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The ozone-oxygen cycle is the process by which ozone is continually regenerated in the Earth's atmosphere.
When ozone in the upper atmosphere is hit by ultraviolet solar radiation, it quickly undergoes a chemical reaction. The tri-atomic ozone molecule becomes bi-atomic molecular oxygen plus a free oxygen atom:
- O3 + radiation → O2 + O
Free atomic oxygen then quickly reacts with other oxygen molecules and forms ozone again, releasing the extra energy as heat.
- O2 + O → O3 + heat
In the process, penetrating UV light has been turned into harmless heat (i. e. infrared radiation). This cycle keeps the ozone layer in a stable balance while protecting the lower atmosphere from UV radiation, which is harmful to most living beings.
Unfortunately, human-made CFCs (chlorofluorocarbon compounds), as well as other gasses containing chlorine, bromine or fluorine, interact with O3 molecules, stripping off the extra oxygen atom and leaving common molecular oxygen. These reactions have caused a measurable decrease in the amount of ozone in the stratosphere, which is known as ozone depletion.
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