Influence of the Apron Parking Stand Management Policy on Aircraft and Ground Support Equipment (GSE) Gaseous Emissions at Airports
Round 1
Reviewer 1 Report
The presentation of the content is so unclear that it is difficult to understand even the basic ideas of the Authors: assumptions taken, simulation procedures used and results obtained - details are discussed below.
Comments to the Authors
1. SI units should be used in a scientific paper. That is why the following units in the “Nomenclature” should be corrected:
[g/HP.h] (gram per horse power multiplied by hour???)
[HP] (horsepower???)
2. Denotations in the “Nomenclature” are defined, but the meaning of these definitions is unclear, e.g. what is the meaning of: “Emission factor of pollutant 'i', in regard to GSE 'l'”, “Damage factor for GSE 'l'”, “Total arrival movements” or “Arrival time frame”? Please give precise definitions of the quantities defined in the “Nomenclature”. Please give also the values of these parameters used during simulations.
3. In several places descriptions in the text are too general, slightly related to the main problems indicated in the paper, e.g. in:
a) section “1. Introduction” - can be entirely removed or can be stressed in one/two important sentences;
b) descriptions in lines 69-76 in section “2. The system and Problem” can be deleted;
c) descriptions about the SIMMOD software can be moved from lines 196-199 to lines 147-149;
d) the section “GSE Characterisation” provides too general descriptions in lines 261-277;
e) the purpose of section “Apron traffic: transfer distance” in lines 281-309 is not clear; descriptions in this section are so imprecise that it is impossible to understand the content, e.g.:
Line 281: “Transfer distances depend on the geometrical arrangement of the passenger terminal apron... GSE equipment. Therefore, some considerations have to be taken into account for its measurement in apron, according to the type of procedure.” - What will be measured? Where will be those “considerations” included?
Lines 293-301: What is the purpose of presenting “considerations” for three procedures?
Lines 302-309: What “Gantt diagrams” do you mean?
f) the purpose and meaning of section “Model 1” in lines 312-337 is unclear - descriptions do not explain the Authors' ideas,
g) descriptions of the obtained results in sections “Models 2 and 3”, lines 340-397 are completely unclear
h) the meaning and purpose of final comments provided in section “5. Discussion” is unclear.
4. Lines 147-155: It is not clear if the second and the third stage of the methodology are implemented with the use of the SIMMOD software or not. If not, then what software is used for those stages? Please explain if the “General methodology diagram” in Fig. 1 is implemented in SIMMOD.
5. Line 227: Denotations in Eq. (3) should be explained, e.g.: $FF_{jk}$, $Fi_{ijk}$...
6. Line 239: The meaning of Fig. 4 is unclear:https://www.youtube.com/watch?v=lPEIo_a5aMc
a) does Fig. 4 present assumed (given) data to further simulations that are to be performed in SIMMOD or does this figure present simulation results obtained from SIMMOD?
b) what do you mean by “Movements per hour” (at the vertical axis)?
c) what do you mean by “Hour” (at the horizontal axis)? is this the hour/the time of day?
d) what do you mean by “real times from scheduled times with a minimal time of 50 minutes and a maximum of 150 minutes” in line 242?
7. Line 278, Tab. 2:
a) it is not clear how the values in Tab. 2 have been obtained,
b) the acronym “TUG” should be explained,
c) what are the units for the values given in Tab. 2?
8. Line 317, Fig. 5:
a) what do you mean by “Delay” in minutes?,
b) what do you mean by “Exclusive use stands, %”?
9. Line 329: “Total produced emissions may rise up to 300%...” - What do you mean by a “300% emission”?
9. Line 331: What is the purpose of the $Z$ and $DelayGND$ variables introduced by Eqs. (7) and (8)? How can one interpret Fig. 6?
10. Line 346, Tab. 4:
a) what do you mean by “Scenario” (1st column)? What are those scenario numbers?
b) how can one interpret the obtained results in Tab. 4?
