What protects us from harmful radiation of the sun?

Much of the harmful UV radiation that the sun emits onto Earth can be absorbed thanks to the chemical bonds in ozone. The energy absorbed by the molecule allows the molecule to split into an oxygen molecule and an oxygen free radical, which is a highly reactive species with an unpaired electron pair.

Two oxygen molecules are created when the free radical combines with another ozone molecule:

Overall, ozone is lost; this is okay on its own, but when CFCs (chlorofluorocarbons) are released into ozone layers, they accelerate the process and eventually cause more ozone to be lost than created. Fortunately, governments all over the world have outlawed CFCs, causing the ozone layer to recover.

The Earth's atmosphere, particularly the ozone layer, protects us from harmful radiation of the sun by absorbing and scattering much of the incoming ultraviolet (UV) radiation.