This paper describes the global distribution of tropospheric N2O mixing ratios measured during the airborne Atmospheric Tomography (ATom) mission.   Much of the paper focuses on the technical aspects of the retrieval method, while the last sections focus on the interpretation of the data, which involves many other co-measured species and complex comparison of profiles and scatterplots.  Overall, this is an important dataset that definitely merits publication.

Below are some suggestions to help clarify and improve the presentation.

Abstract, Line 46-47 (and similar statements in the Conclusion). “This retrieval strategy improved the precision of our N2O measurements by a factor of 3, enabling us to recover the precision to that of previous missions.”  This sentence is confusing since it doesn’t provide a reference point for the factor of 3 (e.g., is this relative to UCATS and PANTHER, to previous QCLS measurement on HIPPO, or something else?).  Also, the use of “recover” implies, without providing context, that something was lost and needed to be recovered.

Line 71, “plus emissions related to human activities such as fertilization, biomass burning”  Please delete fertilization, since this is already covered in the previous sentence about microbial production in soils under cultivation.  Fertilizer provides substrate for the microbes to produce N2O, as opposed to biomass burning and industry, which are abiotic mechanisms.

Line 84-85.  The Valentini source from African rivers seems large.  Is this Tg N2O (as written?) or TgN2O-N?

Line 93.  Should last “an” be “and”?

Lines 108-110 “we present a new retrieval strategy to account for the pressure and temperature dependence of laser-based instruments, specifically for the use of quantum cascade laser spectrometers on aircraft”  Similar to my comments above about lines 46-47, does this imply uncertainties in previous campaigns (HIPPO, ORCAS) where this new strategy was not used?  Or did something go wrong specifically during ATom that required the new strategy?  Please clarify.

Section 2.2 and line 167.  Again, it is unclear whether the “significant improvement in the precision and accuracy of the QCLS N2O data” was necessitated by the damage described in the previous paragraph, or would have been done anyway.

Line 231. Please clarify whether UCATS and PANTHER were also made during ATom.

Line 237.  The term PFP is introduced here without explanation.  Was PFP measured on ATom too?

Line 259,  I would suggest a more formal or quantitative adjective than “great”

Line 290.  Extra “and” in the sentence?

Line 300-302.  This sentence is confusing because Antarctic vortex breakup usually occurs in November or December, not October.  Second, what is the basis for claiming maximum STT in the NH is ending in October?

Lines 303-306.  It seems like there are a lot of variables that might affect these percentages.  For example, how are they affected by the altitude of the observations?   Did each deployment have the same fraction of air sampled at higher altitudes?

Line 310 refers to Figures 3b,e as though they are March/April, but the panels are labeled on the panels as May (?) Similarly, Figures 3c,f are cited as representing Aug/Sep, but are labeled on the panels as October.  Is line 310 just speculation or is it based on ATom data measured early on deployments 3 and 4 (lines 106-107 suggest some April and Sep data were collected)?

Line 319.  Please clarify that the NH-SH gradient of N2O is much smaller than that of CO and SF6.  Otherwise, lines 320-321 don’t make much sense.

Line 322-323.  Please explain in more detail.  What kind of mixing is being described here?

Paragraph starting on 313.  This paragraph could move less abruptly between each species (CO, O3, SF6, CFC12).  Also, it’s not clear why these 4 species were chosen for the Figure 4 scatterplots.  Does each one illustrate a specific new point?

Figure 5.  X-axis labels are overlapping and hard to read on N2O/CH3CN profile.  Perhaps use same scale as N2O/CH4 panel.

Line 382.  H2O2, PAA and CO profiles in Figure 5 are characterized by enhanced values at the surface.  In contrast, N2O is lower at the surface than at 4 km.

Figure 6.  Perhaps point out in second panel that the APO axis is reversed to illustrate the negative correlation to N2O.

Line 414 influences should be “influenced”

Line 416 “with higher APO and lower N2O” would be more meaningful written as “with lower APO and higher N2O” since this is a fall profile in which the ocean thermocline would be deepening, ventilating water enhanced in N2O and depleted in O2.

Line 423 contrasts should be “contrast”

Line 426 the decrease of CO2 seems consistent with the strong biological drawdown of CO2, especially in regions with intensive agriculture, during the spring/summer growing season (e.g., Schuh et al., Global Change Biology (2013) 19, 1424–1439, doi: 10.1111/gcb.12141).  It might be interesting to show a CO2 profile (since so many other species are shown in Fig. 7).

Lines 430-434.  This seems like a very complex mix of influences to disentangle.  Is this even possible?

Line 436-438, why wouldn’t this also be an ocean feature, e.g., from upwelling off the coast of Mauritania (as per Ganesan et al. 2020)?  The N2O v. APO slope is similar in sign and magnitude to that shown in Figure 6, except that in the Fig. 6 panel, the APO axis runs normally (negative to less negative), whereas in the Fig. 7 (and Fig. 8) scatterplot, the APO is reversed to run from negative to more negative. 

Line 448.  Please elaborate “By using a profile specific background.”  Was an atmospheric transport model used in this exercise?

In general, could a common set of species and profiles for Figure 6-8 (or at least Fig 7-8) be chosen and displayed consistently?  It would be easier for the reader to compare and contrast the different points being made with each of these multi-paneled figures.

