Unregulated Emissions from Natural Gas Taxi Based on IVE Model
Round 1
Reviewer 1 Report
This paper conducted experiments to obtain taxi driving conditions and local parameters and employed the IVE localization model for the correction of vehicle emission factors. Overall, the method for identifying the unregulated emissions from the natural gas taxis and the empirical analysis are well elaborated, particularly with a growing interest in vehicle emissions across the world. However, I have the following reservations regarding the research effort presented in the paper. I outline the specific concerns below.
(1) There are many similar attempts that have so far made to estimate the vehicle emissions, so this makes me and readers difficult to understand the originality and novelty of this paper. The authors are recommended to enrich the literature review, discuss the necessity and scientific significance of this work, and clarify the methodological novelty addressed by this research. It is necessary to clearly and confidently clarify the innovative point of the research framework and methodology proposed in this paper compared to the existing studies and conventional methods.
(2) In the discussion section, comparative analysis between the methods used in this paper and conventional methodologies should be clarified more clearly and confidently based on the model results. What shortcomings and disadvantages of conventional methodologies would be resolved by this study? What new findings can be obtained by this study? The discussion section is insufficient.
(3) The authors also should illustrate the generality of this methodology and its main findings. It is needful to demonstrate whether the research framework and methods in this paper can be a generally accepted way for drawing taxi pollutant emission factors.
(4) Environmental scientists and policymakers might be interested in this paper with respect to the monitoring and evaluation tool for capturing the emission characteristics of taxis. What implications can be drawn for environmental planning and policymaking? An additional paragraph discussing the concrete and specific policy implications based on the overall findings would be very helpful.
Author Response
Dear Professor,
I quite appreciate your insightful comments and suggestions. Now I have revised the atmosphere-1159890 exactly according to your comments, and found these comments are very helpful. I hope this revision can make my paper more acceptable. The comments were addressed point by point below.
(1) We have enriched the literature review and added the demonstration of the necessity and importance of the thesis in the introduction part in the revision.
(2) In the second section of the paper, the characteristics of IVE model are discussed, so that readers can better understand the advantages of the proposed method compared with traditional methods.
(3) In the introduction part, we have added the demonstration of the universality of the method in the revision.
(4) A paragraph has been added at the end of the paper to explain the specific benefits from the implementation of the policy and the importance of the implementation of the policy in the revision.
Sincerely,
Hong Zhao
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors,
The article you have submitted for review describes an interesting topic. Reducing emissions generated by means of transport is one of the key tasks that should be fulfilled by humanity.
First of all, there is no more extensive introduction here. It is very modest and should be improved.
The research plan - is interesting, but the conclusions resulting from the research are obvious, even before its implementation. The article does not bring anything new to what is already commonly known.
The final conclusions are too general. Saying that you need to promote the "Oil to Gas" polling, certainly yes, but what next? I think authors should analyze their article and include more factors in their research plan.
Best regards,
Author Response
Dear Professor,
I quite appreciate your insightful comments and suggestions. Now I have revised the atmosphere-1159890 exactly according to your comments, and found these comments are very helpful. I hope this revision can make my paper more acceptable. The comments were addressed point by point below.
(1) We have enriched the introduction part of the article in the revision.
(2) The research purpose of this paper is mainly to provide the basis for the implementation of the policy of "oil to gas", and to obtain the specific benefits after the implementation of the policy.
(3) In the final conclusion, it is analyzed that the "oil to gas" policy can also be improved in terms of economic benefits.
Sincerely,
Hong Zhao
Author Response File: Author Response.pdf
Reviewer 3 Report
This manuscript investigates the emissions of CO, NOx, PM and some other unregulated pollutants from CNG taxi corresponding to normal gasoline taxi. International vehicle emission model and vehicle mass analysis system are applied to obtain the emission factors from these two types of taxis. I suggest a major revision upon its current status, both depending on its technical logic and language quality. For this kind of data mining research, only calculating the average of each parameter is not rigorous enough and more detailed statistical factors are needed. Here are some detailed comments for the authors information.
- IVE is not clarified in the abstract, which should be international vehicle emission?
- The same holds for VMAS, which is vehicle mass analysis system?
- Abstract, so many “emissions” are followed by “is”, a plural noun + a singular verb.
- Please check the usage of “comma” and “full stop”. Some capital letters came directly after a comma, which is not correct.
- Line 39, should be petroleum dependence.
- Line 40, “how to estimate its emission levels is required” the sentence needs to be reformulated.
- Line 44. The sentence needs to be reformulated, currently there are two verbs, “estimated” and “examined” but there is not any conjunction.
- There are several other grammatic errors found in the manuscript.
- Is the title for Table 2 complete?
- Is it proper to distinguish the areas to be higher income or low income? Maybe densely populated area and sparsely populated area will be better?
- Both taxis and taxies are found in the manuscript, please unify.
- Figure 1 only clarified natural gas taxi and gasoline taxi. I don’t know if there are taxis with other fuels. In Europe, diesel engine is widely used for passenger cars also.
- I don’t know if the samples tested in Table 1 are representative enough. If one would like to address the differences between 1.6L taxis and 1.8L taxis, the number of each should be equal. Currently, 1.6L has 15 samples and 1.8L has 35, respectively. Also, if one would like to distinguish the CNG taxis with the gasoline taxis, the number of each is suggested to be equal also. Currently, 89.1% out of 50 taxis are CNG fueled, making the data for gasoline fueled taxis not representative enough. Table 1 shows the complete emission factor of these fifty taxis. For example, number 5 has CO EF of 4.34 which is a 1.8L car, meanwhile another 1.8L car number 13 has only 0.16 EF for CO. The difference is very notable. Number 2, 1.6L car has only 0.01 CO EF but number 39 has 8.02. This indicates that the average of each capacity car is not enough and the standard deviation might be calculated and shown also.
