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The English version of our glossary is currently under construction and will be regularly updated.


A gaseous component of the atmosphere.

Ozone, the triatomic form of oxygen (O3), is a gaseous component of the atmosphere. In the troposphere, it forms both naturally and by photochemical reactions involving gases stemming from human activities (“smog”). Tropospheric ozone is a greenhouse gas. In the stratosphere, ozone is formed by the interplay of ultraviolet solar radiation and molecular oxygen (O2). Stratospheric ozone plays a pivotal part in the stratospheric radiation balance. Its highest concentration is in the ozone layer.