Absorption of ultra-violet radiation
Because bonds between atoms in molecules have varying strengths, it takes different amounts of energy to break them down. The bond between the two oxygen atoms in an oxygen molecule (O2) is really strong and can only be broken down if the molecule absorbs very high energy UV-C radiation. The bonds between the oxygen atoms in ozone are a bit weaker and can be broken down by absorption of slightly less energetic UV-B radiation. Absorption of this highly energetic, short wavelength, radiation by O2 and O3 in the upper atmosphere prevents it reaching the troposphere and destroying O2 and O3 there. Less energetic radiation (with longer wavelengths) reaches the surface of the Earth.