- There are too many abbreviations in the manuscript. It is suggested to have an abbreviation list in the beginning of the paper.
- Line 176, it says the PM emissions will be lower nearly half than the current tax if the fleet transfers from current to the CNG. To be honest, I cannot see any information from Figure 1 about PM, which is not distinguishable.
- There are two “3. Results and discussion” sections in the manuscript.
- The results are about EFs united with g/km and t/y, I don’t know how these results are correlated with the total CO emission for actual taxi of 6411.87t (shown in the conclusion I think). All these total amount of CO, HC, NOx and PM emissions are not direct results from this paper, which I think cannot be the conclusion. There are two reasons, one is that the samples are not representative enough, are there only 1.6L and 1.8L taxis in the city? Are the taxis only powered with CNG and gasoline and no other fuel types? Although this is the case, the number for each capacity and fuel type of the samples are not equal. The other is that the chosen of the roads are not representative enough, there are no highway and country road been tested. The driving condition shown in Table 2 only covers vehicle velocity below 60 km/h. What about the speed above on highway and country road? I think most of the taxis will very often carry passengers from their home to the airport through a highway as well as visit their friends through a country road and these conditions are not considered at all. I don’t mean that this study is not meaningless but only think the samples are not representative enough to draw a conclusion that the entire taxi fleet in the city will emit 6411.87t CO, such an accurate number. The same holds for HC NOx and all the others. Facing that fact that the authors themselves also state that the individual vehicle condition, mileage, engine condition, brake condition, tire condition etc. will also impact the emissions.
Author Response
Dear Professor,
I quite appreciate your insightful comments and suggestions. Now I have revised the atmosphere-1159890 exactly according to your comments, and found these comments are very helpful. I hope this revision can make my paper more acceptable. The comments were addressed point by point below.
(1) We have added full spelling explanation to IVE, International Vehicle Emissions in the revision.
(2) VMAS is Vehicle Mass Analysis System. We have provided full interpretation of VMAS in the revision.
(3) We have correctted the mistakes of "plural noun + singular verb" in the passage in the revision.
(4) We have modified the capitalization of the first word after ', ' in the revision.
(5) We have modified the word usage error in 39 lines in the revision.
(6) We have modified the grammatically incorrect sentence in line 40 in the revision.
(7) We have modified the double verb error in line 44 in the revision.
(8) We have modified several grammatical errors in the article in the revision.
(9) We have modified the headings of Table 2 in the revision.
(10) High-income areas are typically characterized by dense traffic, traffic congestion and slow speed, while low-income areas are on the contrary. These characteristics are exactly what the paper needs to use, so it is reasonable to distinguish high-income areas.
(11) The use of words in the text has been unified, and taxies have been modified to taxis in the revision.
(12) In China, most of the power sources of taxis are natural gas and gasoline, and diesel engines are not as widely used as in European countries.
(13) After the implementation of the policy of "replacing oil with gas" in Qingdao, the proportion of taxis using natural gas has reached more than 85% so far. The field survey data should correspond to the actual situation, so the same proportion of natural gas taxis has been investigated.The temperature, humidity and other conditions shown in the table will affect vehicle emissions, so there is a large emission difference between taxis with the same displacement.The samples selected in this paper are the most representative types of taxis, so a small number of samples are selected.
(14) All abbreviations in the text have been explained in the revision.
(15) We have partly enlarged the PM data in the table in the revision.
(16) Modify the wrong question number used in the text.
(17) The data listed in Table 2 are the vehicle driving conditions in peak hours. The traffic flow on urban roads is congested, especially in peak hours, so the speed of most vehicles is lower than 60km/h.
Sincerely,
Hong Zhao
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The manuscript can be accepted since the author addressed the questions and revised them in the corresponding place.
Author Response
Dear Professor,
I quite appreciate your insightful comments and suggestions. Now I have revised the atmosphere-1159890 exactly according to your comments, and found these comments are very helpful. I hope this revision can make my paper more acceptable. The comments were addressed point by point below.
(1) We have added twenty relevent references and provided sufficient background in introduction section in the revision.
(2) We have added a paragraph in conclusions section, which was supported by results in the revision.
Sincerely,
Hong Zhao
Author Response File: Author Response.pdf
Reviewer 2 Report
Thank you very much for including my comments in your work.
I think your corrections at work are unfortunately minor.
Regards
Author Response
Dear Professor,
I quite appreciate your insightful comments and suggestions. Now I have revised the atmosphere-1159890 exactly according to your comments, and found these comments are very helpful. I hope this revision can make my paper more acceptable. The comments were addressed point by point below.
(1) We have added twenty relevent references and provided sufficient background in introduction section in the revision.
(2) We have added a paragraph in conclusions section, which was supported by results in the revision.
Sincerely,
Hong Zhao
Author Response File: Author Response.pdf
Reviewer 3 Report
It is appreciated the authors made valuable efforts to revise the manuscript. Most of my concerns are addressed in this version. I only hold my opinion on the current conclusion for the CO emission as well as HC, NOx and PM emissions.
Author Response
Dear Professor,
I quite appreciate your insightful comments and suggestions. Now I have revised the atmosphere-1159890 exactly according to your comments, and found these comments are very helpful. I hope this revision can make my paper more acceptable. The comments were addressed point by point below.
(1) We have added twenty relevent references and provided sufficient background in introduction section in the revision.
(2) We have added a paragraph in conclusions section, which was supported by results in the revision.
Sincerely,
Hong Zhao
Author Response File: Author Response.pdf
