Modest Method for Estimating CO₂ Emissions from Container Handling Equipment at Ports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study presents a systematic approach for estimating CO2 emissions at container ports using both container movement data and recorded energy consumption for various cargo-handling equipment.

The mathematical models are properly formulated and verified as robustness test based on a case study in container port.

Although it does not appear to have any theoretical novelty, it is considered an excellent empirical study.

In section 2.6, please explain why you chose this port as a case study.

Author Response

Response to Reviewer #1
Title: Modest method for estimation of CO2 emissions from cargo handling equipment in container port
Comment 1: 
This study presents a systematic approach for estimating CO2 emissions at container ports using both container movement data and recorded energy consumption for various cargo-handling equipment.
Response 1: 
Thank you very much for the constructive comments on this article. We have made significant improvements by thoroughly addressing the reviewer’s comments. 

Comment 2: 
The mathematical models are properly formulated and verified as robustness test based on a case study in container port.
Response 2: 
Thank you very much for the constructive comments on this article. We have made significant improvements by thoroughly addressing the reviewer’s comments. 

Comment 3: 
Although it does not appear to have any theoretical novelty, it is considered an excellent empirical study.
Response 3: 
Thank you very much for the constructive comments on this article. We have made significant improvements by thoroughly addressing the reviewer’s comments. 

Comment 4: 
In section 2.6, please explain why you chose this port as a case study.
Response 4: 
Thank you very much for the constructive comments on this article. The explanation for selecting this terminal as a case study has been added in Section 2.5, page 9 line 276:
‘This terminal was selected because its container handling equipment—rubber-tyred gantry cranes, terminal trucks, and quay cranes—and its parallel layout are representative of the configurations commonly used in non-autonomous container terminals worldwide.’

Reviewer 2 Report

Comments and Suggestions for Authors

The article presented for evaluation is interesting and a good read.  The background in the introduction was correctly outlined. The methodology presented is correct and complete. The results are presented correctly and discussed extensively. A limitation of the paper is that the model verification is based on data from one container port, which limits the ability to generalise the results to other ports with different layouts and equipment.  However, the authors are aware of this and have described this limitation.  However, I have a few comments that the authors should address:

1. Despite the broad presentation of the background to the problem, the results and discussion section needs more direct references to other studies that have conducted similar analyses. A comparison of the results with other works would better place these findings in the context of global research.
2 The results indicate that diesel engine use increases CO₂ emissions. Older equipment may generate higher emissions than modern ones, and this aspect may affect the interpretation of the results.
3 Admittedly, the paper deals with the estimation method, but the authors make some recommendations based on the results. However, a cost-benefit analysis of implementing the proposed emission reduction methods is missing. This type of analysis would show the financial feasibility of the proposed solutions.

Author Response

Response to Reviewer #2

Title: Modest method for estimation of CO2 emissions from cargo handling equipment in container port.

 

 

Comment 1:

The article presented for evaluation is interesting and a good read.  The background in the introduction was correctly outlined. The methodology presented is correct and complete. The results are presented correctly and discussed extensively. A limitation of the paper is that the model verification is based on data from one container port, which limits the ability to generalise the results to other ports with different layouts and equipment.  However, the authors are aware of this and have described this limitation. However, I have a few comments that the authors should address:

1. Despite the broad presentation of the background to the problem, the results and discussion section needs more direct references to other studies that have conducted similar analyses. A comparison of the results with other works would better place these findings in the context of global research.

Response 1:

Thank you very much for the constructive comments on this article. A comparison of CO² emission of other work from various terminals worldwide has been added in Section 3.1, page 11, line 334:

 

‘As a comparison, CO₂ emission rates at ports worldwide vary significantly depending on operational patterns and the specifications of container handling equipment, as detailed in Table 3.’

 

Table 3. Comparison of CO₂ emission from several container terminals

Case Study	CO₂ emission	Reference
Current Study	15.6 kg/TEU
Rotterdam Shortsea Terminal, Netherlands	9.3 kg/TEU	[26]
Noatum Container Terminal Valencia, Spain	11.5 kg/TEU	[27]
Hanno Terminals, Netherlands	24.0 kg/TEU	[26]
Chittagong Container Terminal, Bangladesh	26.5 kg/TEU	[28]

 

 

 

 

Comment 2:

2 The results indicate that diesel engine use increases CO₂ emissions. Older equipment may generate higher emissions than modern ones, and this aspect may affect the interpretation of the results.

