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Ozone decreasing over U.S.

Ozone decreasing over U.S.

The protective ozone layer over the United States and other populated regions in the Northern Hemisphere is thinning at twice the previously reported rate, according to a scientific assessment announced last week by EPA Administrator William K. Reilly.

In 1988, researchers who analyzed satellite and ground-based measurements for the period 1969 to 1986 concluded that winter ozone levels had dropped by 1.7 to 3 percent during that time in the latitude band between New Orleans and the Arctic Circle. But the new analysis, which includes the last several years, shows wintertime ozone values decreasing even faster, at a rate of 6 to 8 percent per decade over the latitude range including the United States.

Scientists believe that chemical pollutants -- principally chlorofluorocarbons and halons -- are causing the ozone depletions over the United States, although they have yet to gather enough data to establish a cause-and-effect relationship. These same compounds generate the Antarctic ozone hole each year.

The new research, conducted by NASA, indicates that the Northern Hemisphere ozone thinning extends into springtime, when most people are exposed to more sunlight. In the region north of Memphis, Tenn., ozone levels for April and May have dropped by 3 to 5 percent over the last decade.

As ozone levels decrease, increasing amounts of the harmful ultraviolet radiation in sunlight penetrate the atmosphere to reach Earth's surface. The EPA estimates that the ozone trends detected in the new study will cause 12 million new cases of skin cancer in the United States over the next 50 years, resulting in 200,000 deaths during that period.
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Title Annotation:ozone layer
Publication:Science News
Date:Apr 13, 1991
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