This manuscript by Cheng et al. collected samples over three years at an interesting site (North Atlantic). They also used various measurement techniques (e.g., CCSEM-EDS and STXM-NEXAFS) for a significant number of samples as well as modeling and provided a unique conclusion regarding particle phases. Thus, I think this study will be an interesting contribution to our understanding of atmospheric aerosol particles.

Major comments.

1. I suggest including a discussion regarding the effect of relative humidity (RH) on the particle phase. Aerosol particle phases are sensitive to the RH when collected (e.g., Bateman et al. 2014 in the reference list). Inorganic aerosol particles can deliquesce, and organic particles can absorb water depending on RH, changing the shapes of sampled particles. The RH values should be obtained from an in-site measurement, if available, (not from a model result with a low spatial resolution) as the particle hygroscopicity is sensitive to the exact RH during the sampling. Although most particles should be in dry condition judging from Table S2, hysteresis phenomena may affect the particle hygroscopicity (e.g., Fig. S10). The current manuscript has a limited discussion regarding the ambient RH, and I suggest more discussion on RH effects for the particle phases. In addition, surface tension may also influence the height of the aspect ratio of sampled particles, and some discussion regarding surface tension may be useful.

2. The authors discuss the CO source contributions using the FLEXPART model. Although the model is acceptable and useful for CO, I wonder if it can be used to interpret the source of aerosol particles, especially for those with aging more than ten days. CO is gas and will not be removed from the atmosphere. On the other hand, a fraction of aerosol particles will be removed by mainly wet depositions during the transport with more than ten days (Table 1). Thus, it is not sure if the estimates of "contribution of source" in the table are valid for aerosol particles. Some explanation will be needed here.

3. Quality of Supporting information is a problem. The figures and captions include many errors, including the title (!), which is different from the manuscript. I wonder if the authors submitted the correct one or a draft version.

Specific comments.

4. Line 158. "an environmental SEM (ESEM) equipped with a FEI Quanta digital field emission gun, operated at 20 kV" and line 213 " Environmental Scanning Electron Microscopy (ESEM, Quanta 3D, Thermo Fisher)"

Are they different ESEM or the same one? The ESEM in line 158 is used for the CCSEM-EDS? It isn't very clear, and please specify them clearly.

5. Line 193 "inorganic components (In)"

In, IN, and "inorganics" are inconsistently used. For example, In is in line 207, "inorganics" is used in line 209, and IN is in line 324. In addition, "In" is confusing as it is like In (preposition).

6. Line 296-297. "Our particles are internally mixed based on tilted transmission electron microscopy (TEM, the titled angle was 70°) (Fig. S8)."

Please explain how to see Fig. S8, i.e., how the TEM image indicates internally mixed particles. Same for the description in line 328

7. Line 317-319. "Sulfate (CNOS and sea salt with sulfate) particles are also very abundant in all samples (~18 to 34 %), suggesting that these particles were involved in cloud processing (Ervens et al., 2011; Kim et al., 2019; Lee et al., 2011, 2012; Zhou et al., 2019)."

I am not sure why they were involved in cloud processing. Sulfate can originate from various processes. Does it mean organosulfates (CNOS)??

8. Line 324-325. states of OC (green), IN (blue), and EC (red) found in S3-3 and S4-2, which are (a) organic particle (green), (b) EC core (red) and coated by OC (green), (c) internally mixed EC (red) and In (cyan) coated by OC (green), and (d) In (cyan) coated by OC (green).

Both "cyan" and "blue" are used for In. I think it should be blue or IN and In are different??

9. Line 373-375. "These results suggest that apart from environmental factors, the inorganic components, the molecular weight of organic compounds, and the O/C ratio (or aging time) all affect the phase state of internally mixed particles."

They are true at specific RH values. For example, < RH 80%, ammonium sulfate is solid (crystal), and > RH 80%, they become liquid (deliquesce). These factors change the specific RH % that changes the particle phase state. Although it says "apart from environmental factors", some words about RH will be useful. Please see my comment 1.