 

Response 2:

Thank you very much for the constructive comments on this article. Additional explanation of this aspect has been added Section 3.1, page 11 line 321:

 

Older diesel-powered equipment tends to have higher emissions due to less efficient engine technology, this study focuses on a port that still predominantly relies on conventional diesel-powered cranes. Therefore, the emissions data in this study reflect the performance of such equipment, which is still common in many terminals globally.

 

Furthermore, the CO₂ emissions are calculated based on the CO₂ emission factors for each type of container handling equipment. Specifically, the CO₂ emission factor for diesel engines is 2.67 kg CO₂ per liter of diesel, as referenced in the 2006 IPCC Guidelines [31]. For electric energy, the CO₂ emission factor depends on the national grid power plant, which varies by region. In this study, the emissions from electric-powered equipment were calculated based on the emission factors provided by the Ministry of Energy and Mineral Resources, ranging from 0.16 to 1.27 kg CO₂ per kWh, depending on the regional energy mix [32].

 

We acknowledge that as the industry moves toward hybrid or electric equipment, the CO₂ emissions from container terminals could decrease significantly, especially if the electricity used in these operations comes from cleaner energy sources. This aspect of future emission reduction is highlighted in the revised manuscript to provide context on how evolving technologies and energy sources will likely influence emission profiles.

 

 

Comment 3:

3 Admittedly, the paper deals with the estimation method, but the authors make some recommendations based on the results. However, a cost-benefit analysis of implementing the proposed emission reduction methods is missing. This type of analysis would show the financial feasibility of the proposed solutions.

Response 3:

Thank you very much for the constructive comments on this article.

This study primarily focuses on the modest method for estimating CO₂ emissions from cargo handling equipment at container ports, in line with systematic research methods for CO₂ emissions outlined in the methodology section. While we present recommendations on the conclusions, the scope of this paper does not include a cost-benefit analysis of implementing the proposed emission reduction methods. We acknowledge that a cost-benefit analysis would be a useful addition for evaluating the financial feasibility of these solutions.

We will certainly consider including a cost-benefit analysis in future research, as this is a critical component for evaluating the practical implementation of emission reduction strategies. Thank you again for your insightful suggestion, which we will incorporate into our future work.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1)The article title could be shortened

2) In lines (9-11 and 39-41) the “International Maritime Organization aims to reduce marine greenhouse gas emissions by 40% by 2030, including in the maritime port sector).

This is a difficult task due to the complexity of port activities and the differences in priorities of countries regarding reductions in carbon emissions in this sector.

I would like to hear the authors’ opinion on this ambitious goal (40% by 2030)!!!

3) The references could be updated (ref: 4, 5,6,7,8, 11, 15, 18,20 etc.)

4) In lines (48-50) “port data in Barcelona” based on ship energy requirements, they found that car operators were the largest contributors, emitting 6 kg of GHG per tonne of cargo handled.

Reference (8) is from 2010, should be updated. (newer data)

5) In lines (52-54) “Other studies have analyzed CO₂ emissions at various ports in India using the formula based on the Intergovernmental Panel on Climate Change (IPCC) guidelines, revealing that refrigerated containers contributed up to 65% of total CO₂ emissions

References (9,10) are from 2012, should be updated (newer data)

6) In lines (110 -114) “The focus on CO₂ emissions in this research aligns closely with the International Maritime Organization's (IMO) targets for reducing greenhouse gas emissions. Several key reasons underpin the decision to concentrate solely on CO₂ emissions. Firstly, CO₂ is the largest contributor to global warming and climate change among all greenhouse gases emitted by port operations”

So, it is not the CO2 Eq. (it is not equivalent) only the contribution of CO₂ gas. the CO₂ actually has the greatest contribution to the greenhouse effect, but there are other gases such as: methane (CH₄), nitrous oxide (N₂O) and other greenhouse gas precursor gases.

Since the electricity that powers the port can be of thermoelectric origin, emissions from this energy source are treated as CO_2eq. (equivalent) emissions. That is, another gas emitted by thermoelectric plants is carbon monoxide (CO), which plays an indirect role, as it reacts with the hydroxyl radical, reducing the concentration of this radical in the atmosphere. However, the hydroxyl radical reduces the concentration of methane gas (which intensifies the greenhouse effect). Therefore, the presence of CO leads to the maintenance of methane in the atmosphere. Carbon monoxide can contribute to the increase in the greenhouse effect, as it participates in the formation of ozone (O₃) in the troposphere. Although the ozone layer is located in the stratosphere, human activities can generate tropospheric ozone, worsening the greenhouse effect. Of course, thermoelectric plants also emit CO₂ (the main greenhouse gas) in addition to nitrogen oxides NOx and sulfur oxides SOx, particulate matter (PM), volatile organic compounds (VOC) and Total organic compounds (TOC-hydrocarbons) which may contain methane (CH₄).

