Ozone Layer: Formation, UV Blocking, Depletion

Ozone layer definition and location

The ozone layer (or ozone shield) is a region of Earth’s stratosphere that contains a relatively high concentration of ozone (O3) and absorbs most of the Sun’s ultraviolet (UV) radiation. Although ozone is only a small fraction of atmospheric gases, it peaks at roughly 8–15 parts per million and is crucial for protecting life by blocking biologically harmful UV, especially UV-B (about 280–315 nm). The ozone layer was discovered in 1913 by French physicists Charles Fabry and Henri Buisson, and later monitored using instruments such as the Dobsonmeter developed by G. M. B. Dobson. In terms of location, the ozone layer is mainly in the lower stratosphere, roughly 15–35 km (about 9–22 miles) above Earth, with thickness that varies seasonally and geographically. Ozone concentrations are generally greatest between about 20 and 40 km, and the layer is thinner near the equator and thicker near the poles. Ozone is produced through photochemical reactions: UV light splits oxygen molecules (O2) into atomic oxygen, which then combines with O2 to form ozone; ozone is also continuously broken down by UV in the ozone–oxygen cycle. The layer can be depleted by catalytic reactions involving chlorine and bromine radicals released from human-made compounds such as CFCs, leading to phenomena like the seasonal “ozone holes,” most pronounced over the poles.

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Ozone concentration and thickness variations

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