Primary Particulate Matter and Aerosol Emissions from Biodiesel Engines During Idling in Plateau Environments of China
Zhong Wang
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
the article deals with a current topic, focused on the emissions of the combustion engine and its impact on the environment, which is very positive. I have the following observations and comments on the article.
- Section "0 How to use this template" should be deleted
- In Table 2, it is necessary to add the standards according to which the Fuel Oil parameters were determined,
- it is necessary to add the accuracy of the measurements
- in Table 2, it would be appropriate to add a reference fuel, pure diesel, and compare it with individual fuels in the graph as well.
- are the experimental conditions (temperature, humidity, gas ratios) sufficiently representative of real conditions?
Thank you
Author Response
Reviewer #1：
Comment 1: Section "0 How to use this template" should be deleted
Response:Thank you to the reviewer for pointing out this issue. We have removed Section 0.How to Use This Template.
Comment 2:In Table 2, it is necessary to add the standards according to which the Fuel Oil parameters were determined.
Response:Thank you to the reviewer for pointing out this issue. We have added the relevant standards in the text. The biodiesel is based on the national standard for diesel engine fuel blending biodiesel, GB/T 20828-2014, and the diesel is based on the national standard GB 19147-2016.
Comment 3:it is necessary to add the accuracy of the measurements
Response:We would like to thank the reviewer for their valuable comments on our work. We understand the importance of improving measurement accuracy for the reliability of the research and conclusions. In this study, the measurement equipment has been rigorously calibrated, and multiple repetitions of the experiments were conducted to ensure the accuracy and consistency of the data. During the experiments, we zeroed the detection equipment after each test and performed calibration at least once a week.
Comment 4:in Table 2, it would be appropriate to add a reference fuel, pure diesel, and compare it with individual fuels in the graph as well.
|
Fuel Name Physical and chemical properties |
B00 |
B10 |
B20 |
B30 |
|
Cetane number |
50 |
50.54 |
50.83 |
51.6 |
|
Oxygen content（%） |
0 |
1.64 |
2.24 |
3.68 |
|
Density(g/ml) |
0.83 |
0.835 |
0.84 |
0.845 |
|
Low calorific value(MJ/kg) |
42.68 |
41.87 |
41.59 |
41.06 |
|
Flash point |
60 |
67 |
74 |
83 |
|
Viscosity(mm2/s) |
2-4 |
3.15 |
3.26 |
3.41 |
Response:We would like to thank the reviewer for their suggestion. We have made revisions to Table 2 in the text, adding the physicochemical properties of pure petrochemical diesel (B00).
Comment 5:are the experimental conditions (temperature, humidity, gas ratios) sufficiently representative of real conditions?
Response:Thank you to the reviewer for pointing out this issueOur experimental conditions were carefully designed to closely mimic real-world environments. The experiment was conducted on August 12, when the temperature in Kunming was 24.7℃, and this was used as the reference temperature for the experiment. The relative humidity was set to <5%, which is the standard practice for smoke chamber experiments. This was done to minimize moisture interference and ensure the accuracy and repeatability of the experimental data. Lower relative humidity effectively reduces the impact of water vapor on chemical reactions, preventing it from acting as a reaction medium or catalyst that could alter the reaction pathways and outcomes. Additionally, at low humidity, the hygroscopic effect on particulate matter is weakened, allowing the experimental results to more accurately reflect its physicochemical properties. In contrast, at high humidity, the absorption of water by particulate matter may lead to changes in volume and mass, affecting measurements.
Regarding the gas ratio, we referred to the historical average concentration of particulate matter in Kunming's environment and considered 28 µg/m³ to be representative of actual conditions. Therefore, the exhaust injection was stopped when the concentration reached 28 µg/m³. In the experiment, we drew on previous experience and adjusted the VOC/NOx ratio to 3:1 (ppbc) by adding propylene. This ratio is widely regarded as typical for urban environments. The experimental conditions described above were designed to simulate and study air quality and pollutant behavior in Kunming's typical environment, ensuring the representativeness and scientific validity of the experiment.
Reviewer 2 Report
Comments and Suggestions for AuthorsEnglish writing needs to be improved; issues with formatting, such as the need for standardization of abbreviations
Line 66 Supplying information about China’s biodiesel emissions situation, such as the composition of biodiesel, the number of biodiesel vehicles in operation, and previous research on the emission characteristics of biodiesel vehicles.
Line 113 Although the experiment was conducted in Kunming, it is not necessarily limited to considering only local conditions. Additionally, despite similar concentrations, there are significant differences in particulate matter properties compared to actual atmospheric conditions.
Line 121, the measurement methods for BC, SOA, and POA have not been provided
Line 190, are the two references here regarding fossil diesel? Why are the BC emissions similar to those of biodiesel?
Line 200, it’s important to pay attention to whether the reaction conditions are consistent during the comparison. The formation of SOA should not only consider direct emissions but also take into account secondary reactions influenced by factors such as light exposure time, O3 concentration, and relative humidity
Line 206, comparing concentrations is meaningless. The factors are not lower than those reported by Deng.
Does Figure 3 have observational data on the total experimental process showing changes in particle number concentrations and their size distribution in both dark environments and after exposure to light?
Comments on the Quality of English LanguageEnglish writing needs to be improved.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors1. The diesel engine used in the experiment is a light-duty vehicle diesel engine. What are the common operating conditions? Why choose Idle operating condition to measure? Suggest adding measurement data from other different operating conditions and conducting analysis.
