15 to 35 km above the Earth's Surface is a layer of ozone that resides in the stratosphere, one of the 7 layers of Earth's atmosphere. Ozone, which is chemically represented by O3, is composed of three oxygen atoms.
There are only three molecules of ozone in 10 million molecules of air in the atmosphere, however it plays a major role in protecting us from 98% of damaging ultraviolet radiation. This is done through a cycle known as the ozone-oxygen-cycle or Chapman Cycle in which ozone converts ultraviolet radiation into heat through a series of chemical reactions.
However, chemicals known as chlorofluorocarbons or CFCs used in aerosols and refrigerants have been the main cause of ozone depletion. When CFCs are exposed to UV radiation, it results in the molecule breaking down in a process called photo-induced scissoring in which a chlorine atom is removed from the rest of the molecule. A chlorine atom can be extremely reactive and therefore reacts with the ozone in the atmosphere converting it into oxygen gas or O2.
Ozone layer damage occurs in thin patches with the most affected area being the poles. The low temperatures of the poles aid in the breakdown of CFCs to chlorine atoms and other molecules. CFCs were used heavily in the industry until 1989 during which the Montreal Protocol banned the production of CFCs. This has resulted in a big drop in CFCs in the atmosphere. Scientist estimate that chlorine levels will return to their natural amounts in 50 years, thus repairing a big portion of the damage caused by CFCs.