Depletion of the ozone layer

What is the ozone?

The ozone layer is a layer in the atmosphere situated between 19 and 48 kilometres above the earth. The ozone concentration up there can be more than ten parts per million. Ozone is formed through a reaction of oxygen with sun light. This process has existed for millions of years, but the nitrogen connections that are present naturally in the atmosphere kept the ozone levels stable. On earth, a large ozone concentration would be harmful. In the atmosphere, however, the ozone is a vital condition for life on earth. It blocks harmful ultraviolet radiation from the sun reaching us.

CFCs

In the 1970's scientists discovered that a substance, which had long been used in fridges, was dangerous for the ozone layer. These substances were chlorofluorocarbons, generally known as CFCs. When CFCs are released, they rise and are broken down by the sun light. The chlorine reacts instantly and destroys the ozone. Each CFC molecule can destroy 100,000 ozone molecules. For that reason, CFCs are banned in many countries. In addition to CFCs, bromihalogens and saltpetre-like oxides from fertilizers can damage the ozone layer. The depletion of the ozone layer has several consequences for life on earth. Skin cancer and cataracts may increase, crops may be damaged and the amount of plankton may decrease. The decrease in the amount of plants and plankton may lead to an increase of the amount of carbon dioxide (CO2) in the atmosphere. This may have further influences on the earth’s climate.

The hole in the ozone layer

At the beginning of the eighties scientists discovered a ‘hole’ in the ozone layer above Antarctica. This hole is not literally a hole, but an area with a lower concentration of ozone. Research with height balloons and weather satellites revealed that the percentage of ozone above Antarctica is generally decreasing.

International agreements

The Montreal Protocol, a treaty for the protection of the ozone layer, was signed in 1987 and ratified by 36 countries. In 1989, the European Union imposed a total ban on the use of CFCs. The United States also agreed on this. In 1995, a hundred countries decided to cease the production of methyl bromide. Methyl bromide would have caused 15 percent of the depletion of the ozone layer in the year 2000. The use of CFCs must end by the year 2010. Hydro chlorofluorocarbons (HCFCs), which damage the ozone layer at a lesser rate, will be tolerated until 2020 as a substitute for the forbidden CFCs. To keep an eye on the ozone depletion, NASA launched the Upper Atmosphere Research Satellite in 1991. At 600 kilometres, this spacecraft measures the ozone variations at different heights in the atmosphere.

Read more

NASA's Earth Observatory article on the Ozone: http://earthobservatory.nasa.gov/Library/Ozone/ozone.html