit obvious interannual increases in the Sichuan Basin, southwestern China during 2013–2019 [58]. O₃ concentrations generally increased during 2014-2020 with a slower increasing rate after 2017, and the highest O₃ concentrations primarily occurred during summer in northern China, and during autumn or spring in southern China [59]. Besides, co-polluted days by ozone (O₃) and PM_2.5 were frequently observed in the Beijing–Tianjin–Hebei (BTH) region in the North China Plain in warm seasons (April–October) of 2013–2020 [60]. In summary, O₃ pollution, as well as PM_2.5, has become the challenge of air pollution prevention and control in Chinese mega cities.

In the current work, O₃ on weekends was significantly higher than that on weekdays during the warm season in the three different functional areas in Shanghai, whereas there exists no significant difference between O₃ on weekdays and weekends in the cold season. The results implied that only controlling emissions from motor vehicles is not effective for pollution control of O₃ in Shanghai despite NO₂ is a precursor of O₃ formation. NOx and volatile organic compound (VOCs) are precursors of O₃ [61]. However, the production of O₃ in urban areas, characterized by high NOx/VOC ratios, is VOC-limited [43]. For example, O₃ formation was simulated by the observation-based model in Shanghai in July 2017 and results revealed that O₃ formation at the urban site was controlled by VOCs [62]. Similar results were also reported in other Chinese mega cities [61,63]. An earlier study built an emission inventory for major anthropogenic air pollutants and VOC species in the YRD region for the year 2007 and found the industrial sources contributed about 69 % of the total VOC emissions, while vehicles only accounted for 12.4% of VOC emissions [64]. A recent study developed improved industrial VOCs emissions inventories for China from 2011 to 2018 and reported an increased trend of annual industrial VOCs emissions with an average annual growth rate of 5.2% [65]. Updated VOCs emission inventory at regional scale was suggested as emerging issues for future research considering the significant influence of regional transport.

The present study has some limitations. Despite long-term analysis of NO₂ and O₃, the study failed to proceed in-depth analysis of ozone formation mechanism due to a lack of data on the concentrations and composition of VOCs. Data on long-term ambient VOC compositions in different functional areas in Shanghai and other megacities is recommended for future studies.

Please see the revised Results Section in Line 169-434.

4- The conclusion section needs rewriting in order to discuss in depth the main findings of this study in more detail. The conclusion should also be revised since some sentences are too generic. In Page 12 Line 318–321, the example given is 'The implication of this study is that the characteristics of air pollution in Chinese megacities are more complicated.' Using the results of the present study, describe in what manner such a complication was recognised. Discuss future research based on research limitations. 

Response：We have rewritten the conclusion section in the revised manuscript, as follows:

Line 474-494:

5. Conclusions

In the study, characteristics of atmospheric pollution were discussed by analyzing daily and hourly concentrations of PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃ in three different functional areas, which is representative of urban, suburban, and rural areas in Shanghai from 2019 to 2021. The frequency of O₃ identified as primary pollutant was 40% in the urban site, 51% in the suburban site, and 71% in the rural site in Shanghai, far higher than that of PM_2.5 (14-21%). The frequency of NO₂ as primary pollutant was 41% in the urban site and 23% in the suburban site. NO₂ and SO₂ presented clear weekend effect, whereas PM_2.5 on weekends seems higher than that on weekdays in urban and suburban areas. In the warm season, O₃ on weekends was higher than that on weekdays in the three sites. However, no significant difference was observed between O₃ on weekdays and weekends in the cold season. Different temporal variations of O₃ in the warm and the cold season were not only resulted from the weakened NO titration effect, but also were related to meteorological conditions. Comparison of variations of pollutants on weekdays and weekends indicated complex nonlinear relationship between primary pollutants and secondary pollutants. Inter-regional and intra-regional transport played an important role in the pollution process in Shanghai. Potential source areas of PM_2.5 in Shanghai mainly included the Yangtze River Delta region and its surrounding areas, whereas Bohai Sea Economic Region in China, North and South Korea were identified as mainly potential source areas of O₃ during all seasons. Different source areas of PM_2.5 and O₃ brought challenges to the coordinated control of PM_2.5 and O₃ in Shanghai.

