Evaluation of the Coupling Coordination Degree Between PM_2.5 and Urbanization Level: A Case in Guangdong Province

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is devoted to the study of the relationship between urbanization and air pollution by dust particles (pm2.5). The authors selected several factors that can represent the urbanization process and compared them with air pollution. Pollution data were obtained from an existing database.

The study of these dependencies is necessary for the implementation of sustainable development of urban areas in China and other countries. The selected methods are consistent with the scale of the study.

There are a number of comments that need to be addressed:
1. Not all links to data sets are presented in the paper. They should be indicated.
2. The link to the supporting materials does not work.
3. There are broken links in the text (for example, lines 274, 342). This needs to be corrected.
4. In the introduction, we are offered a forecast for 2020 (line 40)? I think the proposal is no longer relevant. Can you provide actual data for today?
5. Pay some attention in the introduction to the danger (toxicity, genotoxicity, etc.) of dust of this size and the consequences of its high concentrations.
6. Not all figures are referenced in the text (e.g. 2, 4, 5).
7. All formulas should be referenced (if they are not the author's).
8. In figure 11, it is not clear which municipalities/cities are where. It is difficult to compare this with table 6.
9. What does the color in table 6 mean? Explanations should be added.
10. Why not calculate Moran's within cities/municipal areas.

11. Was a stepwise autocorrelation analysis (stepwise spatial autocorrelation) performed?
12. Why did you not use the overall Getis-Ord index G or the Ripley function K?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a comprehensive and well-structured investigation into the coupling coordination degree between PM2.5 pollutions and urbanization in Guangdong Province. The study is timely and relevant, especially considering the ongoing challenges of balancing rapid urban development with environmental sustainability in China. The authors demonstrate a strong command of geospatial analysis and environmental modeling, particularly through the integration of high-resolution datasets such as CHAP, VIIRS/DMSP nighttime lights, and socioeconomic indicators. With additional clarification on model assumptions, limitations, and causal mechanisms, the paper would be suitable for publication.

However, several aspects require clarification or elaboration. First, while the authors justify the use of nighttime light data as a proxy for urbanization, more discussion is needed regarding its limitations—particularly in low-density or industrial zones where light emissions may not correlate linearly with urban activity. Additionally, while the authors adopt an equal weighting scheme (α = β = 0.5) in the coordination model, they acknowledge the differing roles of urbanization and pollution. It would be valuable to discuss whether a sensitivity analysis was performed to test the robustness of this assumption.

In the analysis of coupling dynamics, the paper identifies turning points in urbanization and pollution, yet the causal mechanisms behind these shifts—particularly the policy effects—could be explored in more depth. For example, how do local vs. national environmental policies influence the observed trends post-2010? Furthermore, the classification of coupling coordination states (severe discordance to advanced coordination) is helpful, but it would be clearer if more examples were given to illustrate how these categories reflect real-world urban planning or industrial practices.

While the authors do an excellent job of explaining statistical methods, the discussion could benefit from a more critical reflection on model limitations. For example, the assumption of monotonic trends in the Mann-Kendall test may oversimplify non-linear urban-environment interactions. Also, the manuscript heavily relies on derived indices; some explanation of how uncertainties in input data (e.g., nightlight calibration, PM2.5 estimation errors) might propagate through to the coupling coordination index would be helpful.

A few questions remain open: How does the coupling coordination model account for intercity spillover effects, especially in the Pearl River Delta where urban clusters are tightly integrated? Are there any feedback mechanisms or time lags considered between urban expansion and air pollution reduction? Lastly, while the authors present spatial patterns and trends effectively, they could enhance the narrative by offering more interpretation of regional differences—why, for instance, do cities like Zhuhai outperform others like Shantou in coordination improvement?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

This study provides a thorough and methodologically sound analysis of the spatiotemporal relationship between PM2.5 concentrations and urbanization levels in Guangdong Province over a 21-year period. The use of a coupled coordination degree model and incorporation of nighttime light data offer innovative ways to assess sustainable urban development. The paper is well-structured, and the findings are supported by solid data analysis.

Overall, the paper presents valuable insights, but minor revisions and clarifications would improve the clarity and robustness of the manuscript.

How was the weight (α and β) in the coupling coordination degree model determined?

Is the temporal resolution of PM2.5 data (daily) properly reflected in the analysis of long-term urbanization trends?

Can the authors justify why only three years (2007, 2014, 2021) were selected for urbanization analysis?

How does the study account for potential biases in nighttime light data from different satellite sensors?

Have other pollutants (e.g., NO₂, O₃) been considered to strengthen the coordination analysis?

What are the limitations of using nighttime light as a proxy for all dimensions of urbanization?

Is there any validation for the inflection points identified through EKC fitting?

How transferable is the proposed model to other provinces or countries with different urbanization dynamics?

Did the authors consider socio-political or policy changes that may affect PM2.5 and urbanization patterns?

