Review of Top-Down Method to Determine Atmospheric Emissions in Port. Case of Study: Port of Veracruz, Mexico

Round 1

Reviewer 1 Report

This review paper assesses in-port emissions from vessels at the port of Veracruz using seven different methodologies. The paper compares the methodologies and notes how differing assumptions of the models result in variation in the emission estimates produced.

General comments:

To me, the strength of this paper is its attempt to compare multiple emission modeling methodologies using the same inputs. Studies like this provide researchers with valuable references when trying to compare emissions inventories developed using different models and assumptions.  

This paper is puzzling because from the title and the the introductory text, it purports to compare top-down methodologies: i.e those methodologies where emissions are calculated in total and allocated down to more granular levels of detail. This is in fact roughly the same definition given in more than one of the sources it cites when defining top-down methods. That said, all of the methods compared are bottom-up methods that take detailed port activity inputs at the vessel-level to calculate emissions and sum them up to form a total inventory for the port. At a very minimum the paper should be revised to reflect this.

Given that this paper actually focuses on bottom-up methods, it would be worth considering including the U.S. EPA's recommended ports emissions inventory methodology along with those compared. The latest version of the U.S. EPA's guidance can be found at: https://www.epa.gov/state-and-local-transportation/port-emissions-inventory-guidance 

I am disappointed that this paper only focuses on emissions at berth. When comparing methodologies it is important to understand how modeling results for all near-port operations such as sitting at anchor or maneuvering within the port. I understand that at the port used for this study, berth operations are the greatest contributor to emissions. However, when comparing methodologies, the analysis is incomplete without including the additional modes of operation.  

Specific comments:

Line 35 - reference [2] (Current Methodologies and Best Practices in Preparing Port Emissions 461 Inventories) is 14 years old and has been replaced with completely new guidance. see the following link for more information: https://www.epa.gov/state-and-local-transportation/port-emissions-inventory-guidance

The paragraph starting on line 103 asserts that despite the effective date of January 1, 2020 the IMO global fuel sulfur standard has not yet been fully adopted. This paragraph does not cite any specific studies or evidence to support this claim. This claim requires strong evidence as it suggests widespread noncompliance with international regulations.

Line 128 - The reference for this sentence is 18 years old. International regulations have since come into effect to regulate SO2 in many areas, and marine vessels routinely operate on 0.1% m/m sulfur fuel within IMO designated SO2 ECAs.  

Line 147 - many of the citations listed here do not match the authors who's names they follow: the citation list for Trozzi and Vaccaro includes [37] which was authored by ENTEC, the list for Cooper and Gustafsson includes references [39],[40],41] by USEPA, ENTEC, and EMEP/EEA respectively.

The paragraph starting on line 285 justifies a 1% fuel sulfur content as being a reasonable average value despite being 2x the internationally regulated fuel sulfur content. While the text claims that international studies suggest that it is a reasonable average value, none are cited. Unless studies clearly demonstrating widespread noncompliance can be cited, 0.5% sulfur would be a more appropriate value to use.

Author Response

Dear Reviewer 1,

Thank you so much for your spent time to review our study entitled “Review top-down method to determine atmospheric emissions in port. Case of study: Port of Veracruz, Mexico”. We appreciate your comments and suggestions made in this review stage. We have integrated your recommendations and suggestions in our study for this new review. The main activity was integrated new data corresponding to fuel consumption and atmospheric emissions in maneuvering position by type of ship for each method considered. Finally, we have updated our results considering 0.5% sulfur content in marine fuel.

Comments and Suggestions for Authors

This review paper assesses in-port emissions from vessels at the port of Veracruz using seven different methodologies. The paper compares the methodologies and notes how differing assumptions of the models result in variation in the emission estimates produced.

Response: 

Thank you for your comment. Indeed, our main objective was to identify the level of fuel consumption and atmospheric emission by type of ship through the top-down method. This particular method is not widely used as the bottom-up method. Therefore, our contribution was to identify what happens with the top-down method considering seven methods. As we have commented in the paper, there are other top-down methods, but they are not applicable in this study because the information is not available in Mexico.

General comments:

To me, the strength of this paper is its attempt to compare multiple emission modeling methodologies using the same inputs. Studies like this provide researchers with valuable references when trying to compare emissions inventories developed using different models and assumptions.

