Ozone is the predominant compound in the upper atmosphere at an altitude of 25 km. Stratospheric ozone is good ozone called because it absorbs solar UV radiation and thus protects us against the risk of skin cancer and other genetic mutations. It also protects the photosynthetic activity of plants.
The abnormal decrease of ozone at the South Pole at the end of the polar winter, when the sun’s appearance was highlighted in 1980. During the late austral winter, when the sun appears The ozone content decreases from 40 to 60%. The maximum deficit is around 20 to 25 km.
Many compounds can destroy ozone (OH, H, NO, Cl, Br, HO 2). A strong correlation between the deficiency and ozone concentrations ClO has been highlighted. The presence of radicals Cl and ClO in the stratosphere is linked to the natural emission of methylene chloride by the oceans and chlorofluorocarbons (CFCs) emitted by human activities. CFCs are very stable molecules. These molecules are transported into the stratosphere where they release chlorine, thereby disturbing the natural balance governing the presence of ozone at this altitude.
The phenomenon of annual decline in ozone concentrations is more pronounced at the South Pole, North Pole that due to different conditions. At the South Pole, a vortex appears in the winter. The temperatures of about – 80 ° – 100 ° C. The clouds then contain fine ice crystals that bind the chlorine as HCl and NO 2 ClO. As soon as the sun reappears, UV free radicals Cl and ClO which react rapidly with ozone. North Pole, there is no formation of Vortex but formation of a multitude of holes.