Polar stratospheric cloud

A cloud of ice or supercooled liquid particles that forms in the cold polar stratosphere. Its particle surfaces enable reactions that convert chlorine compounds into forms that rapidly destroy ozone.

Heterogeneous chemistry: Chemical reactions involving reactants in different phases, such as gases reacting on liquid or solid surfaces. Cloud particles supply surfaces where chlorine reservoir compounds undergo ozone-depleting reactions.
Stratosphere: The atmospheric layer above the troposphere, extending from roughly 10 to 50 kilometers altitude. Polar stratospheric clouds form within this atmospheric layer.
Antarctic ozone hole: The recurring springtime depletion of stratospheric ozone over Antarctica. It is the clearest large-scale case of ozone loss linked to polar stratospheric clouds.
Polar mesospheric cloud: A high-altitude cloud of ice particles that forms near the summer mesopause. It forms far above the stratosphere and does not drive the same polar ozone chemistry.
Chlorine activation: Conversion of relatively stable chlorine compounds into reactive forms that can participate in catalytic ozone destruction. Reactions on cloud particles release reactive chlorine from reservoir compounds.
Polar vortex: A large circulation of strong westerly winds surrounding a polar region in the stratosphere. Its isolation traps cold air in which polar stratospheric clouds can form.
Arctic ozone depletion: Episodes of substantial springtime ozone loss in the Arctic stratosphere. Cold Arctic winters can produce clouds and chlorine activation, though conditions vary greatly by year.
Tropospheric cloud: A cloud that forms in the lowest atmospheric layer, where most weather occurs. Its altitude and typical role differ from the cold stratospheric clouds considered here.
Nitric acid trihydrate: A crystalline compound of nitric acid and water that forms particles in the cold stratosphere. Its particles make up one major type of polar stratospheric cloud.
Nitric acid: A nitrogen-containing acid present in the atmosphere as a gas and in condensed particles. It combines with water to form particles in one class of polar stratospheric clouds.

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