NOTE: You must be careful with electrical energy sources, as their generation may contain other gases that are precursors of greenhouse gases, such as CO and methane itself (CH₄).

7) Lines (166 -167) . and 𝑓_E,_𝐶𝑂2 are CO₂ emission factors from electrical energy sources originating from grid electricity.

NOTE: I see a difficulty: knowing which electrical matrix makes up the grid's electricity, since the sources are mixed. They can be thermoelectric (natural gas, diesel, coal and nuclear), hydroelectric, solar, wind and biomass. Emission factors can vary even in the case of thermoelectric depending on which fuel is used. This is an important point and should be discussed in the article !!!

8)lines (114 -118) “These results show that both models consistently show that the most significant contribution to emissions at container ports is from container cranes, with an emission contribution of >50%, and rubber-tired gantry cranes have a contribution of >25%. In comparison, the remainder is contributed by terminal trucks >10%, while equipment and other tools have a contribution below 5%.”

50% +25% +10% + 5% = 90 %

And the other 10% (missing) comes from where?

9) Line 266 (section 2.6) “Case Study of Container Terminal 500.000 TEUs/Year”  

Suggestion: enter the name of the terminal (port) and the country where it is located

10) The paper identifies container cranes with an emission contribution of >50%, and rubber-tired gantry cranes with a contribution of >25%. The authors then present the solution: these results can provide guidance for research and development in container terminals; further decarbonization can be achieved through the electrification of quay cranes.

What is the cost of electrifying quay cranes? I do not have an idea of ​​the size of this investment, but at first glance it seems to be very expensive.

 

11) The authors could emphasize the results obtained in the article in the conclusions.

 

Author Response

Response to Reviewer #3

Title: Modest method for estimation of CO2 emissions from cargo handling equipment in container port.

 

 

Comment 1:

1)The article title could be shortened

Response 1:

Thank you for your suggestion. We have revised the article title to make it more concise while retaining its core meaning. The updated title is: 'Modest Method for Estimating CO₂ Emissions from Container Handling Equipment at Ports.'

 

Comment 2:

2) In lines (9-11 and 39-41) the “International Maritime Organization aims to reduce marine greenhouse gas emissions by 40% by 2030, including in the maritime port sector).

This is a difficult task due to the complexity of port activities and the differences in priorities of countries regarding reductions in carbon emissions in this sector.

I would like to hear the authors’ opinion on this ambitious goal (40% by 2030)!!!

Response 2:

Thank you for the insightful comment. As an author with a background in naval engineering, in our opinion, in theory, the current technological advancements can support achieving IMO's ambitious 40% reduction target by 2030. However, in practice, this goal remains highly challenging, especially in developing countries, due to the significant technology gaps.

 

Comment 3:

3) The references could be updated (ref: 4, 5,6,7,8, 11, 15, 18,20 etc.)

Response 3:

Thank you for your valuable feedback. I have updated all the references mentioned (ref: 4, 5, 6, 7, 8, 9, 10, 11, 15, 18, 20), ensuring that both the in text-citation and the reference list reflect the most recent and relevant sources.

 

 

Comment 4:

4) In lines (48-50) “port data in Barcelona” based on ship energy requirements, they found that car operators were the largest contributors, emitting 6 kg of GHG per tonne of cargo handled.

Reference (8) is from 2010, should be updated. (newer data)

Response 4:

Thank you for your valuable feedback. I have updated all the references mentioned (ref: 4, 5, 6, 7, 8, 9, 10, 11, 15, 18, 20), ensuring that both the in text-citation and the reference list reflect the most recent and relevant sources.

 

Comment 5:

5) In lines (52-54) “Other studies have analyzed CO₂ emissions at various ports in India using the formula based on the Intergovernmental Panel on Climate Change (IPCC) guidelines, revealing that refrigerated containers contributed up to 65% of total CO₂ emissions

References (9,10) are from 2012, should be updated (newer data)

Response 5:

Thank you for your valuable feedback. I have updated all the references mentioned (ref: 4, 5, 6, 7, 8, 9, 10, 11, 15, 18, 20), ensuring that both the in text-citation and the reference list reflect the most recent and relevant sources.

