Dear authors,

Thank you for submitting your revised manuscript. One of the referees of your initial submission provided a review of this revision as well; the other declined. The former reviewer was satisfied with the changes made. From my own reading, I concur with the reviewer, although have a small number of other minor points I feel should be addressed before publication. I therefore would like a few more minor revisions before the paper is accepted for AMT. I don’t anticipate a need for a further round of review following these.

My comments are as follows:

Section 2.2: Your Supplement contains maps showing the locations of the various monitors in each region. I think that it would be beneficial to move Figure S4 (the map for Pittsburgh, PA) to the main paper file. This is the example “dense” network and it will be useful for the reader to see the distribution of sites (regulatory and low-cost) more clearly. Unfortunately, I know a lot of people won’t look at the Supplement. The other maps of this type are probably fine to keep in the Supplement because there are far fewer monitors in them.

Line 157: There is a missing section reference here (“(see Sect. Error! Reference source not found.).” appears in the manuscript). Please check and correct.

Lines 206-208: “This represents a Level 2 data product, meaning that it includes geophysical variables derived from raw satellite data, but has not yet been transformed to a new temporal or spatial resolution, as is the case for data derived from multiple satellite passes, e.g. monthly average AOD data.” This is not quite true, because MAIAC is in fact transformed from the (irregular) satellite swath grid to an Earth-referenced grid. Also, many level 2 products also coarsen their data compared to level 1 resolution. So I’d streamline this sentence to say something like “This represents a Level 2 data product, meaning that it is provided as a snapshot at the satellite overpass times and has not been aggregated to coarser (e.g. monthly) temporal resolution.” That seems to be the main aspect you were trying to capture with this text.

Section 3.5: I did not find an explicit definition of the seasons used in the paper (here, earlier, or the Figure 7 caption). This should be added somewhere.

Figure 8, and associated discussion: it would be useful to provide uncertainty estimates for these metrics like correlation coefficient. This could be done by e.g. the bootstrap method (sampling the data with replacement many times and showing the resulting standard deviation of the estimates). It is not clear to me how distinct some of these results are from one another given the different data volumes at different locations. This should then be borne in mind when making conclusions.

Lines 516-518: this is true for polar-orbiting sensors, although less so for geostationary platforms. However, until recently the geo sensors haven’t been as capable as polar-orbiting ones so these data haven’t been so widely-used for AOD retrieval. A MAIAC-based approach has been used before, though, e.g. Zhang et al (2011: https://www.atmos-chem-phys.net/11/11977/2011/ and 2013: https://www.atmos-meas-tech.net/6/471/2013/ )

I’d note also that your Figures using Google Maps for the background require attribution of the data sources more directly – see the Google Maps reuse guidelines at https://www.google.com/permissions/geoguidelines/ and, more specifically, https://www.google.com/permissions/geoguidelines/attr-guide/ .

Please let me know if you have any questions.

Best wishes,

Andrew

Dear authors,

Thank your for submitting this further revision. I have read through and am pleased to accept this version of the study for publication in AMT.

For the public record, I note that this revision includes an additional affiliation for the first author of NASA GSFC, which is the same institution at which I work. This affiliation was not present in the initial submission of this manuscript (which included only the French affiliations), and so I was not aware of the shared affiliation until now. I have not to my knowledge met or corresponded with this author. I do not believe that this has affected my handling of this manuscript.

Best wishes,

Andrew