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Normal diatomic oxygen molecules (O2) have two oxygen atoms. Ozone (O3) has three oxygen atoms.
Courtesy of COMET program

Ozone

Ozone is a special kind of oxygen molecule. Normal oxygen molecules (O2), the kind we need to breathe, have two oxygen atoms. Ozone molecules (O3) have three oxygen atoms. Ozone forms when a photon of ultraviolet (UV) "light" from the Sun strikes a normal oxygen molecule, breaking it apart. One of the atoms freed by this photodissociation process attaches itself to another oxygen molecule, converting it into ozone.

Ozone occurs naturally in the ozone layer of Earth's atmosphere. It can also be created as a form of air pollution in the lower troposphere. Ozone can irritate the throat and lungs and causes a burning sensation in eyes.

Ozone in the stratosphere protects us from ultraviolet radiation in sunlight. The ozone layer is sort of like sunscreen for planet Earth. It absorbs most of the incoming UV "light" before it reaches the ground. The ozone molecules which absorb UV radiation later re-radiate the energy as heat, warming the stratosphere.

Various chemicals that humans release into the atmosphere can destroy ozone in the stratosphere. This has caused a thinning of the ozone layer in recent years, and even holes in the ozone layer over Earth's poles.

Ozone molecules are much less stable than regular (O2) oxygen molecules. They are very prone to react chemically with other substances. Ozone is also a type of greenhouse gas. Scientists think it is reponsible for about 3-7% of the greenhouse effect on Earth.

Last modified February 27, 2009 by Randy Russell.

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