In the 7- to 11-mile (11- to 18-kilometer) region, the researchers link a slight increase in ozone to changes in atmospheric transport - perhaps caused by natural variability or human-induced climate warming - rather than atmospheric chemistry. The changes in this altitude range - below the region where ozone-depleting gases derived from human activity are thought to cause ozone depletion - contribute about half of the overall-measured improvement, researchers said.
"There is now widespread agreement in the scientific community that ozone is leveling off in the 18- to 25-kilometer region of the stratosphere because of the Montreal Protocol," Cunnold said. "And we believe there is some tendency toward an increase inozone in this region, though further study is needed to be certain.
"In the 11- to 18-kilometer region, ozone is definitely increasing because of changes in atmospheric dynamics and transport not related to the Montreal Protocol," he added."But we don't know the long-term effect this change will have in this region."
Other recent studies complement these new findings. Among them are a study published in 2003 in the Journal of Geophysical Research, which reported a slowdown in the ozone depletion rate in the upper stratosphere at about 22 to 28 miles altitude (35 to 45kilometers). Newchurch at the University of Alabama in Huntsville led this study in collaboration with: Cunnold, his former Ph.D. advisor; Yang, his former Ph.D. student; and other prominent scientists. Newchurch is also an author on the current paper.
More recently, a study published in the journal Nature on May 3, 2006 indicated a stabilization and
Source:Georgia Institute of Technology Research News