Preprints
https://doi.org/10.5194/amt-2022-17
https://doi.org/10.5194/amt-2022-17
03 Jun 2022
 | 03 Jun 2022
Status: a revised version of this preprint is currently under review for the journal AMT.

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, and 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.

Minqiang Zhou et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-17', Anonymous Referee #1, 05 Jul 2022
  • RC2: 'Comment on amt-2022-17', Dietrich G. Feist, 08 Sep 2023

Minqiang Zhou et al.

Minqiang Zhou et al.

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Short summary
Atmospheric N2O and CH4 columns are successfully retrieved from low-resolution FTIR spectra recorded by a Bruker Vertex 70 FTIR spectrometer. The one-year measurements at Sodankyla show that the N2O total columns retrieved from 125HR and Vertex 70 spectra are -0.3±0.7 % with an R of 0.93. The relative differences between the CH4 total columns retrieved from the 125HR and Vertex spectra are 0.0±0.8 %, with an R of 0.87. Such a technique can help to fill the gap of NDACC N2O and CH4 measurements.