This manuscript reports results relating to N₂O from a series of flights. The manuscript is well written and presents interesting results, that are useful for the rest of the scientific community. My comments are minor, mainly looking to clarify the presentation.

Line 40 – I suggest clarifying “is rapidly increasing” by stating “its mixing ratio is rapidly increasing” (or similar phrasing)

Line 47 and 467 - “factor of 3” relative to what? I know what is meant having read the whole paper, but I think this needs to be explicitly stated in the abstract/ conclusions.

Line 85 – I was surprised that N₂O emissions from tropical river systems in Africa were so high, so I checked this reference. The bibliography of this manuscript is missing an entry for Valentini 2014, which needs to be added in, I assume it’s https://bg.copernicus.org/articles/11/381/2014/. Having skimmed this paper, 3.3 Tg N₂O yr^-1 seems to come from Table 9, which is total emissions for Africa, of which rivers seem to be a minor contributor. Please check where this number came from, and clarify in the text if necessary.

Line 87 – “and the balance from agriculture”, I suggest changing “balance” to “rest”?

Line 97, 465, 501 - “highly resolved” in what?

Figure 2 – the figure caption refers to d-g but no plots are labelled d-g.

Line 310 /Figure 3 – the months of the subplots are inconsistent between the figure and the text.

Line 321 / Figure 4 – the text says Fig. 4a-d, but no subplots are labelled c or d. Each subplot needs to be labelled, and that label used consistently in the text, caption, and figure.

Line 448 - I’m unclear how EDGAR has been used to create a profile, some extra explanation is needed here.

Review of “Impact of stratospheric air and surface emissions on tropospheric nitrous oxide during ATom”

This study develops a N₂O retrieval algorithm for the QCLS airborne instrument that reduces the sensitivity of the measurement to temperature and pressure changes in the aircraft cabin. The performance of the QCLS retrieval of N₂O is evaluated using three additional N₂O instruments during the ATom mission. Anomalies in measured N₂O with respect to background mixing ratios are described. The authors demonstrate how anthropogenic and natural sources of these anomalies can be identified using the suite of chemical tracers collected during ATom. Overall, the paper is well-written and the authors thoroughly characterize a useful dataset. The comments below are minor and are for clarity in the discussion.

Comments:

• Lines 46 – 47: The wording of this sentence is confusing. Did the new retrieval strategy improve measurements by a factor of 3 with respect to previous deployments of the instrument or was spectra collected during previous missions reanalyzed with improved precision? Please reword to clarify.
• Line 76: The list of emission estimates in this paragraph is difficult to process. Could they be summarized more concisely? Also, are there conclusions from the ATom analysis that could be discussed in the context of these studies?
• Line 154: missing comma before “and”
• Line 184 “…with respect to the precision of the original retrievals…”: Please clarify if this is with respect to the original ATom-1 retrievals with the damaged instrument or to all QCLS retrievals during ATom. Overall, the discussion of the calibration improvement and damage to the instrument before ATom-1 seems to be mixed together in this section. Did the damage impact the later ATom missions too?
• Line 250: What do you mean by “common sampling locations”? Are these locations that are representative of the atmospheric background and typically not influenced by anthropogenic emissions? Also, Table S.3 shows median mixing ratios of N₂O measured during ATom, not information about the surface stations as indicated in the text.
• Line 257: Missing “to” in “with respect [to] surface data”
• Line 300: Figure 3f is missing in the figure reference. Strong depletion in N₂O mixing ratios at Southern high latitudes are seen in both Figures 3c and 3f.
• Lines 300 – 302: How does transport in northern high latitudes impact the low mixing ratios of N₂O in the southern high latitudes? Perhaps this is a typo.
• Lines 303 – 306. Please clarify how these percentages are calculated. It does not look like 55% of all observations shown in Figure 3c are depleted in N₂O. Are these percentages calculated for specific latitude ranges?
• Line 310. In Figure 3b and 3e, depleted N₂O is seen in the Northern Hemisphere in March-April, not the Southern Hemisphere.
• Lines 322 – 323: As written, it is not clear what is meant by “range of N₂O-CO mixing lines” and “straight mixing lines”. Does this refer to the L-shaped curve, discussed earlier in the paragraph? Are there examples of different mixing timescales shown in Figure 3 that can be used to demonstrate this concept?
• Line 388: Please specify which short-lived trace gases (and their atmospheric lifetimes) were used in this analysis.
• Line 436: The APO axis is flipped in the N₂O-APO correlation panels between Figure 6 and 7, which makes them difficult to compare. Are the N₂O-APO correlations different between the two figures or does the presence of CO₂ and CH₄ indicate a different source for similar correlations observed during two profiles.
• Please state in the caption of Figure 9 that the observed enhancement in N₂O is based on the profile shown in Figure 8.
• Line 452: It would be helpful to show the profiles for N₂O enhancements due to European and Asian EDGAR emissions in Figure 9 to demonstrate this point.
• Line 461: How does Figure S11 support an anthropogenic origin to the N₂O enhancements seen in Figure 8?
• Overall, Figures 5 – 8 contain a lot of information that can be difficult to digest. Having panels consistent between the figures, as suggested by another reviewer, would help. It would also be helpful to explain in the text why information contained in one figure is different from previously shown figures or why altitude ranges discussed in the text do not match up with the correlation coefficient panels shown in the figures.