Remote Sensing Surveillance of NO₂, SO₂, CO, and AOD along the Suez Canal Pre- and Post-COVID-19 Lockdown Periods and during the Blockage

Round 1

Reviewer 1 Report (New Reviewer)

The authors have assessed the change of NO2, SO2, CO and AOD along the Suez Canal (Egypt) during COVID period. The study is remarkable and the statistics are clearly shown. However, the manuscript requires major revision.

(1) Line 44: The authors have associated the impacts on air quality with sustainability and the enforcement of laws, however the relation is not too direct and obvious. Some more in-between explanations and connections have to be made.

(2) Lines 128-151: There are too many references. Can you categorize these references and summarize them according to its nature and importance, as well as its relation and connection with your current study?

(3) Line 229: air mass value - should it be air mass fraction (AMF)?

(4) Lines 227-250: The authors should highlight the use and success of OMI NO2 and SO2 in recent studies for air pollution monitoring, the following are some references:

https://www.mdpi.com/2072-4292/10/11/1789

https://amt.copernicus.org/preprints/amt-2020-186/amt-2020-186.pdf

https://www.mdpi.com/2072-4292/5/9/4187

(5) Line 245: The authors mentioned how to classify and distinguish "good" SO2 pixels here, but how about the selection of NO2 pixels? What are said to be good pixels?

(6) Line 278: Please check the relevance and assumptions, as well as the validity of the two equations from [64] and [65]. 15% and 20% has already and could lead to huge difference in retrieval or estimation.

(7) Lines 318-319: Other reports have actually mentioned the deficiency of PANDORA NO2 OMI (underestimation), the authors should compare and contrast the use of OMI and Pandora NO2 for different practical applications here.

(8) Line 334: For "cloudiness", do you mean "cloud fraction"?

(9) Lines 366-368: The authors can extend the period of investigation and take average, which can enhance the efficiency and accuracy of tracking spatial distribution of these pollutants.

(10) Line 374: What do you mean by "number of SO2"?

(11) Lines 388-389: Any temporal (e.g., monthly) trends can be shown to explain this point further?

(12) Entire manuscript: The manuscript is lacking of scientific novelty. Could the authors emphasize what is new? what are the technological advancement and breakthrough of this study? What are the most important key message and key scientific ideas of the study?

(13) Lines 511-513: Transport, commerce and air quality may or may not be associated and inter-related. Further investigation is needed before reaching any confirmation. There is not much casual relationship between these attributes.

(14) Lines 519-520: Regarding the justification of methodology of using satellite data, how? Explain in more details.

(15) Line 524: The proposal of using emission inventories should be further elaborated and explained.

As for typo and grammatical errors, please refer to the next box (i.e., the next passage of this review report)

Some typos and grammatical mistakes were detected and found:

Typo / Grammatical Mistakes

Line 74: atmosphere --> atmospheric

Line 75: PM2.5 (2.5 should be underscripted)

Line 102: provide? Check carefully

Line 103: 40%, while SO2, CO and C6H6 concentrations...

Line 106: Please add a "comma" at the end

Line 112: [34], while

Line 131: as compared

Line 135: Please add a "comma" at the end

Line 136: , as compared

Line 139: Remove "by Alqasemi et al."

Line 152: proven that the COVID 19 could impact..

Line 156: compares it with the mean values...

Line 158: Add a "comma" after aims

Line 165: compared with

Line 166-167: Please rephrase the statement here, unclear.

Line 181: is to be --> was

Caption of Figure 1: The study area

Line 190: stationed --> stations

Line 191: can accurately...

Line 232: NO2 (2 should be subscripted)

Line 283: add a "comma" after AOD

Line 284: Remove "on"

Line 285: 2022, and was compared with

Line 286: during the same period

Line 297: As shown from...

Line 308: as compared

Line 323: As shown in Figure 2e

Line 334: Remove "75"

Line 338: Figures

Line 341: averaged

Line 345: remove "by"

Line 348: findings, which has...