This paper is puzzling because from the title and the introductory text, it purports to compare top-down methodologies: i.e those methodologies where emissions are calculated in total and allocated down to more granular levels of detail. This is in fact roughly the same definition given in more than one of the sources it cites when defining top-down methods. That said, all of the methods compared are bottom-up methods that take detailed port activity inputs at the vessel-level to calculate emissions and sum them up to form a total inventory for the port. At a very minimum the paper should be revised to reflect this.

Given that this paper actually focuses on bottom-up methods, it would be worth considering including the U.S. EPA's recommended ports emissions inventory methodology along with those compared. The latest version of the U.S. EPA's guidance can be found at: https://www.epa.gov/state-and-local-transportation/port-emissions-inventory-guidance

I am disappointed that this paper only focuses on emissions at berth. When comparing methodologies, it is important to understand how modeling results for all near-port operations such as sitting at anchor or maneuvering within the port. I understand that at the port used for this study, berth operations are the greatest contributor to emissions. However, when comparing methodologies, the analysis is incomplete without including the additional modes of operation.

Response:

Thank you for your comments and for sharing the USEPA document. We have reviewed the document that you have previously suggested, and we are convinced that it is a document based on the state of the art regarding the different methodologies available to identify the level of atmospheric emission, we know that the method used by the USEPA to determine emissions atmospheric corresponds to bottom-up. The USEPA document does not include how to determine fuel consumption like other references, the objective of this study to determine atmospheric emission. However, we have drafted and included this valuable reference in the document for this new review.

Likewise, we have worked on our database to identify the level of atmospheric emission in the maneuvering stage for each method as you have suggested. We include new graphics in the document to complete this review. All our results have been updated considering the docking and maneuvering emission considering 0.5% as sulfur content for the top-down method

Specific comments: 

Line 35 - reference [2] (Current Methodologies and Best Practices in Preparing Port Emissions 461 Inventories) is 14 years old and has been replaced with completely new guidance. see the following link for more information: https://www.epa.gov/state-and-local-transportation/port-emissions-inventory-guidance

Response:

Thank you for your observation. Given this consideration, we have included the current reference citation in the document without eliminating reference [2] for a better clarification and understanding of the current information.

The paragraph starting on line 103 asserts that despite the effective date of January 1, 2020 the IMO global fuel sulfur standard has not yet been fully adopted. This paragraph does not cite any specific studies or evidence to support this claim. This claim requires strong evidence as it suggests widespread noncompliance with international regulations.

Response:

Thank you for your comment. We have modified this scenario only for Mexico because the port of Veracruz will continue to use fossil fuels for the next few years. We are certain that marine fuel contains between 1 and 1.5% sulfur content. This information was known by asking the captain of the port. However, it is required that in Mexico chemical analyzes of marine fuel be carried out and to identify whether or not the provisions of the IMO are complied with it.

Line 128 - The reference for this sentence is 18 years old. International regulations have since come into effect to regulate SO2 in many areas, and marine vessels routinely operate on 0.1% m/m sulfur fuel within IMO designated SO2 ECAs.

Response:

Thank you for your observation. We consider this reference includes data on the sulfur content in marine fuel for marine diesel oil, gas oil and residual oil. There are few studies that include this type of information and it seemed important to mention it because our study contributes with data on atmospheric emission by sulfur dioxide. It is interesting to note that the IMO has modified the sulfur content from 3.5 to 0.5%. However, 0.1% was not modified within the emission control zones. Mexico does not have ECAs and it is not known in detail if there is a change from marine diesel oil to gas oil in port.

Line 147 - many of the citations listed here do not match the authors who's names they follow: the citation list for Trozzi and Vaccaro includes [37] which was authored by ENTEC, the list for Cooper and Gustafsson includes references [39],[40],41] by USEPA, ENTEC, and EMEP/EEA respectively.

Response:

Thank you for your comment. We understand the clarification, however, we consider that the citation of these studies is representative and specific for each author. Also, we have seen those citations referenced individually in various studies. Therefore, it seems good to us to cite each study to justify the development of our study.

The paragraph starting on line 285 justifies a 1% fuel sulfur content as being a reasonable average value despite being 2x the internationally regulated fuel sulfur content. While the text claims that international studies suggest that it is a reasonable average value, none are cited. Unless studies clearly demonstrating widespread noncompliance can be cited, 0.5% sulfur would be a more appropriate value to use.

