1. The Ozone Hole - what is it ?
The Earth is surrounded by a mixture of different gasses. They create a sheet called atmosphere. In high layers of atmosphere, between 10 and 50 km over the surface of the Earth, there is a thin layer of gas called the ozone. This layer protects the Earth from the harmful sun's radiance.
In 1989 level of ozone over the Antarctic went down about 40-50%. When half or even a greater amount of ozone in high layers of atmosphere has been destroyed the scientists started to talk about a "hole" in the ozone's layer.
In 1987 the so-called "ozone hole" over the Antarctic was as big as the territory of the USA. Its depth was as the deep as the height of the highest mountain peak in the USA - Mount Everest.
2. The ozone layer
The Earth's atmosphere is divided into four individual layers: troposphere, stratosphere, mezosphere and thermosphere. Troposphere reaches on average a height of about 11km over the surface of the Earth. It is even thinner over the Poles and fatter over the equator. The ozone layer is located in the stratosphere.It protects all the living organisms from invisible but harmful radiance of the sun. This dangerous radiance is called ultra violet radiation (UV). The most harmful ray is UV-B. However the majority of radiance is absorbed by ozone layer before it reaches the Earth surface.
3. The Ozone as the greenhouse gas.
The ozone is one of the "greenhouse gasses" which absorb infra-red radiation in the atmosphere. They let sun rays reach Earth, but they trap energy from the sun so the heat does not escape back into space. It causes the increase of temperature on the surface of the Earth and in the lower layers of the atmosphere. This phenomenon is called "greenhouse effect". The Ozone ( O3 ) makes up about 12% of all greenhouse gases.
4. The ozone defeat The Ozone layer is being destroyed because of the release of chlorofluorocarbons ( CFCs) These spread through the world and diffuse into the stratosphere, where they are broken down to release chlorine.
The Ozone Hole is the biggest in the northern hemisphere.
During the Antarctic winter a strong westerly circulation around the continent, known as the circumpolar vortex, builds up in the stratosphere. This effectively cuts off the interior and allows it to cool, with temperatures falling below -80°C at 17 km. Thin clouds form (above), which enable reactions with gases which contain chlorine to take place. When the sun returns in the spring, the chlorine is able to take part in complex catalytic chemical reactions which destroy ozone and create the ozone hole. When the stratosphere warms up again during the late spring and summer, these reactions cease, the circumpolar vortex breaks down and the ozone hole disappears as fresh ozone is brought in.
5. What can we do ?
The most important aim in the struggle to save the ozone layer is the reduction of Freon emission. The scientists from the American Institute of World Natural Supply prepared a possible plan of reducing the existence of the gas which is being discussed. This can be achieved through:
- Initiation of Freon to secondary circulation
- Replacement of harmful phreons by "gentle" Freon
- Initiation of technologies without using Freons.