Ozone hole

The ozone hole is the seasonal severe depletion of stratospheric ozone, especially over Antarctica. It forms when human-produced chemicals release reactive halogens that destroy ozone in the cold polar stratosphere.

Polar stratospheric clouds: Clouds that form in the extremely cold stratosphere and enable chemical reactions that activate chlorine compounds. Their surfaces convert chlorine reservoirs into reactive forms before Antarctic spring sunlight returns.
Chlorofluorocarbons: Synthetic compounds once widely used in refrigeration, aerosols, and foam production that release ozone-destroying chlorine in the stratosphere. Their long-lived emissions supplied most of the chlorine behind the Antarctic depletion.
Montreal Protocol: A 1987 international treaty that phases out production and consumption of ozone-depleting substances. The treaty coordinated the global phaseout of the chemicals responsible for ozone depletion.
Antarctic ozone hole of 1985: The large springtime ozone depletion over Antarctica reported by British scientists in 1985. This report brought the phenomenon to global attention and galvanized policy action.
Ozone recovery: The gradual return of stratospheric ozone toward earlier levels as atmospheric concentrations of ozone-depleting substances decline. Recovery is underway but unfolds over decades because the responsible chemicals persist in the atmosphere.
Chlorine radical: A chlorine atom with an unpaired electron that reacts rapidly with ozone and participates in catalytic destruction cycles. Sunlight releases reactive chlorine that can destroy many ozone molecules through repeated reactions.
Mario Molina: A Mexican chemist who helped establish how chlorofluorocarbons can destroy stratospheric ozone. His research explained the chemical threat that made the ozone hole intelligible.
Ozone layer: The region of the stratosphere containing elevated concentrations of ozone that absorb much of the Sun's ultraviolet radiation. The Antarctic hole is a severe, localized seasonal loss within this protective atmospheric region.
Ozone hole of 2006: A particularly large Antarctic ozone hole observed in 2006, among the largest recorded by area and ozone deficit. Its exceptional scale illustrates how weather conditions shape year-to-year variation.
Atmospheric circulation: Large-scale movements of air that redistribute heat, moisture, and chemical constituents through the atmosphere. Circulation changes affect polar temperatures, ozone transport, and the timing of recovery.

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