What are the policy implications for cities still in the discordance or transitional phase?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

Comments and Suggestions:

1. line 3: there is no subtitle within the title. The subtitle typically conveys the thesis of the essay about the general subject expressed in the title. There should be a colon between the title and subtitle. A possible subtitle might be: "Environmental policy interventions to improve upon the PM2.5 levels in Guangdong Province." and so on. I think a subtitle express the authors' main thesis would enhance the title and paper as a whole.
2. line 23: study description should give the dates the research was conducted in Guangdong Province right after the word "Province," something like: "during 2000 - 2021."
3. line 26: "began to improve." In what respects? Need to state in what respects the alleged improvement occurred; levels of PM2.5? overall air pollution? etc.
4. line 32: "the coupling coordination degree;" although the concept of "coupling" is explained later in the paper, it should be explained in the Abstract and when first introducing the concept in the text of the essay.
5. line 43: after "major public and governmental concern" needs to be followed by the ill effects of PM2.5 to justify alleged concern. Good to follow up with the adverse effects of PM2.5 and to give the source for the claims made in lines 47-48.
6. line 58: "mass migration" should be made more specific and clear: "mass rural-to-urban areas migration."
7. line 67: "innovative methodologies;" examples should be given following: "such as: etc."
8. line 68: acronym "MDCE" should be spelled out for the nonspecialist reader.
9. line 79: "industrial restructuring" should be explained to be clear and rationally useful.
10. line 80: new paragraph needed before: "Urban expansion."
11. line 65: new paragraph needed before: "Empirical studies."
12. line 91: "severe air pollution challenges." Source needed here for this claim to be rationally useful.
13. line 91: new paragraph before: "Against this."
14. line 93: "ecological civilization framework" needs to be explained and clarified for the nonspecialist reader.
15. line 99: end of paragraph needs a statement of the main conclusion of the essay here to end the Introduction section.
16. line 152: need to provide the source for the information presented in this paragraph.
17. line 162: need to provide the source for the information presented in this paragraph.
18. line 182: Figure 2: need to provide full names of abbreviated boxes under "Urbanization indexing" to be clear to nonspecialist reader.
19. lines 193 and 200: should delete unnecessary commas after the word: "intensity" and "zones" respectively in these lines.
20. line 203: Good to provide this Table of methods used and their respective purpose.
21. line 203: Table 2: should indicate what "EKC" represents for the nonspecialist reader.
22. line 229: indicate abbreviation in parenthesis for the measure: "composite nighttime light index "(CNLI)."
23. line 230: Figure 3; subsection heading 2.2.2 PM2.5 "Spatiotemporal pattern analysis" should be moved to the next page so the entire Figure is complete on one page with no breaks.
24. line 246: good provide definition of "coupling," but should occur earlier in the paper and in the Abstract and put label of concept in quotes, hence: "coupling."
25. lines 256-257: need to explain and defend this claim about "pseudo-coordination" as well as the concept.
26. line 272: move section heading: "Results and Discussion" so it is on the same page as the discussion and presentation of the results.
27. line 274: reminder to obtain source should not be in final version of the paper. Find source and insert here. 
28. line 289: "a certain degree of pollution;" needs to be more precise in order to be rationally useful; delete vague wording here.
29. line 283: "during this period;" should indicate the kind of pollution being controlled so add the words: "regarding PM2.5" after last words of sentence: "during this period."
30. line 313: Figure 5 needs to have distributed years at the bottom of the diagram to be useful regarding when these results were achieved; merely listing the time period from 2000 to 2021 in the title of the Figure is not sufficiently clear nor precise. Give years at the bottom of the diagram.
31. line 340: Figure 6: What does "ANLI" stand for? Need to specify to help the reader comprehend the Figure's content.
32. line 342: once again a source is missing and should not have a reminder here in the text. For the final version of the paper, make sure all sources are listed with no reminders in the text.
33. line 349: "transportation networks." Need source here as well as explanation of this claim.
34. line 350: "pollution control measures;" what were they? Need to explain and how they worked to make this claim rationally useful.
35. line 353: Figure 7: specific years are not indicated at the bottom of the graph are needed for the reader to see the years the data represents more clearly.
36. lines 362-363: "sustainable urban development practices." Need to explain this claim and provide some examples to make this claim clear and rationally persuasive.
37. line 365: Figure 8; again years represented by each dot are missing making it difficult to see the development over the years. 
38. line 375: "energy-efficient technologies;" need examples to make claim rationally useful.
39. line 376: "green transition measures;" again need examples to make claim rationally useful.
40. line 379: Figures 9: need years at bottom of the graph to comprehend temporal changes over time.
41. line 384: "EKC hypothesis" needs to be explained for the nonspecialist reader.
42. line 385: "environmental degradation;" need source here for this borrowed information about the EKC.
43. line 402: Figure 10, years at bottom of graphs in the Figure are needed to clear about timing.
44. line 407: "environmental protection infrastructure;" need to clarify and explain to be rationally useful.
45. line 422: "sustainable lifestyles;" need to clarify and provide supporting data for this claim to be rationally persuasive.
46. lines 440 and 443: unnecessary commas should be deleted after the word "emissions" and "environment," respectively.
47. lines 462-463: "annual haze days;" how defined? should explain to be rationally useful.
48. line 478: need a comma after "levels," and before "but."
49. line 482: good use of color in this Table. 
50. line 500: "requires accelerated urbanization;" why? should explain and defend to be rationally useful.
51. lines 510-520: "policy interventions." Like what? Should explain such "policy interventions" in paper and not leave unstated and not discussed. 
52. line 516: new paragraph before the words: "The relationship."

Overall a very good paper that is worthy of being published when all the sources are provided and the specificity of years in the Figures are provided. Important research about the important environmental problem of PM2.5. Be more informative about the policies that are only vaguely referred to.

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors made corrections to the document based on the reviewer's recommendations. 
I believe that the article as a whole is sufficiently informative for publication and can be accepted.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors clearly answered my questions. I recommend it therefore for publication.