The transparency of certain permanent atmospheric gases (like nitrogen and oxygen) to both incoming solar radiation and outgoing thermal radiation is a fundamental physical baseline of atmospheric science and does not require citation.
The claim states that certain gases are nearly transparent to both solar and thermal radiation, which describes the physical properties of major atmospheric constituents like N2 and O2 that lack permanent dipole moments and do not absorb strongly in the visible or main thermal infrared bands. This is a matter of basic physical chemistry and everyday atmospheric observation, making it common knowledge.