From: nasanews
Date: Dec 19 20:48 UTC
Subject: NASA Confirms CFCs Caused Ozone Hole
NASA'S UARS CONFIRMS CFCs CAUSED ANTARCTIC OZONE HOLE
Three years of data from NASA's Upper Atmosphere Research Satellite
(UARS) have provided conclusive evidence that human-made chlorine in
the stratosphere is the cause of the Antarctic ozone hole.
UARS instruments have found chlorofluorocarbons (CFCs)--human-made
products used in electronics and refrigeration systems--in the
stratosphere. The satellite's global data set also has traced
worldwide buildup of stratospheric fluorine gases corresponding to the
breakdown of CFCs, according to NASA scientists.
For many years, scientists have warned that the widespread use of
chlorofluorocarbons in refrigeration, spray cans and foam packaging was
responsible for stratospheric ozone loss. The stratospheric ozone
layer protects people, animals and plants from too much ultraviolet
sunlight. The Antarctic ozone hole is a dramatic example of
stratospheric ozone loss, which most scientists believe is a new
phenomenon caused by the release of chlorine from human-made
chlorofluorocarbons.
In the past few years, some debate has occurred over the origin of
ozone-destroying chlorine. Sea spray and volcanic gases have been put
forth as possible sources for chlorine reaching the stratosphere. The
UARS data have ended that debate.
"These new results confirm our theories about CFCs," said Dr. Mark
Schoeberl, UARS Project Scientist. "The detection of stratospheric
fluorine gases, which are not natural, eliminates the possibility that
chlorine from volcanic eruptions or some other natural source is
responsible for the ozone hole." In addition to CFCs, UARS has
detected hydrogen fluoride, a product of the chemical breakdown of
CFCs, in the stratosphere.
"Hydrogen fluoride has no natural source, it is not produced by
volcanic eruptions or salt spray," said Dr. Anne Douglass, UARS Deputy
Project Scientist. "Furthermore, scientists can calculate how much
chlorine in the stratosphere is man-made using the hydrogen fluoride
data." This calculation shows that almost all of the chlorine in the
stratosphere comes from human-made chlorofluorocarbons.
The UARS measurements of chlorofluorocarbons were made with the
Cryogenic Limb Array Etalon Spectrometer, operated by Dr. Aiden Roche
of Lockheed Palo Alto Research Laboratory. The hydrogen fluoride
measurements were made with the Halogen Occultation Experiment,
operated by Dr. James Russell of NASA's Langley Research Center,
Hampton, VA.
Each year since 1979, the ozone layer thins dramatically over
Antarctica. This sudden change in the ozone was first noticed by
researchers in Antarctica and soon confirmed by NASA satellites. The
unpredicted Antarctic ozone loss gave scientists a challenging puzzle.
Aircraft observations in 1987 showed convincingly that the high
concentrations of chlorine monoxide over Antarctica were destroying
ozone in the lower stratosphere. Most scientists were convinced that a
series of chemical reactions involving chlorine monoxide and ozone led
to the formation of the ozone hole.
Two questions, however, remained: why was the change in the ozone
layer taking place over Antarctica, and what was the source of the
chlorine monoxide? Meteorologists long have known that the Antarctic
stratosphere can be one of the coldest places on the planet. Air is so
cold that wispy clouds can form even in the super-dry stratospheric
air. These clouds, called polar stratospheric clouds, form in the dead
of winter. Scientists believe that chemical reactions on the surface
of the cloud crystals release chlorine from "reservoir" gases, which do
not react with ozone. The chlorine reacts quickly with ozone to form
chlorine monoxide. This reaction begins the catalytic cycle in which
one chlorine atom can ultimately destroy many ozone molecules, leading
to the polar ozone hole.
UARS has measured the winter build up of chlorine monoxide within the
south and north polar regions every year since its launch. UARS has
found that chlorine monoxide appears suddenly in the stratosphere after
the formation of the polar stratospheric clouds. Infrared and
microwave sensors on board UARS are able to track stratospheric clouds
and the chemical changes they cause.
UARS measurements have confirmed that the chlorine monoxide can build
up to extreme levels in the polar regions after polar stratospheric
clouds appear. UARS data also have shown that the meteorology of the
polar stratosphere prevents the chlorine monoxide from dispersing, thus
increasing the ozone loss.
"We are getting daily polar maps of ozone-destroying chemicals," said
Douglass. "These measurements are adding tremendously to our knowledge
of the stratosphere."
The UARS data set also has provided a clearer picture of the overall
chemistry of the stratosphere. UARS instruments have tracked the
levels of chlorine "source" gases (CFCs), intermediate products
(chlorine monoxide) and reservoir gases (hydrogen fluoride, hydrogen
chloride and chlorine nitrate).
Under international treaties controlling the use of ozone-depleting
chemicals, the amounts of CFCs in the atmosphere no longer are
increasing. However, CFCs survive in the atmosphere for many years
before being destroyed by ultraviolet light, and the ozone hole is
expected to persist at current levels through this decade. (Their
stability was one of their biggest assets when they were developed for
industrial use in the 1930s.) Unless other conditions change,
scientists expect the ozone hole to weaken and disappear in the 21st
century.
UARS was the first satellite launched as part of NASA's Mission to
Planet Earth, a comprehensive study of how the Earth's global
environment changes, and how human activities contribute to that
change. Mission to Planet Earth includes satellites, Space Shuttle
instruments, aircraft research and ground teams. Goddard Space Flight
Center, Greenbelt, MD, manages UARS for NASA's Office of Mission to
Planet Earth, Washington, DC.
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- T o d d E. V a n H o o s e a r -
``'''vanhoose@lalaland.cl.msu.edu - vanhoose@msu.edu - vanhoose@lalaland.cl.msu.edu
(._.) Michigan State University - East Lansing, MI USA
(_) Computer Laboratory - Department of Communication
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"I'd love to change the world, but they won't give me the source code!"
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