Comments:

The manuscript Morphological and optical properties of carbonaceous aerosol particles from ship emissions and biomass burning during a summer cruise measurement in the South China Sea investigated the morphological and absorption properties of BC particles in South China Sea, and found that the size and mixing state of BC particles and tar balls differs during ship navigation and stop period, indicate the different aging degrees. Meanwhile, this study revealed biomass burning and fossil fuel combustion contributed respectively to 18–22% and 78–82% of all the BC light absorption, showed that biomass burning was predominantly from the Philippines and South East Asia before and after the summer monsoon during the cruise campaign. Generally, the study is interesting and meaningful. The study still needs some improvements. The manuscript needs some revision in order to be published:

1. What’s the difference between Feret diameters and geometrical diameters? Why you use the former one to describe BC particles and use the latter to describe tar balls? 
2. The Abstract part is too long, maybe it will be better just listing the most important results in abstract.
3. In line 54, what’s the meaning of onion-like graphite layer microstructures? From the TEM image, the BC particles don't look much like onions.
4. As for Figure 6, why just chose some BC particles not all BC particles? Since not all BC particles are included in the discussion, the conclusion that small-sized BCs are more easily encapsulated is not very convincing (In line 295).
5. In line 285, among which were apparently emitted from the own ship (e, f): Why only mention e/f, isn't d also from own ship's emissions?
6. In line 300，since Tar balls were frequently observed during the campaign, then what’s the number fraction of tar balls in all particles?
7. There are mismatches between the appendix images and the image numbers mentioned in the main text: (1)Fig S5 is Map of the ship route, but line 287 says Fig S5 demonstrate "heavily coated internal BC particles were found during stop"; Fig S6 is titled "particles taken during navigation", but line 306 says Fig S6 contains tar ball mix with BC taken during stop. There are many more descriptions that don't match up.
8. In line 335, EC concentrations during SPP, ranging from 0.15 to 22.8 μg m^-3, But the EC concentration range for SPP in Fig 9 is around 1.7, why is that?

This paper investigated the morphology and optical properties of carbonaceous aerosols collected during a ship cruise campaign. The results can help improve the knowledge gap related to ship emissions and aerosol above the ocean. However, there are still many places that need to be improved. Many points need to be better explained, and the manuscript needs to be better organized, making me have difficulty understanding and validating the results. Please see my comments below. I recommend a major revision.

Major comments:

1. It is not very clear to me about your optical property measurements:
   1. For Aethalometer measurements, you must provide all necessary information, like data corrections. Aethalometer measures extinction, which is equal to absorption plus scattering. You should apply a correction for filter scattering based on your filter type. Moreover, did you do any corrections for multi-scattering effects due to particle selves? This can cause overestimations of absorption. Moreover, some brown carbon can absorb at 880 nm, leading to overestimating BC if you consider only BC absorbs at 880 nm. This can be improved by assuming AAE_BC = 1 and applying fitting like babs(lambda)=a lamda^AAE_BC + b lamda^AAE_BrC for all wavelengths. Otherwise, you should call these BC equivalent BC (eBC) since AE33 reports the equivalent mass of BC, which will absorb the same amount of light at that wavelength.
   2. It is not very clear to me how you measure optical EC. Could you provide more details about Sunset optical EC calculation? Does it use the same method as AE33? Since BrC might still significantly absorb at 660 nm (Cheng et al., 2019; Corbin et al., 2019) and you might not be able to correct multi-scattering, filter scattering, and loading effects related to filter-based optical measurements, it is essential to discuss your method. This is also related to OC/EC analysis since pyrolysis EC correction is based on transmission and reflection of 660 nm wavelength. Thus, OC/EC analysis typically overestimates EC (Cheng et al., 2019). Also, did you convert measured OC and EC to organic and black carbon mass since the OC-EC analyzer reports carbon mass in organic and BC, which will be smaller than organic and BC mass due to excluding other elements like oxygen and nitrogen?
   3. It needs to be clarified which method you used for the AAE discussion in your paper. Also, the details of your AAE model need to be included, which makes me unable to understand your results. Moreover, for your AAE model, how did you decide on AAE values of 1 and 2 for FF and BB? I think these values are too low, and I suggest using a range instead of 1 value to account for the uncertainties.
   4. Why do you have AAE values below 1 in Figure 11? Are these noises due to low absorbing particle loading?
2. It is also not very clear to me in some single particle analyses:
   1. Do you measure max Feret or mean Feret diameter or Feret diameter measured at an angle of 90 degrees to max Feret diameter? How many BC particles have you analyzed? I also did not see the details about your Df and lacunarity calculation.
   2. For your TEM imaging, I am very surprised that all organics can be evaporated at only 120 kV after beam focusing since the evaporation should occur during the vacuum process, and beam damage is typically not like this (typically for sulfate, and you will see some residual as the empty frame). I never see coating removed that completely, even with 300 kV acceleration voltage. It only happens during heating TEM experiments by heating the substrate to a few hundred ºC. Did you do EDX mapping on these particles to see spatial distribution in the particles? It will be helpful to determine particle types based on both shape and elemental composition. Your EDX spectrum only shows a few positions, which might not represent the whole particle.
   3. For tar ball particles, did you observe individual tar balls and tar ball aggregates (see Girotto et al., 2018)? Did you take tilted view images to confirm these round particles are spherical since they might not be domelike and flat (see Cheng et al., 2021)? Could you estimate the number fraction of tar balls in the samples?
   4. Could you add more discussion on how you determine aging and fresh particles based on TEM images? Compressed BC is typically more aged and atmospherically processed, and fractal soot is fresh. Moreover, sulfate (aqueous processing) and less viscous organic coating can be indicators of aging. Did you observe this difference in your navigation and stop cases? Moreover, you should observe bimodal distribution in stop cases.
3. I got lost in the different classifications of your samples. Why don’t you use the same classification? Moreover, the classification for the campaign period should not class SPP as an independent period since it is a subset of others.
4. I suggest adding a table in either the main text or SI to show the thresholds you used to identify different sources,
5. Your figure numbers in the main text should be checked carefully since some places refer to wrong figures.

