Study on the Volatile Organic Compound Emission Characteristics of Crumb Rubber-Modified Asphalt
, Dongfang Zhang 1, Peiyu Zhang 2, Yindong Ding 4, Yanping Liu 1, Chunhua Su 2, Qingjun Han 4 and Yiran Li 2Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsTo the Authors,
You are to be commended for this comprehensive and ambitious study on a topic of significant practical and scientific importance. The challenge of mitigating VOC emissions from polymer-modified asphalts lies at the intersection of materials science, polymer chemistry, and environmental engineering, and your systematic approach to untangling the effects of various additives is a valuable contribution. The manuscript is well-structured, and the core finding regarding the starkly different synergistic behavior of SBS with activated versus non-activated crumb rubber is particularly insightful and will undoubtedly be of great interest to the readers of Coatings.
This is a promising piece of research. To further enhance its scientific rigor and impact for publication, I would like to offer the following suggestions for your consideration:
- On a technical note, Figures 3-6 appear to have been subjected to an aspect ratio distortion, which makes the text and data plots stretched and unprofessional. These must be redrawn to be clear and legible.
- Crucially, the abbreviated labels used on the x-axes of these figures (e.g., "SBS-A," "W1," "D1") are inconsistent with the specific sample labels defined in Table 3 (e.g., "SBSA10," "N15W1," "N15D1"). To ensure clarity and prevent misinterpretation, all labels on the figures must be updated to precisely match those in Table 3.
- To improve clarity and precision, the authors are encouraged to present the data from Figures 3 and 4 in tabular form. At present, the bar charts make it difficult to extract exact numerical values, whereas a table would provide clear and accurate figures, enabling more rigorous comparison and deeper analysis by the readers.
- The abstract should be written in a more concise manner, focusing only on the key findings and contributions. In addition, abbreviations should be avoided in the abstract. As a matter of good practice, please ensure that all acronyms are defined at their first point of use within the main text.
- The manuscript is well-written and the core ideas are generally easy to follow. As a final polishing step, the authors are encouraged to engage a professional language editing service to refine the text.
- The authors present an interesting and potentially high-impact observation of a “1+1>2” synergistic effect in the ACR/SBS system. To further strengthen this claim, it would be valuable to provide a more rigorous quantitative comparison. Specifically, demonstrating that the measured VOC reduction of the combined system exceeds the arithmetic sum of the reductions achieved by ACR and SBS individually would substantiate the synergy.
In summary, this is a very good piece of work with important practical implications. The foundations are solid, but the manuscript requires the additional layer of analytical rigor detailed above to be truly convincing. I trust the authors will find these comments constructive and I look forward to seeing a revised version of this promising work.
Author Response
We appreciate the thoughtful review and constructive feedback. Based on the constructive feedback, We will incorporate the recommended changes into the manuscript.
Point 1: On a technical note, Figures 3-6 appear to have been subjected to an aspect ratio distortion, which makes the text and data plots stretched and unprofessional. These must be redrawn to be clear and legible.
Response 1: We will revise these figures to enhance readability, and we appreciate the valuable suggestion.
Point 2: Crucially, the abbreviated labels used on the x-axes of these figures (e.g., "SBS-A," "W1," "D1") are inconsistent with the specific sample labels defined in Table 3 (e.g., "SBSA10," "N15W1," "N15D1"). To ensure clarity and prevent misinterpretation, all labels on the figures must be updated to precisely match those in Table 3.
Response 2: All the labels in the figures have been updated to exactly match those in Table 3.
Point 3: To improve clarity and precision, the authors are encouraged to present the data from Figures 3 and 4 in tabular form. At present, the bar charts make it difficult to extract exact numerical values, whereas a table would provide clear and accurate figures, enabling more rigorous comparison and deeper analysis by the readers.
Response 3: We have converted the data in Fig. 3 and 4 into tabular form, now present in Table 4 and 5 respectively.
Point 4: The abstract should be written in a more concise manner, focusing only on the key findings and contributions. In addition, abbreviations should be avoided in the abstract. As a matter of good practice, please ensure that all acronyms are defined at their first point of use within the main text.
Response 4: The abstract was structured according to the requirements of the journal of Coatings, including the following sections: background, methods, the problem to be solved, key findings, and contributions. Consequently, the sections on key findings and contributions may be insufficient to fully describe the outcomes of this study due to the abstract's word limit (approximately 200 words).
Only the widely accepted abbreviation of styrene-butadiene-styrene (SBS) was used in the abstract; all other abbreviations were omitted. Furthermore, all acronyms are defined at their first occurrence in the main text.
