Atmospheric N2O and CH4 total columns retrieved from low-resolution Fourier transform infrared (FTIR) spectra (Bruker VERTEX 70) in the mid-infrared region

• Published in: Atmospheric Measurement Techniques
• Main Authors: Zhou, Minqiang, Langerock, Bavo, Sha, Mahesh Kumar, Hermans, Christian, Kumps, Nicolas, Kivi, Rigel, Heikkinen, Pauli, Petri, Christof, Notholt, Justus, Chen, Huilin, Mazière, Martine
• Format: Text
• Language: English
• Published: 2023
• Subjects: Sodankylä
• Online Access: https://doi.org/10.5194/amt-16-5593-2023; https://amt.copernicus.org/articles/16/5593/2023/

Nitrous oxide ( N 2 O ) and methane ( CH 4 ) 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 and 0.005 cm −1 , respectively. The N 2 O and the CH 4 retrievals from high-resolution MIR spectra have been well investigated within the Network for the Detection of Atmospheric Composition Change (NDACC) but not for MIR spectra gathered with instruments operating at low spectral resolution. In this study, N 2 O and CH 4 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 N 2 O and CH 4 retrievals are assessed by comparing them with the coincident 125HR retrievals and AirCore measurements. The relative differences between the N 2 O total columns retrieved from 125HR and VERTEX 70 spectra are − 0.3 ± 0.7 (1 σ ) % with a correlation coefficient ( R ) of 0.93. Regarding the CH 4 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 CH 4 total columns retrieved from the 125HR and VERTEX 70 spectra are - 1.3 ± 1.1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="e4eb3ca84fcc097473f089968941be92"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-16-5593-2023-ie00001.svg" width="52pt" height="10pt" src="amt-16-5593-2023-ie00001.png"/></svg:svg> (1 σ ) % with a R value of 0.77. To improve the VERTEX 70 CH 4 retrievals, we propose alternative retrieval microwindows. The relative differences between the CH 4 total columns retrieved from the 125HR and VERTEX 70 spectra in these new windows become 0.0±0.8 (1 σ ) %, along with an increase in the R value to ...