Response:

Thank you for your observation and comment. We have modified our database and results considering 0.5% as sulfur content in marine fuel established by the IMO for a better scenario and treatment of the data of this study. We conclude from this consideration that the emission factor used to estimate atmospheric emissions was 20*s

Reviewer 2 Report

The paper is well made. Data are very exhaustive and proposal for the future are very interesting.

Author Response

Dear Reviewer 2,

We appreciate your spent time to review our study entitled "Review top-down method to determine atmospheric emissions in port. Case of study: Port of Veracruz, Mexico". Thank you to evaluate our study according to your personal opinion. 

Reviewer 3 Report

The subject is timely, and there is a need for papers on this topic. In my opinion, extensive English editing is needed because some sentences are hard to follow, and some expressions are unusual (at least in shipping). Moreover, I have some other concerns and comments given below.

1. Lines 16-20: It is a very long and hard-to-follow sentence; please rewrite it and split it into more sentences.
2. Line 25 - "Liquid vessel" is mentioned - please elaborate on this. What do you consider under a "liquid" vessel? Do you mean tanker?
3. Lines 33-35 - please restructure sentences (in my opinion, there is no need to use authors names in this sentence).
4. Line 39 - Instead of "Gross Tonne", please use Gross Tonnage.
5. Line 44-48: Again, too long and hard to follow sentences, and this sentence contains the paper's aim, so it has to be clear and concise. Please avoid referencing in the sentence where you state your paper's goal.
6. Lines 48-50: It is stated that at least seven methods were found, but there are precisely seven methods used in the paper, so why "at least"?
7. Lines 56-58: It is stated: "For the application of the top-down system of this study corresponding to seven methods, we consider the official and detailed information of the port of Veracruz: type of ship, GT, spent time in port, mainly". Could you please elaborate on this, especially on word mainly? What does it mean?
8. Lines 67-70 - It is stated: "[17], [18], Fuentes et al. [19-20] have promoted the development of inventories of atmospheric emissions of main pollutants that are emitted due to the movement of ships in port using the bottom-up system at the national level in Mexico." Please rewrite the sentence and do not start with the number in the brackets (reference) or general number.
9. Lines 73-75: It is stated: "Therefore, this study clearly reflects the current situation of the movement of ships in port, level of fuel consumption and atmospheric emission by SO2 during 2020 with daily resolution." Is this statement true? Fuel consumption and atmospheric emissions are only estimates and cannot be taken as accurate.
10. Lines 75-80: Very long sentence; please consider splitting it into two. Also, please remember that this study only estimates fuel consumption and atmospheric emissions. Furthermore, only fuel and emissions while berthed were considered; however, there is also a manoeuvring phase during which ME runs.
11. Lines 92-94: Sentences are repeating; please check.
12. Lines 98-99 - It is stated: "When ships are in port, however, emissions are highest in the berthing stage". Do you have a reference for this statement?
13. Lines 143-145 - It is stated: "In this case, the emission factor (20s) indicates that all the sulfur is converted to sulfur dioxide, the chemical reaction corresponds to 100%, and considering one ton of marine fuel". Please elaborate on this.
14. Lines 164-166 - same comment as under 8.
15. Lines 166-167 - same comment as under 8.
16. Line 196 - Phrases "weather force" and "weather direction" are mentioned; please elaborate on this.
17. Lines 208-209 - It is stated: "Currently, Container Ship and Bulk Carrier ships arrive at BN while General Cargo, Carrier, Bulk Carrier, Liquids and Fluids arrive at the BS". What type of ship is "Carrier", and what do is meant by "Liquids " and "Fluids"? Do you mean Tanker and Gas ships? Please elaborate and change the text since this wording is quite confusing.
18. Line 213 - Is it necessary to divide bulk carriers according to cargo they carry? I believe not for this kind of study.
19. Line 214 - a link is used; please use a reference instead.
20. Lines 233-234 - same as under 19.
21. Line 249 - same as under 19.
22. Lines 253-254 - same as under 19.
23. Lines 320-323 - How do you explain the absence of a relationship between the number of ships and atmospheric emissions?
24. "The correlation coefficient (R²) between atmospheric emissions and the number of vessels was 0.38 for all methods except for Van der Gon and Hulskotte method, which presented a correlation 0.24." Please elaborate more on this.
25. The Discussion Section deals with methods used to estimate emissions, not with the study results. This part could be moved to Methodology or Introduction, but Discussion needs to deal with the results of this study.
26. What is the conclusion of the study regarding the methods used? Are they applicable, and why? Is there a method that is most suited for the port of Veracruz? Why?
27. Are there any other limitations than those mentioned in the Introduction section? I suggest moving the study limitation mentioned to the Conclusions Section.
28. Recommendations and Future work should not be separate Sections; they should fall in the Conclusions section as well. Try to elaborate on recommendations (why and how).

