Temperature- and pressure-dependent absorption cross sections of air-broadened isoprene between 810 and 1200 cm-1 for remote sensing of the terrestrial atmosphere

2-Methyl-1,3-butadiene, also known as isoprene, is the dominant biogenic volatile organic compound (BVOC) emitted by terrestrial vegetation. Over recent years it has been demonstrated that isoprene can be measured in the Earth’s atmosphere from remote sensing satellites, in particular by the series of Cross-track Infrared Sounder (CrIS) instruments. The interpretation of these measurements requires an accurate knowledge of the infrared absorption of isoprene in the atmosphere, which requires accurate laboratory spectroscopic data.

This work describes new high-resolution infrared absorption cross sections of isoprene / dry synthetic air over the spectral range 810 – 1200 cm^-1, derived from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26-cm-pathlength cell. Spectra of isoprene / dry synthetic air mixtures were recorded at resolutions between 0.015 and 0.03 cm^-1 (calculated as 0.9/MOPD; MOPD = maximum optical path difference) over a range of temperatures and pressures (50 – 761 Torr and 198 – 310 K). This new cross-section dataset is the first for air-broadened isoprene over a range of pressures and temperatures appropriate for atmospheric conditions, and expands upon the nitrogen-broadened one-atmosphere pressure dataset available from the Pacific Northwest National Laboratory. The new dataset is included in the latest 2024 compilation of the HITRAN database.