Ozone depletion is the gradual thinning of Earths ozone layer in the upper atmosphere caused by the release of chemical compounds containing gaseous chlorine or bromine from industry and other human activities. These compounds are referred to as ozone-depleting substances (ODS) and include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, hydrobromofluorocarbons, chlorobromomethane, and methyl chloroform. ODS are generally very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere. When they break down, they release chlorine or bromine atoms, which then deplete ozone.

Ozone can be destroyed more quickly than it is naturally created. Some compounds release chlorine or bromine when they are exposed to intense UV light in the stratosphere. These compounds contribute to ozone depletion. Chlorine-containing source gases (primarily CFCs and related halocarbons) are the primary cause of ozone depletion. In the presence of UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze ozone destruction. The Cl-catalyzed ozone depletion can take place in the gas phase, but it is dramatically enhanced in the presence of polar stratospheric clouds (PSCs) .

Depletion of the ozone layer by ODS will lead to higher UVB levels, which in turn will cause increased skin cancers and cataracts and potential damage to some marine organisms, plants, and plastics. The thinning of the ozone layer is most pronounced in the polar regions, especially over Antarctica. The ozone hole is actually an area of the stratosphere with extremely low concentrations of ozone that reoccurs every year at the beginning of the Southern Hemisphere spring (August to October) .

In summary, ozone depletion is caused by the release of chemical compounds containing gaseous chlorine or bromine from industry and other human activities, which are referred to as ozone-depleting substances (ODS). These compounds contribute to the thinning of the ozone layer, which leads to higher UVB levels and increased skin cancers, cataracts, and potential damage to some marine organisms, plants, and plastics. Chlorine-containing source gases (primarily CFCs and related halocarbons) are the primary cause of ozone depletion.