O3

Ozone, with the chemical formula O3, is an allotrope of oxygen composed of three oxygen atoms. It is a pale blue gas at room temperature with a sharp, characteristic odor and a high oxidizing potential. Ozone is relatively unstable and tends to decompose back into diatomic oxygen (O2) and a single oxygen atom.

In the atmosphere, ozone occurs in two distinct regions with different roles. In the stratosphere, roughly 10 to 50 kilometers above the Earth’s surface, a layer of ozone forms that absorbs most of the sun’s harmful ultraviolet radiation, particularly ultraviolet-B and ultraviolet-C. This ozone layer protects living organisms from UV-induced damage. In the troposphere, near the surface, ozone is a secondary pollutant formed by photochemical reactions involving nitrogen oxides and volatile organic compounds in the presence of sunlight. Ground-level ozone is a component of urban smog and can persist for hours to days, depending on weather and emission patterns.

Ozone formation and destruction involve photolysis and chemical reactions. Ultraviolet light splits O2 to produce oxygen atoms, which then combine with O2 to form O3. Ozone can be destroyed by reactions with nitric oxide, hydroxyl radicals, and other species, as well as by deposition to surfaces. In the stratosphere, natural and anthropogenic changes in ozone chemistry have led to long-term disturbances known as ozone depletion, historically linked to chlorine- and bromine-containing compounds and addressed by international measures such as the Montreal Protocol.

Industrial uses of ozone include disinfection, water treatment, odor control, and certain sterilization processes. Ozone is generated commercially by corona discharge or ultraviolet photolysis of oxygen. Because of its strong oxidizing power and toxicity, ozone production and application require controlled management and safety measures.