The atmospheric layer found roughly 15–30 kilometers above Earth is called the ozone layer. It is a region of the stratosphere where ozone molecules are relatively concentrated compared with the surrounding air.
Ozone is made of three oxygen atoms, written as O₃. High-energy ultraviolet radiation from the Sun splits ordinary oxygen molecules, and the resulting oxygen atoms can combine with other oxygen molecules to form ozone. Ozone can also absorb ultraviolet radiation and break apart, creating a natural cycle.
The ozone layer is especially important because it absorbs much of the Sun’s harmful UV-B and UV-C radiation. It is not a solid sheet or sharply defined boundary; ozone concentration rises and falls across a broad altitude range.
A common mix-up is confusing stratospheric ozone with ground-level ozone. High in the atmosphere, ozone protects life; near the surface, it is an air pollutant that can irritate lungs and damage plants.