Robert Simmon, NASA GSFC
Fifteen to thirty kilometers up in the atmosphere, in the layer called the stratosphere, ozone is created and destroyed primarily by ultraviolet radiation. The air in the stratosphere is bombarded continuously by ultraviolet radiation from the sun. When high-energy ultraviolet rays strike molecules of ordinary oxygen (O2), they split the molecule into two single oxygen atoms, known as atomic oxygen (O). A freed oxygen atom then can combine with an oxygen molecule to form a molecule of ozone (O3).
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