Ozone–oxygen cycle

The linked atmospheric reactions in which ultraviolet light splits oxygen molecules, oxygen atoms form ozone, and further ultraviolet absorption breaks ozone apart.

Chapman cycle: A set of four reactions describing the formation and destruction of stratospheric ozone from oxygen and ultraviolet light. It gives the classic reaction sequence underlying the ozone–oxygen cycle.
Oxygen: A chemical element with atomic number 8, commonly found in the atmosphere as O₂. O₂ supplies the atoms from which atmospheric ozone is formed.
Ozone layer: The region of the atmosphere with elevated ozone concentrations, chiefly in the stratosphere. The cycle maintains the ozone layer that absorbs incoming ultraviolet radiation.
Ozone-depleting substances: Human-made compounds that release chlorine or bromine in the stratosphere and catalytically destroy ozone. They add rapid ozone-loss pathways absent from the oxygen-only cycle.
Photodissociation: The breakup of a molecule after it absorbs a photon. Ultraviolet photodissociation splits O₂ and O₃ at different stages of the cycle.
Ozone: A triatomic form of oxygen, O₃, that absorbs much of the Sun’s ultraviolet radiation in the stratosphere. Ozone is the molecule repeatedly formed and broken in the cycle.
Ultraviolet index: A scale indicating the strength of sunburn-producing ultraviolet radiation at Earth’s surface. Stratospheric ozone abundance affects how much ultraviolet radiation reaches the ground.
Chlorine catalytic cycle: A set of reactions in which chlorine radicals repeatedly destroy ozone while being regenerated. It contrasts catalytic ozone loss with the cycle’s direct oxygen photochemistry.
Ozone formation: The three-body reaction in which an oxygen atom combines with an oxygen molecule to form ozone. It is the step that turns atomic oxygen into O₃.
Ultraviolet: Electromagnetic radiation with wavelengths shorter than visible light and longer than X-rays. Different ultraviolet wavelengths drive oxygen and ozone photodissociation.

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