O2 has a stronger bond because it is a pure double bond.

O3 has bonds that are intermediate between single and double, so ozone has weaker bonds.

O3 shields us from harmful ultraviolet light entering Earth’s atmosphere.

Photons at wavelengths of 280–320 nm (the most dangerous components of sunlight to humans) are just strong enough to break ozone’s bonds.

In the process, the photons are absorbed.

The same wavelengths of UV light do not have sufficient energy to break

the stronger double bond of O2 so it is transparent to UV and cannot shield us from it.

Chemistry in the Environment:

The Lewis Structure of Ozone