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'''Ozone''' is a chemical [[compound]] consisting of three [[oxygen]] atoms.  It is represented by the symbol O₃.

'''Ozone''' is a chemical [[compound]] consisting of three [[oxygen]] atoms.  It is represented by the symbol O₃.

It is unstable at standard temperatures and pressures, and a powerful [[oxidizer]].  At the earth's surface it occurs naturally as a result of electrical discharges, most prominently, [[lightning]]. It is also created by [[man-made]] sparks, such as in an electrical motor.   

It is unstable at standard temperatures and pressures, and a powerful [[oxidizer]].  At the earth's surface it occurs naturally as a result of electrical discharges, most prominently in the form of [[lightning]]. It is also created by [[man-made]] sparks, such as in an electrical motor.   

In the stratosphere it serves a very important function, by acting to filter out most of the sun's ultraviolet radiation.   

In the stratosphere it serves a very important function, by acting to filter out most of the [[sun]]'s ultraviolet radiation.   

Scientists have measured an annual, tempororary thinning layer of ozone over the north and south poles, called an "ozone hole".<ref>http://ozonewatch.gsfc.nasa.gov/facts/hole.html</ref>

Scientists have measured an annual, temporary thinning layer of ozone over the north and south poles, called an "ozone hole".<ref>http://ozonewatch.gsfc.nasa.gov/facts/hole.html</ref>

What is controversial is much of this is a result of the breakdown of [[chlorofluorocarbons]] and the release of elemental [[chlorine]], which acts as [[catalyst]]s to break down the O₃ molecules.<ref>Chlorofluorocarbons (CFCs) themselves are not involved in the catalytic process; upon reaching the stratosphere, they are subject to higher levels of ultraviolet radiation that decompose the CFC and release atomic chlorine. [http://www.ciesin.columbia.edu/TG/OZ/ozndplt.html Catalytic destruction of ozone] </ref>

Much of this is a result of the breakdown of [[chlorofluorocarbons]] and the release of elemental [[chlorine]], which acts as [[catalyst]]s to break down the O₃ molecules.<ref>Chlorofluorocarbons (CFCs) themselves are not involved in the catalytic process; upon reaching the stratosphere, they are subject to higher levels of ultraviolet radiation that decompose the CFC and release atomic chlorine. [http://www.ciesin.columbia.edu/TG/OZ/ozndplt.html Catalytic destruction of ozone] </ref>

[[Image:Ozonemech.gif|framed|The mechanism by which ozone is broken down in the stratosphere by Cl atoms.  Note that the propagation steps repeat thousands of time, such that one molecule of a CFC can destroy thousands of molecules of O₃]]

[[Image:Ozonemech.gif|framed|The mechanism by which ozone is broken down in the stratosphere by Cl atoms.  Note that the propagation steps repeat thousands of time, such that one molecule of a CFC can destroy thousands of molecules of O₃]]

*In April 1991, the Environmental Protection Agency announced that ozone levels in the Northern Hemisphere shrank as much as 5 percent over the United States in the past 10 years.

*In April 1991, the Environmental Protection Agency announced that ozone levels in the Northern Hemisphere had decreased by as much as 5 percent over the United States in the past 10 years.

*A minority opinion holds that ozone depletion has little to do with CFCs and that the ozone hole may be more natural than man-made. S. Fred Singer, an environmental scientist at the University of Virginia, has argued that a rise in methane or changes in the sun's cycle may affect ozone. He also believes the lack of historical data about ozone depletion makes it difficult to determine if similar changes occurred centuries before hairspray cans were invented. [http://www.coaleducation.org/issues/DEPLET.HTM]

*A minority opinion holds that ozone depletion has little to do with CFCs and that the ozone hole may be more natural than man-made. S. Fred Singer, an environmental scientist at the University of Virginia, has argued that a rise in methane or changes in the sun's cycle may affect ozone. He also believes the lack of historical data about ozone depletion makes it difficult to determine if similar changes occurred centuries before hairspray cans were invented. [http://www.coaleducation.org/issues/DEPLET.HTM]

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[[category:Chemistry]]

[[category:Chemistry]]