Point 5: The manuscript is well-written and the core ideas are generally easy to follow. As a final polishing step, the authors are encouraged to engage a professional language editing service to refine the text.
Response 5: We appreciate your positive assessment and their suggestion for final polishing. We have meticulously proofread the entire manuscript to correct any minor grammatical errors, improve sentence flow, and enhance overall clarity. We believe the language is now precise and clear and meets the journal's standards.
Point 6: The authors present an interesting and potentially high-impact observation of a “1+1>2” synergistic effect in the ACR/SBS system. To further strengthen this claim, it would be valuable to provide a more rigorous quantitative comparison. Specifically, demonstrating that the measured VOC reduction of the combined system exceeds the arithmetic sum of the reductions achieved by ACR and SBS individually would substantiate the synergy.
Response 6: The total VOC emission from the A20 group (20% ACR) was 4605.3 μg/m³, compared to 2919.9 μg/m³ from the SBS group (4% SBS). The calculated cumulative VOC emission for the A20 group plus 50% of the SBS group emission was 6065.2 μg/m³ (4605.3+0.5*2919.9). In contrast, the measured VOC emission from the ACR/SBS group (20% ACR, 2% SBS) was 3092.5 μg/m³, a value significantly lower than the calculated cumulative emission (6065.2 μg/m³). This result demonstrates that combining ACR and SBS significantly reduces total VOC emissions compared to using either modifier individually.
Thank you again for your hard, meticulous work!
Best regards!
Reviewer 2 Report
Comments and Suggestions for AuthorsThis report describes results of emissions from activated and non-activated crumb rubber modified asphalt(CRMA) binders with various additives. Additives in various combinations and amounts included SBS polymer, activated and non-activated crumb rubber, deodorizer, and two warm mix agents. Gases released from the binders at high temperature (180oC) with stirring at 500 rpm were collected. Desorbed gases were analyzed by GC-MS with compound assignments based on matching with spectra in the NIST database. Figure 3 indicates that most of the VOCs were categorized as aromatic hydrocarbons and halogenated alkenes(chlorocarbons). Based on these findings, results for secondary organic aerosols (SOA), ozone formation potential (OFP), and carcinogen risk analysis were determined. One of the warm mix asphalt additives significantly reduced VOCs.
Hot mix asphalt is a major material for road construction covering the majority of paved roads with release of VOCs a real concern. The undertaking of this work is potentially of great value by adding to knowledge in the literature from similar studies. In light of their finding for the compounds released, the authors chose to consider more fully the impact of these VOCs on human health with examination of SOA, OFP and presence of carcinogens. These are worthy initiatives. Unfortunately, the accuracy of the compounds identified is suspect. The authors note that their VOC profiles are distinctly different from prior work(Line 269) without providing details. It seems odd that they do not elaborate. Specifically, presence of a large amount of chlorohydrocarbons in their results is problematic. It is unusual to find halogenated hydrocarbons in asphalt binder and, when they are reported for VOCs, they are a minor component[Wang M, Wang C, Huang S, Yuan H. Study on asphalt volatile organic compounds emission reduction: A state-of-the-art review. Journal of Cleaner Production. 2021 Oct 10;318:128596]. This is a major concern with the study because one does not expect such compounds to be present in source materials (i.e., in asphalt binder, in crumb rubber, or in SBS). No rationale has been provided to explain existence of high levels of chlorohydrocarbons in the VOC samples. In a similar investigation, Zhang et al. list a wide range of compound types in asphalt binder and in crumb rubber with no mention of chlorinated species[ref. 139: Zhang R, Tang N, Zhu H, Xi Y, Cheng H, Liu J, Li R. Compositional analysis and quantitative evaluation of organic emissions from asphalt materials: Improvements and refinements. Journal of Cleaner Production. 2024 Aug 15;467:142936]. The same is true for its absence in another similar study[e.g., ref. 167: Borinelli JB, Portillo-Estrada M, Costa JO, Pajares A, Blom J, Hernando D, Vuye C. Emission reduction agents: A solution to inhibit the emission of harmful volatile organic compounds from crumb rubber modified bitumen. Construction and Building Materials. 2024 Jan 12;411:134455]. Based on the data, one might ask if the asphalt was contaminated or if there was a problem with the analysis of the mass spectra. As such, one must question key findings of the paper. Failure to ensure correct determination of the VOC species undermines the validity of the SOA, OFP and carcinogen results.
Analyzing mass spectra is very complicated. Comparing peaks with the NIST database does not inspire great confidence as a method for the identification of compounds. Stronger evidence must be provided along with an explanation for the presence of chlorocarbons. If the assignment of the halocarbon compounds in Table 4 is correct, then MS isotope analysis of the parent peaks in the spectra has the capacity to generate more convincing evidence in support of these specific chemicals. The authors might wish to consult a colleague familiar with mass spectrometry for that approach.
