the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Atmospheric N2O and CH4 total columns retrieved from low-resolution FTIR spectra (Bruker Vertex 70) in the mid-infrared region
Minqiang Zhou
Bavo Langerock
Mahesh Kumar Sha
Christian Hermans
Nicolas Kumps
Rigel Kivi
Pauli Heikkinen
Christof Petri
Justus Notholt
Huilin Chen
Martine De Mazière
Abstract. Nitrous oxide (N2O) and Methane (CH4) are two important greenhouse gases in the atmosphere. In 2019, mid- infrared (MIR) solar absorption spectra were recorded by a Bruker Vertex 70 spectrometer and a Bruker IFS 125HR spectrometer at Sodankylä, Finland at spectral resolutions of 0.2 cm−1 and 0.005 cm−1, respectively. The N2O and the CH4 retrievals from high-resolution MIR spectra have been well investigated within the Network for Detection of Atmospheric Composition Change (NDACC), but not for MIR spectra gathered with instruments operating at low spectral resolution. In this study, N2O and CH4 retrieval strategies and retrieval uncertainties from the Vertex 70 MIR low-resolution spectra are discussed and presented. The accuracy and precision of the Vertex 70 N2O and CH4 retrievals are assessed by comparing them with the co-located 125HR retrievals and AirCore measurements. The relative differences between the N2O total columns retrieved from 125HR and Vertex 70 spectra are -0.3±0.7(1σ)% with a correlation coefficient (R) of 0.93. Regarding CH4 total column, we first used the same retrieval microwindows for 125HR and Vertex 70 spectra, but there is an underestimation in the Vertex 70 retrievals, especially in summer. The relative differences between the CH4 total columns retrieved from the 125HR and Vertex spectra are -1.3±1.1 % with a R value of 0.77. To improve the Vertex 70 CH4 retrievals, we propose an alternative retrieval microwindows. The relative differences between the CH4 total columns retrieved from the 125HR and Vertex spectra in these new windows become 0.0±0.8 %, along with an increase in R value to 0.87. The co-located AirCore measurements confirm that the Vertex 70 CH4 retrievals using the latter window choice are better, with the relative mean differences between the Vertex CH44 retrievals and AirCore measurements of -1.9 % for the standard NDACC mircrowindows, and of 0.13 % for the alternative microwindows. This study provides an insight into the N2O and CH4 retrievals from the low-resolution (0.2 cm−1) MIR spectra observed with a Vertex 70 spectrometer, and demonstrates the suitability of this kind of instruments for contributing to satellite validation, model verification, and other scientific campaigns with the advantage of their transportability and lower cost compared to standard NDACC-type FTIR instruments.
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Minqiang Zhou et al.
Status: final response (author comments only)
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RC1: 'Comment on amt-2022-17', Anonymous Referee #1, 05 Jul 2022
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AC1: 'Reply on RC1', minqiang zhou, 20 Apr 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2022-17/amt-2022-17-AC1-supplement.pdf
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AC1: 'Reply on RC1', minqiang zhou, 20 Apr 2023
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RC2: 'Comment on amt-2022-17', Dietrich G. Feist, 08 Sep 2023
Dear authors,
first I have to apologize for the long time that this manuscript has spent in review. It was extremely difficult to find reviewers that were not connected with the FRM4GHG project. This project includes a large part of the FTIR community. From the ones I identified, 6 were unavailable, declined or had a conflict of interests. Therefore, I would like to extend special thanks to anonymous reviewer #1 who provided a thorough report on time.
Unfortunately, the whole process took place while I was absorbed by tragic family matters for several months. The backlog that piled up while I was hardly able to work also delayed this review process. I appreciate your understanding that the first author Minqiang Zhou has expressed to me personally already.
Not being able to come up with 2 reviewers in the end, I am forced to resort to an editor's review to finish the process. My own FTIR experience is limited to TCCON hi-resolution retrievals with GGG on the IFS125HR. My experience with NDACC, SFIT4 and low-resolution retrievals is very limited. Therefore, I would only add the minor comments below and leave the detailed corrections to the report already provided by reviewer #1.
Kind regards
Dietrich Feist
Comments:
- I find the naming of the bands 1-6, V1, V2, 3V2, 4V2 confusing. For clarity, please provide a table that describes the major parameters (wave number range, instrument, species retrieved).
- p. 14, l. 7: Do you mean standard deviation with "stds"? Please spell out to avoid confusion.
Citation: https://doi.org/10.5194/amt-2022-17-RC2 -
AC2: 'Reply on RC2', minqiang zhou, 14 Sep 2023
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2022-17/amt-2022-17-AC2-supplement.pdf
Minqiang Zhou et al.
Minqiang Zhou et al.
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