Which atmospheric layer contains most of Earth's ozone?

The stratosphere contains most of Earth’s atmospheric ozone.

The stratosphere lies above the troposphere and extends roughly from 10 to 50 kilometres above Earth’s surface, although its boundaries vary with latitude and season. Most atmospheric ozone is concentrated in its lower and middle regions, forming the ozone layer.

Ozone molecules absorb much of the Sun’s harmful ultraviolet-B and ultraviolet-C radiation. This absorption warms the stratosphere with increasing altitude, producing a temperature pattern opposite to the troposphere, where temperature generally decreases upward. The ozone layer therefore helps shape the stratosphere’s stable structure.

Ozone also exists in the troposphere, where it is a pollutant and a component of smog. Confusing stratospheric ozone with ground-level ozone is a common mistake: the same molecule can be protective high above Earth but harmful when concentrated near the surface. Human-made chlorofluorocarbons caused major ozone depletion, leading to the Montreal Protocol in 1987.