Ozone is formed from the reaction of O2 with atomic oxygen, the latter resulting from the photodissociation of O2 in the upper atmosphere. Ozone is inexistent below 10 km; its opacity becomes comparable to that of H2O above 15 km where its relative abundance may reach 10-5 (see Fig.8.1). At short millimeter wavelengths, it causes narrow absorption lines (mostly above 230 GHz).
The other trace atmospheric components CH4, SO2, CO, N2O, NO, etc.. have very low abundance and, even polar, play no significant role, their maximum opacities being typically more than 10 times smaller than those of ozone.