Concentrations of ethane (C₂H₆) in the lower stratosphere and upper troposphere and acetylene (C₂H₂) in the upper troposphere deduced from atmospheric trace molecule spectroscopy/Spacelab 3 spectra

Volume mixing ratio profiles of ethane (C 2 H 6 ) in the lower stratosphere and upper troposphere and acetylene (C 2 H 2 ) in the upper troposphere have been deduced from analysis of 0.01‐cm −1 ‐resolution infrared solar absorption spectra recorded between 25°N and 31°N latitude. The spectral data were obtained by the ATMOS (Atmospheric Trace Molecule Spectroscopy) Fourier transform spectrometer during the Spacelab 3 shuttle mission on April 30 to May 1, 1985. The investigation was based on nonlinear least squares curve fitting of the ν 7 ; band P Q 3 subbranch near 2976.8 cm −1 and the ν 9 band R Q 0 subbranch near 822.3 cm −1 for C 2 H 6 and of the ν 5 band R 10 and R 19 lines of C 2 H 2 at 755.0056 and 776.0818 cm −1 , respectively. Improvements in the spectroscopic data base for the regions containing these absorption features are reported. The C 2 H 6 results indicate a nearly constant volume mixing ratio of 0.97 parts per billion by volume (ppbv) between 6 and 12 km and a decline to 0.1–0.2 ppbv at 18 km altitude. Measured C 2 H 2 mixing ratios are 0.070–0.092 ppbv between 7.7 and 12.6 km and 0.02 ppbv at 15.1 km. An upper limit of 0.02 ppbv is obtained for the average C 2 H 2 mixing ratio above 16.6 km. The retrieved profiles are compared with previous measurements and model calculations.