I hope that my comments and suggestions will be helpful and improve your paper.

Author Response

Dear reviewer 3,

We appreciate your spent time to review or manuscript entitled “Review top-down method to determine atmospheric emissions in port. Case of study: Port of Veracruz, Mexico”. We have integrated your suggestions and recommendations for this new review and thank you so much for improved our study. We comment you, in this new review there are new data-analysis corresponding to correlation coefficient for each method and new data in maneuvering position. All our data were update with 0.5% sulfur content in marine fuel.

 Comments and Suggestions for Authors

The subject is timely, and there is a need for papers on this topic. In my opinion, extensive English editing is needed because some sentences are hard to follow, and some expressions are unusual (at least in shipping). Moreover, I have some other concerns and comments given below.

Response:

Thank you for your comment. The style and writing to the English language were carried out by our native collaborator from the University of Wisconsin-Milwaukee of the United States. However, for this new review we have modified some ideas and paragraphs for understanding the topic

Lines 16-20: It is a very long and hard-to-follow sentence; please rewrite it and split it into more sentences.

Response:

According to your suggestion we have modified it into more sentences.

Line 25 - "Liquid vessel" is mentioned - please elaborate on this. What do you consider under a "liquid" vessel? Do you mean tanker?

Response:

For this new review we have modified “Liquid vessel” by “Tanker”. Also, we have classified the typology of ship considered in this study.

Lines 33-35 - please restructure sentences (in my opinion, there is no need to use authors names in this sentence).

Response:

Thank you for your comment. We consider that it is necessary to indicate how important is the generation of inventories of atmospheric emissions due to maritime activity based on the two methods that exist at the international level as suggested by those authors. According to the journal specifications, the references are spelled correctly. We hope to understand your comment for this new review.

Line 39 - Instead of "Gross Tonne", please use Gross Tonnage.

Response:

We have modified it. We have changed “Gross Tonne” by “Gross Tonnage” (GT). Thank you for your suggestion.

Line 44-48: Again, too long and hard to follow sentences, and this sentence contains the paper's aim, so it has to be clear and concise. Please avoid referencing in the sentence where you state your paper's goal.

Response:

According to your suggestion we have modified it into more sentences.

Lines 48-50: It is stated that at least seven methods were found, but there are precisely seven methods used in the paper, so why "at least"?

Response:

Thank you for your observation and we are agreeing with you. Specifically, we have found seven methods to determine fuel consumption and atmospheric emission using the top-down method. We have described in our study the existence of other methods based on top-down, but they were not applied in this study because the information is very specific and is a limitation for our study, these methods are not viable in the case of the port of Veracruz. For these reasons, we have deleted "at least".

Lines 56-58: It is stated: "For the application of the top-down system of this study corresponding to seven methods, we consider the official and detailed information of the port of Veracruz: type of ship, GT, spent time in port, mainly". Could you please elaborate on this, especially on word mainly? What does it mean?

Response:

Thanks for your question. We have corrected the central idea of this paragraph indicating that for the estimation of fuel consumption and atmospheric emission we have based ourselves on the typology of ships that arrive at the port of Veracruz.

Lines 67-70 - It is stated: "[17], [18], Fuentes et al. [19-20] have promoted the development of inventories of atmospheric emissions of main pollutants that are emitted due to the movement of ships in port using the bottom-up system at the national level in Mexico." Please rewrite the sentence and do not start with the number in the brackets (reference) or general number.

Response:

According to your suggestion we have modified it. Thank you for your suggestion.