Specific comments:

1. L50-51, “Carbonaceous aerosols … 2020).” BrC is a special subset of OC, so it should not be parallel with OC and BC.
2. L59-61, “BrC typically … respectively).” This is not true. BC should have a higher imaginary part or MAC from Visible to NIR-IR than BrC.
3. L64-66, “These particles … 2005).” Tar balls belong to BrC because they are light absorbing organic.
4. L87-88, “When BC … 2021).” Well internally mixed means different species are homogeneously distributed inside a particle, which is impossible for BC and other materials. Also, the shielding and lensing effects should depend on the coating thickness (Lack and Cappa, 2010).
5. DKL-2 should be a two-stage cascade impactor. What is the cut-off size for the other stage? Are there any references to validate the cut-off size? Section S1 is not necessary if someone has already published these results. Moreover, Section S1 is a theoretical calculation. Did you test the cut-off size? Did you only collect on stage with 50% cut-off = 0.2 μm? Why did it not include the other stage?
6. L153-154, “The BC mass … time resolution.” I do not think AE33 has a time resolution of 1 second.
7. L176-177, “Here, … campaign.” How do you determine this value? These should be instrumenting noise or contamination, not your detection limit. You should use a standard with a known concentration to calibrate the detection limit.
8. L178-180, “The measurements … the ship.” Do you have any references for these instruments? What is the time resolution? What are their uncertainties?
9. L197-198, “The navigation … TEM samples).” Is the relative wind direction relative to the North or ship direction? How did you determine the criteria for wind speed and direction?
10. L203-204, “Here, we … transport.” Could you provide details about how did you distinguish these? Based on chemical composition? Other ship emissions might not be easy to separate from your ship emission.
11. L207-208, “Here, we … variations.” I suggest using a subscript to indicate BC mass from OC-EC or AE33. It is unclear to me.
12. Figure 1. The color bar needs to be clarified. I suggest using colors with higher color resolution.
13. L250-252, “It should be …. html.en.” It is not shown as an increase in wind speed and RH and a decrease in pressure in Figure 2 for the typhoon period. Could you explain that? Moreover, I suggest adding a SI figure to show the typhoon.
14. L253-257, “Figure 3 … 80-280º”. I expect a detailed discussion of Figure 3 since that tells lots of important information. Why do you see more BC after the monsoon, which I expect pollution will be removed by rain? Also, why do you see more BC before May 8th? Or OC, did you observe any diurnal trend or other trend? I suggest labeling the sampling period and path in Figures 2 and 3 by adding shaded areas—same suggestion for all other time serial figures.
15. L262-264, “The choice of … 2007).” You should adjust the bin width to make the distance between each bin is constant in log scale. I suggest using same bin size to help reader visualize easily.
16. L275-277, “The BC … 2020a).” It is hard to see the coating in a and c. Both look like embedded to me. Do you have better images?
17. L284-285, “Comparatively … (e,f).” How did you know this? This is not clear to me.
18. L286-287, “In addition, … (Fig. S5).” They could also be condensation of organic during cooling after emitted from engine if you do not see them spread out (high viscous).
19. Figure 6: Does Fig 6 just show results from a portion of BC you imaged? If yes, why don’t you show all of them? Do you think your results is statistically significant since your sample number is very low.
20. L294-295, “Figure 6 … during transport.” This is unclear to me. Please explain this in detail. Did you observe smaller particles have more coating? If yes, have you tried to quantify the size change after removing coating?
21. L296-298, “Comparatively, … particles.” I did not see significantly difference in lacunarity by looking at the figure. I suggest making a plot as size change vs lacunarity to support your statement.
22. Figure 7, I cannot see your tar ball. Please mark them in your figures. Also, the scales and text in figures a-c are very difficult to read. Please change a color. Same comments for Figure S9. Fig. 7c looks like thick OC coated soot since I did not see any beam damage, which is typically generated during engine emission. Do you refer amorphous carbon agglomerates to OC or soot?
23. 3-3.4, “The difference … origin.” Which difference you are referring here? Size, number, shape, or something else?
24. Section 3.3. I feel it might be better to move Section 3.3 before Section 3.1.
25. L327-347, “The BC concentrations … Sun et al., 2023).” This paragraph does not fit here and should be moved to section 3.5. BC from AE33 does not agree with OC/EC, but their trend agrees. Moreover, I am not sure how could you get optical EC time resolution of 1 min since that should be only measured before thermal process. The R square is also very low for the fitting of AE33 BC and optical EC. Higher AE33 BC and optical EC is because overestimation by assuming only BC absorbing at long wavelength and multi-scattering effects.
26. Figure 9 is not clear to me. Figure 9 is not clear to me. What is the x axis? Should you also have a box plot for EC rather than a single value? You can show two plots (one for OC/EC ratio and the other one for EC) for all periods combined. The whisker should not touch axis. Also, I suggest using violin plot instead of box so that you can show distribution.
27. L333-334, “Notably … during SPP.” Please add uncertainties.
28. Figure 10. Please add more tick labels in b and c since current version does not tell the timestamp.
29. 369-371, “Notably, … (Fig. 10a).” Why do you have a range of BC mass concentration? Is this the BC mass concentration at each wavelength? AE33 reports mass equivalent to the mass of BC absorbs same amount of light, not real BC mass.

