The ozone layer is a thin layer within the Earth's atmosphere that absorbs a large proportion of ultraviolet light coming from the Sun. Because the ozone layer is so protective, it is vital to life on Earth. Ozone particles are very dynamic and can be broken apart and reformed readily. However, recently ozone has been broken down at a higher rate and so is in a state of depletion.
Ozone is a compound consisting of three oxygen molecules bound together (O3). When ultraviolet radiation strikes ozone, it is broken down into a single (O) and double (O2) oxygen molecules. Because the single oxygen molecule is highly reactive, it is attracted to the O2 molecule and the two reattach, forming an ozone molecule. This cycle of breaking apart and reforming is known as the ozone-oxygen cycle.
The ozone layer is slowly being depleted by humankind at a rate of nearly 1/2 a percent per year. While the destruction and reconstruction of ozone is routine in the ozone-oxygen cycle, there are chemicals being introduced into the ozone layer that cause the destruction of ozone radically and permanently. Molecules such as chlorine and bromine are put into the atomosphere in the form of chlorofluorocarbons and bromofluorocarbons (CFCs and BFCs, respectively). These molecules ravage ozone molecules, breaking them apart and tying them up so they cannot reform.
Aerosol cans, which formerly contained CFCs have been banned nearly worldwide since the 1970s. However, there are countries that still include CFCs inside aerosol cans as propellants. Furthermore, once a CFC finds its way into the stratosphere, it stays there for long periods of time so the damage in ongoing.
Most of the Earth's ozone is within the stratosphere, which is 10 to 50 km above the surface of the Earth. Within the stratosphere, the ozone layer is only a very thin layer located approximately in the center of the stratosphere.
Ozone is responsible for blocking nearly all the ultraviolet radiation that would otherwise strike the Earth. Even small increases in ultraviolet radiation would be devastating to nearly all species of both plants and animals. Ultraviolet radiation causes direct damage to plants and can increase the number of skin cancers among humans.
Ozone in the trophosphere, where human beings live and breathe, is considered a pollutant. While it is the same molecule, ozone in the trophosphere is produced when ultraviolet light strikes pollutants produced by the combustion of fuel. Ironically, depletion of stratospheric ozone can lead to an increase in trophospheric ozone because of the increase in UV radiation striking the surface of the Earth.
The ozone hole is not exactly a hole in the ozone layer as much as it is a severe depletion of ozone in a specific area. This thinning layer of ozone is found near the poles during certain times of the year.
In Antarctica the ozone hole is largest from September to December, when nearly half of the ozone layer in this region is depleted. This thinning occurs during the part of the year when this region of the world receives more sunlight, which also means an increase in UV radiation and, thus, increased CFC activity.