How does the Sun’s ultraviolet radiation help create Earth’s ozone layer?

The Sun’s ultraviolet (UV) radiation plays a critical role in the formation of Earth’s ozone layer through a process known as photodissociation.1

When high-energy solar photons from the Sun strike oxygen molecules ($O_2$) in the stratosphere, the energy breaks the chemical bonds holding the oxygen atoms together. This reaction releases individual, highly reactive oxygen atoms. These free oxygen atoms then collide and bond with intact oxygen molecules ($O_2$) to create ozone ($O_3$).1

This continuous cycle is essential for life on Earth, as the resulting ozone layer acts as a protective shield that absorbs the most harmful ultraviolet radiation before it can reach the surface. While this process is vital for atmospheric protection, it is distinct from the creation of ground-level ozone, which is a component of smog formed by photochemical reactions involving human-made pollutants.123