Author Response File: Author Response.docx

Reviewer 3 Report

Dear Editor

After a detailed analysis of the manuscript, entitled: “Characteristics of Atmospheric Pollution in A Chinese Megacity: Insights From Three Different Functional Areas”, I suggest ACCEPT the manuscript with minor corrections:

1 - The title is very well reasoned. Congratulations to the authors.

2 - The techniques were applied correctly, congratulations to the authors.

3 - The resolution of Figure 1 needs to be improved.

4 - Figure 3 needs to be enlarged, with better resolution.

Congratulations on the great work, it was a privilege to evaluate this manuscript

Author Response

Dear Editor

After a detailed analysis of the manuscript, entitled: “Characteristics of Atmospheric Pollution in A Chinese Megacity: Insights From Three Different Functional Areas”, I suggest ACCEPT the manuscript with minor corrections:

1 - The title is very well reasoned. Congratulations to the authors.

Response：We appreciated the reviewer’s time and made positive comments on this manuscript.

2 - The techniques were applied correctly, congratulations to the authors.

Response：We appreciated the reviewer’s time and made positive comments on this manuscript.

3 - The resolution of Figure 1 needs to be improved.

Response：Figure 1 is clear in the word file, but is not clear when converted in PDF format. We don't know what went wrong. Please see Figure 1 in the revised manuscript in the word file. We also submitted the original picture of each figure with good resolution.

24 - Figure 3 needs to be enlarged, with better resolution.

Response：Figure 3 is clear in the word file, but is not clear when converted in PDF format. We don't know what went wrong. Please see Figure 3 in the revised manuscript in the word file. We also submitted the original picture of each figure with good resolution.

Congratulations on the great work, it was a privilege to evaluate this manuscript

Response：We appreciated the reviewer’s time and made positive comments on this manuscript.

Author Response File: Author Response.docx

Reviewer 4 Report

In the present manuscript, six atmospheric pollutants including PM_2.5, PM₁₀, SO₂, NO_2, CO, and O₃. have been investigated on a daily and hourly basis in three different functional areas (Semi-urban, urban and rural) in Shanghai during 2019-2021. Backward trajectories analysis and potential source contribution function analysis have been analyzed. I recommend this manuscript for publication after revision.

The detailed review comments are given below.

1.    In highest concentration of each pollutant has not been mentioned in the manuscript, only the percentage contribution of each pollutant has been mentioned in the manuscript. The author should include the highest and minimum concentrations of pollutants.

2.    Author should include a description of CO and SO₂ as not the primary contributor to atmospheric pollution in this research study.

3.    In the backward trajectories plot Fig. 4 “cluster mean of trajectories (1-5), here 1-5 is not clear, the author should make it clear in the manuscript as well as in fig. the average seasonal basis of variation in the trajectories of the three-year study period should be described in the manuscript.

4.    Author has included the figure of meteorological parameters, but there is no significance has been described in the manuscript. There is a correlation between meteorological parameters and the concentration of pollutants, but in this study, it has not been determined. The author should include the correlation.

Author Response

In the present manuscript, six atmospheric pollutants including PM_2.5, PM₁₀, SO₂, NO_2, CO, and O₃. have been investigated on a daily and hourly basis in three different functional areas (Semi-urban, urban and rural) in Shanghai during 2019-2021. Backward trajectories analysis and potential source contribution function analysis have been analyzed. I recommend this manuscript for publication after revision.

The detailed review comments are given below.

1. In highest concentration of each pollutant has not been mentioned in the manuscript, only the percentage contribution of each pollutant has been mentioned in the manuscript. The author should include the highest and minimum concentrations of pollutants.

