FOR IMMEDIATE RELEASE
Contact: Barbara McGehan
The process of recovery of the ozone layer is in its first stages, scientists at the Commerce Department's National Oceanic and Atmospheric Administration said today. Data from instrumented NOAA balloons at the South Pole indicate that the ozone hole, while severe, is similar to that observed in 1998.
Although small variations in the severity of the ozone hole from year to year are expected, the fact that the 1999 hole was no larger or deeper than that in 1998 is good news, according to David Hofmann, director of the Climate Monitoring and Diagnostics Laboratory in Boulder, Colo.
"This observation means that chlorine is no longer increasing in the stratosphere, which is the first step to recovery. Our job now is to keep watch on both the ozone hole and ozone-destroying molecules in the atmosphere to make sure that the road to recovery does not meet any unexpected detours," Hofmann said.
Balloon soundings at the South Pole showed that as in the past several years, ozone was totally destroyed between about nine and 13 miles altitude. Total column ozone averaged about 100 Dobson units between Sept. 25 and Oct. 5, the period of lowest ozone values, which is similar to the lowest values in 1998. A Dobson unit is a unit of measurement that describes the thickness of the ozone layer in a column directly above the location being measured. Prior to the springtime ozone depletion period in Antarctica, total ozone readings are about 275-300 Dobson Units.
Each spring, when the sun rises over Antarctica,
chemical reactions involving chlorine from man-made CFCs, or
chlororfluorocarbons, occur in the stratosphere, destroying ozone
and causing the "ozone
hole." An international assessment of the status of
the global ozone layer, produced by hundreds of scientists for
the World Meteorological
Observations from instruments aboard both NOAA and NASA satellites showed that the size of this year's Antarctic ozone hole was somewhat smaller than last year. Such year-to-year variations in the area covered by the ozone hole are expected. Hofmann says that "since chlorine in the atmosphere is reaching nearly constant levels, annual variations in temperature, which affect the rate of the chemical reactions, will be the dominant factor in determining small differences in both the area covered by the ozone hole, as measured by satellites, and the depth of the ozone hole, as measured by balloons." Total recovery of the ozone hole back to levels observed before 1980 will take at least 50 years.
Balloon-borne ozone profiles and an animation of the profiles from the South Pole are available at : http://www.cmdl.noaa.gov/
For color images of the ozone hole as observed
by NOAA satellites: http://www.cpc.ncep.noaa.gov/