The manuscript presents novel findings concerning ship emissions, with a focus on intermediate and semi-volatile organic compounds. The results reveal the enhancement of organic compounds following the transition from high-sulfur to low-sulfur fuels. The manuscript is well written and provides meaningful information to our knowledge. However, there are several questions and comments that require attention:

1.    Lines 63-66: This sentence is ambiguous in terms of the contribution proportion of SO2. It is suggested to be revised.

2.    Line 87: Does PM refer to mass or number? It needs to be made clear.

3.    Line 98: The aging of VOCs to form intermediates is equally important for SOA.

Examination of long-time aging process on volatile organic compounds emitted from solid fuel combustion in a rural area of China. Chemosphere 333 (2023) 138957.

4.    Line 108: Provide the full name of “WRF-Chem”

5.    Line 118 and 102: The emission of IVOCs from various sources are important for the SOA production. It is recommended to enrich the expression, and the following study can be referred to：

Emission of Intermediate Volatile Organic Compounds from Animal Dung and Coal Combustion and Its Contribution to Secondary Organic Aerosol Formation in Qinghai-Tibet Plateau, China. Environmental Science & Technology 2024 58 (25), 11118-11127.

6.    Section 2: In this study, some data statistical analyses were involved. It is necessary to add the methods used in the statistical analyses mentioned in the text, such as significance tests, etc.

7.    Lines 151-152: The parameters of fuels are the most important information in this study. It is suggested that the Table S2 be placed in the main text.

8.    Line 167: A total of 64 sets of gas-phase and particle-phase I/SVOCs samples were collected in this study, involving various engine types, fuels, and operating modes. Please add a table detailing exactly in what fuel, what type of engine, and under what operating modes, etc. these samples were collected.

9.    Line 202: In formula (1), when calculating EF, has the influence of organic carbon in gaseous phase been considered? How large is the error?

10.    Lines 312-319: Here reveals a very interesting research result that high-quality fuel leads to higher organic matter emissions. What do you think are the reasons for the increase in VOCs/IVOCs emission factors after the switch from high-sulfur oil to low-sulfur fuel?

11.    Section 3.2: How do the influencing factors such as fuel type, engine type and operating conditions interact to affect the final combustion process and I/SVOCs emissions? Give more explanations. 

12.    Lines 353-357: Incomplete combustion is regarded as an important reason for the increase of I/SVOCs with low-sulfur fuel. Can more convincing evidence, such as combustion efficiencies of the engines with different types of fuels, be provided in this study to support the conclusion given here? 

13.    Figure 2: Explain the meanings of the different symbols in this box plot, such as which one represents the average value, the median, etc. Besides, what method was used to calculate the P value?

14.    Lines 410-412: Given that UCM accounts for a very high proportion of total I/SVOCs, what do you think the future research on UCM should be carried out, and is it necessary to further identify more compounds and what analytical methods should be used?

15.    Section 3.4: It is reasonable to divide the volatile range with normal alkanes as indicators. However, when discussing the differences in volatile distribution under different fuel types, only the phenomenon was described. How did the differences in fuel composition eventually lead to changes in volatile distribution? Can a summary of this part be made based on the component differences of different fuels?

16.    Figure 4: In the figure involving Hopanes, some error bars are covered. 

17.    Figure 5 and Figure 6: The meanings of the Y-axis titles have not been clearly explained.

18.    Figure 6: In the legend, the word "Hopanes" is misspelled. 

19.    Figure 7: Could the total error bar of SOAFP be given? 

This study systematically evaluated the impact of improving marine fuel quality on I/SVOC emissions. An innovative finding revealed that transitioning from low-sulfur to ultra-low-sulfur oil led to a significant increase in I/SVOC emissions, which in turn elevated the secondary organic aerosol formation potential (SOAFP). Additionally, it also found that I/SVOC emissions from inland ships are substantial and should not be overlooked. The findings provide valuable insights for the development of future ultra-low-sulfur oil policies. However, several questions still require further elaboration and explanation.

(1) I fully understand the challenges the authors face in conducting ship emission tests. However, from the perspective of improving the quality of the paper, since one of the key innovations is updating the emission factors, there should be further discussion on how the new emission factors impact the pollutant emissions in the inventory or the total amount of SOA formation.

(2) It is suggested that Table S2 be placed in the main text.

(3) Line 243-244: In the study of emissions from different types of ships (OGVs and ICSs), are there any significant differences in the emission characteristics of I/SVOCs between new ships in this study and old ships from previous studies of the same type? If so, what could be the reasons for these differences?