10. Line 409-410. "Typically, particles with the same area equivalent diameter but higher TCA are more viscous (more solid-like) since they are less flat in shape (Fraund et al., 2020; Tomlin et al., 2020)."

The particle height may be also influenced by its surface tension if they are liquid. Please see my comment 1.

11. Figure 1. Please indicate what are the color indicate and what are the boxes and numbers.

12. Figure 2. These "solid black cycles" (circle?) are difficult to see with dark blue background.

13. Figure 3. Although I can imagine what the inserted normalized number fractions with size distributions in the upper right of each panel mean, it is better to have some explanation, especially the meanings of Y-axes.

14. Figure 4. Please indicate which samples were used for each panel.

15. Figure 5. Is panel (b) SA1 or SA2?

Table 1 indicates that 29.8% of SA1 particles are solid. Although I see SA1 includes relatively more semisolid particles, I cannot see solid particles. Could you indicate some examples of solid particles in the SEM images using ambient samples?

I also suggest adding RH values when collected for these samples.  

16. Figure 6. In panel (a), there are 3 or 4 solid particles in SA2, but the solid particle % in SA2 is 0.0 in Table 1. Are they correct?

Supplementary information

I do not think I could indicate all errors. Please check the data carefully (or maybe it is a wrong file?).  

17. The title is different from the main text.

18. Line 21. "where Tg,w is equal to 136 K, is the Tg for pure water,"

Tgw is 136K, correct?

" is the Tg for pure water " is correct?

19. Equation S3. C_real=(123.2±1.4)−(4.738±0.214)log(H)−(1.186±0.02)C_measured.

This equation indicates that less measured C atomic percentages yield a high "real" C percentage. I.e., if a particle includes no measured carbon percent (0%), it will have ~100 % of real C percent (by assuming H = 1). Although I do not have a way to check the accuracy, it is difficult to believe the result without more explanation. The calculation may influence the results in Figure S2, in which a fraction of particles consists of only C (no O nor other elements).

The equation S4 is also questionable. How can O=0%, which is seen in Fig. S2, be achieved?

O_real=(13.68±0.18)−(0.3413±0.0636)log(H)+(0.2579 ± 0.0072)O_measured (S4)

20. Line 49-51. "Since the particles are spheric, the measured area equivalent diameter (μm) is approximately equal to the height of particles. Therefore, when applying the correction function on our CCSEM-EDX data, we need to estimate the H by dividing the longest diameter retrieved from CCSEM-EDX measurement by the aspect ratio retrieved from tilted images (see Sect. 3.3.2). "

Do you have all aspect ratio data for all EDS measured particles? I think the aspect ratio was measured using ESEM, and the EDS was by CCSEM-EDS.

21. Table S1. Are there CCSEM data that can be listed for these samples?

22. Figure S2. These data, especially for C, look different between those from SA1 to S6 and those from S3-1 to S4-4 (different sampling periods). Are there any technical differences?

Potassium (K) may be used for a biomass-burning tracer. Have you checked it?

23. Figure S3. If you go to "No" and "No," you will find a question "Al+Si+Fe+Fe>Na", where you have double Fe.

24. Figure S4. Panel (a). There is "S-2," but it should be "S3-2." Y-axis should have "100" instead of "00". The caption should be "June" instead of "Jun."

25. Figure S5. The caption indicates from (a) to (i), whereas the panels are from (a) to (h).

26. Figure S7. "Jun" should be "June." Panel (a) and (b) is upside down. The legend in the panel (a, bottom) is overlapped with the plot.

27. Figure S8. Please indicate where we should see. Please see my comment 6.

28. Figure S9. The colors in OCInEC and In are nearly the same and cannot be distinguished. For example, in panel (f), it is difficult to identify if the light blue is OCInEC or In.

29. Figure S10. "Mean ambient temperature (blue)"

In the caption, the temperature is "blue," but in the legend, it is green. Same for Tg,org.

