Info about ozone layer depletion

The ozone hole over the Antarctic forms each year in August as the Southern Hemisphere summer begins, eventually dissipating by November. Found throughout the Earth�s atmo�sphere, ozone is particularly rich in the lower stratosphere, a region commonly referred to as the ozone layer, between about 10 and 30 kilometers above the planet�s surface. (The layer of atmosphere just below the stratosphere is the troposphere, where we live and breathe.) The ozone layer blocks harmful ultraviolet rays linked to skin cancer.

The hole is the result of chlorofluorocarbons (CFCs) and other chlorine- and bromine-containing gases interacting with two naturally occurring phenomena in the stratosphere. One is the polar vortex, a sort of atmospheric cyclone above Antarctica that is strongest in winter when temperatures are below negative 80 degrees Celsius. The other is polar stratospheric clouds (PSCs), or nacreous clouds when visible, that also form in the extreme polar winter.

The PSCs provide an excellent chemical platform for setting chlorine and bromine free to run amok and destroy ozone in the presence of sunlight. The vortex then circulates the ozone-destroying chemicals quickly until it weakens later in the summer.

CFCs and other ozone-depleting substances were used in the manufacture of aerosol sprays and refrigerants, slowly creeping from the surface into the atmosphere. However, most countries have largely discontinued the use of CFCs thanks to the Montreal Protocol, an international treaty signed in 1987 to protect atmospheric ozone.

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