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 ?
Protection of ozone layer, the ultimate objective of the Montreal Protocol on Substances that deplete the ozone layer, is must to allow the life on earth to prosper in a sustainable manner.
UV-B is also absorbed by ozone layer in the stratosphere and only 2-3% of it reaches the earth's surface.
If the production of such gases was not prevented, the ozone layer would be destroyed, threatening life on the earth, he explained.
On this International Day for the Preservation of the Ozone Layer, I commend all who have made the Montreal Protocol such an outstanding example of international cooperation.
The next chapters contain description of the methods used for the monitoring of (i) the solar UV radiation and the measurement of ozone layer thickness, (ii) presentation of obtained results with discussion and finally (iii) conclusion.
It was in 1994 that the UN General Assembly announced September 16 as International Day for the preservation of the Ozone Layer.
If we succeed in taking all the necessary measures, the ozone layer is expected to repair itself within the next five decades.
He said, emission of CFC in the air damages ozone layer which ultimately allows harmful Ultraviolet-B radiations of the Sun on the Earth.
MoE Secretary Muhammad Javed Malik said depletion of Ozone layer was a serious global issue equally important like other environmental problems such as pollution, drought and desertification, loss of forests, disposal of solid and liquid wastes and loss of biodiversity.
The invisible ozone layer exists high in the stratosphere, or a layer of the atmosphere that is roughly 10 to 50 kilometers (6 to 31 miles) above Earth.
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.