Overview
The Ozone layer is a layer in the lower stratosphere, 15 km to 35 km above the earth's surface that contains relatively high concentrations of ozone. The ozone layer provides protection from the sun's UV rays by absorbing 97 - 99 percent of the rays before they hit the earth. It's especially the more harmful UV-B and UV-C rays that are absorbed.
Ozone depletion occurs when free radical catalysts like nitric oxide (NO), hydroxyl (OH), atomic chlorine (Cl) and atomic bromine (Br) where they initiate and catalyze a chain reaction that breaks down the ozone molecules. The release of large quantities of manmade organohalogen compunds, especially chlorofluorcarbons (CFCs) and bromofluorocarbons since the late 1970s are strongly considered to be the cause of ozone depletion and the formation of the “ozone hole” over the Antarctic in winter and late spring.
The reason ozone depletion is observed more over Antarctica than the Arctic or other parts of the earth is due to temperature and wind conditions. The colder temperatures (as low as -80º C) observed in the stratosphere over the Antarctic, particularly in winter and spring, are more conducive for chemical reactions and ozone depletion; but also the transport of ozone rich air into the Arctic stratosphere by winds from lower latitudes is more prevalent than in the Antarctic stratosphere.
Since CFCs were banned in products with the Montreal Protocol of 1987 the severity of ozone depletion has been observed to have lessened as predicted by scientists.
Wikipedia, Ozone Layer
Wikipedia, Ozone Depletion
NOAA Earth System Research Laboratory
Supporting Viewpoints
NASA Ozone Resource: Each year, the depleted region in Earth's protective ozone layer over the Antarctic, or "ozone hole," reaches its largest size during a period in September. Data from NASA's Earth-observing Aura satellite show that during 2007 the ozone hole peaked in size on September 13, reaching a maximum area extent of 9.7 million square miles – just larger than the size of North America. That's "pretty average," says Paul Newman, an atmospheric scientist at NASA Goddard Space Fight Center, when compared to the area of ozone holes measured over the last 15 years. Still, the extent this year was "very big," he says, compared to 1970s when the hole did not yet exist.
While the media focus has been on the number of incidences of skin cancers in , the UV rays from the reduced ozone layer could also affect marine life, as the source of their food, microscopic algae called phytoplankton at the bottom of the food chain are subjected to higher UV-B rays.
Supporting Websites
NOAA Earth System Research Laboratory
US Environmental Protection Agency
The Ozone Hole
European Environment Agency
Beyond Discovery
Weather Underground
The Climate Institute
Real Climat
University of Cambridge, Centre for Atmospheric Science
Opposing Viewpoints
At the time the theories about the cause of the ozone hole first came out, there were numerous skeptics that questioned the validity of the theory and the economic viability of discontinuing use of CFCs. Since then most of those skeptics have been quieted by the overwhelming evidence linking ozone depletion to CFCs, although there remain some questions of how this process occurs in the stratosphere. |