9/13/2007-Goddard Space Flight Center
Keeps Eye on Ozone Layer Amid Montreal Protocol’s Success
NASA scientists will join researchers from around the world to celebrate
the 20th anniversary of the Montreal Protocol, an international treaty
designed to reduce the hole in Earth's protective ozone layer. The United
Nations Environment Programme will host the meeting from Sept. 23 to 26 in
Athens, Greece. NASA scientists study climate change and research the timing
of the recovery of the ozone layer.
right: The Antarctic
ozone hole on Sept. 24, 2006, depicted in blue and purple, was equal in size
to the largest single-day area of 11.4 million square miles on record,
previously reached on Sept. 9, 2000. The levels of ozone depleting compounds
in the atmosphere continue to drop, thanks to 20 years of scientific
advances following the signing of the Montreal Protocol. Credit: NASA
"The Montreal Protocol has been a resounding success," said Richard
Stolarski, a speaker at the symposium from NASA's Goddard Space Flight
Center, Greenbelt, Md. "The effect can be seen in the leveling off of
chlorine compounds in the atmosphere and the beginning of their decline."
Since the Montreal Protocol was signed on Sept. 16, 1987, more than 100
nations have agreed to limit the production and release of compounds,
notably human-produced chlorofluorocarbons, known as CFCs. CFCs and a list
of other compounds are known to degrade the layer of ozone in the
stratosphere that shields life from the sun's ultraviolet radiation. That
process gives rise to the ozone hole above Antarctica.
Today, space-based instruments aboard NASA's Aura satellite monitor the
chemical make-up of the atmosphere and collect data that will help
researchers better understand ozone chemistry through computer models. While
the data show that average chlorine levels are beginning to decline,
springtime ozone depletion in the polar regions continues to be a prominent
Image left: Preparations are made to the final mapping instrument,
which launched in 1996 and was decommissioned in May 2007. Thirty years of
the Total Ozone Mapping Spectrometer (TOMS) program afforded researchers
with tools to assess the size of Earth's ozone hole. Credit: NASA
"The goal now is to ensure that CFCs and other emissions continue to fall
to below the levels that produce an ozone hole," said Goddard's Anne
Douglass, the deputy project scientist for Aura. "This won't happen until
NASA and National Oceanic and Atmospheric Administration scientists
announced in 2006 that the hole was the largest ever observed, at 10.6
million square miles. The size of the hole will approach its annual peak in
late September. Scientists at the symposium will discuss 20 years of
scientific progress, as well as how best to monitor the atmosphere to ensure
the goals of the treaty are realized.
In addition to the current satellite measurements, NASA research efforts
use data collected on the ground, in the air and from previous missions.
Data from past satellite observations have been essential to understanding
ozone depletion. NASA's Total Ozone Mapping Spectrometer, or TOMS, was one
of NASA's signature ozone research achievements. TOMS launched in 1978 and
was decommissioned in May 2007.
"The TOMS images of the Antarctic ozone hole caused worldwide alarm and
thus played a key role in the Montreal Protocol and other international
agreements to phase out the offending chemicals from our environment," said
Goddard's Pawan Bhartia, project scientist for the mission. In addition,
measurements from the Stratospheric Aerosol and Gas Experiment, along with
the Microwave Limb Sounder and the Halogen Occultation Experiment aboard the
Upper Atmospheric Research Satellite, were important to scientists'
understanding of ozone.
Image right: The Aura satellite, seen here in an artist's
rendition, houses instruments that monitor the chemical make-up of the
atmosphere and help researchers understand ozone chemistry. Credit: NASA
Scientists collect atmospheric composition data from ground-based
monitoring stations around the world. Researchers have collected
measurements since 1978 for nearly all compounds identified in the Montreal
Protocol. The data come from coastal monitoring stations used in previous
missions and as part of the NASA-sponsored Advanced Global Atmospheric Gases
Airborne instruments have been a critical piece of the scientific search
to find the cause of ozone depletion, and they remain central to NASA's
research efforts today.
Data from NASA's Airborne Antarctic Ozone Experiment in 1987 "provided the
smoking gun measurements that nailed down the cause of the ozone hole being
the increase of CFCs combined with the unique meteorology of the Antarctic,"
Stolarski said. Since then, NASA has sponsored several airborne field
campaigns that have furthered understanding of the chemical processes
These measurements are key for researchers working to predict the future
of the global ozone layer. The differences between loss and recovery of
ozone at the poles and in non-polar regions are complex. "Such complexity
has led to heated debates over the timing and extent of recovery," said Ross
Salawitch, an atmospheric chemist at the Jet Propulsion Laboratory,
The modern focus in ozone research also has shifted to include the effects
of climate change. "Twenty years ago we went out of our way to separate
ozone depletion from climate change," Salawitch said. "After a decade of
looking at data, the community realizes they are linked in subtle but
profoundly important ways."