Line mixing effects in solar occultation spectra of the lower stratosphere: measurements and comparisons with calculations for the 1932-cm^−1 CO_2Q branch

Abstract

Line mixing effects have been observed in a CO₂Q branch recorded in 0.01-cm⁻¹ resolution IR solar occultation spectra of the lower stratosphere. The spectral data were obtained by the Atmospheric Trace Molecule Spectroscopy Fourier transform spectrometer during the Spacelab 3 shuttle mission in the spring of 1985. Analysis of the 1932.47-cm⁻¹ (11102)←(00001) band Q branch of ¹²C¹⁶O₂ shows absorption coefficients below the band origin ~0.62 times those calculated using a standard Voigt line shape function. Calculations of line mixing using the Lorentz halfwidths of the lines and a simple energy gap scaling law to parametrize rotational energy transfer reproduce the observed absorption coefficients to ~10%. The present results provide the first quantitative information on air-broadened line mixing effects in a Q branch at low temperatures (~210 K) and show that these effects are significant even at the low pressures of the lower stratosphere (~100 mbar).