"(g) S3-2, (g) S4-3, (h) S4-4, and (i) S4-54. " There are two (g) in the caption. (i) should be S4-5 but no (i) in the panel (!!).

"uncertainties in RH (See SI). " Which SI should we see. we are now in SI.

30. References. The reference style is different from that of ACP.

31. Line 134 "Zieger, P. and Va, O" Please check the authors' name.

The authors described the phase states of aerosol particles collected in the North Atlantic FT and tried to explore the transport patterns of the aerosol particles. Such research topic is interesting for the atmospheric communities, and also the scope of the research is suitable in ACP journal. However, after carefully reviewing this manuscript, the evidence are rather weak to support the results, and conclusion is too generalized. In addition, many errors in the text, figures, Tables, and SI can be founded.

Major comments:

• During the laboratory experiments for the phase determination, at which relative humidity and temperature the ESEM did the authors perform? This should be clearly stated in the manuscript. The main issue is that how the authors can conclude the phase states of the aerosol particles if the relative humidity and temperature during the experiments were different compared to the field measurement periods? The phase states of aerosols are temperature- and relative humidity-dependent, and thus it didn’t convince me whether the conclusion is still valid or not. This should be clearly mentioned through the manuscript. The authors should also show the ambient RH and temperature at the monitoring site in a figure and table.
• Regarding the technique of the tiled aspect ratios to determine the phase state of aerosols, I am confusing this technique is reliable for aerosols consisting of mixtures of organic materials and inorganic compounds. The authors should validate and carefully described the evaluation of the results with comparison to previous phase studies using well-known mixtures or commercial standards comprising organic and inorganics. I cannot find such validation from Cheng et al. 2021.
• Figures and SI should be revised (see also below). Moreover, all figures in SI should be mentioned in the main text.

Minor comments:

• Page 5 line 136: The author should provide more details about stored conditions by mentioning temperature. Furthermore, the authors have to mention the stored period before the experiment due to evaporation issue.
• The authors should provide details about the particle regeneration in the experimental section if it regenerated from the collected samples.
• There are too many academic terms in the manuscript and it is suggested to add a table to summarize all acronyms and full names. The authors repeatedly used a similar abbreviation for the OC component with different names such as Organic (OC) (Page 7 line 192), and organic carbonaceous (OC) (Page 6 line 170). Abbreviation similarity should be consistent without repetition.
• Page 4 line 119: The author mentioned “This study focuses on detailed individual particle analysis on Pico 2017”. In addition, on page 6 line 172, the authors mentioned “CCSEM-EDX based particle classification for Pico 2014 can be found in Lata et al., 2021, and that for Pico 2015 will be discussed in our future work”. However, some data relevant to the phase state for the 2014 and 2015 shown in Fig. 5. Also, total carbon absorption (TCA) data showed in fig 6 for Pico 2014, and Pico 2015. It makes confusion to the readers regarding which data Pico 2014, Pico 2015, or Pico 2017 is exactly discussed in this manuscript. To avoid more confusion author has to focus more on Pico 2017 data or the data relevant to Pico 2014 and Pico 2015 should move to SI.
• Page 8: In the result and discussion section, the description of Fig. 1 looks confusing and keeps the reader browsing to keep up with the text. The text is littered with redundant statements in parentheses that re-state what has just been explained. Please specify them clearly.
• Page 10 lines 290-294: More careful and detailed description are needed for Fig. 2 by comparing it with the reported study because size distribution is a very important factor when defining the physicochemical properties of an ambient particle. Also, please add how you measured in Experimental.
• To make this manuscript understandable to the readers, I would like to suggest the authors move data relevant Pico 2014, Pico 2015 to the supporting information. It has been already published.
• The authors didn’t describe clearly which samples were used for Fig. 4 which is relevant to STXM/NEXAFS spectra, Is that data relevant to Pico 2017? Even though there is no clear evidence in the description part (Page 11 line 323 to 329).
• Please clarify the captions of the SI.
• The title should be revised based on the main findings.