11. Line 395, Fig. 16: What do you mean by “Units”?
12. Line 408: How have you obtained the formula:
$%Se^2 (1-%Aes)DF$?
13. Lines 399-401: “The results of the different management scenario... risk/environmental analysis.” - The meaning of these sentences is unclear.
14. Line 403: “Therefore, the existence of an optimal point depends on the combination...” - What do you mean by “an optimal point”?
15. Line 455, Fig. 19: What do you mean by “Cumulative frequency” (vertical axis)?
Language mistakes
Line 2: “Title Influence of the apron...” -> “Influence of the apron...”
Line 13: “... the aircraft are allocated...” -> “... the aircrafts are allocated...”
Line 89: “... Mirkovic and Tosic, who addresses the problem...” -> “... Mikrovic and Tosic, who address the problem...”
Line 91: “... all aircraft can use all stands...” -> “... all aircrafts can use all stands...”
Line 93: “... number of aircraft...” -> “... number of aircrafts...”
Line 235: “... to analyses a representative...” -> “... to analyze a representative...”
Line 238: “The Fig. 4 shows the arrival and departure profiles...” -> “Arrival and departure profiles... are shown in Fig. 4”
Line 272: “In the appendix C it presents the factor considers.” -> “In Appendix C the considered factors are presented.”
Line 275: “... in the Table 2...” -> “... in Table 2...”
Line 319: “In the Fig. 5...” -> “In Fig. 5...”
Line 344: “... in the Table 4...” -> “... in Table 4...”
Line 348: “... the emission produces by the processes...” -> “... the emission produced by the processes...”
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
Dear Editor,
Thank you for sending me the attached manuscript “
Influence of the apron parking stand management policy on aircraft and Ground Support Equipment (GSE) gaseous emissions at airports” for review.
This manuscript investigates the concept of a hybrid apron with a fixed number of parking positions considering the management model influence for the average delay per aircraft and the gaseous emissions generated by aircraft and ground support equipment (GSE) altogether It is meaningful to discuss this issue under the enhancing attention on airport emissions and CORSIA. The manuscript is well-written and structured. My comments are listed below:
- In the abstract, it is suggested to add some results and data obtained from this work.
- In the introduction section, aerosol emissions and their control technologies from other developing countries, for example, China, is suggested to be mentioned and discussed.
https://www.sciencedirect.com/science/article/abs/pii/S1352231017308701
- Previous research also demonstrated that, urbanization may have influences on air pollutions or GHGs emissions. In the discussion section or introduction section, the authors are suggested to shortly discuss the effects of urbanization on airport emissions.
https://www.sciencedirect.com/science/article/abs/pii/S092134491930360X
- Activities and emissions of rural households are also suggested to be mentioned in this work. Due to large emissions from solid fuels in rural households. For example:
https://www.sciencedirect.com/science/article/abs/pii/S0959652617316189
https://www.sciencedirect.com/science/article/abs/pii/S0960148118302611
- section 3.3.1, the authors are suggested to provide reasons why you made these assumptions. What are these parameters mean? If there is any uncertainty when you made these assumptions?
- In the conclusion section, the authors are suggested to be extended with some discussions on what are the further implications of this work. Is it possible to learn from the case study in other countries?
- if it is possible to include CO2 in this research? It would be more interested as the CORSIA is an important policy should not be ignored.
- figure 16, the authors are suggested to provide data of each column on the figure, it is difficult to read the data.
