In an unpolluted atmosphere, this cycle of production and decomposition is in balance. The man-made chemicals, once popular refrigerants, rise into the stratosphere where they are broken down by the Sun's rays. Free chlorine atoms then act as catalysts to decompose ozone. The whole process requires complex meteorological conditions that are peculiar to the polar stratosphere during the long, dark winter months. It is only when these conditions have been established and the sunlight returns in the Antarctic spring that the infamous ozone hole starts to appear.
Scientists are also worried about ozone depletion in the Northern Hemisphere.
They predict that we will see the ozone hole for many decades to come, until global efforts to reduce CFC emission begin to take effect. The BBC is not responsible for the content of external internet sites.