In the current study, gaseous and particulate I/SVOCs emitted from four HDDVs were analyzed using GC×GC-MS. The emission factors as well as the composition of I/SVOCs were reported. Overall, the experiments were nicely done and the data are well analyzed. The current contribution is a welcome addition to the field. There are several places in the paper are a bit obscure as detailed in the comments below. Beyond these, I do not see any major obstacles to publication.

Specific comments:

(1) The experiments were well organized. My general question is the innovation of the current study. The I/SVOC emissions as well as their compositions from heavy diesel vehicles have been widely reported, including the studies from their own group. Any new findings that the authors would like to highlight in the current one?

(2) Line 24: “Compounds such as phenol, …. appeared only in HMV emissions”. These are compounds that are widely observed in vehicle emissions. Any reason for their disappearance in LMV emission? Are there any potential artifacts in the sample analysis?

(3) Line 179: “Oxy-PAH&Oxy-benzene”, I don’t think the abbreviations were pre-defined. Also, what compounds specifically do they represent? I noticed the authors also separately classify “phenol” instead of grouping them into “Oxy-benzene”.

(4) Line 190: the emission factors of ISVOCs between LMV and HMV differs quite a lot according to Figure 2a. And according to Figure 3, the fractional contributions from different components are also different for HMV and LMV. Hence, I’m not sure it is appropriate to present the average volatility distributions of I/SVOCs from the entire fleet. Could Figure 1 be separated into LMV and HMV?

(5) Line 225: How many sets of the tests were performed? Does each data point on Figure 2b represents the average emission factor for each entire 1800s test cycle? Also, I hesitate to agree that gaseous I/SVOCs show good correlation with THC because the datapoints on Figure 2b concentrates at two ends of the fitted line, which might affect the reliability of the linear regression. Any more evidence on this point? Or any other supporting references?

(6) The influence of temperature on emission is interesting. What are the variations of other pollutants with the changes in temperature, i.e., THC, NOX, CO, etc?

(7) The overall presentation is acceptable, but English could do with improvement in places.

This manuscript investigates the gaseous and particulate I/SVOC emission factors (EFs) of high-mileage vehicles (HMVs) and low-mileage vehicles (LMVs) under varying ambient temperatures using TD-GC×GC-MS. The authors provide a comprehensive analysis of the variations in emission factors and their chemical components, identifying a linear correlation between I/SVOC EFs and the modified combustion efficiency (MCE). The experimental methodology is thorough and reliable, and the findings present a significant advancement in understanding I/SVOC emissions from heavy duty diesel vehicles (HDDVs). The results have practical implications, particularly for researchers developing I/SVOC emission inventories and secondary organic aerosol (SOA) prediction. Overall, I recommend accepting this manuscript following minor revisions.

1. In section 2.1, the authors describe the information of the four in-use HDDVs. But the vehicle brand and the engine model of the HDDVs, which are closely related to the vehicle emission are not given. The related information should be given, and some discussion about the uncertainty caused by these differences and the aging of the engine should be included in the manuscript.
2. In Section 2.1, it is better to give the dilution ratio of the exhaust. In addition, was the temperature of the sampling pipe maintained as a certain level to reduce thermophoretic and condensational losses?
3. In Section 2.2, the authors describe the method to remove effects of absorption on the quartz filter when calculating the total I/SVOCs. The gas phase of I/SVOCs are collected after a PTFE filter, but the separation of gas and particle I/SVOCs after the PTFE may break the equilibrium of gas/particle I/SVOCs and lead to evaporation of particle I/SVOCs, which may overestimate the Qgas. It is better to provide some discussion on the uncertainty of this method.
4. The sentence “…by He et al. (2022b)” in line 132 is missing a period at the end. Please correct this.
5. Some phrases should use standard abbreviations. For instance, the phrase “...as shown in Figure 1” in line 177 should be revised to “...as shown in Fig. 1.” Ensure consistent abbreviation usage throughout the manuscript.
6. In line 227, the “2” in “R2=0.9” is not in superscript. Please adjust the formatting for accuracy.
7. The steps for qualitatively identifying organic compounds using mass spectrometry principles require further elaboration. Could the authors provide a detailed description of these procedures in the methods section?
8. Specify the number of test repetitions conducted for each vehicle. Additionally, indicate the sample sizes used for all calculations involving averages to enhance the transparency and reproducibility of the results.
9. In Line 237-238: “The EF ratios across different volatility bins decreased with decreasing volatility, highlighting that the elevated I/SVOC EFs of HMVs were primarily due to a marked increase in organics within the volatility range of bins 2 to 6.”. But according to the Fig 3, the I/SVOCs EFs of HMVs and LMVs exhibited a rebound within the volatility range of bins 2 to 4. Is there any explanation for this phenomenon?
10. Around line 240, there’s a comparison of the proportions of HMV and LMV organic compounds; was there also a comparison of different component emission factors (EFs) between HMV and LMV? Are all substances higher in HMV?
11. The introduction and the section on SOA prediction would benefit from additional supporting references. Consider including following studies that explore the generation and sources of urban particulate matter to provide a more robust foundation for your discussion.

• Jacob M. Sommers, Craig A. Stroud, Max G. Adam, Jason O'Brien, Jeffrey R. Brook, Katherine Hayden, Alex K. Y. Lee, Kun Li, John Liggio, Cristian Mihele, Richard L. Mittermeier, Robin G. Stevens, Mengistu Wolde, Andreas Zuend, Patrick L. Hayes (2022) Evaluating SOA formation from different sources of semi- and intermediate-volatility organic compounds from the Athabasca oil sands. Environmental Science: Atmospheres. DOI: 10.1039/d1ea00053e.
• Qingsong Wang; Juntao Huo; Hui Chen*; Yusen Duan; Qingyan Fu; Yi Sun; Kun Zhang; Ling Huang; Yangjun Wang; Jiani Tan; Li Li*; Lina Wang; Dan Li; Christian George; Abdelwahid Mellouki, &Jianmin Chen (2023) Traffic, marine ships and nucleation as the main sources of ultrafine particles in suburban Shanghai, China. Environmental Science: Atmospheres. DOI: 10.1039/d3ea00096f.
• Ling Huang, Hanqing Liu, Greg Yarwood, Gary Wilson, Jun Tao, Zhiwei Han, Dongsheng Ji, Yangjun Wang, Li Li*. Modeling of secondary organic aerosols (SOA) based on two commonly used air quality models in China: Consistent S/IVOCs contribution but large differences in SOA aging. Science of the Total Environment 2023, 903, 166162. https://doi.org/10.1016/j.scitotenv.2023.166162.
• Yangjun Wang; Miao Ning; Qingfang Su; Lijuan Wang*; Sen Jiang; Yueyi Feng; Weiling Wu; Qian Tang; Shiyu Hou; Jinting Bian; Ling Huang; Guibin Lu; Kasemsan Manomaiphiboon; Burcak Kaynak; Kun Zhang; Hui Chen, &Li Li* (2024) Designing regional joint prevention and control schemes of PM2.5 based on source apportionment of chemical transport model: A case study of a heavy pollution episode. Journal of Cleaner Production. DOI: 10.1016/j.jclepro.2024.142313.
• Sahir Azmi, Mukesh Sharma (2023) Global PM₅ and secondary organic aerosols (SOA) levels with sectorial contribution to anthropogenic and biogenic SOA formation. Chemosphere. https://doi.org/10.1016/j.chemosphere.2023.139195.