Ozone hole is smaller than last year.
"Before the patient can recover, it has to stop getting sicker. The hole doesn't seem to be getting bigger. This is the first indication that we have of what we expect," says David J. Hofmann of the National Oceanic and Atmospheric Administration in Boulder, Colo.
The ozone hole develops in the stratosphere over Antarctica in the Southern Hemisphere's springtime, when sunlight returns to the polar region. The light catalyzes chemical reactions involving chlorine and bromine pollutants that destroy ozone.
Satellite measurements reveal that the ozone hole was slightly smaller this year, covering an area of 25.0 million square kilometers on Sept. 15, compared with last year's record size of 27.2 million sq km, says Richard D. McPeters of NASA's Goddard Space Hight Center in Greenbelt, Md. (SN: 10/17/98, p.246).
Satellite- and balloon-borne instruments showed that the amount of ozone over Antarctica bottomed out in early October at a value of 90 to 92 Dobson units, the same as last year.
Researchers have recently documented that the amount of ozone-destroying compounds in the atmosphere has stopped rising, thanks to international limits on these chemicals (SN: 3/9/96, p.151). It will take a decade or more, however, before the ozone hole actually starts to shrink by a significant amount, says Hofmann. The difference between 1999 and 1998 resulted from year-to-year fluctuations in Antarctic weather, he says.
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|Article Type:||Brief Article|
|Date:||Oct 23, 1999|
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