Ozone (O3) is substance consisting of three oxygen atoms per molecule. At standard temperature and pressure, this is a blue gas. Ozone forms a dark blue liquid, below -112 C, and a dark blue solid, below -193 C. Ozone is notable for its ability to absorb solar radiation. Ozone is created, naturally, within the ozone layer. Ozone is "depleted" by chlorofluorocarbons.
Ozone in the earth's atmosphere is generally created by ultraviolet light which breaks apart O2 molecules, creating atomic oxygen. The atomic oxygen then combines with an unbroken molecule, to create O3. Sometimes the individual oxygen atoms will combine with N2 to create a nitrogen oxide[?]; which, when affected by visible light, may create ozone.
The ozone molecule is also unstable and when ultraviolet light hits ozone it splits into a molecule of O2 and an atom of atomic oxygen, a continuing process called the ozone-oxygen cycle[?]. This cycle can be disrupted by the presence of atomic chlorine, fluorine or bromine in the atmosphere; these elements are found in certain stable compounds, especially chlorofluorocarbons (CFCs) which may find their way to the stratosphere and there be liberated by the action of ultraviolet light on them. The NOx cycle for the formation of Ozone can also be broken by the presence of atmospheric water, reducing NOx to a more stable form.
Ozone is a highly corrosive and poisonous substance and a common pollutant. It has a sharp, pungent odour. It's present in low concentrations throughout the Earth's atmosphere. It is formed naturally from O2 by electrical discharges, e.g., lightning, and by action of high energy electromagnetic radiation.
The highest levels of ozone in the atmosphere are in the stratosphere, in a region also known as the ozone layer. Here it filters out much ultraviolet light from the Sun that would be harmful to most forms of life. The standard way to express ozone amounts in the atmosphere is by using Dobson units. Ozone used in industry is measured in ppm (OSHA exposure limits for example), and percent weight.
Industrially, Ozone is used to: