Dear Authors:

Thank you for your response to the referee comments and your manuscript revisions. Both referees expressed that the manuscript would be strengthened by further calculations/analysis and one felt that it should be recharacterized as a measurement report if no further analysis was performed. Given the unique aspects of the dataset and the analysis included, I support publication as a research article. After carefully considering all the documents, it is my opinion that several revisions are required before the manuscript is suitable for publication in ACP. Several of these relate to instances where responses to referee comments were informative in the response document but were not included in edits to the main document. Please consider the comments below. Unless otherwise noted, line numbers refer to the track changes version of the manuscript.

Main comments

1. I suggest you consider rewriting many of the chemical formulas to better reflect the ions. For some (non-exhaustive) examples HI2O6- is probably better written as (HIO3)IO3-, (SO4)H3O- is probably better as (H2O)HSO4-, (SO4)3H5- is better as (H2SO4)2HSO4-, etc. This will be more aligned with how these ions have been represented in past works and also increases the ease of reading.
2. Section 2.1: Please add more details regarding the PSM even though more extensive details are given in the cited work. It is important that the basics are conveyed without having to reference another manuscript. Something along the response given to Dr. Brean’s comment regarding line 98 (of the original document) is sufficient.
3. Line 117: Please add a sentence or two similar to the response given to Dr. Brean’s comment regarding line 117 (of the original document) regarding the similarities/differences to PSCF.
4. Line 144-145: “…(NH3(H2SO4)3HSO4-, in the peaklist unknown0085).” is confusing wording to the reader. I suggest that you make it clear that this peak was assigned later on and provide the ppm difference between the assignment and the unknown. Please also include the assignment in the peak list.
5. Lines 153-155: The wording here makes it sound like the lack of peaks can be quantitatively explained by these factors. I suggest rewording to make it clear these are possible reasons.
6. Figure 1: I suggest considering enhancing the intensity of the peaks above approximately m/z 250 by using a scaling factor. Alternatively, a log scale y-axis may make it easier to see some of the peaks.
7. Figures 2 & 3: Personally, I found the examples presented in the response to questions posed by both referees more compelling as it further enhanced the strong relationships that are discussed in the manuscript. Particularly the strong positive correlations get lost when overlaid on the numerous slightly positive correlations. Additionally, I’m not sure if this is possible, but is there a way (perhaps using coloring) to identify the ions that are called out in table 2? That would help the reader follow the arguments made in the manuscript.
8. Line 295: Following up on Dr. Brean’s comment, the diel profile may be more consistent with organonitrate production from NO3 radical chemistry than from OH + NOx chemistry. This could plausibly explain the difference in the diel profile between your work and the Bianchi et al work.
9. Line 355: I suggest including the further information on the attribution of non-sea-salt sulfate from DMS and SO2 from Australia provided in response to Dr. Jokinen’s comment on line 344.
10. Figure 8: I don’t understand why from ~12:00-19:00, the N1-10 timeseries in the lower panel of (a) is at zero while the upper panel shows high counts in the 2-10 nm region for most of the time period and N1-3 is also non-zero. Is it because these are all from different instruments? If so, how does this disagreement impact conclusions/interpretations about particle counts at these lowest sizes throughout the manuscript?
11. Discussion starting at line 423: API-TOF is best suited for capturing NPF happening at the measurement location and thus events identified as transported events in your previous work would likely not be observable as the characteristic NPF API-TOF peaks. I think it would strengthen the manuscript to include some of the information provided in your previous manuscript about if any/all of these were classified as transported events by your previous analysis and thus might explain the lack of larger ions observed by the API-TOF. Are there differences in the ions observed between transported and regional event days?
12. Figures 9 and 10: I agree with both referees that it would be nice to see this version in a non-stacked view so that the reader can more clearly see the diel variations. I agree with your point in the response that the figure is too busy when all of the ions are included. However, many of the ions/ion groups are extremely low and poorly resolved in the current figure as well. I think a simplified figure including the most important ions (either because of overall intensity or because they are discussed substantially in the manuscript) would be appropriate. Placing such a figure in supporting information would be appropriate. In Figure 10, please state the number of event and non-event days.

Technical

1. Line 106: Please specify the inner and outer diameters of the tubing. Please also provide the flow rate into the instrument.
2. Both m/Z and m/Q are used in the manuscript. Please standardize.
3. Lines 169-170: Everything in the list with the exception of HOMs are given in their ion form. I suggest saying identifying HOMs as the observed ion (e.g., HOMs clustered with NO3-).
4. Lines 257-258: Please include units on the condensation sink values.
5. Figure 6: Please include a legend for land and marine. I also find this figure very difficult to read as the panels are small and the seasonal variations are muted due to the use of a log scale. In figure 5, the diel cycles were more apparent making the figure easier to interpret than this one. I suggest considering only showing the most important panels in Figure 6 in the main text and making them larger. The other ones can be put into supporting information. Would a non log plot help make the seasonal cycles more apparent?
6. Section 3.5.2: I think the name of this section should be modified to reflect that it discusses sub 10 nm particle days and not specifically true NPF.

Congrats!