Some of the trends of the composition in Figure 3 are not what would be expected for the relative changes in amounts of sample mixtures. While GC-MS has been commonly used in studies of VOCs from asphalt binders, some question the effectiveness of MS for precise quantitative measurements[Urban PL. Quantitative mass spectrometry: an overview. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 2016 Oct 28;374(2079):20150382]. The addition of a section on limitations to the study would have strengthened the paper.
Minor points:
Provide additional information about the chemical nature of the additives.
The composition of Table 3 should be more specific. Are the amounts of additives given percentages of the final overall mass or the percentage relative to the asphalt?
Confirm that generation of VOCs with the warm mix asphalt was also carried out at 180oC.
Use consistent nomenclature for compounds in Tables 3 and 4 and at places in the text: 1,1-dichlorothene is the same as 1,1-dichloroethylene; dichloromethane is the same as methylene chloride; trichloromethane is the same as chloroform
Line 399: Trichloro?
Line 544: styrene
Author Response
We appreciate the thoughtful review and constructive feedback. Based on the constructive feedback, We will incorporate the recommended changes into the manuscript.
Point 1: Hot mix asphalt is a major material for road construction covering the majority of paved roads with release of VOCs a real concern. The undertaking of this work is potentially of great value by adding to knowledge in the literature from similar studies. In light of their finding for the compounds released, the authors chose to consider more fully the impact of these VOCs on human health with examination of SOA, OFP and presence of carcinogens. These are worthy initiatives. Unfortunately, the accuracy of the compounds identified is suspect. The authors note that their VOC profiles are distinctly different from prior work(Line 269) without providing details. It seems odd that they do not elaborate. Specifically, presence of a large amount of chlorohydrocarbons in their results is problematic. It is unusual to find halogenated hydrocarbons in asphalt binder and, when they are reported for VOCs, they are a minor component[Wang M, Wang C, Huang S, Yuan H. Study on asphalt volatile organic compounds emission reduction: A state-of-the-art review. Journal of Cleaner Production. 2021 Oct 10;318:128596]. This is a major concern with the study because one does not expect such compounds to be present in source materials (i.e., in asphalt binder, in crumb rubber, or in SBS). No rationale has been provided to explain existence of high levels of chlorohydrocarbons in the VOC samples. In a similar investigation, Zhang et al. list a wide range of compound types in asphalt binder and in crumb rubber with no mention of chlorinated species[ref. 139: Zhang R, Tang N, Zhu H, Xi Y, Cheng H, Liu J, Li R. Compositional analysis and quantitative evaluation of organic emissions from asphalt materials: Improvements and refinements. Journal of Cleaner Production. 2024 Aug 15;467:142936]. The same is true for its absence in another similar study[e.g., ref. 167: Borinelli JB, Portillo-Estrada M, Costa JO, Pajares A, Blom J, Hernando D, Vuye C. Emission reduction agents: A solution to inhibit the emission of harmful volatile organic compounds from crumb rubber modified bitumen. Construction and Building Materials. 2024 Jan 12;411:134455]. Based on the data, one might ask if the asphalt was contaminated or if there was a problem with the analysis of the mass spectra. As such, one must question key findings of the paper. Failure to ensure correct determination of the VOC species undermines the validity of the SOA, OFP and carcinogen results.
Response 1: A primary issue encountered in this study was the unexpected presence and high concentration of trichloroethylene. We therefore thoroughly re-examined the sample preparation, testing, and GC-MS analytical procedures. Throughout the preparation and VOC testing procedures, kerosene—not trichloroethylene—was adopted as the cleaning solvent. A review of GC-MS results from other, unrelated programs also detected trichloroethylene in some instances. We consulted another team with over twenty years of asphalt research experience; they reported a similar, recurring finding of trichloroethylene in studies where its use as a contaminant during preparation and testing had been rigorously excluded. Finally, the original base asphalt was melted, and its VOCs were collected using cleaned apparatus; trichloroethylene was detected again in these emissions. A literature review revealed that only reference [138] has reported the presence of trichloro ethylene. We acknowledge the valuable suggestion that the asphalt itself may be the source of contamination. To address this, three types of base asphalt will be selected for future study to determine if the material itself is the source and to control for this variable.
