New infrared absorption cross sections for the infrared limb sounding of carbon tetrafluoride (CF4)

Abstract

Carbon tetrafluoride (CF4), also known as tetrafluoromethane and sometimes CFC-14, has a natural lithospheric source, however the enhanced modern-day concentrations relative to this natural source have arisen from leaks into the atmosphere by industry, most significantly related to the production of aluminium and semiconductors. A potent greenhouse gas, with one of the longest atmospheric lifetimes of 50,000 years, the abundance of carbon tetrafluoride is steadily increasing in the atmosphere. In order to monitor its concentration profiles using infrared sounders, accurate laboratory spectroscopic data are required. This work describes new high-resolution infrared absorption cross sections of pure and air-broadened carbon tetrafluoride over the spectral range 1190–1336 cm−1, derived from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26-cm-pathlength cell. Spectra were recorded at resolutions between 0.0018 and 0.03 cm−1 (calculated as 0.9/MOPD; MOPD = maximum optical path difference) over a range of atmospherically relevant temperatures (190 – 296 K) and pressures (up to 760 Torr). These new absorption cross sections improve upon those previously used for remote sensing, and will provide a more accurate basis for retrievals in the future.