General comments:

The authors present the field observation data of atmospheric trace components observed at a remote island in Japan and analyze the data using a backward trajectory technique, a three-dimensional model, and source apportionment based on a multiple linear regression method. Materials presented in the manuscript are interesting and well suited to the scope of the current journal. The manuscript is well written, and the logic is fine. The manuscript will be accepted in the journal after the authors revise the manuscript by reflecting the following general and specific comments.

1. The authors use the term “anthropogenic sources”, but it can be divided into combustion and non-combustion sources and this separation might be the key to the study. BC and CO are mainly coming from the combustion sources, and probably so as Pb, but may not the case for Cu. Could you stress more on the existence and impacts of non-combustion sources of elements for your analysis? For instance, does the IMPACT model consider non-combustion sources for Pb and Cu? If not, can it be a cause of underestimation of simulated Cu at the observation site? If the authors neglected the contribution of elements from non-combustion sources because the sizes of aerosols are larger than PM₅ and thus the out of scope of the study, please mention this in the manuscript. There may be certain levels of non-combustion origins for anthropogenic Fe, too.

Specific comments:

Abstract:

2. Ln. 10: “impact ocean biogeochemistry” -> “impact human health and ocean biogeochemistry”, because the authors mentioned the impact of human health as well, in the latter part of abstract (Ln. 26) and in the Introduction section (First paragraph, regarding reactive oxygen species).

3. Ln. 13: “S” is not mentioned in the abstract and rather “Mn” may be an important element in this study. Please consider including Mn in the sentence, at least. It is up to authors’ decision whether to exclude S from the sentence, though.

4. Ln. 20: It is relating to the major comment #1, but I am not sure whether derivations of Pb/CO and Cu/CO ratios are meaningful or not, because numerators (Pb and Cu) may come from both non-combustion and combustion sources, while denominator only comes from combustion sources.

Material and methods:

5. Ln. 119: “15 and 50 kV”. Why are two different voltage levels used in the analysis?

6. Ln. 128: Please explain more about the “uncertainties” here. What are the exact measures for the values? Are they normalized errors? Are they the uncertainties of PX-375 data against the reference data, that are measured by IC and ICP-MS? Or are they relative errors between PX-375 and IC/ICP-MS?

7. Lns. 142-145: Please include time period also. “(6600)” in Ln. 156 may be the number of trajectories but I have no idea why the total number is 6600. Time resolution of trajectory is hourly, so 24 (hrs) x 3 (layers) x 90 (days) = 6480, a little bit different from 6600, but anyway the same order. However, as written later in Lns. 157-158, L in Eq. 1 is based on 4 hourly values to match with the time resolution of PX-375, so that the orders of L may be smaller, around 1620, right?

Results and Discussion

8. Lns. 190-191, “with small Japanese emission impacts”: Fig. S2 indicates the residence time of trajectories and does not tell the impact of emissions. The impacts of emission depend on emission flux and distance from the source. Please rephrase the relevant sentence by what Fig. S2 really tells.

9. Lns. 192-193: It is not clear why the authors present Fig. S3. Probably “Notably, air masses … during the observation period.” is the reason why, but some more words may be needed to make the readers compelling. Please add some more words to explain why the fact that no correlation is found between residence time over the continent and APT in Fig. S3 is important for the analysis (and for which analysis?) of this study.

10. Lns. 243-245. “rainout” means in-cloud scavenging, right? “wet depositions” includes both in-cloud and below-cloud maybe. Do the authors intend to mean that the deposition mechanisms of BC and Pb/Cu are different? Or the same (both removed by in-cloud and/or below-cloud scavenging)? Anyway, please explain why the authors assume so? Is it because mixing-state and sizes of BC, Pb, and Cu are different (or similar) with each other?

11. Ln. 274, Fig. 4: Please reconfirm the unit of APT. It was “mm h” in Fig. 3 as well as main text, while “mm” here. Please also check it in Figs. 5, and S10, and elsewhere, if any.

12. Ln. 277: “Cu has characteristics of emission and mixing states different from BC and Pb”. This is interesting and can be an answer for my comments #1 and #10. Not only “emission” and “mixing state”, but also “size” may be an important factor to affect wet removal and thus determine the transport efficiency, but why is it not included? Is “size” already included in “emission” or “mixing state”?