Response: We revised the text to describe the highest and minimum concentrations of pollutants as suggested, as seen in Line 180-201:

Frequencies of PM_2.5, PM₁₀, NO₂ and O₃ as primary pollutants in urban, suburban, and rural areas in Shanghai during 2019-2021 were summarized in Table 2. From urban area XH to rural area CM, the frequency of NO₂ as the primary pollutant is significantly dropped from 41% to 3%, which was consistent with that rural area in Shanghai was less affected by vehicular emissions. Annual concentration of NO₂ in urban XH, suburban QP and rural CM was 41 (daily minimum-maximum: 3-120) μg/m³, 36 (4-108) μg/m³, and 18 (1-92) μg/m³, respectively. On the contrary, the frequency of O₃ as the primary pollutant increased from 40% to 71%, from urban area XH to rural area CM. MDA 8h O₃ (Maximum daily 8-hour average concentration of O₃) ranged from 13 μg/m³ to 276 μg/m³ in CM, from 14 μg/m³ to 261 μg/m³ in QP, and from 8 μg/m³ to 253 μg/m³ in XH. Weakened titration effect of NO on O₃ (NO+O₃→NO₂+O₂) probably resulted in higher O₃ concentration in rural areas [33]. The frequencies of PM_2.5 as the primary pollutant were comparable, which were 14% in XH, 21% in QP and 20% in CM. Annual PM_2.5 levels were similar in the three different functional areas, which were 31 (3-161) μg/m³ for XH, 35 (4-162) μg/m³ for QP and 30 (2-149) μg/m³ for CM. The frequencies of PM₁₀ as the primary pollutant were low in the three areas in Shanghai, only 5-6%. The highest daily PM₁₀ was observed during a dust storm event occurred in March 30, 2021, with PM₁₀ ranging from 284 μg/m³ to 316 μg/m³ in the three distinctive functional areas. It should be pointed out that QP, classified as suburban area, is located at the junction of Jiangsu Province, Zhejiang Province and Shanghai. Affected by multi-source emissions, the pollution characteristics of QP are more complicated. In summary, O₃, instead of PM_2.5, has become the most significant pollutant affecting air quality in Shanghai.

 

2. Author should include a description of CO and SO₂as not the primary contributor to atmospheric pollution in this research study.

Response：We added explanation of CO and SO₂ as not the primary contributor to atmospheric pollution and revised the text as suggested, as seen in Line 171-179 in the following:

Line 171-179:

The primary pollutant refers to the pollutant with the largest air quality sub-index when the air quality index is higher than 50. CO and SO₂ have never been identified as the primary pollutants in Shanghai, 2019-2021 due to their low concentrations. The annual average concentrations of SO₂ in the three different functional areas were 5-6 μg/m³, which were much lower than the annual average concentration limit specified in the national ambient air quality standard (GB3095-2012, 60 μg/m³). Daily CO in XH, QP and CM ranged from 0.2-1.5 mg/m³, 0.3-1.4 mg/m³, and 0.1-1.3 mg/m³, respectively, which satisfied daily limit specified in the national ambient air quality standard (4 mg/m³).

 

3. In the backward trajectories plot Fig. 4 “cluster mean of trajectories (1-5), here 1-5 is not clear, the author should make it clear in the manuscript as well as in fig. the average seasonal basis of variation in the trajectories of the three-year study period should be described in the manuscript.

Response: We described Figure 4 in depth as suggested. Please see the revised text in Line 278-303:

 Lifetime of NO₂ ranges from a few hours to days [42]and O₃ lifetime ranges from several days to weeks [43], and thus can be transported from one place to another. Regional and inter-regional transport play an important role in air pollution [44-48]. The urban site XH, located in the middle Shanghai, was selected as the start source for backward trajectory clustering analysis. Seasonal cluster-mean backward-trajectories and average concentration of pollutants corresponding to each cluster in Shanghai was shown in Figure 4. In spring, Cluster 1 (red, 12.11%) indicated trajectories carrying polluted air masses with the highest concentrations of all pollutants (50 μg/m³ of NO₂, 53 μg/m³ of PM_2.5, 93 μg/m³ of O₃, and 78 μg/m³ of PM₁₀), followed by Cluster 4 (blue, 16.70%). Cluster 1 represented the air mass trajectory of long-range transportation (inter-regional), which started from Inner Mongolia in the North China Plain. Cluster 4 represented the air mass trajectory of short-range transportation (intra-regional), which started from Jiangxi Province in Eastern China. In summer, Cluster 1 (blue) and Cluster 4 (purple) were polluted trajectories which accounted for 41.26%. Cluster 1 (blue, 29.95%) originated from Guangdong Province in the Pearl River Delta, which indicated transregional transport of pollutants. Cluster 4 (purple, 11.31%), representative of short-range transportation within the Yangtze River Delta (intra-regional), brought the highest concentration of pollutants in summer. In autumn, air masses in Cluster 4 (purple, 11.70%) brought the highest concentration of PM_2.5 (44 μg/m³), PM₁₀ (73 μg/m³) and NO₂ (55 μg/m³) through long distance transport, whereas Cluster 3 (yellow, 9.38%), brought the highest concentration of O₃ (84 μg/m³) by short distance transport within the Yangtze River Delta. The contribution of inter-regional transport on O₃ level over the YRD region in summer had been estimated to be 20%-44% [49]. In winter, the four clusters of trajectories were from long-range transport. Cluster 1 (red, 23.94%) brought the highest concentration of PM_2.5 (65 μg/m³), PM₁₀ (71 μg/m³) and NO₂ (69 μg/m³), whereas Cluster 2 (purple, 26.37%) brought the highest concentration of O₃ (54 μg/m³).

 

4. Author has included the figure of meteorological parameters, but there is no significance has been described in the manuscript. There is a correlation between meteorological parameters and the concentration of pollutants, but in this study, it has not been determined. The author should include the correlation.

Response: Meteorological parameters were only measured at the suburban site labeled QP in 2021. We mentioned wind speed, wind direction and relative humidity in typical case events in revised the text, as follows:

Line 383-385：

Wind direction was changed during the pollution episode, from northwest wind to northeast wind (Figure 6. (a)), which agreed well with trajectory analysis.

Line 390-393:

In addition, low wind speed and high relative humidity favor accumulation and transformation of pollutants from local emissions.

 

 

Author Response File: Author Response.docx

Reviewer 5 Report

Review: Characteristics of Atmospheric Pollution in A Chinese Megacity: Insights From Three Different Functional Areas 

This paper compared the air quality of PM2.5, PM10, SO2, NO2, CO, and O3 in three regions of Shanghai, a large city in China.

The contents of the text are as follows.

In the introduction part, air pollutants were briefly introduced and various parts such as the Chinese government's response and control direction were introduced.

In the method, a detailed description of the measurement site was given.

A clear path and summary of the data were organized.

The backward trajectory calculation method was clearly explained.

In the results and discussion, the primary pollutants in the three regions, the difference between weekdays and weekends, regional traffic, and source regions were clearly identified. In addition, case studies of similar studies were also conducted.

The results summarized the above test without problems.

It is necessary to check the number and DOI in the References part.

Accordingly, there is no major problem for this paper to be published in  sustainability journal.

Author Response

Review: Characteristics of Atmospheric Pollution in A Chinese Megacity: Insights From Three Different Functional Areas 

This paper compared the air quality of PM2.5, PM10, SO2, NO2, CO, and O3 in three regions of Shanghai, a large city in China.

The contents of the text are as follows.

In the introduction part, air pollutants were briefly introduced and various parts such as the Chinese government's response and control direction were introduced.

In the method, a detailed description of the measurement site was given.

A clear path and summary of the data were organized.

The backward trajectory calculation method was clearly explained.

In the results and discussion, the primary pollutants in the three regions, the difference between weekdays and weekends, regional traffic, and source regions were clearly identified. In addition, case studies of similar studies were also conducted.

The results summarized the above test without problems.

It is necessary to check the number and DOI in the References part.

Accordingly, there is no major problem for this paper to be published in sustainability journal.

Response：We appreciated the reviewer’s time and made positive comments on this manuscript. We checked the text formatting of References as suggested.

Round 2

Reviewer 2 Report

Thank you for your responses to my comments. The article has been developed and can be recommended for publication.  Best