Point 2: Analyzing mass spectra is very complicated. Comparing peaks with the NIST database does not inspire great confidence as a method for the identification of compounds. Stronger evidence must be provided along with an explanation for the presence of chlorocarbons. If the assignment of the halocarbon compounds in Table 4 is correct, then MS isotope analysis of the parent peaks in the spectra has the capacity to generate more convincing evidence in support of these specific chemicals. The authors might wish to consult a colleague familiar with mass spectrometry for that approach.
Response 2: We thank the reviewer for this insightful comment regarding the identification of halocarbon compounds. We agree that comparison with the NIST database alone can be insufficient for definitive confirmation, and we appreciate the suggestion of using isotope pattern analysis.
However, due to current instrumental constraints, we are unable to perform the high-resolution mass spectrometry necessary for the precise isotope ratio analysis of the parent peaks, as suggested by the reviewer.
To strengthen our assignment within these limitations, we have carefully re-examined the isotope patterns in our existing low-resolution spectra. While less definitive, the observed M+2 peak ratios for the chlorinated compounds (e.g., approximately 1:3 for dichloro-, 1:1 for trichloro-) are consistent with the expected natural abundance of chlorine-35 and chlorine-37.
We acknowledge that this remains an inferential approach. Therefore, in the revised manuscript, we have toned down our language from "confirmation" to "tentative identification based on convergent evidence" and have cited the instrumental limitation in our discussion.
We once again thank the reviewer for raising this critical point. Conducting a dedicated high-resolution MS study to conclusively identify these compounds is a priority for our future work.
Point 3: Some of the trends of the composition in Figure 3 are not what would be expected for the relative changes in amounts of sample mixtures. While GC-MS has been commonly used in studies of VOCs from asphalt binders, some question the effectiveness of MS for precise quantitative measurements[Urban PL. Quantitative mass spectrometry: an overview. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 2016 Oct 28;374(2079):20150382]. The addition of a section on limitations to the study would have strengthened the paper.
Response 3: Thank you for your insightful comments regarding the quantitative trends in Figure 3 and the general limitations of MS-based quantification. We agree that these are critical points for establishing the validity of our findings.
We acknowledge that the observed compositional trends require careful interpretation. To ensure the reliability of this data, we performed all analyses in parallel experiments. The results showed a high degree of reproducibility. This indicates that the trends presented in Figure 3 are robust and representative, despite their complexity.
We thank the reviewer for highlighting this important methodological consideration and for providing the relevant reference. We fully agree that a discussion on limitations strengthens a paper's scientific rigor. As suggested, we have added the disccussion about limitations of the study to the manuscript. This discussion now explicitly discusses the potential constraints of GC-MS for precise quantification, as raised by Urban PL. (2016).
Point 4: Provide additional information about the chemical nature of the additives.
Response 4: The additives used in this study—namely, SBS, warm-mix agents, and a deodorant—were obtained from commercial suppliers; their specific chemical compositions are proprietary and cannot be disclosed.
Point 5: The composition of Table 3 should be more specific. Are the amounts of additives given percentages of the final overall mass or the percentage relative to the asphalt?
Response 5: Additive content is expressed as a percentage relative to the mass of the asphalt binder, and composition details in Table 3 have been specified in new manuscript.
Point 6: Confirm that generation of VOCs with the warm mix asphalt was also carried out at 180℃.
Response 6: The explanation have been specified in the revised manuscript.
Point 7: Use consistent nomenclature for compounds in Tables 3 and 4 and at places in the text: 1,1-dichlorothene is the same as 1,1-dichloroethylene; dichloromethane is the same as methylene chloride; trichloromethane is the same as chloroform
Line 399: Trichloro?
Line 544: styrene.
Response 7: All identified errors have been corrected in the manuscript.
Thank you again for your hard, meticulous work!
Best regards!
Reviewer 3 Report
Comments and Suggestions for AuthorsReviewer’s comments:
The problems under consideration in the manuscript are of the utmost importance. They are, first, utilization of crash rubber and, secondly, modified asphalt production. The manuscript demonstrates very careful work of authors with literature (170 references) and highly detailed VOC (Volatile Organic Compounds) emission mechanist analysis (section 4.5). Important aspects of VOC emission are considered as well, namely their influence on the atmospheric aerosols and ozone formation, as well as human carcinogen risk analysis. However, let us consider several appeared:
- Total number of detected VOCs was 21 compounds only. It seems too small for such objects as asphalt samples. The real number of compounds emitted from asphalt at 180ï‚°C should be more than several hundred. The main reason of that may be the temperature of desorption from tubes with Tenax-TA that was not enough for high boiling organic compounds. Unfortunately it is not indicated in the Experimental. Was criofocusing used during thermal desorption – no comments.
