Ozone is an unstable molecule made up of three oxygen atoms (O3). It is found at two levels in the atmosphere. Near the ground , it is toxic , notably for the respiratory tract and mucosa.This ozone is generated by pollution , mainly from motor vehicles. Ozone is also found at high altitude in the stratosphere. Here , there is a "layer" some 20 to 25 km above the Earth , wich is formed through equilibrium between its formation and destruction under the effect of solar radiation, from temperature changes and from presence of other chemical substances. This layer protects us from some of the harmful rays of the sun , such as ultraviolet radiation.
When we talk about the hole in the ozone layer it is in this stratospheric ozone.The discover of a hole in the ozone layer goes back to the 1980s. It was in the Antartic that the first ground measurements of ozone levels produced some surprising results. As early as 1985 , Joseph Farman , from the British Antarctic Survey, published the results of his observations in Nture. A "hole" , or a drop in concentration , albeit temporary but very marked, appeared each spring in the stratospheric ozone layer above the Antartic. This phenomenon mainly occured in the lower stratosphere. What is the situation today ? The next year , his phenomenon was investigated by NASA , the American Space Agency. A report drawn up with the help of some hundred or so experts from all over the world suggested that stratospheric ozone concentration had fallen on average by 1.7 to 3% in the northern hemisphere between 1969 and 1986 , despite major annual variations.However , by the end of the 1980s , the scientific community had reached agreement about the cause of this depletion in both the Antarctic and Arctic regions : halogenated hydrocarbons, and particulary the notorious CFCs ( chlorofluorocarbons).
Further observational and laboratory studies showed that the ozone's seasonal disappearance was indeed linked to chemical reactions in the upper atmosphere wich were being triggered by the verry low temperatures existing above the Arctic in winter.The size of the hole in the ozone layer above the Arctic oscilates wildly. An absolute record was attained in 2000, when the hole covered an area of 29.2 milion Km2 . In 2001 and 2002 , the trend seemed to be downwards, but this respite was of short duration.On september 22 , 2004 at the peak of the phenomenon a hole of 24.2 milion km2.Because of the enormous proportions the Antarctic hole in the ozone layer has reached in recent years , its first direct effects on human populations in Latin America are now starting to be felt. Higher levels of ultraviolet rays emitted by the sun , wich are filtered less by the stratospheric ozone reach the ground , increasing the risks of skin cancer and cataract.
Source:RTD info Magazine on European Research.
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