What is Ozone?

Ozone (O3) is a highly reactive gas composed of three oxygen atoms. It's both naturally occurring in the Earth's upper atmosphere (stratosphere) and man-made. Stratospheric ozone shields the Earth from harmful ultraviolet (UV) radiation. Ground-level ozone (tropospheric ozone) is a major component of smog and can be harmful to human health and the environment. Ozone is also used industrially as a disinfectant and bleaching agent.