Line 366: "as compared"

Line 375: add a "comma" after period

Line 412: clear --> noticed

Line 418: could also be

Line 419: In Figure 8

Line 422: averaged

Line 423: Add a "comma" after 2020 and 2021 respectively

Line 426: noticed increment of energy demand was recorded...

Line 432: add a "comma" after part

Line 438: Add a "comma" after [32]

Line 457: were --> was

Line 473: in --> of

Line 474: as compared

Line 475: add a "comma" after [81]

Line 476: who --> which

Line 478: as compared

Line 483: Rephrase "which may be due to resuming industrial production".

Line 500: Contrastingly --> In contrast

Line 502: attributable --> attributed

Line 504: as compared

Line 516: short-lived, thus...

Line 495: Section 4, not 5

A serious round of grammatical checking is needed.

Author Response

Dear Reviewer,

Thanks for providing all of these valuable comments. They really helped in improving the quality of the manuscript. We have carefully addressed all of your comments. Attached file contains a reply to all of your comments.

Regards,

Authors

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

Comments to the Authors:

• In general, the aim of manuscript is very good; it need major correction to qualify text only. There are errors of figures number along text, especially in result and discussion part. In addition, authors wrote they study pollutants levels along the Suez Canal, why they add figures of Egypt? it need to changed into figures contain study area only.

In abstract:

• No. of words was 411 words, need to summary. (According to Instructions for Authors: The abstract should be a total of about 200 words maximum. The abstract should follow the style of structured abstracts, but without headings: 1) Background; 2) Methods; 3) Results; and 4) Conclusion).
• Authors wrote” The COVID-19 pandemic probably played a significant role in decreasing NO₂ by about 6.5% and SO₂ by about 35%” although they explain the decrease due to “which is mainly due to the reduction in car traffic and industrial activities during the pandemic”. This need clear explanation to show effect of COVID-19 pandemic on decrease pollutants levels.
• Author wrote “It can be concluded that the containment measures applied during the COVID-19 pandemic was having a positive impact on the environment”. What is Egyptian containment applied during the COVID-19 pandemic to decrease pollutants levels? Is decrease in levels due to reduction in car traffic and industrial activities during the pandemic or due to Egyptian containment applied during the COVID-19 pandemic?

In Introduction:

• In line 75: “particulate matter 2.5” should be changed into “fine particulate matter”.
• In line 101: “PM₁₀” should be changed into “respirable particulate matter (PM₁₀)”.
• In line 75: “particulate matter 2.5” should be changed into “fine particulate matter”.

Results and Discussion

• In lines 296-307: Figure 2a not present in text.
• Figures (2a-2d) showed NO₂ levels in Egypt. What about study area? Authors should add figures of NO₂ levels at study area only.
• In line 324: author should define “DU” as “Dobson unit (DU)”.
• In lines 296-307: Figure 2a not present in text.
• In lines 350-368: Supplementary Figures S1 not present in text.
• In lines 369: authors discuss figure 7, and did not discuss figures 4, 5, and 6 in text.
• Are figures 5 and 6 the same in figure 2? If yes, why was replicated?
• In line 369: authors wrote “From Figure 7, the relative difference in SO₂ concentration” Is figure 7 contain SO₂ or CO levels?
• Paragraph (line 369 – 384) need to check-in, I think it contain errors in figures number.

Conclusions

• Authors wrote “This study highlights the impact of the COVID-19 pandemic and the obstruction of the Suez Canal by the Ever-Given ship (March 23^rd – April 2^nd, 2021)” but results and discussion highlighted COVID-19 pandemic only, I think it is enough for this study, and obstruction of the Suez Canal by the Ever-Given ship (March 23^rd – April 2^nd, 2021) should be clarifying in another case study during period of March 23^rd – April 2^nd, 2021.

References

• Reference [86] not present in text.

Author Response

Dear Reviewer,

Thanks for providing all of these valuable comments. They really helped in improving the quality of the manuscript. We have carefully addressed all of your comments. Attached file contains a reply to all of your comments.