Cheng et al. made a comprehensive investigation on the sources, chemical composition, and phase state of long-range transported free tropospheric particles based on individual particle analysis using multi-modal micro-spectroscopy techniques. This study found that most particles were in the liquid state and highlighted the importance of considering the mixing state, emission source, and transport patterns of particles when estimating particle phase state in the free troposphere. Though the findings are expected, the observation data provide valuable information constraining the physiochemical properties of aerosols in the free troposphere which is important in assessing aerosol associated climate effects. I agree with the comments of the other two referees that this manuscript can be published only after a major revision as there are too many errors in the submitted version.

Major comments:

1. My major concern is on the Section 3.3.2, the phase state of particles during long-range transport. The authors mainly investigated the phase state of organic particles applying the temperature and RH along the air mass transport path, and found that organic particles would likely be solid in most of the times. As the particle viscosity depends significantly on RH as pointed by the other two referees, I doubt the meaningfulness investigating the phase state at each air mass path with a wide variation in RH as shown in Fig. S10. I suggest adding a figure showing the variation of predicted viscosity with RH and T (similar to the figures in (Li and Shiraiwa 2019, Petters, Kreidenweis et al. 2019)) and investigating the phase state at free troposphere-relevant conditions. In addition, the authors applied a single value for the dry glass transition temperature, which, however, would be changed due to the change in the chemical composition during the long range transport. Finally, could the authors add some discussion that based on the inorganic component types you have observed, how you expect the phase state variation of inorganic components during the long range transport at free tropospheric RH and T? It would be helpful supporting the implication what you wrote in the Conclusion section that the particles in the FT probably remain liquid.

2. Mixing state plays an important role in the phase state of ambient particles; however, the authors did not mention other factors that may impact phase state significantly. Besides the influences of surface tension on aspect ratio and thus the prediction of phase state mentioned by Referee #1, the influence of particle size should be considered and discussed as well. Several studies have found that the size of particles influence the viscosity (Cheng, Su et al. 2015, Petters and Kasparoglu 2020). Did you see the difference in the phase state between the particles collected on the 3^rd and 4^th states of the impactor? Would the change of particle size affect the phase state during the long range transport? Secondly, the authors only mentioned the inorganic components could decrease the viscosity of internally mixed particles. They missed a recent study showing that increasing inorganic fraction can increase aerosol viscosity through cooperative ion-molecule interactions (Richards, Trobaugh et al. 2020).

Specific comments:

Manuscript:

1. I recall the comments by the other two referees that the RH in the ESEM should be clearly pointed out as the particle phase state depends significantly on RH.

2. Give the full name of “SEM” at Line 68 instead of at Line 71. Are SEM and ESEM the same?

3. Line 125. Change “Experimental” to Experiments.

4. Line 177-178. “87 for S3 and 37 for S5 for Pico 2015, and 142 and 171 particles for S3-3 and S4-2 for Pico 2017”. These data are not same as those in Table S2 and Table S3. Please check which are correct.

5. Line 190, I don’t understand what TCA is proportional to?

6. Line 245. Explain how you determined the air mass source is wildfire from “CO source contributions”.

7. Line 277-281, the data described for SA1, SA2 and SA3 are different from the corresponding data in Table 1.

8. Line 284-286, “and S1, S3, and S6 were influenced by both anthropogenic and wildfire CO emissions in North America (~56 %, ~79 %, ~40 %, and ~59 % for anthropogenic CO source, and ~42 %, ~19 %, ~53 %, and ~25 % for wildfire CO sources, respectively).” Check the values (there are four values for three samples).

9. Line 289. Change “Chemical-resolved” to “Chemically-resolved”.

10. Line 292. Change “>400 particles cm-3” to “>400 particles cm^-3”

11. Line 296. “Our particles are internally mixed based on tilted transmission electron microscopy (TEM, the titled angle was 70°) (Fig. S8).”, Line 328. “This observation is consistent with their STXM images and tilted TEM images (Fig. S8)”. Give a more detailed explanation how an internal mixing state is determined? Line 297. Change “titled angle” to “tilted angle”.