- The majority from these 21 analytes was low boiling chlorinated compounds, including the principal trichloroethylene. The reasons and chemical sources for their large number remain unclear. The section 4.5 contains no words about chloroderivatives.
If the relationships (1) and (2) (section 3.3) are important for further discussion, the examples of real evaluations should be provided.
- In the lines 496-497 we read: “… SBS reduces … n-alkane emission by 41.11% …”. It is a little strange, because no n-alkanes were detected among VOCs.
- There are several errors in chemical terminology in Table 4, namely:
Serial No. 17: o-toluene – senseless chemical name;
Serial No. 19: 1,3,5-triethyltoluene – the same;
Serial No. 20: 1,2,4-triethyltoluene – the same
At the same time correct misprinting for No. 21: should be “1,2,4-“ instead of “1. 2,4-”.
- The reviewer strongly recommends paying attention to the need to round off numbers, namely:
Abstract, line 27: 73.11%. It is not necessary to use so high precision. The value 73% seems enough.
Line 29: 68.86 – 81.48%. The same.
Line 31: 19.8 – 79.4. The same.
Line 262: 2919.9 mkg/m3. Five significant digits. Neither 2919.8, nor 2920.0, but very precisely 2919.9. The transformation of this number into 2.9 mg/m3 looks preferable.
Line 263: 1368
Line 289: 73.11%
Line 299: 34.02%
Line 300: 17.56%
Lines 304-305: 1.92% and 32.99%
Lines 330-331: 81.48%, 68.85%, 32.85%
Line 334: 15.30%
Line 354: 55.6 to 91.2%. Why not 56 to 91%? It is more than enough.
Line 428: 1143.9 mkg/m3.
Not all examples are listed here; the rest need to be found and corrected. It can be done quickly, but answering the questions above means the major revision of the manuscript.
Author Response
We appreciate the thoughtful review and constructive feedback. Based on the constructive feedback, We will incorporate the recommended changes into the manuscript.
Point 1: Total number of detected VOCs was 21 compounds only. It seems too small for such objects as asphalt samples. The real number of compounds emitted from asphalt at 180°C should be more than several hundred. The main reason of that may be the temperature of desorption from tubes with Tenax-TA that was not enough for high boiling organic compounds. Unfortunately it is not indicated in the Experimental. Was criofocusing used during thermal desorption – no comments.
Response 1: Thank you for raising this critical methodological point. We agree that asphalt samples typically emit a complex mixture of VOCs, and the number of compounds we detected (21) is indeed lower than what might be expected. We appreciate the opportunity to clarify our methodology.
The thermal desorption conditions have been detailed in Section 2.4, including the specific desorption temperature (300 °C) for tubes packed with Tenax-TA. We selected this temperature as it is at the upper operational limit recommended for Tenax-TA and is sufficient to desorb a wide range of VOCs up to n-Câ‚„â‚€. Furthermore, a cryofocusing step was indeed employed using a focusing trap cooled to -10 °C prior to rapid thermal desorption into the GC column. This step is crucial for sharpening peak shapes and enhancing detection sensitivity. We apologize for this omission in the original manuscript and have now explicitly added this detail to Section 2.4.
We believe the number of compounds we report is representative of our specific analytical focus. Our method, with the parameters described, was optimized to target semi-volatile organic compounds (SVOCs) and heavier VOCs that are most relevant to the odor and chemical profile of our modified asphalt binders, rather than the very lightest volatile compounds (e.g., methane, ethane, ethylene). The 21 compounds we identified and quantified were the most abundant and consistent species under our experimental conditions.
We have revised the manuscript to include the cryofocusing step and to better justify the scope of our analytical method.
Point 2: - The majority from these 21 analytes was low boiling chlorinated compounds, including the principal trichloroethylene. The reasons and chemical sources for their large number remain unclear. The section 4.5 contains no words about chloroderivatives.
Response 2: Thank you for this insightful observation regarding the prevalence of low-boiling chlorinated compounds and the need for a clearer discussion on their potential sources. We agree that this is a critical point for interpretation. We have substantially revised Section 4.2 to address the unexpected presence and high concentration of trichloro ethylene.
As now detailed in Section 4.2, a primary issue encountered in this study was the unexpected presence and high concentration of trichloroethylene. To identify its source, we thoroughly re-examined our sample preparation, testing, and GC-MS analytical procedures. We confirmed that throughout the preparation and VOC testing procedures, kerosene—not trichloro ethylene—was adopted as the cleaning solvent. Furthermore, a review of GC-MS results from other, unrelated programs within our institution also detected trichloro ethylene in some instances, suggesting a more widespread or systemic issue. We then consulted another team with over twenty years of asphalt research experience; they reported a similar, recurring finding of trichloro ethylene in studies where its use as a contaminant during preparation and testing had been rigorously excluded. Most critically, to rule out laboratory contamination, we melted samples of the original base asphalt and collected their VOCs using meticulously cleaned apparatus; trichloro ethylene was detected again in these emissions. A literature review revealed that only reference [138] has reported a similar presence of trichloro ethylene, indicating this is a rare and poorly understood phenomenon.
