Depletion of the ozone layer: introduction
The environmental theme 'Depletion of the ozone layer' concerns ozone in the stratosphere. This layer, about 15 to 30 kilometres high, naturally contains relatively high concentrations of ozone. This ozone prevents high levels of ultraviolet (UV) radiation reaching the earth.
There has been a fall in the amount of ozone in the stratosphere. The resulting increase in UV radiation can have numerous short-term and long-term health effects on people. It also has an impact on the natural environment (both on land and in water) and the food chain.
Depletion of the ozone layer
Nitrogen, chlorine and bromine compounds reduce the concentration of ozone in the stratosphere. Most chlorine and bromine compounds entering the atmosphere since the beginning of the twentieth century have been of anthropogenic origin, consisting of chlorofluorocarbons (CFCs), halones, hydrochlorofluorocarbons (HCFCs) and methyl bromide. These substances are mainly used as coolants in refrigerators, for dry cleaning, in aerosols, as fire extinguishing agents, for foam production and for soil disinfectants (methyl bromide). Nitrous oxide (N2O) contributes most nitrogen compounds in the stratosphere. This gas comes mainly from natural sources, but humans also bring some into the atmosphere.
Thickness of the ozone layer
Measurements have shown that, since approximately 1980, the ozone layer has become thinner. It is expected that it will be at its thinnest in about 2000, after which it may start to recover. Complete recovery will take approximately 50 years.
Relevant substances
CFC = Fully halogenated chlorofluorocarbon
HCFC = partially halogenated hydrochlorofluorocarbon
HFC = Hydrofluorocarbon
PFC = Perfluorcarbon
Halons = Hydrocarbons with one or more bromine atoms