12. Line 298. “Fig. 2(b to i) show” should be Fig. 3(b to i).

13. Line 304. “area equivalence diameter” . Do you mean “area equivalent diameter”?

14. Line 306. The values of 79.6% and 1.1% did not match the values in Table S2.

15. Line 323. “Figure 4 shows the STXM-NEXAFS Carbon K-edge chemical speciation maps and spectra of four typical particle mixing states of OC (green), IN (blue), and EC (red) found in S3-3 and S4-2, which are (a) organic particle (green), (b) EC core (red) and coated by OC (green), (c) internally mixed EC (red) and In (cyan) coated by OC (green), and (d) In (cyan) coated by OC (green)”. Do “blue” and “cyan” both indicate the inorganics? DO “IN” and “In” both indicate the inorganics? And the description here is different from the caption of Figure 4.

16. Line 331. Check Figure S9 is for the results of all samples of only seven samples.

17. Line 332. “S3-3 and S4-4 samples”. Do you actually mean S3-3 and S4-2 samples? I do not see S4-4 in Figure S9, and in Table S2, the sample analyzed by STXM-NEXAFS is sample S4-1. Also check the values that did not match the ones in Table S2.

18. Line 344. “Figure 5 shows violin plots of the ‘corrected’ aspect ratio (left) and representative tilted images (right) for Pico 2014 (a to c), Pico 2015 (d to i), and Pico 2017 (j to q).” The description here is different from the caption of Fig. 5. Correct it.

19. Line 368. “The substantial fraction of solid and semisolid particles might be less oxidized”. In Table 1, I found that SA1 and S6, whose average aging time is both longer than 16 days, have smaller fraction of liquid particles than other samples. Can you explain why the fraction of liquid particles is smaller with longer aging time?

20. Line 379. Change “5(a, d, e, I, and j to o))” to “5(a, d, e, i, and j to o))”

21. Line 383. “For S4-2, a possible reason is that the volatile and less viscous species of particles collected on the TEM grid have already evaporated and left these tiny residuals around those big particles (see Fig. 5(f) right panel) due to difference in temperature, RH, and pressure between OMP and SEM chamber.” Does this problem also exist in the experiments of other samples?

22. Line 402. I did not see the viscosity of BBOA predicted in DeRieux et al. (2018) is up to 10 ¹² Pa s. I suggest you only show what is the range of the viscosity under the atmospherically relevant RH. Add Li et al. (2020) who also calculated the viscosity of BBOA based on volalilty distributions (Li, Day et al. 2020).

23. Line 416. “Shaded areas represent regions of different phase states (liquid: blue, semisolid: green, and solid: red), with the boundaries of each region based on (O’Brien et al., 2014).” Can you give a more detaied explaination how to get the boundary lines?

24. Line 430. “We used the density (ρ_org), hygroscopicity (κ_org), and dry glass transition temperature (T_g,org,0) of organic particles as reported by Schum et al., 2018 (see SI) since we do not have molecular compositions for our samples and Schum et al., 2018’s samples were also collected at OMP during the same seasonal period (June and July).”. The previous analysis in this manuscript mentioned that the composition of organic matter is quite different for different samples. Therefore, T_g,org,0 would be changed. There are three samples in the study of Schum et al. (2018), and the estimated T_g are also varied. Discussion of the uncertainties in T_g,org,0 is betted added.

25. Line 441, also cite (Schmedding, Rasool et al. 2020, Li, Carlton et al. 2021).

26. Line 490, cite (Li, Carlton et al. 2021, Shrivastava, Rasool et al. 2022).

27. Line 930. Change “solid black cycles” to “solid black circles”?

28. There is no need to use italics in the columns 12 and 13 in the first row in Table 1.

29. What does the colorbar in Figure 1 indicate?

30. The inserted figures should be described in the caption of Figure 3.

31. Change “SA1” to “SA2” for panel b in Figure 5.

Supporting Information：

Line 2. The title in the supplementary is different from the title in the manuscript.