 

Comment 6:

6) In lines (110 -114) “The focus on CO₂ emissions in this research aligns closely with the International Maritime Organization's (IMO) targets for reducing greenhouse gas emissions. Several key reasons underpin the decision to concentrate solely on CO₂ emissions. Firstly, CO₂ is the largest contributor to global warming and climate change among all greenhouse gases emitted by port operations”

So, it is not the CO2 Eq. (it is not equivalent) only the contribution of CO2 gas. the CO2 actually has the greatest contribution to the greenhouse effect, but there are other gases such as: methane (CH4), nitrous oxide (N2O) and other greenhouse gas precursor gases.

Since the electricity that powers the port can be of thermoelectric origin, emissions from this energy source are treated as CO2eq. (equivalent) emissions. That is, another gas emitted by thermoelectric plants is carbon monoxide (CO), which plays an indirect role, as it reacts with the hydroxyl radical, reducing the concentration of this radical in the atmosphere. However, the hydroxyl radical reduces the concentration of methane gas (which intensifies the greenhouse effect). Therefore, the presence of CO leads to the maintenance of methane in the atmosphere. Carbon monoxide can contribute to the increase in the greenhouse effect, as it participates in the formation of ozone (O3) in the troposphere. Although the ozone layer is located in the stratosphere, human activities can generate tropospheric ozone, worsening the greenhouse effect. Of course, thermoelectric plants also emit CO2 (the main greenhouse gas) in addition to nitrogen oxides NOx and sulfur oxides SOx, particulate matter (PM), volatile organic compounds (VOC) and Total organic compounds (TOC-hydrocarbons) which may contain methane (CH4).

NOTE: You must be careful with electrical energy sources, as their generation may contain other gases that are precursors of greenhouse gases, such as CO and methane itself (CH4).

Response 6:

Thank you for your insightful comment. The referenced section has been revised to clarify the focus on CO₂ emissions rather than greenhouse gas emissions.

 

 

Comment 7: 7) Lines (166 -167) . and ?E,??2 are CO₂ emission factors from electrical energy sources originating from grid electricity.

NOTE: I see a difficulty: knowing which electrical matrix makes up the grid's electricity, since the sources are mixed. They can be thermoelectric (natural gas, diesel, coal and nuclear), hydroelectric, solar, wind and biomass. Emission factors can vary even in the case of thermoelectric depending on which fuel is used. This is an important point and should be discussed in the article !!!

Response 7:

Thank you for your insightful comment. You raise an important issue regarding the variability of emission factors for electricity sources, which are a key component of estimating CO₂ emissions. Additional explanation has been added to Section 2.2, Page 5, Line 160

 

 

Comment 8: 8)lines (114 -118) “These results show that both models consistently show that the most significant contribution to emissions at container ports is from container cranes, with an emission contribution of >50%, and rubber-tired gantry cranes have a contribution of >25%. In comparison, the remainder is contributed by terminal trucks >10%, while equipment and other tools have a contribution below 5%.”

50% +25% +10% + 5% = 90 %

And the other 10% (missing) comes from where?

Response 8:

Thank you for your valuable comment. To clarify the emission contributions at container ports, we have revised the text to include the exact percentages. The emission contributions from different equipment are as follows: Container cranes account for 56%, rubber-tired gantry (RTG) cranes contribute 27%, terminal trucks account for 14%, and reach stackers/side loaders contribute 2%.

 

Comment 9: 9) Line 266 (section 2.6) “Case Study of Container Terminal 500.000 TEUs/Year” 

Suggestion: enter the name of the terminal (port) and the country where it is located.

Response 9:

Thank you for your helpful suggestion. In response, we have updated the subsection title to provide more clarity. Additionally, we have included the geographical location of the container terminal, including its latitude and longitude, in Figure 4 line 297

 

Comment 10: 10) The paper identifies container cranes with an emission contribution of >50%, and rubber-tired gantry cranes with a contribution of >25%. The authors then present the solution: these results can provide guidance for research and development in container terminals; further decarbonization can be achieved through the electrification of quay cranes.

What is the cost of electrifying quay cranes? I do not have an idea of the size of this investment, but at first glance it seems to be very expensive.