Based on this convergent evidence, the base asphalt itself is likely the primary source of these chlorinated compounds, potentially originating from certain crude oil sources or recycling processes. We acknowledge this as a significant limitation of the current study.
We thank the reviewer for prompting this crucial discussion, which has significantly strengthened the manuscript.
Point 3: If the relationships (1) and (2) (section 3.3) are important for further discussion, the examples of real evaluations should be provided.
Response 3: Thank you for raising this important point. We agree that providing explicit examples reinforces the validity and applicability of the proposed relationships.
The data presented in Figure 5 were indeed calculated by applying Equations (1) and (2) from Section 3.3 to the empirical data shown in Table 4, Table 6, and Figure 3.
To enhance clarity and meet your suggestion, we will add an explanatory paragraph in Section 3.3 illustrating step-by-step sample calculations using specific values drawn from these sources.
Point 4: - In the lines 496-497 we read: “… SBS reduces … n-alkane emission by 41.11% …”. It is a little strange, because no n-alkanes were detected among VOCs.
Response 4: Thank you for catching this inconsistency. You are correct that no n-alkanes were detected in our VOC analysis, making the stated reduction erroneous. We have removed the incorrect sentence regarding n-alkane emission reduction from the revised manuscript.
We appreciate your careful reading and valuable feedback, which has helped enhance the accuracy of our work..
Point 5: - There are several errors in chemical terminology in Table 4, namely:
Serial No. 17: o-toluene–senseless chemical name;
Serial No. 19: 1,3,5-triethyltoluene – the same;
Serial No. 20: 1,2,4-triethyltoluene – the same
At the same time correct misprinting for No. 21: should be “1,2,4-“ instead of “1. 2,4-”.
Response 5: Thank you for identifying the inaccuracies in chemical terminology within our manuscript. We have thoroughly reviewed the text and corrected all instances of improper nomenclature, ambiguous abbreviations, and non-standard representations in the revised version. Standardization of compound names according to IUPAC conventions (e.g., "trichloroethylene" instead of abbreviated forms).
Point 6: - The reviewer strongly recommends paying attention to the need to round off numbers, namely:
Abstract, line 27: 73.11%. It is not necessary to use so high precision. The value 73% seems enough.
Line 29: 68.86 – 81.48%. The same.
Line 31: 19.8 – 79.4. The same.
Line 262: 2919.9 mkg/m3. Five significant digits. Neither 2919.8, nor 2920.0, but very precisely 2919.9. The transformation of this number into 2.9 mg/m3 looks preferable.
Line 263: 1368
Line 289: 73.11%
Line 299: 34.02%
Line 300: 17.56%
Lines 304-305: 1.92% and 32.99%
Lines 330-331: 81.48%, 68.85%, 32.85%
Line 334: 15.30%
Line 354: 55.6 to 91.2%. Why not 56 to 91%? It is more than enough.
Line 428: 1143.9 mkg/m3.
Not all examples are listed here; the rest need to be found and corrected. It can be done quickly, but answering the questions above means the major revision of the manuscript.
Response 6: Thank you for highlighting the issue of numerical rounding in our manuscript. We have thoroughly reviewed the entire document and standardized all numerical values according to appropriate rounding rules to ensure consistency and accuracy. The revisions have been applied to data presentation in tables, figures, and text descriptions throughout the manuscript.
We appreciate your valuable feedback, which has significantly improved the precision of our work.
Thank you again for your hard, meticulous work!
Best regards!
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsWe thank the authors for their careful and thorough responses to our comments. All points have been addressed satisfactorily. The revisions have significantly improved the clarity and quality of the manuscript.
We are satisfied with the responses and believe the manuscript is now suitable for publication.
Author Response
We sincerely thank the reviewers for their valuable feedback on our manuscript and the considerable effort they have devoted to this process. Your insightful guidance and rigorous suggestions have been instrumental in enhancing the quality of our paper.
We are very pleased to learn that our responses to the comments and the corresponding revisions have met with your approval. Your recognition is a significant encouragement to our research work and strengthens our confidence in future academic endeavors.
Once again, we appreciate your constructive comments and consistent support. We look forward to the opportunity to contribute to the field with the publication of this study under your guidance.
