Preprints
https://doi.org/10.5194/amt-2022-17
https://doi.org/10.5194/amt-2022-17
 
03 Jun 2022
03 Jun 2022
Status: 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 Zhou1,2, Bavo Langerock2, Mahesh Kumar Sha2, Christian Hermans2, Nicolas Kumps2, Rigel Kivi3, Pauli Heikkinen3, Christof Petri4, Justus Notholt4, Huilin Chen5,6, and Martine De Mazière2 Minqiang Zhou et al.
  • 1CNRC & LAGEO, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
  • 2Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
  • 3Finnish Meteorological Institute, Space and Earth Observation Centre, Sodankylä, Finland
  • 4Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • 5Centre for Isotope Research (CIO), Energy and Sustainability Research Institute Groningen (ESRIG), University of Groningen, Groningen, the Netherlands
  • 6Joint International Research Laboratory of Atmospheric and Earth System Sciences, School of Atmospheric Sciences, Nanjing University, Nanjing, China

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: open (until 08 Jul 2022)

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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.