Closer to the ground, in the troposphere, ozone is considered a pollutant with harmful effects on breathing and plants. However, the layer of “good” ozone lies in the stratosphere, between 20 to 40 kilometers from ground. It blocks most of the harmful ultraviolet rays that increase the risk of skin cancer, reduce yields in certain crops and also stress marine life from reaching the earth from sun (“Ozone - Good Up High Bad Nearby” 2009).
The depletion of the ozone layer has been most noticeable over the Antarctic region where a “hole” is seasonally created every year in spring since late 1970s. This hole, actually a large area in the stratosphere with severely depleted ozone, grew to 26 million square kilometers in 1998 and its largest size recorded was in 2006 when it touched 29 million square kilometers (“Ozone hole maximum is up on 2007” 2008).
The stratosphere above the Antarctic is crucial to maintaining the global average concentration of ozone layer. Ozone is unequally distributed around the globe and is concentrated near the poles (Is total ozone uniform over the globe?). The flow of winds to and from poles keeps the ozone in circulation globally. Depletion over the Antarctic, the area of highest concentration, contributes considerably to the net effect of overall ozone reduction in the atmosphere. It is also here that the thinning of this layer is most dramatic. Unlike other places, the chemicals, such as CFCs, that destroy ozone get trapped over the Antarctic during the dark winter through a unique phenomenon, the “polar vortex”, and become part of clouds that are unique to this region. Extreme cold also creates ice crystals in these clouds. During spring and summer, as the temperature warms, the ice crystals initiate reactions that break down the CFCs into more active chlorine molecules. These, in turn, break down the ozone molecules into oxygen (“Ozone Facts: What is the Ozone Hole?” 2009). As the ice