Please find attached the comments on amt-2024-84.

General comments

The authors assess the impact of the different calibration methods used in the GAW-PFR and SKYNET networks on the AOD retrievals. For their analysis they use data from inter-comparison campaigns that took place in Davos and Rome.

While the study is scientifically sound the language of the paper must be improved substantially before it is published. In the following I recommend some indicative linguistic and technical corrections, but further work has to be done by the authors. Ideally a native English speaker should edit the manuscript.

Minor corrections

The authors use many acronyms in the document. A table summarizing the acronyms and their definitions would be useful for the readers.

I also recommend that the authors should write a few lines (e.g., in the introduction) about the novelty and the usefulness of their study.

L18: “The major”. Do the authors mean “The main”? Furthermore, while the authors write here that AOD uncertainties are mostly due to the calibration method, in lines 22-23 they write that they did not find any association between the calibration performance and the variability in aerosol properties. This is confusing.

L19: “Underestimation of AOD compared to GAW-PFR”. The AOD from which network?

L20: “Underestimation in the ILP calibration”. What is underestimated?

L23: “variability in” instead of “variability of”?

L28-29: “between … calibrations”. Do the authors mean the AOD retrieved the two methods?

L31: “AOD retrieved using ILP” instead of “ILP”

L40: The phrase “the major driver” is not correct. It should be either “the main driver” or “a major driver”

L43: Delete “a”

L47-48: “AOD is … of aerosols”. Please rephrase.

L63: “Due to the differences …”. Differences in what?

L66: “of all types” instead “from all types”

L69: “that the instrument” instead of “the instrument”

L70-73: Please re-write clearer. Furthermore, the next sentence (“The conventionally … instruments”) repeats the same things that the authors write in lines 70-73.

 L85: Replace  “One of the main differences are”  with “One of the main differences between … is”

L91: “a Memorantum of Understanding” instead of “and Memorantum of Understanding”

L96: “using both,” instead of "both with”

L118: “centered at” instead of "centered on”

L141: “or diffuse sky radiance” instead of “and diffuse sky radiance”

L226: “the difference  … 1-2 nm”. Is there any reference that can be used to support this statement? Can the authors explain why the difference can be up to 2 nm?

L235: “differ in” instead of “differ on”

L253: Larger than what?

L266: add “were used” after “retrievals”

L282: Is there any reference for Eq. 8?

L292-293: The manuscript is not clear at this point. Do the authors mean that the TOC from OMI overpasses is used in the PFR algorithm?

L332: “number of retrievals” instead of “retrievals”

L366: “II and 3”: please be consistent with the numbering

L373: Delete in that case”

L375: Using the same numbering in the supplement and in the main text is confusing. Please change the format of the numbering in the figures and tables in the supplement (e.g., Fig. S1, Fig S2, …, Table S1, …).

L407: “due to” instead of “due”

L412: Changes in the instruments’ performance?

L414: “An … 870 nm”: Please rephrase

Figures 2-4: It would help to somehow show the months at which each box corresponds.

L460-461: Please rephrase.

L467: “was found” instead of “in”?

L483: As an additional indicator?

L511: “for both locations” instead of “both locations”

L513-514: Delete “and”

L561: “% difference” instead of "%difference”

L562: and the transferred calibration?

L572: Delete “be”

L578: “At  … Rome”: Please rephrase

L582: “at 870 nm it is” instead of “at 870 nm”

L606: “that there is a” instead of “the significance of the”

L618:”and thus it may show” instead of “it may show”

L625: “-0.004” instead of "-004”?

L716: in the PFR performance?

L730: “is” instead of “.is”