High resolution measurements of atmospheric transmission of sunlight from space to altitudes of 12.2 km, 8.53 km, and 5.48 km made over Johnston Island are reported. The spectral region covered is 4.0–5.3 µm. Comparisons of the measured transmission with theoretically synthesized transmission curves are presented. It is shown that the sharp spectral features due to molecular line-by-line absorption can be predicted accurately while the modeling of the continuum absorption features needs further development. A discussion of the current models for CO₂ and N₂ continuum absorption is presented. An alternative mechanism is proposed for continuum absorption, which is based on the spectral properties of atmospheric van der Waals molecular complexes such as CO₂.N₂ and N₂.N₂ dimers.