The Impact of Changes in Anthropogenic Activity Caused by COVID-19 Lockdown on Reducing Nitrogen Dioxide Levels in Thailand Using Nighttime Light Intensity

Round 1

Reviewer 1 Report

 

Dear Authors,

The subject is interesting and urgent however the text is a bit confusing. Why are Corona death numbers presented at the introduction when the manuscript actually deals with the curfew? The reader lacks certain information on how the curfew was regulated, which business was involved etc.

Furthermore, the article lacks information on the regulations for lighting or suggestions by the authors why they think the NTL data indicated a drop in the use of artificial light at night. Was infrastructure less lit or was the reduction in traffic the sole reason for the reduction?

The two parameters air pollution and artificial light at night differ timely, traffic mainly occurs during daytime and artificial light at night is a night time tool, how can the two still correlate? It would be helpful to be better introduced into the timing of correlating traffic and night time light. The sun-rise and -set as well as the main hours of traffic or shop openings are for example important information. Then the authors need to discuss how the satellite data can be used as a tool for daytime activity. Mentioning the timing of when the satellite crosses over Thailand.

The authors need to discuss other studies as the method was used in literature before (find citation examples below).

Often the authors talk about an association between light and air pollution. But this evidence is not drawn here. There might be an associated effect but the authors only calculated the correlation between the two separate effects.

How about other existing literature around the world? It would be very informative to learn more about how the relationship between light and air pollution has changed in other countries. Further studies in comparison of different climate situations and different political conditions (strictness of lock downs) are needed to be discussed. At this point it is important to highlight that the data of the article presents monitoring of only two years. But, the results can be confirmed with data from other studies.

The results and conclusions are fine, but the authors should discuss that further studies and maybe transnational actions would be helpful.

Specific recommendations:

Abstract: lines 24-25, is here an association presented or rather a correlation?

Introduction: line 33, why are the deaths mentioned at such a prominent point? The article is about human activity not about the virulence. Rather focus on the areas that were in strict lock down and compare countries with more activities and different conditions during the pandemic.

Lines 62-65: A verb is missing.

Discussion: lines 236-239, “As Thailand is a developing country, constant changes in pollutant levels are common. This implies that tracking yearly NO2 changes from 2019, especially in urban areas, will provide a better understanding of such changes. Hence, we focused only on yearly changes in this study.” Actually, the authors did not compare on a yearly base, but only the changes in two subsequent years.

Conclusion: line 253, “This study presents the local association…” is quite bold. The study rather highlights the correlation between night time light and air pollution during the COVID pandemic. The data indicates that an association might be given, thus the tool of NTL should be further explored as a remote tool for measuring anthropogenic activities.

Literature to be discussed:

·       Jechow, A., & Hölker, F. (2020). Evidence that reduced air and road traffic decreased artificial night-time skyglow during COVID-19 lockdown in Berlin, Germany. Remote Sensing, 12(20), 3412.

·       Liu, Q., Sha, D., Liu, W., Houser, P., Zhang, L., Hou, R., ... & Yang, C. (2020). Spatiotemporal patterns of COVID-19 impact on human activities and environment in mainland China using nighttime light and air quality data. Remote Sensing, 12(10), 1576.

·       Bustamante-Calabria, M., Sánchez de Miguel, A., Martín-Ruiz, S., Ortiz, J. L., Vílchez, J. M., Pelegrina, A., ... & Gaston, K. J. (2021). Effects of the COVID-19 lockdown on urban light emissions: ground and satellite comparison. Remote Sensing, 13(2), 258.

·       Kovács, K. D. (2022). Nighttime Light Emissions Explain the Decline in NO2 during a COVID-19-induced Total Lockdown in France. Geographia Technica, 17(1/2022), 104-115.

Author Response

Thank you very much again for your kind efforts to help improve our manuscript.

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The study essentially sought to explore whether the reduction in the intensity of human activity during the governmental lockdown in the context of a novel coronavirus pandemic would lead to changes in airborne nitrogen dioxide concentrations. The reduction in human activity intensity during the lockdown period would have some indirect effect on the sources of nitrogen dioxide emissions. This is the scientific hypothesis on which the study is based. Overall, this is an interesting issue.

However, the following questions and work still need to be addressed further.

1. The monthly composited product of VIIRS NTL has a spatial resolution of about 500m, which is far from the resolution of the TROPOMI product of the Sentinel-5 Precursor (S5P) satellite. How did you get the two to be analyzed at the same spatial scale? There is no detail in the manuscript about the spatial upscaling treatment of the monthly composited products of VIIRS NTL.

2. Lines 114-119: Give reasons and justification for the logarithmic transformation used to treat the variables.

3. why is the nighttime light intensity during the lockdown period of 2020 (March 18, 2020, to June 30, 2020) in Fig. 3 higher than during the same period of 2019? I do not see a good causal relationship between this and the lockdown actions taken by the Thai government in the graph.

4. In addition to the built-up area, the area of orchards, planted forests, and cropland is also larger. But what relationship does this have with the decline in nitrogen dioxide under the conditions of the lockdown measures? That is, are there more people on these land types? What is the relationship with the sources of nitrogen dioxide emissions? This is not clearly articulated in the manuscript.

5. Annual change data for 2019 and 2020 were used in the study, but for 2020 the focus was on the lockdown period. The description of the time should be clearer. For example, the start and end of the lockdown should be highlighted in Figure 3 to make it easier for the reader to understand.

6. lines 47-50: Relevant references should be added to the lockdown measures taken by the Thai government.

7. Lines 73-74: Literature references should be added regarding the close correlation between nitrogen dioxide concentrations and human activities to support the scientific hypothesis and clarify the contextual basis.

8. The primary sources of nitrogen dioxide production in Thailand and their regional differences should be presented in the background.

9. Lines 93-95: The elaboration is rather vague. The research and application of TROPOMI in nitrogen dioxide monitoring should be directly elaborated and several relevant references should be cited.

10. The preceding ¥ character in the title bar of Figure 3 should be deleted, and the symbol for nitrogen dioxide in the vertical coordinate title of Figure 3b should use a subscript.

11. Formulas on the use of subscripts for the symbols of nitrogen dioxide should be carefully checked.

12. Lines 147-148: There is a duplication of figure titles.

13. The references should be consistent, standardized, and rigorous according to the format specified in the journal.

14. Multiple results in the text describe areas such as Bangkok, yet only the administrative division of Bangkok is added to the description in Figure 7, which should be added to other corresponding figures as well.

15. Lines 172-180: The description of the results should be more detailed and explain the results.

Author Response

Thank you very much again for your kind efforts to help improve our manuscript.

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This is a good study of the relationship between NO2 and anthropogenic activity during the first lock-down period of Thailand in 2020. The correlation coefficients between the log-transformed NTL and NO2 are presented. There are some suggestions are as follows:

1.     About the title, this paper mainly focuses on the relationship between NO2 and anthropogenic activity, and the coronavirus disease outbreak is not the direct factor for NO2 reduction. I suggest the title can be changed to ‘Impact of the anthropogenic activity lockdown on nitrogen dioxide level reduction in Thailand examined using night-time light intensity’.

2.     Figure 2 can be deleted. The COVID-19 case number has no strong correlation with the content of this paper.

3.     About figure 3, ‘¥’ should be delete in title. I suggest to change one linetype, in order to distinguish them in black and white printing.

4.     In the part 2.2, you should give explain why using log-transformed NTL and NO2.

5.     In the part 3.1, ‘The comparison on daily NO2 values…’, should be ‘daily’ or ‘monthly’?

6.     About Figure 4 and Figure5, the NO2 values and NTL intensity values are daily mean or monthly mean? Please give more details about the figure data.

7.     In the table 1, how to use the count number in this study, please give some descriptions.

8.     In the part 3.2, the correlation coefficients ‘r=0.33’, ‘r=0.38’, the ‘r’ is Beta1 of equation (1)?

Author Response

Thank you very much again for your kind efforts to help improve our manuscript.

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have addressed most of the issues previously raised. However, there are still some issues that need to be improved. It is suggested that these issues be revised for publication.

1. The authors believe that the problems shown in Figure 3 are due to the implementation of different levels of lockdown zoning, resulting in some areas that may not be affected as much by the first lockdown. And, the national average does not reflect the impact of the lockdown on NTL and NO2. If this is the case, why not go separately by lockdown zones to establish the relationship between the decline of NTL and NO2? I suggest that this part adds the relationship between NTL and NO2 changes in each zone on the basis of national scale to better illustrate your findings.

2. The authors suggest that the relationship between orchards, plantations, and farmland and the decline of NO2 during the lockdown may be indirect. However, this is not explained very clearly. In particular, it is very puzzling that the NO2 changes in a large area in the north, as seen in Figure 6. Does the lockdown indirectly lead to changes in biomass burning or chemical nitrogen fertilizer application? This is why I previously asked the authors to elaborate on the main sources of NO2 emissions in Thailand in the context of the study area. Perhaps the authors should be able to find a more plausible explanation through their research.

3. There are also some minor issues that need to be further optimized by the authors. For example, the font in the figure legend is too small to read, the width setting of Table 1, and some other formatting issues.

Author Response

Thank you very much again for your kind efforts to help improve our manuscript.

Please see the attachment.

Author Response File: Author Response.pdf