Ozone layer

The ozone layer, or ozonosphere, is that part of the Earth's stratosphere which contains relatively high concentrations of ozone (O{{sub|3}}). "Relatively high" means a few parts per million, much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere. The ozone layer was discovered in 1913 by the french physicists Charles Fabry and Henri Buisson. Its properties were explored in detail by the British meteorologist G.M.B. Dobson, who developed a simple spectrophotometer that could be used to measure stratospheric ozone from the ground.

Ozone depletion

The ozone layer can be depleted by free radical catalysts, including nitric oxide (NO), hydroxyl (OH), and atomic chlorine and bromine (see ozone depletion). While there are natural sources for all of these species, the concentrations of Cl and Br have increased markedly in recent years due to the release of large quantities of manmade organohalogen compounds, especially chlorofluorocarbons (CFCs). These highly stable compounds find their way to the stratosphere, where Cl and Br atoms are liberated by the action of ultraviolet light on them. Each chlorine atom is capable of breaking down approximately one hundred thousand ozone molecules during the time that it resides in the stratosphere, and bromine is even more efficient. Ozone levels, over the northern hemisphere, have been dropping by ~4% per decade. Over approximately 5% of the Earth's surface, around the north and south poles, much larger (but seasonal) declines have been seen; these are the ozone holes.

Related Topics:
Chlorine - Bromine - Ozone depletion - Chlorofluorocarbon - Stratosphere - Northern hemisphere - Ozone hole

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Regulation

On January 23, 1978 Sweden became the first nation to ban CFC-containing aerosol sprays that are thought to damage the ozone layer. The United States and other developed nations followed suit soon after. Chlorofluorocarbons continued to be used in other applications, such as refrigeration and industrial cleaning, until after the discovery of the antarctic ozone hole in 1985. After negotiation of an international treaty (the Montreal Protocol), CFC production

Related Topics:
January 23 - 1978 - Sweden - Aerosol spray - Ozone hole - Montreal Protocol

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was sharply limited beginning in 1987 and phased out completely by 1996.

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On August 2, 2003, scientists announced that the depletion of the ozone layer may be slowing down due to the international ban on chlorofluorocarbons. http://news.independent.co.uk/world/environment/story.jsp?story=429802 Three satellites and three ground stations confirmed that the upper atmosphere ozone depletion rate has slowed down significantly during the past decade. The study was organized by the American Geophysical Union. Some breakdown can be expected to continue due to CFCs used by nations which have not banned them, and due to gases which are already in the stratosphere.

Related Topics:
August 2 - 2003 - Chlorofluorocarbons - American Geophysical Union

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