Please see the attached file "amt_2023_143_round1.pdf".

This paper describes an ozone and meteorological measurement system mounted on two different hexacopter UAS, flown over land and near water, and compared with fixed sensors.  UAS measurements in the atmosphere are rapidly becoming more common (as demonstrated in the references cited here), and though they have limitations from instrument weight and power consumption, they could potentially make important measurements of meteorology, atmospheric trace gases and aerosols.  This work can be considered as a step toward progress in this area, especially in terms of the high spatial resolution measurements useful in studies of the boundary layer and lake breeze/land breeze events.  However, the manuscript in its current form is not as informative as it could be, and could use a bit of rewriting.  To make a more meaningful contribution to the literature, I recommend the following changes:

The paper should be restructured to emphasize the measurement technology aspects, both since it is in review at Atmospheric Measurement Techniques, but also because this is really much of the new and useful information contained in the manuscript.  (Although I also agree that section 3.3 has some interesting science in it.)  First, I would move the paragraph about the Personal Ozone Monitor (POM), now 2.3, to the start of the Materials and Methods and make it 2.1.  The iMet sensor could go right after that.  The authors can decide whether to have a section of its own for the UAS used in the three studies, but right now there is just the bare minimum of description of the two UAS.  Can anything be added to describe why these were chosen, what the necessary characteristics of a UAS for this research are, how they worked as an airframe/sensor package, and how they could be improved?  Also, the introduction could be changed to emphasize more the potential for UAS measurements in the boundary layer or near-shore environment to add to our understanding of chemical composition and atmospheric structure there.  This might only require a few sentences added or rewritten, but it would help the paper become more coherent and targeted.  Finally, in the Results and Discussion section, how do these results compare with the previous experiments of Li et al. 2020 for ozone?  The POM (because of its very low weight and power consumption) is a very attractive sensor for UAS use, but did it work?  Can it work?  If not, what sensor (from 2B or elsewhere) would be needed, and how much extra weight does that require?  What would need to be changed to optimize the UAS for this kind of experiment?  Again, this should not take a lot of space, but would improve the impact of the manuscript.

Specific comments:

P.1, l. 30 “organic decomposition”?  Some biogenic VOCs are emitted through decomposition processes, but other natural sources like isoprene, terpenes, and some alcohols are emitted directly from plants.

P.2, l. 42-44 There is nothing in the Beekman et al., 1997 reference about tethered balloons over water (it does discuss tropopause folding events).  Is there supposed to be a different reference for the first part of this sentence?  But really, the two parts of this sentence don’t go together (ground to 1500 m vs. upper troposphere).

l. 48 I think this reference should be to Li et al., 2020 (comparison with the airship), not 2021 (primarily VOCs, and I saw no mention of an airship in the manuscript). Is Li et al., 2020 the most closely related paper to this manuscript (or perhaps that is Guimaras et al., 2020, or Gronoff et al., or several of them)? It does use a fixed-wing UAS rather than a hexacopter though.  But it seems to have a thorough evaluation section of the instruments and measurements.  It seems like the discussion section of this manuscript might need to include a bit more related to this paper.  Are your results comparable or similar to Figure 5a (or 7a, or 8) in Li et al., 2020?  In addition, please take a look at papers citing Li et al., 2020.  A few relevant ones are cited here (such as Q. Chen et al., 2020), but I think there are a couple of others that might be cited as well.  How about L. Chen et al., 2022?  I did not do a thorough search; the authors should do that.

l.49 What is the correct reference here?  I did not notice anything in either Li et al. paper about Generalized Additive Models, but I did not read either of them thoroughly.

P.3, l.82 That is great that there is “improved performance and viability” but is that shown or demonstrated in the following sections?  How can you do that without referring back to the results in the cited literature?

P.5, l. 125 A 15 minute flight time is not ideal.  Is there any way to get a similar platform with longer flight duration?  (Again, this can be addressed in the discussion section.)

P.6, l. 180 Why does the filter need batteries or power?  Perhaps I don’t understand what the filter is, or what it is used for.

P.7, l. 184 Are these the actual accuracy and precision (considering the comparisons with other instruments) or just calculated from the formula from 2B?  line 202 would suggest that the accuracy is not as good in flight.  And compare with l. 245-246 and l. 252.  Seems like the text needs to be made consistent on this.

P.8, Table 1 The gradients measured by the POM were generally not distinguishable from zero.  So the statement on l. 201 is technically true, but not very helpful.  Glad to see that the results led to the subsequent improvements described later in that paragraph.

P.11, Figure 3a How does this figure compare with a similar one in Li et al. 2020?  (See earlier comments above.)  Again, this can be addressed in the discussion section or wherever it makes the most sense.

P.14, l. 313 This sentence is a little confusing, with both tethered balloons and UAS.  I think it can be changed slightly to make it clearer.

P.15, Figure 4 I find it hard to distinguish the two profiles on June 18.  By adding a top axis for ozone, you would have 4 traces on panels b, c, and d, so that might be confusing too.  Perhaps just making the traces line+symbols (by adding reasonably thick gray and black lines for the two profiles, respectively, to the color-coded circles) it would be easy enough to follow.  Right now, I had to examine this figure very closely while reading the text on P. 13-14 in order to understand it.

P.16 After editing the rest of the paper, perhaps the conclusions section could be strengthened and made more useful to readers.

P.17-24 There is an extensive reference section, but a few of the references I checked do not seem to correspond to what is in the main text of the manuscript.  Is it possible to check at least the most important references against the text?  Maybe all of them?

Figure S3 I can’t tell the difference in the symbols between the two tower instruments.  But that’s probably OK (if they agree with each other); the colors clearly mark the different elevations.  In the legend, can you put the two 122 m symbols next to each other?  The figure clearly shows the data from both the tower and the UAS.

I don’t think you really need all the Figures S4-S10.  Just one or two for reference would be fine.

Perhaps the same comment for Figures S12-16, though these are at least related to the data shown in Figure 4.

I definitely think that some of Figures S17-21 could be dropped.

In Figure S22, are the dashed lines a running average?  Perhaps that should go into the caption.

Technical and proofreading comments:

P.2, l. 57 “create”?

P.3, l. 93 “and”?  “on land”?

P.5, l. 115 Are the times correct for 2020 flights?  Just wondering, because 6 pm is later than 11 am.  Maybe just reorder the two times.

l. 130-132 This sentence is a little odd-sounding. I assume the UAS measurements were just a small part of the overall campaign. (It’s fine up to “shoreline”, but then rest of the sentence implies that the UAS was the purpose of the project.)

P.6, l. 168 Please add a comma after “spectroscopy”.

P.13, l. 308 What do you mean by “fumigation”?  (This may be OK, I’m not sure.)