High above our heads in a layer of the atmosphere known as the stratosphere is a small amount of ozone gas. The 'ozone layer' absorbs harmful ultraviolet radiation from the sun. Scientist measure ozone layer thickness by measuring how much ultraviolet radiation reaches the ground, using a Dobson ozone spectrophotometer. Ozone layer thickness is measured in Dobson units. The higher the number the thicker the ozone layer.
Ozone is produced and destroyed naturally.
Since the 1970s, gases produced for commercial purposes have been destroying the ozone layer, upsetting the natural equilibrium that existed. It is planned that by 2005 in developed countries and 2015 in developing countries, the use of ozone depleting gases, such as CFCs, will be phased out. See the following animated model to understand How ozone is destroyed by CFCs . The following tables presents ozone measurements made in Dobson units at the Halley research station in Antarctica by the British Antarctic Survey. Use a different colour for each year.