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Frequently Asked Questions about the Ozone Hole
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What is the ozone hole?
The "ozone hole" is a loss of stratospheric ozone in springtime over
Antarctica, peaking in September. The ozone hole area is defined as the
size of the region with total ozone below 220 Dobson units (DU). Dobson
Units are a unit of measurement that refer to the thickness of the ozone
layer in a vertical column from the surface to the top of the
atmosphere, a quantity called the "total column ozone amount." Prior to
1979, total column ozone values over Antarctica never fell below 220 DU.
The hole has been proven to be a result of human activities--the release
of huge quantities of chlorofluorocarbons (CFCs) and other ozone
depleting substances into the atmosphere.
How big was the 2007 ozone hole, and is it getting bigger?
Every four years, a team of many of the top scientists researching ozone
depletion put together a comprehensive summary of the scientific
knowledge on the subject, under the auspices of the World Meteorological
Organization (WMO). According to their most recent assessment, (WMO,
2006), monthly total column ozone amounts in September and October
have continued to be 40 to 50% below pre-ozone-hole values, with up to
70% decreases for periods of a week or so. During the last decade, the
average ozone hole area in the spring has increased in size, but not as
rapidly as during the 1980s. It is not yet possible to say whether the
area of the ozone hole has maximized. However, chlorine in the
stratosphere has reached nearly constant levels and is expected to start
declining, so the ozone hole may have seen its maximum size. Annual
variations in temperature will probably be the dominant factor in
determining differences in size of the ozone hole in the near future,
due to the importance of cold-weather Polar Stratospheric Clouds (PSCs)
that act as reactive surfaces to accelerate ozone destruction.
The 2007 hole was fairly average when compared to those of the past 15 years. On September 13, 2007, the hole reached it maximum size of 24 million square kilometers (9.3 million square miles), a full 18% smaller than the 2006 hole. The 2006 hole reached its maximum size of 29 million square kilometers (11.3 million square miles) on September 24, 2006, according to NASA. This is very close to the record ozone hole size of September 10, 2000, uOzone Hole FAQ : Weather Undergroundg m Dating Adult hOzone Hole FAQ : Weather Undergroundi b Free