- line 408, the function is not in the right place.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript by Di Bernadi el al. examines the potential gaseous emissions from aircraft and ground support equipment (GSE) due to ground congestion and delays. This study first uses SIMMOD to simulate aircraft operations on the airport apron and applies different scenarios with varying gate assignment policy. The aircraft operation results are then integrated with GSE activities, and CO and NOx emissions are computed for different scenarios to investigate the potential impact of delays and movements on emissions. The emission results from different scenarios indicate that delay can have a huge impact on CO and NOx depending on the gate usage and GSE NOx emissions can vary a lot given different gate policies. Although there were many previous researches on aircraft management and their impact on emissions, this study demonstrates a quantitative approach that focused on a real-world airport scenario, which can provide valuable insight into airport apron planning and construction, air traffic management, and resources distributions. However, major revisions to address the following comments are still needed before acceptance for publication:
- In the results section, many variables were poorly defined and hard to follow along the text and figures; some of them were not included in the nomenclature table in the beginning of the text.
- Given the complexity of the analysis, it is understandable that many assumptions were made throughout the study. However, for a work that may have impact on real-world policies, the limitations of assumptions and the results' applicability to real life need to be addressed.
- The discussion session only presents quantitative results and more qualitative discussion should be made. In addition to the what addressed in the above point, it is also missing the comparison of this study with previous ones.
- Revise the writing and the way to present data carefully. There were many long and repetitive sentences that only present numbers. These can be simplified by using tables, captions, figures, etc. Throwing too many numbers at once made it difficult to follow the actual analysis and explanation.
Specific Comments:
Page 8 Table 2: Specify units of time in the table
Page 10 Line 330-331: The definition of Z is not very clear; please rewrite the sentence.
Page 10 Equation 8: It is never explicitly explained what’s the difference between DelayGND and Delay. In addition, maybe one short explanation of why Z only goes up to 0.4 would be helpful.
Page 11 Table 4: Is there any reason why the specific combination of Aes and Se were chosen for these scenarios?
Page 11 Line 348-350: In reality, the change of gate assignment policy will probably change the aircraft and type of flight, so the statement here is not very convincing. Please elaborate on the qualitative trend of how GSE would change accordingly if the gate assignment policy changes. For example, a scenario where the airlines with larger aircrafts are aggregated as compared to randomly distributed. What presented in Page 13 Figure 12 can be expanded in this sense.
Page 12 Figure 7-10: I get the idea that you want to show both the absolute values and the distributions will change for different scenarios, but I don’t think that the data here should take these many figures to present. Especially given that movement emissions don’t change much. A table might be more straightforward in this case. Besides, only CO and NOx data are presented here, but are there any other gaseous components that might be important (e.g. CO2)? Is it possible to either show some results/previous work or elaborate on the possible trends of those?
Page 14 Figure 13-16: Similarly, the way to present data here is not efficient and straightforward. Please consider using a table or combining these figures into one.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
I am mostly satisfied with most of the Authors’ explanations/corrections in the text. However, a few points may still be improved.
Particularly I would appeal to the Authors to simplify the sentences/the style of writing - to let most Readers better understand the content.
Comments to the Authors
1. OK, if such units like g/HPh (gram per horse power multiplied by hour) are allowed in the “Aerospace” journal than I accept the Authors’ explanations.
2. OK - I believe most Readers of “Aerospace” are familiar with those definitions.
3.
a) OK, I can understand the Authors’ situation when two Reviewers request completely different changes in the paper - so perhaps it is better not to change anything in section 1;
b) personally I would prefer if instead of the descriptions in lines 69-76, the Authors explain the definitions mentioned in my comment #2;
c) OK;
d) OK;
e)
Line 281: OK;
Lines 293-301: OK;
Lines 302-309: From the Authors’ explanations I try to understand that it is the ground service who are supposed to develop Gantt diagrams - not the Authors (as the researchers)??
f), g) and h) some details about the difficulties in understanding the content are given below; however I would once again appeal to the Authors to simplify the sentences/the style of writing....
