Study Sheds Light on Ozone Hole Chemistry
Map of chlorine
monoxide, the primary agent of ozone destruction in the Antarctic 'ozone hole,'
as measured by the Microwave Limb Sounder instrument on NASA's Aura satellite at
an altitude of approximately 18 kilometers (11.2 miles) within the ozone layer.
Image credit: NASA/JPL
2010-PASADENA, Calif. – A new NASA study of Earth's polar ozone layer reinforces
scientists' understanding of how human-produced chlorine chemicals involved in
the destruction of ozone interact with each other.
A team of scientists led by Michelle Santee of NASA's Jet Propulsion Laboratory,
Pasadena, Calif., examined how nighttime temperatures affect chlorine monoxide,
a key chemical involved in ozone destruction. Combining NASA satellite
measurements with a state-of-the-art chemical model, they found this
relationship to be more consistent with recent laboratory work than with some
older laboratory and field observational data. This verification is important,
because scientists have not been able to conduct appropriate laboratory
experiments relevant to understanding how polar chlorine monoxide behaves at
night at the lowest temperatures of the stratosphere, Earth's second lowest
Santee and her team published their findings this month in the Proceedings of
the National Academy of Sciences. The data came from the Microwave Limb Sounder
instrument on NASA's Aura satellite.
"Our comprehensive study uses multiple years of Arctic and Antarctic satellite
observations to quantify the nighttime balance of ozone-destroying chlorine
chemical compounds," said Santee. "By gaining a better knowledge of this
balance, scientists will be able to make more accurate predictions of polar
ozone loss, especially in twilight and in the Arctic, where conditions are often
only marginally favorable for ozone destruction."
At night, chlorine monoxide molecules combine to form chlorine peroxide, and the
balance between these two chemicals is highly temperature-sensitive. Studying
this balance quantitatively is challenging. Previous studies in the laboratory
and using aircraft and satellites had found significantly different degrees of
balance. The Microwave Limb Sounder's very large number of measurements has
quantified this balance far better than before.
The new research contributes to scientific understanding of the phenomenon more
commonly known as the "ozone hole." Each year in late winter and early spring in
the southern hemisphere, chlorine and bromine from human-produced compounds
cause the nearly total destruction of ozone in Earth's stratosphere in a layer
about 20 kilometers (12 miles) above Antarctica. These source gases that are
responsible for the greatest destruction of the ozone layer are now declining in
response to the 1985 Montreal Protocol and its amendments.
Since its launch in 2004, the Microwave Limb Sounder has monitored most of the
polar regions of both hemispheres daily, compiling tens of thousands of
measurements of nighttime chlorine monoxide levels, along with various other
chemicals, including ozone. These data are allowing scientists to test their
understanding of chlorine-related chemistry on an unprecedented scale.
For more information on the Microwave Limb Sounder, see
JPL is managed for NASA by the California Institute of Technology in Pasadena.
Alan Buis 818-354-0880
Jet Propulsion Laboratory, Pasadena, Calif.