Reviewer 2 Report
Comments and Suggestions for AuthorsAn adequate response has been provided for the major concern regarding chlorocarbons. Equipment limitations precluded carrying out isotope analysis of the mass spectra. However, the revision notes that finding trichloroethyene is counter to expectation.
Warm mix additives reduce VOCs by allowing lower temperature processing through a reduction in viscosity. Less volatile components will not vaporize with less thermal energy. To actually investigate the value of these additives, one would have expected the experiments with them to be conducted at different temperatures from the other samples. A reader knowledgeable about warm mix additives might be confused. The method section should make explicitly clear that the conditions for the warm mix additive were the same as the other tests.
Author Response
Thank you for your valuable and insightful comments. We greatly appreciate your thorough review and have revised the manuscript accordingly to address your concerns.
Point 1: An adequate response has been provided for the major concern regarding chlorocarbons. Equipment limitations precluded carrying out isotope analysis of the mass spectra. However, the revision notes that finding trichloroethyene is counter to expectation.
Response 1: We understand your concern regarding the unexpected finding of trichloroethylene. The point you raised about equipment limitations precluding isotope analysis of the mass spectra is well taken. We have explicitly noted that this finding is counter to expectation, highlighting the unusual nature of the result for the readers.
Point 2: Warm mix additives reduce VOCs by allowing lower temperature processing through a reduction in viscosity. Less volatile components will not vaporize with less thermal energy. To actually investigate the value of these additives, one would have expected the experiments with them to be conducted at different temperatures from the other samples. A reader knowledgeable about warm mix additives might be confused. The method section should make explicitly clear that the conditions for the warm mix additive were the same as the other tests.
Response 2: We sincerely thank you for your critical comment regarding the experimental design for evaluating the warm mix additives. You are absolutely correct that to truly isolate and investigate the value of these additives, one would ideally conduct experiments at different temperatures compared to the control samples. We apologize for any confusion caused by the lack of clarity in the Methods section.
Action Taken: We will revise the Methodology section to include an explicit statement: "In this study, all samples, including those with and without the warm mix additive, were tested under identical temperature conditions. This approach was taken to control for the temperature variable and to isolate the effect of the additive itself on viscosity and VOC reduction."
Furthermore, we will acknowledge this methodological choice as a limitation in the Discussion section and suggest that future work explore a range of processing temperatures.
Thank you again for your hard, meticulous work!
Best regards!
Reviewer 3 Report
Comments and Suggestions for AuthorsReviewer’s comments:
As we can see, the Authors have corrected all the points recommended in the previous review, including compliance with rounding rules. However, this process cannot be considered complete. The problem is the data in Table 4, which was not mentioned in the review. Some values of Total Concentration, HKE, and ARHs (mkg/m3) presented with five significant digits (e.g., 4605.3, 3512.8, and 1092.5 in the last line) remain unacceptable. Obviously, should be 4.6, 3.5, and 1.1 mg/m3. The reviewer believed that it was not worth listing all the data that required rounding in the review, and the Authors would correct the rest by analogy.
Unfortunately, there is still another important problem left. It is the principal (pseudo-principal) component of asphalt emission – trichloroethylene. We can read the final Authors’ conclusion about trichloroethylene in the lines 381-390 (quote):
“Trichloroethylene was detected in all samples, with concentrations ranging from 20% to 79%, consistent with the reference [135]. Therefore, based on convergent evidence for its tentative identification, trichloroethylene — which exhibited the highest concentration in most samples — is the primary target for mitigation, with the exception of samples SA15 and N15W2. However, it is widely accepted that trichloroethylene should not be present in asphalt binder, SBS, or CR. This consensus contrasts sharply with the findings of this study. This discrepancy may be attributed to limitations inherent in the GC–MS methodology [165] or to specific instrumental constraints” (the end of quote).
At first, every specialist in mass spectrometry knows that tentative mass spectrometric identification of trichloroethylene is absolutely impossible. This compound has a completely unique mass spectrum. This statement can be easily verified using, for example, NIST database. Hence, we can talk about correct identification of this compound. Thus, if trichloroethylene was identified correctly and “should not be present in asphalt binder”, it is really indicates “the problems in GC-MS methodology, or specific instrumental constraints”. In that case, several pages of “Results and Discussion” devoted just to trichloroethylene look completely illogical. The reviewer cannot agree with this interpretation and strongly recommends to the Authors to find the source of “illegal” trichloroethylene in the experimental operations. Let us exclude the mysticism.
Unfortunately, in my opinion, without that the manuscript cannot be recommended for publication.
