Ozone (O3) in the stratosphere is created by the
action of photons of ultraviolet light (hf), with wavelength
shorter than 242 nm, on oxygen (O2). A third body (M),
which may be an oxygen or nitrogen molecule is needed to carry
away the excess kinetic energy. Ozone is mainly created above
regions where the sun is high in the sky.
O2 + hf -> O + O
O2 + O + M -> O3 + M
Ozone can be destroyed by the action of light with a wavelength
shorter than 1180 nm.
O3 + hf -> O2 + O
O + O3 + M -> O2 + M
These two reactions sequences, together with many other more
complex ones, balance to give an average of around 300 DU of
ozone.