Atmospheric Gases Block UV <290 nm The column of absorbing gas
in the path of incoming radiation includes atomic and molecular
nitrogen and oxygen and their products. These gases block all
short wave ultraviolet radiation. Molecular oxygen in the
stratosphere (10 to 48 km) absorbs short wave (up to 242.4 nm
from the ground state and with very strong bands from 50-100 nm,
and 140-175 nm) ultraviolet and photodissociates. The atomic
oxygen produced leads to the production of ozone. Ozone strongly
absorbs longer wave ultraviolet in the Hartley and Huggins bands
from 200 - 360 nm (Fig. 1), and has additional weak absorption
bands in the visible (Chappius bands from 450 - 750 nm) and
infrared.Fig. 1 Transmittance of ozone layer. Absorption in the
Herzberg continuum of the abundant molecular oxygen blocks most
ultraviolet up to ca. 250 nm. Rayleigh scattering by air
molecules (Fig. 2) and the strong ozone absorption from 200 -
290 nm determine the terrestrial ultraviolet edge at around 290
nm. Ozone absorption is v