Lines 73-75: It is stated: "Therefore, this study clearly reflects the current situation of the movement of ships in port, level of fuel consumption and atmospheric emission by SO2 during 2020 with daily resolution." Is this statement true? Fuel consumption and atmospheric emissions are only estimating and cannot be taken as accurate.

Response:

We are convinced that the results of this study represent a fundamental advance in the identification of the level of fuel consumption and atmospheric emission by type of ship on a daily basis using the top-down system for one of the most important ports in Mexico. However, we are agreeing with you that they are estimates based on algorithms and depending on the input data the results will be different. Given this consideration, we have modified the corresponding paragraph and eliminated "current situation" so as not to generate controversy about this.

Lines 75-80: Very long sentence; please consider splitting it into two. Also, please remember that this study only estimates fuel consumption and atmospheric emissions. Furthermore, only fuel and emissions while berthed were considered; however, there is also a maneuvering phase during which ME runs.

Response:

We are agreeing with you. For this new review we have integrated the atmospheric emission level during the maneuvering stage to reinforce our study because in this stage the main and auxiliary engine are also used. The results indicate that there is more fuel consumption in the maneuvering stage, however, the emission level is lower compared to the docking stage.

Lines 92-94: Sentences are repeating; please check.

Response:

Thank you for your observation, we have modified this sentence.

Lines 98-99 - It is stated: "When ships are in port, however, emissions are highest in the berthing stage". Do you have a reference for this statement?

Response:

Thank you for your comment. Indeed, the references cited in the text, for example, Gutierrez et al [46-47], Viana et al. [29], Prati et al. [30], Xiao et al. [31] and Wang et al. [32] indicate that the highest emissions occur in the docking stage. Likewise, our results indicate that atmospheric emissions are higher in the docking stage than in the maneuver, remember that in this new review we have included atmospheric emissions in the maneuvering stage.

Lines 143-145 - It is stated: "In this case, the emission factor (20s) indicates that all the sulfur is converted to sulfur dioxide, the chemical reaction corresponds to 100%, and considering one ton of marine fuel". Please elaborate on this.

Response:

Thank you for your comment. We have integrated the corresponding information to determine the emission factor 20s considering the stoichiometry of the reaction.

Lines 164-166 - same comment as under 8.

Response:

According to your suggestion we have modified it. Thank you for your comment.

 Lines 166-167 - same comment as under 8.

Response:

According to your suggestion we have modified it. Thank you for your comment.

Line 196 - Phrases "weather force" and "weather direction" are mentioned; please elaborate on this.

Response:

Specifically, these factors are very important to consider in the level of atmospheric emission and fuel consumption because the waves have an effect on the speed and power that the ship experiences. Faced with a meteorological effect, the ship experiences sudden changes in power and speed, increasing fuel consumption as well as the level of atmospheric emission.

Lines 208-209 - It is stated: "Currently, Container Ship and Bulk Carrier ships arrive at BN while General Cargo, Carrier, Bulk Carrier, Liquids and Fluids arrive at the BS". What type of ship is "Carrier", and what do is meant by "Liquids " and "Fluids"? Do you mean Tanker and Gas ships? Please elaborate and change the text since this wording is quite confusing.

Response:

Thank you for your comment and observation. For this new review we have integrated the correct name of the vessels considered in this study. The correct classification is: General Cargo, RoRo Cargo, Container, Bulk Agricultural, Bulk Mineral, Tanker (before Liquid), and Chemical (before Fluid).

Line 213 - Is it necessary to divide bulk carriers according to cargo they carry? I believe not for this kind of study.

Response:

In this case, it is very important to make a distinction between these two types of ship because the length of stay (Table 8) and GT level (Table 1) is different, therefore, the emission level is different.

Line 214 - a link is used; please use a reference instead.

Response:

Thank you so much for your suggestion. We have modified it in this new review.

Lines 233-234 - same as under 19.

Response:

Thank you so much for your suggestion. We have modified it in this new review.

Line 249 - same as under 19.

Response:

Thank you so much for your suggestion. We have modified it in this new review.

Lines 253-254 - same as under 19.

Response:

Thank you so much for your suggestion. We have modified it in this new review.

Lines 320-323 - How do you explain the absence of a relationship between the number of ships and atmospheric emissions?