4. Lines 147-155: OK.
5. Line 227: OK, I believe most Readers of “Aerospace” are familiar with those denotations.
6.
a) the Authors’ response: “...To sum up, the figure shows the simulation results...” - thank you for this explanation - the descriptions of Fig. 4 in section 4 are so unclear that I was convinced that Fig. 4 presents assumptions taken for calculations made in the SIMMOD software - maybe you should reconsider improving those descriptions;
b) the Authors’ response: “A movement is a landing or takeoff (including the procedures necessary for each of them to occur).” - please include this explanation in the text below Fig. 4;
c) the Authors’ response: “It is the time of the day....” - please include this explanation in the text below Fig. 4;
d) the Authors’ response: “During simulation, the arrival time is programmed. The departure times arise from the distribution of the time in which the aircraft remained on land. This time comes from the distributions indicated on Annex B (this time ranges between 50 and 150 min.) - I think the Authors’ response may be more descriptive than: “real times from scheduled times with a minimal time of 50 minutes and a maximum of 150 minutes”;
7. Line 278, Tab. 2:
a) OK - thank you for the explanations in the text,
b) OK,
c) OK - thank you for the explanations in the text.
8. Line 317, Fig. 5:
a) the Authors’ response: “the delay in minutes is the time necessary to meet the requirements of a second aircraft when, at the same time, two aircraft request the same service....” - thank you for this explanation - maybe the Readers of the paper will need such explanation too - particularly for Fig. 5?
b) the Authors’ response: “they can only be used by a particular airline” - thank you for this explanation.
9. The Authors’ response: “In all scenarios, there are emissions produced by the aircraft operation. However, in the analyzed scenarios, the difference between the scenario with less emissions and the one that presents more emissions reaches up to 300%.” - I understand this explanation but this 300% increase in emissions cannot be seen in Fig. 5 nor in Fig. 6. This large emissions increase cannot be seen also in Figs. 7, 9 nor 12.
9. The Authors’ response: “Delay increases as the value of variable Z (a compound variable) increases.” - this explanation is clear - I asked about the physical interpretation of $Z$ variable.
10. Line 346, Tab. 4:
a) and b) - thanks for your explanations; reading the descriptions above Tab. 4 I was sure Tab. 4 presents simulation results; consider e.g. the following in lines 361-363:
“... the results obtained for an DF of 0.80 (which, from the capacity point of view...) in Table 4 are presented.” - please try to use less complicated statements/sentences about your assumptions/results.
11. OK, thanks for replacing Fig. 16 with Tab. 9 - I think Tab. 9 is more descriptive.
12. OK.
13. The Authors’ response: “The results cannot be extrapolated to all airports but they serve as a guide and reference to compare values and orders of magnitude.” - please include this sentence in the text instead of “The results of the different management scenario... risk/environmental analysis.”
14. OK.
15. OK.
Language mistakes
Thank you for the corrections in the text and also for pointing me out that the plural of “aircraft” is “aircraft” - all the time we learn new things.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Reviewer 2 Report
Dear Editor
Thank you for sending me the revised manuscript.
May I suggest that, the manuscript could be accepted after the authors revise the language furhter. Now there are still some language issues.
Author Response
Taking into account the reviews regarding language and lack of clarity, we did our best to simplify language without compromising the content of our research. A full linguistic review was conducted to make sure the text was as direct as possible. Sometimes, content took precedence over simplicity, but that was only to avoid ambiguities that could compromise the interpretation of the facts and analysis we present in this paper. We did our best to reduce wordiness and double-checked punctuation (particularly the use of commas and stops).
We hope these changes help improve the clarity and readability of the text.
Reviewer 3 Report
Most my previous concerns have been addressed and I do appreciate the new discussion on gate assignment policy.
Author Response
Taking into account the reviews regarding language and lack of clarity, we did our best to simplify language without compromising the content of our research. A full linguistic review was conducted to make sure the text was as direct as possible. Sometimes, content took precedence over simplicity, but that was only to avoid ambiguities that could compromise the interpretation of the facts and analysis we present in this paper. We did our best to reduce wordiness and double-checked punctuation (particularly the use of commas and stops).
We hope these changes help improve the clarity and readability of the text.
