ozone layer

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ozone layer



region of the stratospherestratosphere
, second lowest layer of the earth's atmosphere. The level from which it extends outward varies with latitude; it begins c.5 1-2 mi (9 km) above the poles, c.6 or 7 mi (c.10 or 11 km) in the middle latitudes, and c.10 mi (16 km) at the equator, and extends outward c.
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 containing relatively high concentrations of ozoneozone
, an allotropic form of the chemical element oxygen (see allotropy). Pure ozone is an unstable, faintly bluish gas with a characteristic fresh, penetrating odor. The gas has a density of 2.144 grams per liter at STP.
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, located at altitudes of 12–30 mi (19–48 km) above the earth's surface. Ozone in the ozone layer is formed by the action of solar ultraviolet light on oxygen.

The ozone layer prevents most ultraviolet (UV) and other high-energy radiation from penetrating to the earth's surface but does allow through sufficient ultraviolet rays to support the activation of vitamin D in humans. The full radiation, if unhindered by this filtering effect, would destroy animal tissue. Higher levels of radiation resulting from the depletion of the ozone layer have been linked with increases in skin cancersskin cancer,
malignant tumor of the skin. The most common types of skin cancer are basal cell carcinoma, squamous cell carcinoma, and melanoma. Rarer forms include mycosis fungoides (a type of lymphoma) and Kaposi's sarcoma.
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 and cataractscataract,
in medicine, opacity of the lens of the eye, which impairs vision. In the young, cataracts are generally congenital or hereditary; later they are usually the result of degenerative changes brought on by aging or systemic disease (diabetes).
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 and have been implicated in the decline of certain amphibian species.

In 1974 scientists warned that certain industrial chemicals, e.g., chlorofluorocarbonschlorofluorocarbons
(CFCs), organic compounds that contain carbon, chlorine, and fluorine atoms. CFCs are highly effective refrigerants that were developed in response to the pressing need to eliminate toxic and flammable substances, such as sulfur dioxide and ammonia, in
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 (CFCs) and to a lesser extent, halons and carbon tetrachloride, could migrate to the stratosphere. There, sunlight could free the chlorine or bromine atoms to form chlorine monoxide or other chemicals, which would deplete upper-atmospheric ozone. A seasonal decrease, or "hole," in the ozone layer above Antarctica, first discovered in 1982 and reported in 1985, was the first confirmation of a thinning of the layer. The hole occurs over Antarctica because the extreme cold helps the very high clouds characteristic of that area form tiny ice particles of water and nitric acid, which facilitate the chemical reactions involved. In addition, the polar winds, which follow a swirling pattern, create a confined vortex, trapping the chemicals. When the Antarctic spring sun rises in August or September and hits the trapped chemicals, a chain reaction begins in which chlorine, bromine (from the halons), and ice crystals react with the ozone and destroy it very quickly. The effect usually lasts through November. There is a corresponding hole over the Arctic that similarly appears in the spring, although in some years warmer winters there do not result in a major depletion of the ozone layer. A global thinning of the ozone layer results as ozone-rich air from the remaining ozone layer flows into the ozone-poor areas.

Minimum ozone levels in the Antarctic decreased steadily throughout the 1990s, and less dramatic decreases have been found above other areas of the world. In 2000 (and again in 2003 and 2006) the hole reached a record size, extending over more than 10.5 million sq mi (27 million sq km), an area greater than that of North America. In 1987 an international agreement, the Montreal ProtocolMontreal Protocol,
officially the Protocol on Substances That Deplete the Ozone Layer, treaty signed on Sept. 16, 1987, at Montreal by 25 nations; 168 nations are now parties to the accord.
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, was reached on reducing the production of ozone-depleting compounds. Revisions in 1992 called for an end to the production of the worst of such compounds by 1996, and CFC emissions dropped dramatically by 1993. Recovery of the ozone layer, however, is expected to take 50 to 100 years. Damage to the ozone layer can also be caused by sulfuric acid droplets produced by volcanic eruptions.

ozone layer

(oh -zohn) See atmospheric layers.

Ozone layer

Defined by the EPA (U.S. Environmental Protection Agency) as the protective layer of atmosphere 1215 miles above the ground that absorbs some of the sun’s ultraviolet rays, reducing the amount of potentially harmful radiation reaching the earth’s surface. Ozone depletion is caused by the breakdown of certain chlorine-and/ or bromine-containing compounds such as CFCs (chlorofluorocarbons) or halons.

ozone layer

[′ō‚zōn ‚lā·ər]


ozonosphereclick for a larger image
The general stratum of the upper atmosphere in which there is an appreciable ozone concentration and ozone plays an important part in the radiative balance of the atmosphere. It lies roughly between 6 and 30 miles (10–50 km), with the maximum ozone concentration at about 12 to 15 miles (20–25 km). Also known as an ozone layer.
References in periodicals archive ?
Thirty years ago, the international community had signed the Vienna Convention for the Protection of the Ozone Layer.
There was a team of 300 scientists, co-chaired by Newman, assessed the ozone layers once in every four years.
Levels of most ozone-depleting chemicals in the atmosphere have been gradually declining since an international treaty to protect the ozone layer, the 1987 Montreal Protocol, was signed.
To help protect the ozone layer stop using aerosols, use roll-ons, and also walk, don't take the car
And it claimed that international efforts to protect the ozone layer have averted millions of cases of skin cancer worldwide.
If we succeed in taking all the necessary measures, the ozone layer is expected to repair itself within the next five decades.
Meeting or exceeding GreenChill certification criteria will help prevent deterioration of the Earth's protective ozone layer and is combating climate change, the EPA says.
Emission of CFC in the air damages ozone layer which causes cancer, cataract (Blindness), skin aging and suppression of body immune system," he said addressing the workshop organised by Ozone Cell of Ministry of Environment in collaboration with UNEP.
Under the theme "Montreal Protocol--Global Partnership for Global Benefits," the OzonAction Branch of the United Nations Environment Programme (UNEP); the United Nations Educational, scientific and Cultural Organization (UNESCO); the United Nations Children's Fund (UNICEF); and the World Health Organization (WHO) announced the launch of the new OzoAction Education Pack for Secondary Schools entitled "High Sky" during the celebration of the International Day for the Preservation of the Ozone Layer in September.
But the same type of debate occurred in the 1980s when atmospheric scientists found that a widely used class of chemicals was damaging the Earth's protective ozone layer.
In this way, the GEF made a significant contribution to the ongoing success of the Montreal Protocol, and to the hope the world now holds for a repair of the damage done to the ozone layer and the detrimental impact it has had on the health of the earth and its inhabitants.
THE Earth's ozone layer appears to be slowly recovering thanks to the introduction of a global ban on chlorine pollutants, scientists said today.