Response 10:

Thank you for your comment. According to data from the Electric Power Research Institute (EPRI), the investment required for electrifying quay cranes is often more cost-effective compared to diesel cranes. While the initial capital for electrification may appear high, long-term savings in fuel and maintenance costs, along with emissions reductions, make it a more economical option over time.

 

 https://restservice.epri.com/publicdownload/000000000001020510/0/Product

 

 

Comment 11: 11) The authors could emphasize the results obtained in the article in the conclusions.

Response 11:

Thank you for your suggestion. In the revised conclusion, we have emphasized the key results obtained in our study. Specifically, our analysis identifies that quayside container cranes are the most significant contributors to emissions, accounting for 56% of the total, followed by rubber-tired gantry cranes at 27%, and terminal trucks at 14%. Additionally, the emissions per TEU for the terminal were calculated at 15.6 kg/TEU. These findings are now highlighted in the conclusion to provide a clear summary of the results and their implications for emissions management at container ports.

 

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This paper had developed a model and investigated the Estimation of CO2 Emissions from Cargo Handling Equipment in Container Port. The results are interesting. However, the manuscript has some defect. Thus, I suggest that the paper be major REVISION before it is considered for publication. Thus, the authors should revise the manuscript accordingly. The following hints may help the authors：

Q1: The abstract should be improved. The abstract of the paper includes four parts: purpose, methods, results, and conclusion. 

Q2: In line 98, the author said “based on movement activities and energy consumption”. The author should introduce the differences and respective advantages of the two methods. Why did the author choose these two methods?

Q3: In paper, the emission of carbon dioxide from ships is not only related to ports, but also to factors such as climate, environment, and ship structural parameters. Therefore, the author's model should be further deepened. If possible, it should be further improved

Q4: The writing and grammar should be extensively improved. The current version of the manuscript is hard to read.

Q5: The Discussion and Results section is written too simply, and the authors are advised to rewrite the Discussion and Results section. In addition, the practical application and significance of this study should be further elaborated in the result. It should only contain the important achievements, harvested information and new discoveries of this manuscript. The author is suggested to rewrite the section.

Comments on the Quality of English Language

Please see the Comments and Suggestions for Authors.

Author Response

Response to Reviewer #4

Title: Modest method for estimation of CO2 emissions from cargo handling equipment in container port.

 

 

Comment 1: This paper had developed a model and investigated the Estimation of CO2 Emissions from Cargo Handling Equipment in Container Port. The results are interesting. However, the manuscript has some defect. Thus, I suggest that the paper be major REVISION before it is considered for publication. Thus, the authors should revise the manuscript accordingly. The following hints may help the authors：

Q1: The abstract should be improved. The abstract of the paper includes four parts: purpose, methods, results, and conclusion.

Response 1:

Thank you very much for the constructive comments on this article. The abstract has been revised more structured, dividing it into clear sections for backgrounds, purpose, methods, results, and conclusions:

 

‘The maritime industry is under increasing pressure to reduce CO₂ emissions, with the International Maritime Organization (IMO) setting a target to reduce greenhouse gas emissions by 40% by 2030, including emissions from the port sector. However, accurate and reliable methods for estimating CO₂ emissions at container ports, which are significant contributors to maritime emissions, are still lacking. This study aims to address this gap by evaluating a novel method for estimating CO₂ emissions at container ports. The proposed method utilizes cargo handling equipment movement theory, quantifying both vertical and horizontal movements based on the number of containers handling equipment’s. The emissions for each piece of equipment are estimated by multiplying the movement quantity by the respective emission factor. To validate the model, a robustness test compares the estimated CO₂ emissions with actual energy consumption data from the port. A case study was conducted at a container port with an annual capacity of over 500,000 TEUs and a parallel layout type. The estimated CO₂ emissions were approximately 8,183 tons per year, with container cranes contributing over 50%, rubber-tired gantry cranes over 25%, and terminal trucks over 10%. The method demonstrated an accuracy with a deviation of less than 1%. This research offers a fast, reliable approach for estimating baseline CO₂ emissions at container ports, providing valuable insights for port authorities and policymakers to develop more effective emission reduction strategies.’

 

 

Comment 2: Q2: In line 98, the author said “based on movement activities and energy consumption”. The author should introduce the differences and respective advantages of the two methods. Why did the author choose these two methods?