References:

Cheng, Z., Atwi, K., Onyima, T., Saleh, R., 2019. Investigating the dependence of light-absorption properties of combustion carbonaceous aerosols on combustion conditions. Aerosol Sci. Technol. 53, 419–434. https://doi.org/10.1080/02786826.2019.1566593

Cheng, Z., Sharma, N., Tseng, K.P., Kovarik, L., China, S., 2021. Direct observation and assessment of phase states of ambient and lab-generated sub-micron particles upon humidification. RSC Adv. 11, 15264–15272. https://doi.org/10.1039/d1ra02530a

Corbin, J.C., Czech, H., Massabò, D., de Mongeot, F.B., Jakobi, G., Liu, F., Lobo, P., Mennucci, C., Mensah, A.A., Orasche, J., Pieber, S.M., Prévôt, A.S.H., Stengel, B., Tay, L.-L., Zanatta, M., Zimmermann, R., El Haddad, I., Gysel, M., 2019. Infrared-absorbing carbonaceous tar can dominate light absorption by marine-engine exhaust. npj Clim. Atmos. Sci. 2. https://doi.org/10.1038/s41612-019-0069-5

Girotto, G., Bhandari, J., Gorkowski, K., Scarnato, B. V, Capek, T., Marinoni, A., Veghte, D.P., Kulkarni, G., Aiken, A.C., Dubey, M., Mazzoleni, C., 2018. Fractal-like Tar Ball Aggregates from Wildfire Smoke. Environ. Sci. Technol. Lett. 5, 360−365. https://doi.org/10.1021/acs.estlett.8b00229

Lack, D.A., Cappa, C.D., 2010. Impact of brown and clear carbon on light absorption enhancement, single scatter albedo and absorption wavelength dependence of black carbon. Atmos. Chem. Phys. 10, 4207–4220. https://doi.org/10.5194/acp-10-4207-2010