2. The format of the paper writing is incorrect. The 0 paragraph of the paper is not necessary.
3. The data cited in reference number 25 in the introduction to illustrate the current situation of diesel engines in China is completely inappropriate. Reference number 25 is data from 2017 and cannot represent the current situation. Please change and modify.
4. The introduction should include the latest international research progress on the formation process and reduction measures of diesel engine particles and aerosols, as well as the current research status in China. It should be supplemented
5. The data in Fig 2 does not need to be compared with gasoline engines, as the fuel characteristics of the engine in Figure 2 are different and the combustion process is also significantly different.
6. What is the situation in the plateau environment and plains mentioned in the title of the paper? The paper should analyze the formation process and characteristics of particles and aerosols in the high-altitude environment, rather than simply summarizing experimental data with charts.
7. The conclusion that biodiesel reduces particulate emissions from diesel engines has been confirmed by many researchers. Additional discussions should be provided on the principles of reducing aerosols. And it is also suggested to give explanation.
Author Response
Reviewer #3：
Comment 1:The diesel engine used in the experiment is a light-duty vehicle diesel engine. What are the common operating conditions? Why choose Idle operating condition to measure? Suggest adding measurement data from other different operating conditions and conducting analysis.
Response:We appreciate the reviewer's suggestion. Common operating conditions for light-duty diesel engines include idling, low-load, medium-load, high-load, and rapid acceleration conditions. The reason we chose to test under idling conditions is as follows:
1.Many studies also use idling conditions as the experimental basis. Therefore, by comparing the emissions of different fuels under idling conditions, we can provide valuable reference data for future policy development and pollutant control.
2.In the idling state, the engine experiences incomplete combustion, producing more unburned substances, particularly BC and other pollutants. Therefore, studying the emission characteristics under idling conditions helps understand the emission behavior of different fuels (such as biodiesel and conventional diesel) under low-temperature and low-load conditions.
3.Under idling conditions, the engine load is lower, and the experimental conditions are more stable, ensuring the accuracy and repeatability of the emission data. Compared to high-load or acceleration conditions, idling experiments reduce the interference of other variables (such as changes in power demand) on the emission measurements.
Comment 2:The format of the paper writing is incorrect. The 0 paragraph of the paper is not necessary.
Response:We greatly appreciate the reviewer for pointing out this error. We have removed it from the original text.
Comment 3:The data cited in reference number 25 in the introduction to illustrate the current situation of diesel engines in China is completely inappropriate. Reference number 25 is data from 2017 and cannot represent the current situation. Please change and modify.
Response:We greatly appreciate the reviewer for pointing out the issue. The data was outdated, and we have corrected it to the latest data from 2023.
Comment 4:The introduction should include the latest international research progress on the formation process and reduction measures of diesel engine particles and aerosols, as well as the current research status in China. It should be supplemented
Response:We would like to thank the reviewer for their suggestion. We have reorganized the introduction section and added the latest international research on the formation processes of diesel engine particulate matter and aerosols, as well as emission reduction measures, along with the current research status in China.
Comment 5:The data in Fig 2 does not need to be compared with gasoline engines, as the fuel characteristics of the engine in Figure 2 are different and the combustion process is also significantly different.
Response:We thank the reviewer for pointing out the issue. We have revised Figure 2 by removing the unnecessary comparison with gasoline engines.
Comment 6:What is the situation in the plateau environment and plains mentioned in the title of the paper? The paper should analyze the formation process and characteristics of particles and aerosols in the high-altitude environment, rather than simply summarizing experimental data with charts.
Response:Thank you for the reviewer’s suggestion. The high-altitude environment and its comparison with plains is indeed a crucial aspect of our study. In this paper, our focus is on the emission characteristics of particulate matter and aerosols from vehicles operating at idle in high-altitude environments. At high elevations, the air density is lower, and oxygen content is reduced, which can significantly affect the combustion process and thus the formation and emission of particulate matter and aerosols. Compared to plains, the climatic conditions, temperature, and humidity at high altitudes are different, which may lead to different impacts on the formation processes and characteristics of particulate matter.
In high-altitude regions, the lower atmospheric pressure and reduced oxygen supply may result in incomplete combustion, leading to higher emissions of particulate matter, such as black carbon and organic aerosols. Additionally, the air quality in high-altitude regions is more susceptible to the accumulation of local pollutants, potentially exacerbating aerosol formation. In contrast, in plains, due to different atmospheric conditions, the emission and formation mechanisms of particulate matter and aerosols may differ. Thus, a comparative analysis between high-altitude and plain environments is essential.
Our research aims not just to present experimental data, but to thoroughly analyze the formation process of particulate matter and aerosols in high-altitude environments, considering factors such as emission factors, climate conditions, and combustion characteristics, and how these factors influence the type and concentration of emissions. We plan to extend this research with experiments at different altitudes in the future to further investigate the impact of altitude on particulate emissions, providing more scientific data to support air quality management and environmental policies for high-altitude regions.
Comment 7: The conclusion that biodiesel reduces particulate emissions from diesel engines has been confirmed by many researchers. Additional discussions should be provided on the principles of reducing aerosols. And it is also suggested to give explanation.
Response:Thank you for the reviewer’s suggestions. The reduction of aerosols can be addressed through optimization of the combustion process, temperature control, and the synergistic effects of exhaust treatment technologies. However, in this paper, we primarily focus on the comparison of bioaerosol emissions with traditional diesel and present, for the first time, an experimental study on the exhaust from biodiesel combustion in a chamber. In the future, we will focus on comparative experiments related to aerosol reduction methods. Additionally, we are already conducting experiments on the emission characteristics of motor vehicle exhaust with and without the use of post-treatment technologies, and we will publish the results soon.