Regards,

Authors

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

This manuscript entitled “Remote sensing surveillance of NO2, SO2, CO and AOD along the Suez Canal Pre and Post COVID-19 Lockdown Periods and during the blockage” mainly describes the effect of Covid-19 restrictions on the measured emissions along the Suez Canal. The valuable data are useful and important in terms of understanding restrictions on the measured emission parameters. On the other hand, the manuscript should be improved. I would suggest that the authors sincerely consider the following comments in the review/reconsider the valuable data and discussion.

Line 284-285 “For each pollutant, the data was obtained for the study period from 2020 to 2022 and compared to the mean value of the data from previous year (2019) for the same period.” However Lines 200-201 “The value for the years 2020, 2021, and 2022 are compared to the mean value from previous years (2017, 2018, and 2019) as a baseline, and the results are then, analyzed.” Why baseline is different for pollutants? Especially for aerosol optical depth as compared to other pollutants?

It would be better to show the main anthropogenic sources (i.e. ports, power plants, highways, industrial areas) in Figure 1.

Line 385-387 “High NO2 and SO2 concentrations were also reported in some areas without the presence of any anthropogenic activities (Figures 2a to 2h), where there is a high possibility of short distance transportation of pollutants from areas with heavier pollutants to neighboring areas. Meteorology should be effective on the measured high concentrations. Therefore, it would be better to add wind rose and show the main anthropogenic sources in Figure 1. to support your findings.

Line 413. “PPbv” should be “ppbv” therefore the unit should be corrected through the manuscript and in the Figures.

Line 471. “This is mainly due to the increase in the number of ships passing through the canal.” It would be better to add statistical data into the manuscript about the passing ships through the canal each year.

Author Response

Dear Reviewer,

Thanks for providing all of these valuable comments. They really helped in improving the quality of the manuscript. We have carefully addressed all of your comments. Attached file contains a reply to all of your comments.

Regards,

Authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report (New Reviewer)

The revised manuscript looks very comprehensive now, and it is more reader friendly. To further improve the quality, there are 3 more minor comments:

(1) Regarding the justification of satellite data, using low-cost sensors and citizen-based monitoring network are possible ways and future outlook. The authors can include this future mission in Conclusion / Discussion. Some references that have used low-cost sensors and citizen-based monitoring network in developing cities are as follows, please refer to these references and cite them accordingly:

https://www.sciencedirect.com/science/article/pii/S1352231020301497

https://www.sciencedirect.com/science/article/pii/S0048969721068455

https://www.sciencedirect.com/science/article/pii/S1877050922021706

 

(2) Regarding the excessive references in Review point Number 2: Please just adopt the references in Egypt, UAE, India and Morocco. Other references should be removed.

(3) Regarding the validity of MODIS AOD, please refer to its official documents and cite relevant references.

After addressing these 3 further comments, I think the manuscript is ready to be published.

The Language is alright now

Author Response

First, We appreciate your time and effort for providing your valuable feedback on our manuscript. Below is the responses to your comments:

(1) Regarding the justification of satellite data, using low-cost sensors and citizen-based monitoring network are possible ways and future outlook. The authors can include this future mission in Conclusion / Discussion. Some references that have used low-cost sensors and citizen-based monitoring network in developing cities are as follows, please refer to these references and cite them accordingly:
https://www.sciencedirect.com/science/article/pii/S1352231020301497
https://www.sciencedirect.com/science/article/pii/S0048969721068455
https://www.sciencedirect.com/science/article/pii/S1877050922021706

Response: Thanks for your valuable comment. The future mission has been included in the Conclusion section. We have also mentioned the 3 references that have used low-cost sensors and citizen-based monitoring network.
 
(2) Regarding the excessive references in Review point Number 2: Please just adopt the references in Egypt, UAE, India and Morocco. Other references should be removed.

Response: Thanks for your valuable comment. We have removed the following paragraph with its relevant references:

"Sicard et al. [43] used satellite data to analyze the impact of the COVID-19 pandemic on air quality in four Southern European cities (Nice, Rome, Valencia and Turin) and Wuhan (China), and found a significant decrease in NOx levels by about 56% in all cities during the lockdown period. "

"A study conducted in the United Arab Emirates by [46] have reported a decline in Aerosol Optical Depth and NO2 concentration by 3.7% and 23.7%, respectively."
 
