The ozone layer in Earth’s stratosphere absorbs most of the Sun’s ultraviolet (UV) radiation. It contains high concentrations of ozone (O3).

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The ozone layer can be depleted by free radical catalysts. In 1978, the United States, Canada, and Norway enacted bans on chlorofluorocarbon containing aerosol sprays that damage the ozone layer, then after the discovery of the Antarctic ozone hole in 1985, other countries followed suit. Today, all of the world’s 197 countries have signed the treaty.

Satellites can provide measurements of atmospheric ozone and monitor distribution changes with the seasons.