Antarctic ozone hole

A seasonal, severe thinning of stratospheric ozone over Antarctica, strongest during Southern Hemisphere spring. It results from chemical reactions on polar stratospheric clouds and human-made chlorine and bromine compounds.

Polar stratospheric clouds: Clouds that form in the very cold stratosphere and provide surfaces for chemical reactions involving chlorine compounds. Their surfaces convert chlorine reservoirs into forms that sunlight can activate over Antarctica.
Farman, Gardiner, and Shanklin: British Antarctic Survey scientists who reported dramatic springtime ozone declines over Antarctica in 1985. Their measurements established the unexpected scale of Antarctic spring depletion.
Ultraviolet index: A scale describing the intensity of sunburn-producing ultraviolet radiation at Earth’s surface. Reduced ozone can raise surface UV levels, reflected in elevated UV index readings.
Arctic ozone depletion: A winter and spring reduction of stratospheric ozone over the Arctic, varying strongly with meteorological conditions. The Arctic can lose ozone, but its warmer, less stable vortex usually prevents Antarctic-scale holes.
Chlorine radical: A chlorine atom with an unpaired electron that reacts rapidly with ozone and participates in catalytic cycles. Sunlight releases reactive chlorine that drives much of the springtime ozone loss.
British Antarctic Survey: The United Kingdom’s national organization for research in Antarctica and the Southern Ocean. Its Halley Bay observations produced the measurements that revealed the ozone hole.
Skin cancer: A group of cancers arising from abnormal growth of skin cells, with ultraviolet exposure a major risk factor. Greater ultraviolet exposure from ozone loss increases risks associated with skin damage.
Ozone depletion: A reduction in the amount of ozone in a region of the atmosphere over time. The Antarctic ozone hole is an unusually severe, geographically concentrated form of this broader phenomenon.
Ozone depletion cycle: A catalytic chemical sequence in which reactive species destroy ozone and are regenerated. Chlorine-catalyzed cycles explain how a small amount of chlorine can destroy many ozone molecules.
Dobson spectrophotometer: An instrument that measures total atmospheric ozone by comparing ultraviolet light at selected wavelengths. Long-running Antarctic observations with this instrument made the seasonal decline detectable.

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