Response 2:

Thank you very much for the constructive comments on this article. Additional explanation of these methods has been added Section 2, page 3 line 92:

 

‘The movement-based method focuses on physical activities within the terminal, such as container handling and truck movements, this approach provides insights into the emissions generated by different types of equipment involved in both horizontal and vertical movements. Conversely, the energy consumption method relies on actual recorded data of fuel and electricity usage at the port, this method offers a direct measure of emissions. The dual use of these methods enables to cross-validate the CO₂ emission estimates from movement activities with recorded energy consumption data, enhancing the robustness and reliability of our findings. This comparative approach ensures a comprehensive and accurate understanding of CO₂ emissions at the container terminal, allowing for effective emission reduction strategies.’

 

 

Comment 3:

Q3: In paper, the emission of carbon dioxide from ships is not only related to ports, but also to factors such as climate, environment, and ship structural parameters. Therefore, the author's model should be further deepened. If possible, it should be further improved

Response 3:

Thank you very much for the constructive comments on this article. We acknowledge that CO₂ emissions from ships are influenced by various factors, including climate, environment, and ship structural parameters. However, this study specifically focuses on the emission estimation related to container handling operations at ports. The model presented in this paper is centered on the processes involved in container handling, which can be categorized into three main stages (ss illustrated in Figure 2): handling at the quay crane, transfer by trucks, and handling at the storage yard. The container handling is further categorized into vertical and horizontal movements. This simplicity is key to ensuring the model can be used for quick calculations, making it practical for port authorities to assess emissions regularly. We appreciate your suggestion to consider expanding the scope of the model and will certainly explore the inclusion of these additional factors in future studies.

 

Figure 2. Typical container movement and prime mover in container port

 

 

 

Comment 4:

Q4: The writing and grammar should be extensively improved. The current version of the manuscript is hard to read.

Response 4:

Thank you very much for the constructive comments on this article. In this revision, the writing and grammar have been extensively improved to enhance readability and clarity. To ensure the highest quality, we utilized the MDPI English Language Editing Services, which specialize in academic manuscripts.

 

 

 

Comment 5:

Q5: The Discussion and Results section is written too simply, and the authors are advised to rewrite the Discussion and Results section. In addition, the practical application and significance of this study should be further elaborated in the result. It should only contain the important achievements, harvested information and new discoveries of this manuscript. The author is suggested to rewrite the section.

Response 5:

Thank you for your valuable suggestion. In this revision, the Discussion and Results section to provide a more detailed and structured analysis, emphasizing the practical application and significance of the study while focusing on the key achievements, harvested information, and new discoveries.

 

The important achievements of this study (stated in section 3.2 page 14 line…) include the robustness of the proposed CO₂ emission estimation model. The robustness test results, shown in Figure 7, demonstrate a strong correlation between the CO₂ emission estimates based on the movement model and those based on energy consumption, with an R-square value close to 1. This indicates high reliability and accuracy of the proposed model.

 

The harvested information (stated in section 3.1 page 12 line…) derived from the model includes the CO₂ emission estimates for specific container handling equipment. For instance, container cranes contribute approximately 4,581 tons/year, rubber-tired gantry cranes 2,183 tons/year, terminal trucks 1,184 tons/year, and reach stackers 234 tons/year, resulting in a total CO₂ emission of approximately 8,183 tons/year for the case study port. These estimates highlight the dominant contribution of container cranes, accounting for over 50% of total emissions, followed by rubber-tired gantry cranes and terminal trucks. Moreover, the study confirms that CO₂ emissions at container ports are influenced by the type of equipment used and the port layout.

 

The new discovery of this research (stated in section 3.1 page 12 line…) is the normalized CO₂ emission rate per container, calculated as 15.6 kg/TEU. This value is consistent with prior studies, which report emission rates ranging from 9.3 to 26.5 kg/TEU [26,27,28]. Such findings validate the proposed model’s reliability and provide a benchmark for comparing CO₂ emissions at container ports. To further contextualize these results, Table 3 presents a comparison of CO₂ emission rates at ports worldwide, illustrating significant variations based on operational patterns, equipment specifications, and terminal layouts.

 

This study's practical significance lies in offering a quick, reliable, and scalable method for estimating CO₂ emissions at container ports. This model can guide port authorities and policymakers in identifying emission hotspots, optimizing equipment use, and implementing targeted emission reduction strategies.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The article can be accepted

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have carried out a thorough and careful revision and the revised manuscript improved a lot in terms of technical quality and language. Therefore, I would recommend it for publication in the Journal.