Response:

Thanks for your question. The answer is not easy because several factors influence the level of estimation. However, the number of vessels, length of stay and GT level are the factors that affect the correlation parameter. It cannot be considered that the greater the number of ships, increase the level of atmospheric emission because the GT level is fundamental in the algorithm to determine the power of the main and auxiliary engine, the arrival of ships (type of ships) is different every day.

"The correlation coefficient (R²) between atmospheric emissions and the number of vessels was 0.38 for all methods except for Van der Gon and Hulskotte method, which presented a correlation 0.24." Please elaborate more on this.

Response:

According to the analysis of the Pearson correlation coefficient between the number of vessels and the atmospheric emission level for each method, we have found that these parameters are not directly related; that is, factors such as length of stay, type of vessels per day, and GT level affect the relationship between these two factors.

The Discussion Section deals with methods used to estimate emissions, not with the study results. This part could be moved to Methodology or Introduction, but Discussion needs to deal with the results of this study.

Response:

Thank you for your suggestion. We have responded to your request by removing the discussion section and integrating it into the results obtained for a better interpretation.

What is the conclusion of the study regarding the methods used? Are they applicable, and why? Is there a method that is most suited for the port of Veracruz? Why?

Response:

Thank you for your questions. In the conclusion section we have commented that the Trozzi and Vaccaro methods represented a first scenario to determine the level of fuel consumption and atmospheric emission considering GT-data only. The unique method that we consider not viable to use in Mexico corresponding to Van der Gon and Hulskotte because the typology of vessels is operating at local region (Europe). However, the Van der Gon and Hulkskotte method is functional considering vessel GT-data near to 1000. We concluded that methods based on typology of vessels, GT-data, LF corresponding to maneuver and berthing position, power of ME and AE, that is, Schrooten and Goldsworthy methods are applicable at international level to determine level of fuel consumption and atmospheric emissions.

Are there any other limitations than those mentioned in the Introduction section? I suggest moving the study limitation mentioned to the Conclusions Section.

Response:

Our limitations for the development of this study were to access the automatic identification system for the corresponding information on the route of the vessels and time of stay in real time as well as determine the fuel consumption and atmospheric emission in the anchoring stage.

Recommendations and Future work should not be separate Sections; they should fall in the Conclusions section as well. Try to elaborate on recommendations (why and how).

Response:

Thanks for your suggestions. Originally the Recommendations and Future Work were not split. However, the JMSE considered making these splits. Based on your comments, we have indicated in more detail how to carry out our recommendations.

Reviewer 4 Report

The comments are reported in the attached document.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 4,

We are gratefully for your spent time to review our study entitled “Review top-down method to determine atmospheric emissions in port. Case of study: Port of Veracruz, Mexico”. Thank you for your comments and suggestions which were integrated in our manuscript for this new review. For this new review, there are new analysis of data corresponding to fuel consumption and atmospheric emissions in maneuver position. All our results were updated considering to 0.5% sulfur content in marine fuel according to another reviewers.

Comments on the paper

The study reviewed seven top-down methodologies to estimate atmospheric ship emission at Veracruz Port in Mexico.

This work is very interesting and is relevant for the topics published in Journal of Marine Science and Engineering. The form of the paper must be also improved (there are several repetitions in the manuscript that make it difficult to read). On my opinion a restructuring and rewriting of some part of the manuscript should be necessary. For this reason, my recommendation is: accepted with major revision.

Response:

Thanks for your comments. We are convinced that your suggestions and comments will strengthen our study for possible publication in JMSE during this new revision stage.

Chapter 1: Introduction.

Lines 41-43, pg. 1: “...but exhibits some inconsistencies in its calculation methodology according to Saputra et al. [5], [6] and 42 Knezevic et al. [7]. Always in introduction, lines 50-52, pg. 2 “According to the studies carried out by [6], Knezevic 50 et al. [7], Johansson et al. [9], and Toscano and Murena [10] the top-down method presents inconsistencies in the results. Clearly, inconsistencies in calculation methodology reflect in the results, I suggest to the authors to join these sentences.

Response:

Thank you so much for your observation, we have modified these sentences in this new review.

Lines 62-63, pg. 1: “The limitation of our study consisted in not using the automatic identification system (AIS) generated in the port”.

