I thoroughly reviewed this manuscript. I agree that the subject of the review is very essential. This paper presents the characteristic of the particulate I/SVOCs from chassis dynamometer tests of HDDVs complying with multiple emission standards. Interestingly, this paper provides a versatile approach and could be applied into other significant sources prevailing in typical environments. This may have implications for environmental management. I have listed some specific comments (see below) for this paper, and it is recommended to make revision before publication.

1. EF and OA in Line 30. These abbreviations have to be explained in their first appearance in the text. Check throughout the manuscript. These are readily recognizable only to the more experienced reader.
2. In Introduction, from Line 36 to Line 42, so much dated references are cited, such as: Line 38, Lines 39-40, Line 42. A better presentation is needed along with up-to-date references. The Introduction should be rephrased.
3. Lines 77-78. You expressed “a comprehensive characterization of speciated g-p partition of vehicle emission is yet to achieve”. However, there is no reference, please give some to confirm it.
4. The format of the paper still needs to be improved. Such as, Line 80: “integrate” and Line 145: “Nest”. Please modify it.
5. Line 164. You said “w_c is the mass fraction of carbon (0.86) in the diesel fuel”. How do you get this value 0.86? There is not any analysis about the reason or any reference to support it.
6. Line 173. The sentence “alkane is the most abundant species” is not smooth. Please confirm words “is” and “species” are conflict whether or not?
7. Line 173-175. The two sentences expressed similar idea. It is recommended that they can be combined into one part.
8. Lines 190-198. This chapter you gave the results about EF. Lines 173-189, the average HDDV-emitted particulate I/SVOCs EFs of cold-start and hot-start driving cycles are expressed, respectively. However, you do not distinguish the results about cold-start and hot-start in Lines 190-198. Please give an explanation.
9. Line 225. What is the meaning of O-I/SVOCs? You analyzed volatility distribution of I/SVOCs before. What is the difference between O-I/SVOCs and I/SVOCs?
10. Lines 266-269.There is some confusion regarding what you refer as the respective fractions. You gave three ratio change results under W_cold condition and W_hot condition. However, what do the three ratio change results correspond to, P1, P2, P3 or may be P3, P2, P1...? Please write it clearly.
11. Line 309. The same as Q5. The sentence “The particle fraction decreases to less than 1% between log10C* = −1 to 2 μg m^-3” is not smooth. Please modify it.

This work collected the particulate intermediate-volatility and semi-volatile organic compounds (I/SVOC) from heavy-duty diesel vehicles (HDDVs) by conducting chassis dynamometer tests. They analyzed the particulate I/SVOCs using two-dimensional gas chromatography time-of-flight mass spectrometry (GC  GC-ToF-MS), speciated the unresolved complex mixtures (UCMs), and reported the emission factor (EF) distribution under diverse driving conditions. Besides, they examined the gas-particle (g-p) partitioning of different compound categories and addressed how the sampling artifacts would affect the quantification of organic compounds. Overall, I think the paper is worthy of publication and meets the interest of the reader of this journal. Suggestions and comments are provided below:

1. We know that oxygenated groups, i.e., hydroxyl and carboxylic groups, are not well detected in GC-MS without derivatization with MSTFA. How would you detect those oxygenated compounds without the derivatization and guarantee the recoveries in particular?
2. In section 3.3, when addressing the I/SVOC distribution, the criteria of O:C ratio of 0.3, 0,4, and 0.5 are deployed. Could you explain why the specific numbers are used?
3. Line 101, it is mentioned that three replicated experiments are conducted. What is the repeatability of the measurements, e.g., reporting the standard deviation? Readers may be interested in the repeatability to confirm the robustness of the methods.
4. It seems that many categories, such as O-I/SVOCs, do not have authentic standards. How are these I/SVOCs identified and quantified? The authors should address these compound categories' identification in the main text or in the supporting information.
5. The uncertainty assessment of the emission factors should be presented to convince the reader of the quantification method, either in the main text or the supporting information.
6. Fig 2 shows that the "phenol benzylic alcohol" is the most abundant O-I/SVOC species. Could you give some example compounds of this category, and what are the implications with abundant emission of these compounds?
7. Line 340, please check throughout the main text and keep “GC × GC” uniform.

He et al. reported the the emission factors of the particulate intermediate and semi-volatile organic compounds by the heavy-duty diesel vehicles, using the two-dimensional gas chromatography time-of-flight mass spectrometry. The authors discussed the volatility distribution of the grouped 21 categories from different driving conditions and discussed the gas and particle phase distribution. The speciated data from the vehicular emission sources is useful for understanding the ambient environmental data, where locational specific source profiles are quite limited. Thus, I would suggest the publication if the author can address my following comments:

1. The abbreviation of ISVOCs and SVOCs in the title should be specified.
2. Line 30: “EF” should be defined.
3. Line 69: it should be “sub-cooled liquid vapor pressure”
4. Lines 83-84, the sentence “Particulate I/SVOCs at ascending speed stages are collected and analysed separately” is a repeat to line 79-80, please revise the statement.
5. Line 101: revise “duplicated” to “repeated”
6. Line 106: repeated words of “”monitored collected”.
7. Line 117: “Field blank samples are collected collocated at the upstream of the emission pipeline”. This sentence is grammatically incorrect, please revise.
8. Line 120: “A total of 36 filter samples plus 3 field blanks were collected…” please specify the detailed sampling information, e.g., how many samples from the non-(DPF + DOC) vehicles, etc.?
9. Lines 145 and 146: revise “Nest” to “Next”; “elusion” to “elution”.
10. Line 151-155: the specific molecular information of the quantified species should be specified, maybe in the supporting information. For example, what is the carbon range of the measured alkanes, alkenes, cycloalkanes, and hopanes, etc.? The information is necessary as the g-p partitioning are highly associated with the intrinsic chemical properties of the compounds. Besides, the naming of the 4-ring PAHs₂₀₂ and 4-ring PAHs₂₂₈ looks weird, and it is not consistent in the main text and in the legend of Figure 2.
11. There is a negative value of removal efficiency of gas phase data for 4 ring PAHs in Table S2, please check.
12. Line 197: what does the “Mono-aromatic compounds” refer to, as it is not within the 21 categories? Is it alkyl benzenes? Please specify.
13. Figure 1. I’m confused why there are only six data point for each category, while the sample numbers are 36?
14. What is the “O-I/SVOCs”? the definition should be given.
15. Figure 5, the babel “ >0.3, >0.4 and >0.5” should be presented on the x-axis, current format is not clear.
16. Line 297: “However, the vapor loss to the Teflon surface has long been a concern, especially in smog chamber community”. Does the author mean Quartz?
17. Lines 298-300: “OA concentration in the tailpipe is orders of magnitude higher than that in the ambient air even after the dilution in the CVS system, which would facilitate partitioning to the particle phase.” This statement seems not consistent with the results shown in Figure 6, where most of the measured I/SVOCs are in the gas phase, not in the particle phase.
18. Has the author measured the total OA concentration? If you did, you can try to model the g-p distribution using Pankow absorption theory (Pankow, 1994), and to see if it can explain the gas-phase dominant results for the I/SVOCs. And also, why the phase distribution of hopanes is distinctly different between non-(DPF + DOC) vehicles and (DPF + DOC) vehicles, any particular explanations?Reference: Pankow, J. F. (1994). An absorption model of gas/particle partitioning of organic compounds in the atmosphere. Atmospheric Environment, 28(2), 185-188.