Author Response
We appreciate the thoughtful review and constructive feedback. Based on the constructive feedback, We will incorporate the recommended changes into the manuscript.
Point 1: As we can see, the Authors have corrected all the points recommended in the previous review, including compliance with rounding rules. However, this process cannot be considered complete. The problem is the data in Table 4, which was not mentioned in the review. Some values of Total Concentration, HKE, and ARHs (mkg/m3) presented with five significant digits (e.g., 4605.3, 3512.8, and 1092.5 in the last line) remain unacceptable. Obviously, should be 4.6, 3.5, and 1.1 mg/m3. The reviewer believed that it was not worth listing all the data that required rounding in the review, and the Authors would correct the rest by analogy.
Response 1: We sincerely thank you for pointing out this oversight. You are absolutely correct that the values (e.g., 4605.3, 3512.8, 1092.5 μg/m³) should be presented as 4.6, 3.5, and 1.1 mg/m³ in accordance with rounding rules and unit consistency. We apologize for this error and will thoroughly review and correct Table 4 and all similar data throughout the manuscript to ensure full compliance with the rules for significant figures.
Point 2: Unfortunately, there is still another important problem left. It is the principal (pseudo-principal) component of asphalt emission – trichloroethylene. We can read the final Authors’ conclusion about trichloroethylene in the lines 381-390 (quote):
“Trichloroethylene was detected in all samples, with concentrations ranging from 20% to 79%, consistent with the reference [135]. Therefore, based on convergent evidence for its tentative identification, trichloroethylene — which exhibited the highest concentration in most samples — is the primary target for mitigation, with the exception of samples SA15 and N15W2. However, it is widely accepted that trichloroethylene should not be present in asphalt binder, SBS, or CR. This consensus contrasts sharply with the findings of this study. This discrepancy may be attributed to limitations inherent in the GC–MS methodology [165] or to specific instrumental constraints” (the end of quote).
At first, every specialist in mass spectrometry knows that tentative mass spectrometric identification of trichloroethylene is absolutely impossible. This compound has a completely unique mass spectrum. This statement can be easily verified using, for example, NIST database. Hence, we can talk about correct identification of this compound. Thus, if trichloroethylene was identified correctly and “should not be present in asphalt binder”, it is really indicates “the problems in GC-MS methodology, or specific instrumental constraints”. In that case, several pages of “Results and Discussion” devoted just to trichloroethylene look completely illogical. The reviewer cannot agree with this interpretation and strongly recommends to the Authors to find the source of “illegal” trichloroethylene in the experimental operations. Let us exclude the mysticism.
Response 2: We sincerely thank the reviewer for this critical and insightful comment regarding the detection and interpretation of trichloroethylene in our study. We agree entirely with your assessment and apologize for the logical inconsistencies in our original discussion. Please find below our point-by-point response to the issues raised.
You are absolutely correct that trichloroethylene possesses a unique mass spectrum, making a "tentative identification" implausible. We apologize for this inaccurate terminology. The identification was, in fact, definitive and was confirmed by matching against the NIST mass spectral database. We will revise the manuscript throughout to replace "tentative identification" with "definitive identification" to reflect this certainty.
We fully accept your recommendation to investigate the experimental source of the trichloroethylene rather than attributing its presence solely to instrumental constraints. As you aptly stated, a definitive identification of a compound that "should not be present" logically necessitates a search for its origin within the experimental workflow.
Following your advice, we have re-examined our entire experimental process. Crucially, we have already performed a repeat analysis of the base asphalt emissions using a new, clean container prior to obtaining the full set of results reported in the manuscript. Trichloroethylene was consistently detected in these repeat analyses of the base asphalt itself.
Therefore, we conclude that the most probable source is that the base asphalt was contaminated prior to our experimentation. This finding completely alters the interpretation of our results. We will comprehensively rewrite the "Results and Discussion" section to:
Remove all conclusions presenting trichloroethylene as a "principal component of asphalt emission" or a "primary target for mitigation."
Clearly state that the compound is a contaminant likely present in the original base asphalt material.
Reassess the overall results and their implications by removing the contribution from this contaminant, ensuring logical rigor.
We agree that future work must focus on verifying this conclusion. Our revised manuscript will explicitly state that subsequent studies must first verify the purity of the base asphalt source to eliminate the influence of such unusual composition or contamination. This is essential for accurately assessing the true VOC profile of asphalt materials.
We are grateful for your guidance, which has been invaluable in identifying a critical flaw in our initial interpretation and significantly improving the quality of our work. We will conduct a thorough revision of the manuscript accordingly.
Thank you again for your hard, meticulous work!
Best regards!
