Abstract
Two atmospheric trace gases, namely methane and carbon monoxide have been considered in this study. Fourier transform absorption spectra of the 2–0 band of 12C16O mixed with CO2 have been recorded at total pressures from 156 to 1212 hPa and at 4 different temperatures between 240 K and 283 K. CO2 pressure-induced line broadening and line shift coefficients, and the associated temperature dependence have been measured in an multi-spectrum non-linear least squares analysis using Voigt profiles with an asymmetric profile due to line mixing. The measured CO2-broadening and CO2-shift parameters were compared with theoretical values, calculated by collaborators. In addition, the CO2-broadening and shift coefficients have been calculated for individual temperatures using the Exponential Power Gap (EPG) semi-empirical method. We also discuss the retrieved line shape parameters for Methane transitions in the spectral range known as the Methane Octad. We used high resolution spectra of pure methane and of dilute mixtures of methane in dry air, recorded with high signal to noise ratio at temperatures between 148 K and room temperature using the Bruker IFS 125 HR Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory, Pasadena, California. Theoretical calculations for line parameters have been performed and the results are compared with the previously published values and with the line parameters available in the GEISA2015 [1] and HITRAN2012 [2] databases.
Highlights
The success of spectroscopic planetary atmospheric remote sensing studies often relies on having highly accurate sets of laboratory data for line parameters of the majority of atmospheric trace constituents, to interpret them
Due to the importance of methane as a trace atmospheric gas and a greenhouse gas and its contributions to the terrestrial Carbon Cycle, we have carried out a precise line shape study to obtain the self- and air half-width coefficients, self- and air-shift coefficients and the off-diagonal relaxation matrix element coefficients for methane transitions in the spectral range known among spectroscopists as the "methane octad"
The temperature dependence of the CO2 broadening coefficients measured in this work using the 3 line shape models are presented in figure 2
Summary
The success of spectroscopic planetary atmospheric remote sensing studies often relies on having highly accurate sets of laboratory data for line parameters of the majority of atmospheric trace constituents, to interpret them. [10] is intended to extend the knowledge for line parameters of CO broadened by CO2, over a range of temperatures For this propose, we have used number of 21 spectra of CO/CO2 mixtures recorded using Fourier transform spectrometer at University of Brussels. Due to the importance of methane as a trace atmospheric gas and a greenhouse gas and its contributions to the terrestrial Carbon Cycle, we have carried out a precise line shape study to obtain the self- and air half-width coefficients, self- and air-shift coefficients and the off-diagonal relaxation matrix element coefficients for methane transitions in the spectral range known among spectroscopists as the "methane octad". The high resolution absorption spectra of the 2–0 band of carbon monoxide mixed with carbon dioxide at total pressures ranging from 156 to 1212 hPa and at 4 different temperatures between about 240 K and 283 K have been recorded using a Bruker IFS 125 HR Fourier transform spectrometer. Of the 14 spectra, 8 spectra were recorded with pure methane samples and 6 of the spectra were obtained with dilute mixtures of 12CH4 in dry air
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