The ozone molecule (O₃) is made up of three oxygen atoms. It is a form of oxygen that is less stable than the diatomic oxygen (O₂) that makes up about 21% of the Earth's atmosphere. Ozone is found mostly in the stratosphere, where it forms the ozone layer that protects the Earth's surface from harmful ultraviolet radiation from the sun. Ozone can also be found at ground level, where it is a pollutant and component of smog.