The AIS data provide, for each ship in a certain period and in a specific location, static information (MMSI number, type, and length) and dynamic information (the ship’s position, i.e. latitude and longitude, course over ground (COG), speed over ground (SOG), and UTC. These are a typical input data of bottom-up methodology, in fact in according to the definition of Wang et al., 2007 1: Bottom-up approaches estimate ship- and route-specific emissions based on historical ship movements, ship attributes, and ship emissions factors. For this reason, I disagree with this finding, and I suggest deleting it.

1 Wang, C., Corbett, J. J., & Firestone, J. (2007). Modeling energy use and emissions from North American shipping: application of the ship traffic, energy, and environment model. Environmental science & technology, 41(9), 3226-3232.

Response:

We appreciate your comment. In agreement with the other reviewers, we have incorporated part of this idea in the concluding section. We consider that the use of AIS is not strictly a limitation for the development of this study, but it was necessary to clarify that this type of information is confidential in Mexico.

Lines 65-67, pg. 2; “The objective of the development of this study was to characterize the port of Veracruz respect to fuel consumption and atmospheric emission by type of ship because it is under expansion”. This sentence is a repetition of lines 44-47: “The essence of this study consisted in the review of the top-down system to estimate atmospheric emissions by sulfur dioxide (SO2) due to the movement of ships in port with application to one of the most important ports in Mexico due to its expansion located in the Gulf of Mexico, Port of Veracruz”.

Response:

Thank you so much for your observation, we have modified these sentences in this new review.

Lines 75-80, pg.2: “The results of this study with daily resolution will strengthen the use of air quality models because there is no detailed information on fuel consumption by type of ship in Mexico, which is an important factor in decision-making for the application of air quality models when the emission source is considered as a punctual source according to Fuentes et al. [21], Jagangiri et al. [22], Murena et al. [23], Bai et al. [24], Mocerino et al. [25] and Pan et al. [26].”

The air dispersion models use the emission data as input. For this reason, the results of this study, in terms of ship emissions should be used in air dispersion models. I suggest to the authors to reformulate this sentence.

What the authors mean by the results of this study with daily resolution will strengthen the use of air quality models?

Response:

Thank you for your comments and suggestions. The use of air quality models works based on the detailed information of the emission source, for example, we consider that when the ship is in the docking stage, it is considered as a point source of emission. Therefore, the information regarding the height and diameter of the chimney, the speed and temperature of the exhaust gases and the resolution of the atmospheric emission level as well as the type of terrain are factors that influence the level of concentration. The daily resolution allows to identify the temporal variability of the concentrations obtained by the air quality model and its comparison with the international reference concentration levels in an hourly or daily average. This allows to identify in detail environmental pollution events during the day depending on the atmospheric stability of the area of interest.

Chapter 2: Background

The paragraphs 2.1 “International Maritime Organization and Marine Pollution Regulations” and 2.2 “Sulfur content in marine fuel” are closely related and in some case redundant. I suggest merging these two paragraphs in one.

Response:

Thank you for your comment. We have attended your suggestion in this new review, and we are according with you merging these two paragraphs in one.

Paragraph 2.4 “Top-down method to determine atmospheric emissions” contains some repetition reported in Introduction.

The authors could revise the paragraph 2.4.

Response:

Thank you for your suggestion. We have modified this section 2.4 for this new review.

Chapter 4: Methodology

Table 4, pg.7: It seems that the equations to calculate fuel consumption provided by Schrooten et al. [13] and Goldsworthy and Goldsworthy [15] are the same.

The authors should explain, which are the differences between the two methods.

Response:

Thank you for your comment. At this consideration, the only difference in these methods corresponding to conversion of units to obtain Mg_fuel/h. Schrooten et al [13] utilized 1.1x10^-6as a unit conversion, moreover Goldsworthy and Goldsworthy [15] utilized a factor of 1000 to obtain kg, however, to obtain Mg directly it is necessary the 1x10^-6as a unit factor. We consider that Schrooten et al [13] utilized 1.1x10^-6as a unit conversion according to their emission model called MOPSEA.

Round 2

Reviewer 3 Report

The authors revised the paper according to the given comments and suggestions, and the paper seems much improved. Therefore, I do not have more comments.

Reviewer 4 Report

I am satisfied with the author’s responses to my questions/comments raised in my initial review. The revised  manuscript is easier to follow based on feedback from the reviewers.  I recommend that the revised paper be accepted in present form.