Model, software, and database for computation of line-mixing effects in infrared Q branches of atmospheric CO2 -: I.: Symmetric isotopomers

A theoretical model based on the energy-corrected sudden approximation is used in order to account for line-mixing effects in infrared Q branches of symmetric isotopomers of CO2, Its performance is demonstrated by comparisons with a large number (about 130) of CO2-N-2 and CO2-O-2 laboratory spectra recorded by several instrument setup: nine Q branches of different vibrational symmetries lying between 1 and 17 mu m are investigated in wide ranges of pressure (0.05-10 atm) and temperature 1200-300 K). The model is used to generate a set of suitable parameters and FORTRAN software (available by ftp for the calculation of the absorption within (CO2)-C-12-O-16, (CO2)-C-13-O-16, and (CO2)-C-12-O-18 infrared Q branches under atmospheric conditions, which can be easily included in existing radiance/transmission computer codes. Comparisons are made between many (about 280) computed atmospheric spectra and values measured using two different balloon-borne high-resolution Fourier transform instruments: transmission (solar occultation) as well as radiance (limb emission) measurements of seven Q branches between 13 and 17 mu m for a large range of atmospheric air masses and pressure/temperature conditions have been used, including the v(2), band of both (CO2)-C-12-O-16 and (CO2)-C-13-O-16, The results confirm the need to account for the effects of line-mixing and demonstrate the capability of the model to represent accurately the absorption in regions which are often used for temperature/pressure sounding of the atmosphere by space instruments. Finally, quantitative criteria assessing the validity of the widely used Rosenkranz first-order approximation are given, (C) 1998 Elsevier Science Ltd. All rights reserved.