New and improved infrared absorption cross sections for chlorodifluoromethane (HCFC-22)

Abstract

Abstract. The most widely used hydrochlorofluorocarbon (HCFC) commercially since the 1930s has been chlorodifluoromethane, or HCFC-22, which has the undesirable effect of depleting stratospheric ozone. As this molecule is currently being phased out under the Montreal Protocol, monitoring its concentration profiles using infrared sounders crucially requires accurate laboratory spectroscopic data. This work describes new high-resolution infrared absorption cross sections of chlorodifluoromethane over the spectral range 730-1380 cm −1 , determined from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26 cm pathlength cell. Spectra of chlorodifluoromethane/dry synthetic air mixtures were recorded at resolutions between 0.01 and 0.03 cm −1 (calculated as 0.9/MOPD; MOPD denotes the maximum optical path difference) over a range of temperatures and pressures appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN (HIgh-resolution TRANsmission) and GEISA (Gestion et Etude des Informations Spectroscopiques Atmosphériques) databases; in particular it provides coverage over a wider range of pressures and temperatures, has more accurate wavenumber scales, more consistent integrated band intensities, improved signalto-noise, is free of channel fringing, and additionally covers the ν 2 and ν 7 bands.

Improved FTIR retrieval strategy for HCFC-22 (CHClF2), comparisons with in situ and satellite datasets with the support of models, and determination of its long-term trend above Jungfraujoch

“…We retrieve total columns with 66 ± 6 % (2σ) of tropospheric contribution. The main potential improvement that could be brought to our retrieval strategy would be to build a new pseudo-linelist from recently determined cross-sections (Harrison, 2016). The systematic uncertainty could be this way minimized and, moreover, the ν3 feature (near 1100 cm -1 ) could be investigated again.…”

“…HCFC-22 presents strong absorption band systems in the infrared spectral region (Harrison, 2016): the main features are the Coriolis-coupled doublets ν3 (~1108.7 cm -1 ) and ν8 (~1127.1 cm -1 ) and the Q-branches ν4 (~809.3 cm -1 ) and 2ν6 (~829.1 cm -1 ). The well isolated but unresolved 2ν6 Q-branch is one of the narrowest and most intense features of HCFC-22.…”

New and improved infrared absorption cross sections for trichlorofluoromethane (CFC-11)

“…The experimental setup at the Molecular Spectroscopy Facility (MSF), Rutherford Appleton Laboratory (RAL), and the experimental procedures have been described previously for related measurements (e.g. Harrison et al, 2010;Harrison, 2015bHarrison, , 2016; the reader is referred to one of these previous studies for more information. Instrumental parameters associated with the Fourier transform spectrometer (FTS) used for the measurements, sample details, and the cell configuration are summarised in Table 2.…”

“…The procedure used to generate absorption cross sections from measured spectra has been reported previously (e.g. Harrison et al, 2010;Harrison, 2015bHarrison, , 2016, so the full details are not provided here. The wavenumber scale of the (Rothman et al, 2013).…”

Improved FTIR retrieval strategy for HCFC-22 (CHClF<sub>2</sub>), comparisons with in situ and satellite datasets with the support of models, and determination of its long-term trend above Jungfraujoch

“…A priori profiles of HCFC-22 and all interfering species, with the exception of water vapour, are also computed from a climatology of WACCM v4 outputs for the 1980-2020 time period. The solar line compilation supplied by Hase et al (2006) has been assumed for non-telluric absorptions.…”