Adachi et al. conducted a comprehensive transmission electron microscopy analysis to understand the tarball formation, concentration, and properties. Overall, the study is well organized, and the paper is well written. The results have a potentially high impact on understanding biomass burning aerosol climate effects. I have a few minor comments that I hope can be used to help the authors further improve the paper.

Comments:

1. The paper used the assumption that none TB carbonaceous aerosols’ area-equivalent diameter is approximately twice the volume-equivalent diameter to estimate their volume. However, this study has acquired tilted images, which wight be a better and more direct way to estimate the volume of particles (Cheng et al., 2023, 2021)It might be worth discussing the uncertainty between these two methods and considering using the aspect ratio to calculate the volume in future studies.
2. I suggest adding a sentence to acknowledge the caveat that volatile and semivolatile species in the particles could be lost in the high-vacuum TEM chamber, causing shape deformation. Typically, the particle height will reduce, but the base will maintain the same area due to the fraction and adhere force.
3. Could you provide any estimation of how much C and O could come from the formvar due to the penetration effect? Also, the C, N, and O from EDX are semiquantitative.
4. I suggest adding Si maps to figure 2 since you discussed Si in section 3.1.2.
5. Would it be a potential reason that the increase fraction of TBs with atmospheric aging time is due to the sink of volatile species due to rapid dilution with air and rapid decomposition?
6. Do you think that those inorganics in the carbonaceous could be formed during the condensation phase of the flame where carbonaceous species in TB condensed on the inorganic compounds or the inorganic compounds diffused into TBs?
7. Figure S3 caption is unclear to me. Is the y-axis the fraction of aggregated TBs in the sample? It is not very clear to me what is the number of samples containing TBs? Is this the total number of particles analyzed in that sample? How many TEM grids have you analyzed?
8. Mathai et al., 2023 show that TBs with and without inclusion have different optical properties (Mathai et al., 2023). It will be nice to link that study with your findings.

References:

Cheng, Z., Sharma, N., Tseng, K. P., Kovarik, L., and China, S.: 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, 2021.

Cheng, Z., Morgenstern, M., Henning, S., Zhang, B., Roberts, G. C., Fraund, M., Marcus, M. A., Lata, N. N., Fialho, P., Mazzoleni, L., Wehner, B., Mazzoleni, C., and China, S.: Cloud condensation nuclei activity of internally mixed particle populations at a remote marine free troposphere site in the North Atlantic Ocean, Sci. Total Environ., 904, 166865, https://doi.org/10.1016/j.scitotenv.2023.166865, 2023.

Mathai, S., Veghte, D., Kovarik, L., Mazzoleni, C., Tseng, K., Bucci, S., Capek, T., Cheng, Z., Marinoni, A., and China, S.: Optical Properties of Individual Tar Balls in the Free Troposphere, Environ. Sci. Technol., 57, 16834–16842, https://doi.org/10.1021/acs.est.3c03498, 2023.

The paper reports the abundance of TBs from several fires in the US. TBs can have an important role in the climate impact of fires and, therefore, the work is worth publication. The methods used seem sound and the exposition is mostly clear. The results are very interesting. I have only a few comments to follow.

General comments

-    I am not clear about the inlet used and the impact that the aircraft speed might have had on the samples, especially the size cut of the impactor. It would be helpful if the authors could comment on this aspect as that might affect the interpretation of their size results.

-    In some cases, I found some details to be glossed over a bit too much. Some more on this in the specific comments next.

Specific comments

-    Line 22: This is a not too critical and arguable terminology suggestion. “As the samples aged…” the authors probably refer to the particles aging, not the sample aging, correct? The samples have been analyzed probably a long time after collection, so the time the authors refer to is for the particles at the time of sampling, not for the sample itself. Same in line 24 and section 2.2.

-    Line 24: If the fraction (not the concentration itself) of TBs is decreasing that should not be due to dilution alone. Does the decrease in fraction indicate some sort of selective removal?

-    Line 99: Perhaps “measured” should be “analyzed” 

-    Table 1: Would it be possible for the authors to estimate statistical errors on the fractions? One could at least use counting statistics to estimate the potential error.  

-    Line 107: What are “archived winds”? Can you archive wind?

-    Line 114: Could the authors explain why they favored the Formvar substrates? This becomes evident only later in the paper.

-    Section 2.4. How much time passed between sampling and analysis? Does that potentially impact the interpretation of the results?

-    Line 127: Would that ratio depend on the viscosity of the particle? Same for line 197.

-    Paragraph starting at line 152:  It would be useful to provide some more detail on the deep learning approach.

-    Lines 199-200: Units?

-    Line 223: How were TBs being sampled in clouds? Was a CVI being used, or are these interstitial TBs? Also, how was the coating being identified?

-    Libe 232: “short electron beam” how short? And why?

-    Line 262: By “size” the authors indicate the diameter or the radius?

-    Line 268: Is this aspect ratio an average over all the TBs measured or only for those that showed some deformation?

-    Figure 4: There seems to be a smaller mode in the TBs size distribution. Can the authors comment on this smaller mode?

-    Line 285: How was the 1% error being estimated? This also connects to one of my previous comments. Same for the 2% in the next line.

-    Lines 287-288: It would be useful if the authors would provide the method used to estimate the uncertainties in detail.

-    Line 288: Perhaps I missed it, but what does the enhancement ratio represent, and how is calculated? Why is important? The definition is reported in Figure 5 and perhaps was discussed earlier in the paper, but it might be good to elaborate some more on it.

-    Figure 5: The x-axis labels are very small and hard to read. 

-    Figure 7: This is a beautiful result. Perhaps it would help to identify the TBs on the images to clearly underline the increase in fraction.

-    Line 339: As mentioned earlier, I am not clear how a “fraction” would decrease with dilution alone. Was some selective scavenging going on, or was secondary organic aerosol forming and so dominating more the particle population?

-    Figure 8: I am confused by the color/symbol explanation in the caption. For example, the authors mention red diamonds, blue squares, and black circles, but there are also red circles in panel (e). Probably those should also be diamonds. Also, I see that the colors/symbols represent different flight patterns, but what patterns do the authors refer to? 

-    Line 364: “conclude” what?

-    Line 387: As mentioned before, what is implied by “in cloud”? Are these interstitial or residual TBs?

-    Line 393: “trace of water” perhaps that should be “trace of water-soluble matter”? Same for line 397.

-    Line 398: why does the lack of change in shape indicate that the particles are not hygroscopic? 

-    Line 400: I am not convinced that this evidence is very strong as detailed here.

-    Line 415: “Increases of N” is this in TBs only?