Line 21. “where T_g,w is equal to 136 K, is the T_g for pure water”. Cite (Kohl, Bachmann et al. 2005).

Line 29. “Moreover, k_GT, T_g,w, κ_org, and ρ_org were assumed to be 2.5 (Shiraiwa et al. 2017), 309 K (Schum et al. 2018), 0.12 (Schum et al. 2018), and 1.4 g cm^-3 (Schum et al. 2018), respectively.” Why 309 K is for T_g,w？Check it.

Figure S2. What the x-axis stands for in figures b to r?

In Figure S2 and Figure S3, are the relative atomic ratios of elements same as the relative element weight?

Figure S4. Change “Jun” to “June”.

In Fig. S5-S6, I don’t understand why the residence time is in percentage and how did you calculate it?

In the caption of Figure S10, “Mean ambient temperature (blue) and the predicted RH-dependent T_g,org values (green)”. The ambient T is actually in green and T_g,org is in blue in the figure.

References

Cheng, Y., H. Su, T. Koop, E. Mikhailov and U. Pöschl (2015). "Size dependence of phase transitions in aerosol nanoparticles." Nature Communications 6: 5923.

Kohl, I., L. Bachmann, A. Hallbrucker, E. Mayer and T. Loerting (2005). "Liquid-like relaxation in hyperquenched water at [less-than-or-equal]140 K." Physical Chemistry Chemical Physics 7(17): 3210-3220.

Li, Y., A. G. Carlton and M. Shiraiwa (2021). "Diurnal and Seasonal Variations in the Phase State of Secondary Organic Aerosol Material over the Contiguous US Simulated in CMAQ." ACS Earth and Space Chemistry.

Li, Y., D. A. Day, H. Stark, J. L. Jimenez and M. Shiraiwa (2020). "Predictions of the glass transition temperature and viscosity of organic aerosols from volatility distributions." Atmos. Chem. Phys. 20(13): 8103-8122.

Li, Y. and M. Shiraiwa (2019). "Timescales of secondary organic aerosols to reach equilibrium at various temperatures and relative humidities." Atmos. Chem. Phys. 19(9): 5959-5971.

Petters, M. and S. Kasparoglu (2020). "Predicting the influence of particle size on the glass transition temperature and viscosity of secondary organic material." Scientific Reports 10(1): 15170.

Petters, S. S., S. M. Kreidenweis, A. P. Grieshop, P. J. Ziemann and M. D. Petters (2019). "Temperature- and humidity-dependent phase states of secondary organic aerosols." Geophys. Res. Lett. 46.

Richards, D. S., K. L. Trobaugh, J. Hajek-Herrera, C. L. Price, C. S. Sheldon, J. F. Davies and R. D. Davis (2020). "Ion-molecule interactions enable unexpected phase transitions in organic-inorganic aerosol." Science Advances 6(47): eabb5643.

Schmedding, R., Q. Z. Rasool, Y. Zhang, H. O. T. Pye, H. Zhang, Y. Chen, J. D. Surratt, F. D. Lopez-Hilfiker, J. A. Thornton, A. H. Goldstein and W. Vizuete (2020). "Predicting secondary organic aerosol phase state and viscosity and its effect on multiphase chemistry in a regional-scale air quality model." Atmos. Chem. Phys. 20(13): 8201-8225.

Shrivastava, M., Q. Z. Rasool, B. Zhao, M. Octaviani, R. A. Zaveri, A. Zelenyuk, B. Gaudet, Y. Liu, J. E. Shilling, J. Schneider, C. Schulz, M. Zöger, S. T. Martin, J. Ye, A. Guenther, R. F. Souza, M. Wendisch and U. Pöschl (2022). "Tight Coupling of Surface and In-Plant Biochemistry and Convection Governs Key Fine Particulate Components over the Amazon Rainforest." ACS Earth and Space Chemistry 6(2): 380-390.