13. Ln. 295: “the removal processes and emissions of Cu were not properly simulated by the IMPACT model”. I have an opposite impression from the authors for what Fig. 5 tells: constant Model/Obs ratio of Cu for different APT regions means wet removal processes of Cu in the model were rather successful! Could you explain more about the difference of wet removal calculations for BC, Pb, and Cu in the IMPACT model? (It should already be written in the description paper, Ito and Miyakawa, 2023, but please explain here again, because trends of BC/Pb and Cu are remarkably different in Fig. 5).

14. Ln. 304, Fig. S7: Are they correlations for observations or IMPACT? The panels look correlations for observation data, but from the main text, they might be the data of IMPACT, because the relevant paragraph in the main text mentions IMPACT in the beginning. Please specify.

15. Ln. 357: “dust-Mn concentrations were underestimated by the IMPACT model”. Why could it happen, although the simulated dust-Fe is successful? Dust-Mn and dust-Fe are simulated using the same total dust mass concentrations, right? I mean, dust-Mn and dust-Fe are derived from the common dust emission scheme. Is it because the Mn-content set in the model (global scale?) is very different from that in reality (Asian dust)? How are the Fe and Mn contents in the model different (or similar) from NIES CRM NO. 30 Gobi Kosa Dust, for example?

16. Lns. 383-386: I am wondering if the denominators in Fig. S11 of all studies (Jeong, Wang, and IMPACT) are the same. Are they really PM_2.5-dust only or total PM_2.5 concentrations during the dust events, which includes components other than dust. The simulation may be the former, but for observations could be the latter.

Conclusions

17. Lns. 457-458, “such as elemental concentrations and mixing states”. Probably size distribution is also important, as commented in #12. Or does the term “mixing state” include size information as well?

Supporting information

18. Sect. S1: Cl^- is used for the contribution of sea-salt particles but it is evaporative so Na⁺ may be a better indicator. Na⁺ may be difficult to be analyzed by ICP-MS or PX-375, but you have IC data, right? Why didn’t you use IC Na⁺ data for your analysis? This is also an additional comment on the main text, in Lns. 228-231, instead of Ca²⁺, non-sea-salt Ca²⁺ (derived by assuming Na⁺ as fully originated from sea-salt) can be a better indicator for dust aerosols. (Certainly, you don’t need nss-Ca²⁺, as you have already Si as a good indicator)

19. Caption of Fig. S8: what do you mean by “stacked”? (MPOA was stacked on the modeled SS).

Abstract:

Ln 10: 1^st sentence can be changed to ‘Trace metals in aerosol particles impact Earth’s radiative balance, ocean biogeochemistry, and human health.’ (as mentioned in the introduction). Also removing ‘therefore’ from the second sentence is suggested since it is not a conclusion for the previous one.

Ln 26: Using the word ‘Minor’ for anthropogenic contribution of Fe is not recommended. Maybe using the term ‘not dominant’ like used in conclusions is better.

Introduction:

Ln 42: Change ‘has been concerned’ to ‘has been a concern’.

Materials and methods:

Ln 118: Was the 4h analysis time period used so that sufficient mass could be collected on the tape, or for some other reason?

Ln 128: How were these uncertainties calculated?

Ln 146: Is there a particular reason why three-day APT was considered?

Results:

Ln 250: States that ‘Cu has different emission sources from BC, Pb and CO’. The correlations of Pb and Cu v/s BC/CO are not drastically different, so can that really imply a different emission source altogether?

Ln 690: Fig 4 and 5 give units of APT as mm, whereas Fig 3 gives it as mm h. Which is the correct one? Please check other figs in SI as well.

Ln 295: Looking at Fig 5, it seems that Cu is simulated well by the IMPACT model, due to its consistent M/O across different APT ranges, but the text states otherwise. Can you elaborate more on this?

Conclusions:

Ln 448: States that ‘emission sources of these metals share the region where the large CO (and BC) emission sources are located.’ I understand that this conclusion is based on CWT results. However, it is confusing to understand that Cu has a different emission source based on correlations but a similar region of emission. Please explain this part more clearly, and make edits to similar sentences made in the abstract and results too.

Ln 460: BC is used as a tracer for anthropogenic emissions. What is novel about this part?