Infrared absorption cross sections for methanol

Infrared absorption cross sections for methanol, CH3OH, have been determined near 3.4 and 10 μm from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3 m. Methanol/dry synthetic air mixtures were prepared and spectra were recorded at 0.015 cm−1 resolution (calculated as 0.9/MOPD) at a number of temperatures and pressures (50-760 Torr and 204-296 K) appropriate for atmospheric conditions. Intensities were calibrated using composite methanol spectra taken from the Pacific Northwest National Laboratory (PNNL) IR database. The new measurements in the 10 μm region indicate problems with the existing methanol spectroscopic line parameters in the HITRAN database, which will impact the accuracy of satellite retrievals.

► Methanol infrared absorption cross sections have been determined near 3.4 and 10 μm. ► They cover temperatures from 204 to 296 K and appropriate atmospheric pressures. ► They will allow retrievals of methanol abundances from IR remote-sensing instruments. ► The 10 μm cross sections highlight problems with methanol line parameters in HITRAN.