(4) Line 423-425: Considering the importance of fatty acids in ship exhausts, what are the possible sources of fatty acids in the atmosphere besides fuel combustion? And how can their contributions from different sources be differentiated and quantified?

(5) Section 3.5: In the investigation of SOA formation potential, the contribution of different I/SVOC components is discussed. How sensitive is the SOA formation potential to variations in the relative proportions of these components? Could a minor alteration in the ratio of specific I/SVOCs significantly influence overall SOA formation?

(6) In the conclusion section, in addition to summarizing the main findings, it would be valuable to propose potential future research directions based on the limitations identified in this study. For instance, with respect to the UCM analysis, it is crucial to elaborate on the specific enhancements required for the experimental methodology. Are there alternative extraction techniques or advanced analytical instruments that could potentially enhance the identification and quantification of UCM components, such as GC×GC-MS? A more comprehensive investigation into these aspects would substantially enhance the value of the conclusion and more effectively guide future research endeavors.

(7) It is recommended to review and standardize the unit notations for better readability：For example, in the process of converting original measurement data into emission factors, the presentation of units for each variable in the text is not coherent enough. For the concentration representation of some chemical substances, such as the concentration of certain substances in the gas or particle phase in the description of sampling and analysis processes, there is no explanation in different paragraphs or charts whether different representation methods or units are used. The author should review and standardize the unit notations for better understanding.

(8) Figure 4: It is necessary to improve the readability.

Figure 6: the word “hapones” should be corrected to “hopanes”

(9) The article contains several minor grammatical and expressive errors that require thorough examination and correction to enhance its overall quality.

Line 406-408: “composition” and “compositions” should be unified;

Line 413: “accounting for average of... ” is an incorrect expression and should be changed to “ accounting for an average of... ”

Review for “Enhanced emission of intermediate/semi-volatile organic matters in both gas and particle phases from ship exhausts with low-sulfur fuels” by Xiao et al.

In this study, the authors evaluated the impact of the transition from high-sulfur to low-sulfur on intermediate/semi-volatile organic matters (I/SVOCs) from ocean-going vessels and inland cargo ships. An increase of I/SVOCs has been found as the sulfur content decreased. This novel finding is very helpful for future oil policies. Although this is an interesting paper, certain clarification and revisions are needed. I recommend the publication after the authors address my comments below.

Major comment:

My major concern lies in the measurement. Section 2 should provide further details about the measurement. What is the clean air used in the sampling system, is it the same as zero air where there is no particle? It is important that the system isolates particles and gases originating exclusively from the ship exhaust, minimizing the potential for contamination from external sources. What measures have been taken to ensure this? Besides, is there a cutoff size of the aerosol or is it total suspended particles (TSP)? What is the uncertainty of the measurement? How long is the sampling time? How many samples were collected? It is beneficial to include a table giving an overview of all the samples, including the ship, engine type, fuel type, and operating mode, similar to Table S2 in Zhang et al. (2024). It can be put in the supplement.

Specific comments:

1. Line 57-58. “shipping emissions are responsible for 25% of fine particulate matter” globally? Please clarify.
2. Line 358-366. It seems that when analyzing the impact of operating mode (Fig. 2b), all the OGVs and ICSs, fuel types, and engine types are used. Will the result be different if we investigate samples with the same fuel and engine types to exclude their impact?
3. Figure 2 in line 402. I would suggest replacing the x-axis label with the figure title. More details are needed in the figure caption. The elements of boxplots need to be added. Besides, I do not see error bars. By error bars, the authors might mean whiskers. How many samples are there in each box, it will be more robust if the amount of samples could be shown.
4. 372-374. This sentence needs to be revised. Is an “and” missing?
5. Figure 3 in line 453. Why Fig. 3b is called “distributions”? Do the authors mean fractions? I would suggest the same as Fig. 2 that more details need to be added in the figure caption.
6. Figure 4 in line 545. Please improve the readability.
7. Line 592: The hopanes is not discernible in Fig. 6.
8. Figure 6 in line 597. Hapones should be hopanes. It is necessary to improve the readability. The authors can try to use the log scale. More details need to be added in the figure caption as well.

Reference:

Zhang, F., Xiao, B., Liu, Z., Zhang, Y., Tian, C., Li, R., Wu, C., Lei, Y., Zhang, S., Wan, X., Chen, Y., Han, Y., Cui, M., Huang, C., Wang, H., Chen, Y., and Wang, G.: Real-world emission characteristics of VOCs from typical cargo ships and their potential contributions to secondary organic aerosol and O3  under low-sulfur fuel policies, Atmos. Chem. Phys., 24, 8999–9017, https://doi.org/10.5194/acp-24-8999-2024, 2024.