(3) Regarding the validity of MODIS AOD, please refer to its official documents and cite relevant references.

Response: Thanks for your valuable comment. We have added the relevant references. 
https://www.mdpi.com/2072-4292/13/1/2
https://link.springer.com/article/10.1007/s10661-023-11118-8
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL099733
https://ladsweb.modaps.eosdis.nasa.gov/

Reviewer 2 Report (New Reviewer)

Thanks for your efforts.. 

Author Response

We appreciate your time and effort for providing your valuable feedback on our manuscript.

Reviewer 3 Report (New Reviewer)

The necessary corrections were done, therefore the revised manuscript can be accepted in this form.

Author Response

We appreciate your time and effort for providing your valuable feedback on our manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

- Time windows for comparison of data in different years (roughly two weeks to one month) might not be valuable since the meteo conditions may change a lot from year to year.

- Figures 10-14 are not mentioned in the text, may be explained better.

- Aren't the CO conc. variations too low (also having in mind the ppb/v order of magnitude) to be declared as increase ? Please explain. 

-Too many figures, some may be moved to the Suppl.

- Available (concrete) data on emission inventory should be added to discussion. 

 

Author Response

Comment: Time windows for comparison of data in different years (roughly two weeks to one month) might not be valuable since the meteo conditions may change a lot from year to year.

Response: We acknowledge that this is one of the study’s limitations. We are constrained by the Ever given blockage event duration, which lasted almost 7 days. Therefore, we picked to analyze records from January to April. 

Comment: Figures 10-14 are not mentioned in the text but may be explained better.

Response: We added their explanation, however, Figures 11 and 13 were moved to the supplementary section. 

Comment: Aren't the CO conc. variations too low (also having in mind the ppb/v order of magnitude) to be declared as an increase? Please explain. 

Response: CO concentration exhibited a slight increase, ranging from 5% up to 10%, that may or may not be attributable to the Suez Canal blockage. 

Comment: Too many figures, some may be moved to the Suppl.

Response: We moved some of the figures there.

Comment: Available (concrete) data on emission inventory should be added to the discussion. 

Response: In our research, data on the emissions inventory in the region were not found in any published source. We contacted the Suez Canal Authority requesting the provision of their data on emissions inventory. The Suez Canal Authority indicated that they do not currently possess this data as there are not any operating ground stations for measuring these emissions in the study region

Reviewer 2 Report

I still feel that this manuscript's contribution to science/novelty is little.

Author Response

Comment: I still feel that this manuscript's contribution to science/novelty is little.

Response: This is the first study to be done on the Suez Canal related to the COVID-19 lockdown impact on the air quality and investigating the impact of the Ever given blockage event on the air quality.  

Reviewer 3 Report

The authors improved the paper in accordance with the recommendations. It is recommended to decrease the number of the keywords.

Author Response

Comment: The authors improved the paper in accordance with the recommendations. It is recommended to decrease the number of keywords.

Response: Thanks for your positive feedback. We have reduced the number of keywords. 

Round 2

Reviewer 1 Report

Author responses have shown limitations of the study that should be included  into Discussion and Conclusion sections of the Manuscript.

 -lines 248, 249: ..... as AODAERONET × ±0.05 ± 248 0.15 [53] and AODAERONET × ±0.05 ± 0.20 [54].......- should be corrected.

  

Author Response

Q1: Author responses have shown limitations of the study that should be included  into Discussion and Conclusion sections of the Manuscript.

A1: We have added the limitation at the end of the conclusion section. We added the following statement:

"In our research, data on the emissions inventory in the region were not found in any published source. Additionally, there are not any operating ground stations for measuring the studied emissions in the study region."

Q2:  -lines 248, 249: ..... as AODAERONET × ±0.05 ± 248 0.15 [53] and AODAERONET × ±0.05 ± 0.20 [54].......- should be corrected.

A2: It has been corrected.