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ozone layer |
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ozone layer or ozonosphere, region of the stratosphere stratosphere , 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.
..... Click the link for more information. containing relatively high concentrations of ozone ozone , 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. ..... Click the link for more information. , 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 cancers skin 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. In 1974 scientists warned that certain industrial chemicals, e.g., chlorofluorocarbons chlorofluorocarbons (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 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 Protocol Montreal 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. ozone layeror ozonosphereRegion in the upper atmosphere, about 6–30 mi (10–50 km) high, with significant concentrations of ozone, formed by the effect of solar ultraviolet (UV) radiation on oxygen and also present in trace quantities elsewhere in earth's atmosphere. Ozone strongly absorbs solar UV radiation, causing atmospheric temperature to climb to about 30°F (0°C) at the top of the layer, and preventing much of this radiation from reaching earth's surface, where it would injure many living things. Chlorofluorocarbons, or CFCs, and some other air pollutants that diffuse into the ozone layer destroy ozone. In the mid-1980s, scientists discovered that a “hole”—an area where the ozone is up to 50% thinner than normal—develops periodically in the ozone layer above Antarctica. This severe regional depletion, explained as a natural seasonal depletion, appears to have been exacerbated by the effects of CFCs, and may have led to an increase in skin cancer caused by UV exposure. Restrictions on the manufacture and use of CFCs and other ozone-destroying pollutants were imposed in 1978. ozone layer [′ō‚zōn ‚lāยทər] (meteorology) Want to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit the webmaster's page for free fun content. |
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