Ozone Layer

ozone layer or ozonosphere, region of the stratosphere containing relatively high concentrations of ozone, 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 and cataracts and have been implicated in the decline of certain amphibian species.

In 1974 scientists warned that certain industrial chemicals, e.g., chlorofluorocarbons (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 Protocol, 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.

The Columbia Encyclopedia, 6th ed. Copyright© 2014, The Columbia University Press.

Selected full-text books and articles on this topic

Protecting the Ozone Layer: Science and Strategy
Edward A. Parson.
Oxford University Press, 2003
The Ozone Layer: A Philosophy of Science Perspective
Maureen Christie.
Cambridge University Press, 2001
Transnational Environmental Policy: Reconstructing Ozone
Reiner Grundmann.
Routledge, 2001
Principles of International Environmental Law
Philippe Sands.
Cambridge University Press, 2003 (2nd edition)
Librarian’s tip: Chap. 8 "Atmosphere"
Ozone's Janus Face: Ground-Level Ozone Presents One of the Most Complex Air-Quality Issues Facing the Nation Today
Meagher, James F.
Forum for Applied Research and Public Policy, Vol. 16, No. 3, Fall 2001
Evildoer or Do-Gooder: Getting the Goods on Ozone
Fisher, Diane K.
The Technology Teacher, Vol. 68, No. 1, September 2008
PEER-REVIEWED PERIODICAL
Peer-reviewed publications on Questia are publications containing articles which were subject to evaluation for accuracy and substance by professional peers of the article's author(s).
Unlayering of the Ozone: An Earth Sans Sunscreen
Shanklin, Jonathan.
UN Chronicle, Vol. 46, No. 3-4, September 2009
Ozone Nation; EPA Standard Panned by the People
Weinhold, Bob.
Environmental Health Perspectives, Vol. 116, No. 7, July 2008
PEER-REVIEWED PERIODICAL
Peer-reviewed publications on Questia are publications containing articles which were subject to evaluation for accuracy and substance by professional peers of the article's author(s).
Global Public Goods: International Cooperation in the 21st Century
Inge Kaul; Isabelle Grunberg; Marc A. Stern.
Oxford University Press, 1999
The Environmental Debate: A Documentary History
Peninah Neimark; Peter Rhoades Mott.
Greenwood Press, 1999
Librarian’s tip: Includes Montreal Protocol 1987, UN Convention 1992 and 1985 on Ozone Depletion
Climate Change, Tropospheric Ozone and Particulate Matter, and Health Impacts
Ebi, Kristie L.; McGregor, Glenn.
Environmental Health Perspectives, Vol. 116, No. 11, November 2008
PEER-REVIEWED PERIODICAL
Peer-reviewed publications on Questia are publications containing articles which were subject to evaluation for accuracy and substance by professional peers of the article's author(s).
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