NASA satellite observations have provided the first
evidence the rate of ozone depletion in the Earth’s upper
atmosphere is decreasing. This may indicate the first stage
of ozone layer recovery.
From an analysis of ozone observations from NASA’s first and
second Stratospheric Aerosol and Gas Experiment (SAGE) and
the Halogen Occultation Experiment (HALOE) satellite
instruments, scientists have found less ozone depletion in
the upper stratosphere (22-28 miles altitude) after 1997.
The American Geophysical Union Journal of Geophysical
Research has accepted a paper for publication on these
results.
This decrease in the rate of ozone depletion is consistent
with the decline in the atmospheric abundance of man-made
chorine and bromine-containing chemicals that have been
documented by satellite, balloon, aircraft and ground based
measurements.
Concerns about ozone depletion in the upper atmosphere or
stratosphere led to ratification of the Montreal Protocol on
Substances that Deplete the Ozone Layer by the international
community in 1987. The protocol restricts the manufacture
and use of human-made, ozone-depleting compounds, such as
chlorofluorocarbons and halons.
“Ozone is still decreasing but just not as fast,” said Mike
Newchurch, associate professor at the University of Alabama,
Huntsville, Ala., and lead scientist on the study. “We are
still decades away from total ozone recovery. There are a
number of remaining uncertainties such as the effect of
climate change on ozone recovery. Hence, there is a need to
continue this precise long-term ozone data record,” he said.
“This finding would have been impossible had either SAGE II
or HALOE not lasted so long past their normal mission
lifetime,” said Joe Zawodny, scientist on the SAGE II
satellite instrument science team at NASA’s Langley Research
Center, Hampton, Va.
SAGE II is approaching the 19th anniversary of its launch,
and HALOE has been returning data for 11 years. Scientists
also used international ground networks to confirm these
data from satellite results.
SAGE I was launched on the Applications Explorer Mission-B
spacecraft in 1979; the Earth Radiation Budget Satellite
carried SAGE II into orbit in 1984. The Space Shuttle
Discovery carried HALOE into space on the Upper Atmosphere
Research Satellite in 1991.
NASA’s Earth Science Enterprise funded this research in an
effort to better understand and protect our home planet. The
ozone layer protects the Earth’s surface from the sun’s
harmful ultraviolet rays. Ultraviolet radiation can
contribute to skin cancer and cataracts in humans and harm
other animals and plants. Ozone depletion in the
stratosphere also causes the ozone hole that occurs each
spring over Antarctica.
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