08 Mar 2021
08 Mar 2021
Impact of stratospheric air and surface emissions on tropospheric nitrous oxide during ATom
- 1John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
- 2CIMEL Electronique, Paris, 75011, France
- 3Izaña Atmospheric Research Centre, Santa Cruz de Tenerife, 38001, Spain
- 4Dept. of Earth and Environmental Science, Lamont-Doherty Earth Observatory, Columbia University, New York, NY 10964, USA
- 5Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., Billerica, MA 01821, USA
- 6NOAA Global Monitoring Laboratory, Boulder, CO 80305, USA
- 7Cooperative Institute for Research in Environmental Sciences, CIRES, University of Colorado Boulder, Boulder, CO 80309, USA
- 8NOAA Chemical Sciences Laboratory, Boulder, CO 80305, USA
- 9Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
- 10Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
- 11NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- 12Earth Observing Laboratory, National Center for Atmospheric Research (NCAR), Boulder, CO 80301, USA
- 13Atmospheric Chemistry Observations & Modeling Lab, NCAR, Boulder, CO 80301, USA
- 14Center for Aerosol and Cloud Chemistry, Aerodyne Research, Inc., Billerica, MA, 01821, USA
- 15Scripps Institution of Oceanography, University of California San Diego, CA 92037, USA
- 1John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
- 2CIMEL Electronique, Paris, 75011, France
- 3Izaña Atmospheric Research Centre, Santa Cruz de Tenerife, 38001, Spain
- 4Dept. of Earth and Environmental Science, Lamont-Doherty Earth Observatory, Columbia University, New York, NY 10964, USA
- 5Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., Billerica, MA 01821, USA
- 6NOAA Global Monitoring Laboratory, Boulder, CO 80305, USA
- 7Cooperative Institute for Research in Environmental Sciences, CIRES, University of Colorado Boulder, Boulder, CO 80309, USA
- 8NOAA Chemical Sciences Laboratory, Boulder, CO 80305, USA
- 9Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
- 10Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
- 11NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- 12Earth Observing Laboratory, National Center for Atmospheric Research (NCAR), Boulder, CO 80301, USA
- 13Atmospheric Chemistry Observations & Modeling Lab, NCAR, Boulder, CO 80301, USA
- 14Center for Aerosol and Cloud Chemistry, Aerodyne Research, Inc., Billerica, MA, 01821, USA
- 15Scripps Institution of Oceanography, University of California San Diego, CA 92037, USA
Abstract. Nitrous oxide (N2O) is both a greenhouse gas in the troposphere and an ozone depleting substance in the stratosphere and is rapidly increasing in the atmosphere. The spatial distribution of N2O emissions and the sources leading to rising concentrations in the global atmosphere are highly uncertain. We measured the global distribution of tropospheric N2O mixing ratios during the airborne Atmospheric Tomography (ATom) mission. ATom measured mixing ratios of ~300 gas species and aerosol properties in 647 vertical profiles spanning the Pacific, Atlantic, Arctic, and much of the Southern Ocean basins, from nearly Pole to Pole, over four seasons (2016–2018). We measured N2O mixing ratios at 1 Hz using a Quantum Cascade Laser Spectrometer and a new spectral retrieval method to account for the pressure and temperature sensitivity of the instrument when deployed on aircraft. 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. Most of the variance of N2O mixing ratios in the troposphere is driven by the influence of N2O-depleted stratospheric air, especially at mid and high latitudes. We observe the downward propagation of lower N2O mixing ratios (compared to surface stations) that tracks the influence of stratosphere-troposphere exchange through the tropospheric column down to the surface, resulting in a seasonal minimum at the surface 2–3 months after the peak stratosphere-to-troposphere exchange in spring. The highest N2O mixing ratios occur close to the equator, extending through the boundary layer and free troposphere. We observed influences from a complex and diverse mixture of N2O sources, with emission source types identified using the rich suite of chemical species measured on ATom and with the geographical origin calculated using an atmospheric transport model. Although ATom flights were mostly over the oceans, the most prominent N2O enhancements were associated with anthropogenic emissions, including industry, oil and gas, urban and biomass burning, especially in the tropical Atlantic outflow from Africa. Enhanced N2O mixing ratios are mostly associated with pollution-related tracers arriving from the coastal area of Nigeria. Peaks of N2O are often well-correlated with indicators of photochemical processing, suggesting possible unexpected source processes. The difficulty of separating the mixture of different sources in the atmosphere contributes to uncertainties in the N2O global budget. The extensive data set from ATom will help improve the understanding of N2O emission processes and their representation in global models.
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Yenny Gonzalez et al.
Status: open (until 05 May 2021)
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RC1: 'Comment on acp-2021-167', Anonymous Referee #1, 30 Mar 2021
reply
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.
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RC2: 'Comment on acp-2021-167', Anonymous Referee #2, 06 Apr 2021
reply
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.
Yenny Gonzalez et al.
Data sets
ATom: Merged Atmospheric Chemistry, Trace Gases, and Aerosols S. C. Wofsy, S. Afshar, H. M. Allen, E. C. Apel, E. C. Asher, B. Barletta, J. Bent, H. Bian, B. C. Biggs, D. R. Blake, N. Blake, I. Bourgeois, C. A. Brock, W. H. Brune, J. W. Budney, T. P. Bui, A. Butler, P. Campuzano-Jost, C. S. Chang, M. Chin, R. Commane, G. Correa, J. D. Crounse, P. D. Cullis, B. C. Daube, D. A. Day, J. M. Dean-Day, J. E. Dibb, J. P. DiGangi, G. S. Diskin, M. Dollner, J. W. Elkins, F. Erdesz, A. M. Fiore, C. M. Flynn, K. D. Froyd, D. W. Gesler, S. R. Hall, T. F. Hanisco, R. A. Hannun, A. J. Hills, E. J. Hintsa, A. Hoffman, R. S. Hornbrook, L. G. Huey, S. Hughes, J. L. Jimenez, B. J. Johnson, J. M. Katich, R. F. Keeling, M. J. Kim, A. Kupc, L. R. Lait, J.-F. Lamarque, J. Liu, K. McKain, R. J. Mclaughlin, S. Meinardi, D. O. Miller, S. A. Montzka, F. L. Moore, E. J. Morgan, D. M. Murphy, L. T. Murray, B. A. Nault, J. A. Neuman, P. A. Newman, J. M. Nicely, X. Pan, W. Paplawsky, J. Peischl, M. J. Prather, D. J. Price, E. A. Ray, J. M. Reeves, M. Richardson, A. W. Rollins, K. H. Rosenlof, T. B. Ryerson, E. Scheuer, G. P. Schill, J. C. Schroder, J. P. Schwarz, J. M. St.Clair, S. D. Steenrod, B. B. Stephens, S. A. Strode, C. Sweeney, D. Tanner, A. P. Teng, A. B. Thames, C. R. Thompson, K. Ullmann, P. R. Veres, N. Vieznor, N. L. Wagner, A. Watt, R. Weber, B. Weinzierl, P. O. Wennberg, C. J. Williamson, J. C. Wilson, G. M. Wolfe, C. T. Woods, and L. H. Zeng https://doi.org/10.3334/ORNLDAAC/1581
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