The authors present a detailed explanation for selective reabsorption by the CO2 ν3-band when passing its optical emission through an atmospheric-pressure air column (60 cm long, 410 ppm CO2) connecting a microwave-discharge cell and the entrance window of a high-resolution Fourier Transform spectrometer. The CO2 band shapes are explained with a two-temperature model of emission and foreground absorption. Selective CO2 atmospheric reabsorption is a common effect in optical emission measurements. It primarily affects the fundamental infrared bands, which comprise the main part of the missing laboratory emission and must be taken into account in (exo)planetary atmospheric models.