December 18, 2000

RECOVERY OF ARCTIC OZONE LAYER MAY TAKE LONGER THAN EXPECTED

Scientists expect that recovery of the Arctic ozone layer may be slower
than previously expected because of unusually low stratospheric
temperatures.

Low temperatures have recently increased ozone losses over the Arctic
despite the phase out of chlorine-containing chlorofluorocarbons and halons.
Researchers noted large losses of stratospheric ozone observed in the Arctic
last spring and the highest local ozone loss ever observed at any given
altitude in that region was recorded with losses at greater than 70%.

Researchers will be holding a press briefing on their findings at the
American Geophysical Union's (AGU) Annual Fall Meeting on December 15 at
4:00 p.m. (Pacific Time) in room 112 at the Moscone Center in San Francisco.
Their research based on new results from recent U.S. and European field
campaigns studying Arctic ozone loss suggests that chlorine and bromine may
destroy more ozone than expected if greenhouse gases continue to increase
and stratospheric temperatures become colder. Paul A. Newman of NASA's
Goddard Space Flight Center in Greenbelt, Md. will introduce panelists Mark
R. Schoeberl, James G. Anderson and Dale Hurst at the press briefing.

These panelists have worked on the joint SAGE III Ozone Loss and
Validation Experiment (SOLVE) and Third European Stratospheric Experiment on
Ozone (THESEO 2000) and obtained comprehensive measurements of halogen
compounds (chlorine and bromine) that have given them a better understanding
of how human-produced compounds destroy the ozone layer. These observations
have shown how factors other than CFCs and halons contribute to winter ozone
decreases.

Deployed from Kiruna, Sweden, balloon and aircraft measurements along
with satellite observations of organic and reactive halogen species and
other long-lived compounds in the stratosphere were obtained within the
Arctic vortex between December 1999 and March 2000. These observations show
that chlorine levels in the stratosphere have peaked and are predicted to
decrease throughout this century. Observations of large ozone losses last
winter in the Arctic have given scientists a better understanding of how
human-produced compounds destroy the ozone layer.

Newman said, "Chlorine and bromine destroy stratospheric ozone in the
Arctic when they are converted into harmful forms on the surfaces of
stratospheric cloud particles." Most of this chlorine and bromine comes from
human-produced compounds such as CFCs and halons. Newman noted, however,
that the observations also show that the total equivalent chlorine
(including bromine and chlorine) levels in the stratosphere have peaked or
nearly peaked at all levels in the stratosphere. Projections of future
declines in the total amount of chlorine and bromine released in the
atmosphere over the next decade will not slow down as rapidly as the past
decade. Most of the improvement in chlorine was made-up by the decline of
methyl chloroform, which will essentially disappear in the next few years.
If these future projections hold true, it suggests that Arctic ozone losses
will persist into the 2050-2070 period.

According to the panelists, Arctic ozone should recover as we progress
through the next century and amounts of chlorine and bromine continue their
decline, but other factors including greenhouse-induced cooling of the
stratosphere could delay future recovery of ozone levels.

Mark R. Schoeberl, a physicist from Goddard will address ozone loss as
observed from satellite, balloons and aircraft. James G. Anderson of Harvard
University in Cambridge, Mass., will discuss the chemistry of the polar
vortex during last winter, and how that chemistry yields information on the
coupling of climate change to ozone losses. Dale Hurst from the University
of Colorado in Boulder, Colo., will present results on the trends of CFCs,
halons, and other trace gases in the stratosphere that have contributed to
ozone loss.

SOLVE is a measurement campaign designed to examine the processes
controlling ozone levels at mid- to high latitudes.

More information and images about the U.S. SOLVE and European THESEO
components can be found at:

SOLVE - http://cloud1.arc.nasa.gov/solve/
http://svs.gsfc.nasa.gov/imagewall/solve.html

THESEO 2000 - http://www.ozone-sec.ch.cam.ac.uk.