the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
25 Jan 2021
25 Jan 2021
UAS Chromatograph for Atmospheric Trace Species (UCATS) – a versatile instrument for trace gas measurements on airborne platforms
- 1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, 80309, U.S.A.
- 2Global Monitoring Laboratory, NOAA, Boulder, CO 80305, U.S.A.
- 3Chemical Sciences Laboratory, NOAA, Boulder, CO 80305, U.S.A.
- 4Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, U.S.A.
- 5Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109
- 6NASA Langley Research Center, Hampton, VA 23681, U.S.A.
- 7NASA Ames Research Center, Mountain View, CA 94035, U.S.A.
- 1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, 80309, U.S.A.
- 2Global Monitoring Laboratory, NOAA, Boulder, CO 80305, U.S.A.
- 3Chemical Sciences Laboratory, NOAA, Boulder, CO 80305, U.S.A.
- 4Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, U.S.A.
- 5Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109
- 6NASA Langley Research Center, Hampton, VA 23681, U.S.A.
- 7NASA Ames Research Center, Mountain View, CA 94035, U.S.A.
Abstract. UCATS (the UAS Chromatograph for Atmospheric Trace Species) was designed and built for observations of important atmospheric trace gases from unmanned aircraft systems (UAS) in the upper troposphere and lower stratosphere (UT/LS). Initially it measured major chlorofluorocarbons (CFCs) and the stratospheric transport tracers nitrous oxide (N2O) and sulfur hexafluoride (SF6), using gas chromatography with electron capture detection. Compact ozone (O3) and water vapor (H2O) instruments were added to enhance science missions on platforms with relatively small payloads. Over the past decade, UCATS has been reconfigured to measure methane (CH4), carbon monoxide (CO), and molecular hydrogen (H2) instead of CFCs and has undergone numerous upgrades to its subsystems. It has served as part of large payloads on stratospheric UAS missions to probe the tropical tropopause region and transport of air into the stratosphere, in piloted aircraft studies of greenhouse gases, transport, and chemistry in the troposphere, and will soon return to the study of stratospheric ozone depletion, one of the original goals for UCATS. Each deployment brought different challenges, which were largely met or resolved. The design, capabilities, modifications and some results from UCATS are shown and described here, including changes for upcoming missions.
Eric J. Hintsa et al.
Status: final response (author comments only)
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RC1: 'Comment on amt-2020-496', Anonymous Referee #1, 16 Feb 2021
The paper by Hintsa et al. attempts to present the NOAA UCATS instrument and discuss its measurement quality. The instrument was deployed on a series of missions over the past 15 years and has evolved considerably during this period. This latter fact presents the main problem I have with the paper. It does not describe one state of the instrument to a degree where this could be seen as a documentation or possibly as a reference for other instrument devellopers. Rather the paper describes in partly qualitative form the evolution of the instrument over time, partly in a narrative manner. As this evolution spans 15 years, it is virtually impossible to document everything with the desired accuracy. My suggestion would, however, be to add more detail to the description of the most recent set-up. In particular I would like to see more quantitative description of some of the GC parameters (column lengths, flow rates, temperatures) and also chromatogramms of the GC channels. In particular I missed information on detector non-linearity for the ECD channels and also on in-flight calibration frequency and in-flight precision vs. laboratory precision. If the authors estimate all this to be too much detail, I would also be happy to see this as supplementary material. I also suggest that table A1 should be moved to the main part of the publication, whereas the remaining figures in the Appendix could also be moved to a supplement. Next to these more general comment I have a couple of more specific comments given below. Overall the paper fits well into the scope of AMT and I believe it should be published once these points have been adressed.
p. 3. l. 14-18. I suggest to include some references to ECD detector doping here.
p. 3l. 35: is there a model Nr. for the Maycomm hygrometer?
p.5. l. 34.: as such papers will be around for a longer time period, I suggest not to use term like "upcoming", as this will be outdated in a short time. Rather use planned for the year X. Similar issues are found at other places in the manuscript. (e.g. p.19., l. 29, p. 20., l. 10)).
p.8. l. 48.: I find this "trend-correction" very problematic. While this may be o.k. for SF6 (rather constant trend, very small chemical loss), it is not appropriate for N2O, where due to chemical loss, such a "trend-correction" should be done using a percentage increase. In both cases, this is very crude and it should be clear that some differences may remain which are due to trends.
p. 10. l. 22: and Fig 4: It seems to me that the QCLS data are systematically higher in the troposphere. Have you checked absolute calibration scales? Please also discuss possible ECD non-linearity as mentioned above. This might be able to explain the significant deviations at low N2O values.
p. 12. l. 17 and Figure 5: The correlation between N2O and SF6 looks quite remarkable. Could the authors add some more discussion on this? Are these data from different hemispheres?
- RC2: 'Comment on amt-2020-496', Marc von Hobe, 02 Mar 2021
Eric J. Hintsa et al.
Eric J. Hintsa et al.
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