Spectra calculations in central and wing regions of CO₂ IR bands between 10 and 20μm. II. Atmospheric solar occultation spectra

The theoretical approach based on the Energy Corrected Sudden Approximation presented in the previous companion paper is used in order to account for line-mixing effects in infrared bands of CO₂. Its performance, which was demonstrated using laboratory spectra is confirmed here by considering atmospheric transmission in the 10-14 μm region. Comparisons are made between forward calculations of atmospheric transmission spectra and values measured using two different solar occultation experiments based on high resolution Fourier transform instruments. The results demonstrate that neglecting line-mixing and using a Voigt model can lead to a very large overestimation of absorption that may extend over more than 300 cm^-1 in the wing of the CO₂ ν₂ band. They also demonstrate the capability of our model to represent accurately the absorption in the entire region for a variety of atmospheric paths. Among positive consequences of the quality of the model, the possibility of retrieving amounts of (heavy) trace gases with weak and broad absorption features is demonstrated.