Ozone is highly corrosive and is a poisonous substance and a common pollutant. It has a sharp, pungent odour. It is present in low concentrations throughout the Earth's atmosphere. It is also formed from O2 by electrical discharges, e.g., lightning, and by action of high energy electromagnetic radiation. Some electrical equipment generates levels of ozone that a human can easily smell; this is especially true if there is a spark gap or a very high voltage.
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.
Ozone in the earth's atmosphere is generally created by ultraviolet light which breaks apart O2 molecules, creating atomicoxygen. 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.
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 can be used for bleachinging substances and for killing bacteria. Many municipal drinking water systems kill bacteria with ozone instead of the more common chlorine. Ozone does not form organochlorine compounds, but it also does not remain in the water after treatment, so some systems introduce a small amount of chlorine to prevent bacterial growth in the pipes.
Ozone has a number of medical uses. It can be used to affect the body's antioxidant-prooxidant balance, since the body usually reacts to its presence by producing antioxidant enzymes.
Ozone therapy has blossomed into a thriving field of alternative medicine, and there are a host of claimed applications above and beyond what has actually been verified by studies. Ozone treatments can be dangerous, however, since ozone is in fact highly corrosive.
In the USA ozone therapy is illegal, as the FDA has not approved its use on humans. At least one death has been attributed to application of ozone through insufflation in the USA.
Ozone has been found to convert cholesterol in the blood stream to plaque (which causes hardening and narrowing of arteries). Ozone has been studied extensively, and found to be carcinogenic to some animals (and not others), and a mutagen to some bacteria.