ARCTIC OZONE DEPLETION LINKED TO LONGEVITY OF POLAR STRATOSPHERIC CLOUDS
A significant decline in ozone over the Arctic last winter was due to
an increase in the area and longevity of polar stratospheric clouds (PSCs),
according to a group of researchers who participated in a large,
international atmospheric science campaign.
The ozone-destroying clouds are made of ice and nitric acid, said
University of Colorado at Boulder Professor Owen B. Toon, one of five
project scientists heading up NASA's SAGE III Ozone Loss and Validation
Experiment, or SOLVE. The massive SOLVE project involved satellites,
aircraft, balloons and ground-based instruments operated from December 1999
through March 2000 by more than 200 scientists and support staff from the
United States, Canada, Europe, Russia and Japan.
"Even very small numbers of particles in PSCs can efficiently remove
nitrogen from the stratosphere," said Eric Jensen, a scientist at NASA Ames
Research Center, located in California's Silicon Valley. "We found that
the clouds lasted longer during the 1999-2000 winter than during past
winters, allowing greater ozone depletion over the Arctic."
Polar stratospheric clouds generally form about 13 miles above the
poles where temperatures can drop to minus 110 degrees Fahrenheit and
below, said Toon, a professor in CU-Boulder's Laboratory for Atmospheric
and Space Physics. The SOLVE campaign was staged out of Kiruna, Sweden.
In some parts of the Arctic stratosphere -- which is located from
about 10 miles to 30 miles above Earth -- ozone concentrations declined as
much as 60 percent from November 1999 through March 2000. The fragile
stratospheric ozone layer shields life on Earth from the harmful effects of
ultraviolet radiation.
Toon was the co-project scientist in charge of NASA's DC-8 aircraft
that made about 25 flights over the region last winter. He will
participate in a news briefing on the subject at the spring meeting of the
American Geophysical Union to be held May 30 to June 3 in Washington DC.
Other panelists include Eric Jensen of NASA's Ames Research Center, Moffett
Field, CA.; Edward Browell of NASA's Langley Research Center, Hampton, VA;
Ken Carslaw of the University of Leeds in the United Kingdom; and Michael
Kurylo of NASA's Upper Atmosphere Research Program, NASA Headquarters,
Washington, DC.
Although seasonal ozone loss is more severe in the Antarctic, the
ozone loss in the Arctic presents potentially more serious health problems
to human beings, said Toon. Ozone-depleted air from the Arctic drifts
south toward North America, Europe and Russia each spring, increasing the
amounts of ultraviolet light reaching Earth's surface in the highly
populated mid-latitudes and potentially causing increases in several types
of cancer.
Most chlorine compounds pumped into Earth's atmosphere in recent
decades by human activity initially were tied up as chlorine nitlth problems
to human beings, said Toon. Ozone-depleted air from the Arctic drifts
south toward North America, Europe and Russia each spring, increasing the
amounts of ultraviolet light reaching Earth's surface in the highly
populated mid-latitudes and potentially causing increases in several types
of cancer.
Most chlorine compounds pumped into Earth's atmosphere in recent
decades by human activity initially were tied up as chlorine nitlth problems
to human beings, said Toon. Ozone-depleted air from the Arctic drifts
south toward North America, Europe and Russia each spring, increasing the
amounts of ultraviolet light reaching Earth's surface in the highly
populated mid-latitudes and potentially causing increases in several types
of cancer.
Most chlorine compounds pumped into Earth's atmosphere in recent
decades by human activity initially were tied up as chlorine nitrate or
hydrochloric acid, both of which are non-reactive. But if there is a
surface area to attach to like the polar stratospheric cloud ice crystals,
the chlorine compounds change into ozone-gobbling chlorine radicals in late
winter and early spring after reacting with sunlight.
The greenhouse effect, which warms Earth near its surface, may
ironically be cooling the stratosphere enough to cause these clouds to form
earlier and persist longer. Greenhouse gases are radiating energy and heat
away from the upper stratosphere, creating prime conditions for polar
stratospheric cloud formation.
"With the clouds persisting longer, we are seeing greater ozone losses
even though the amount of chlorine in the atmosphere has declined
slightly," said Toon. Manufacture of chlorofluorocarbons ceased in 1996 in
signatory countries under the terms of the Montreal Protocol and its
amendments.
Color photos of polar stratospheric clouds from SOLVE are available on
the Internet at:
http://www.george.arc.nasa.gov/dx/basket/pix/pscpix/PSCcloudcaps/PSCpix.html.
Downlink information for obtaining video footage of polar stratospheric
clouds can be obtained on NASA-TV's Internet site at:
http://www.nasa.gov/ntv.
NASA TV video footage will be available starting
May 30 at noon EDT
on GE-2, transponder 9C at 85 degrees West longitude, with vertical
polarization. Frequency is on 3880.0 megahertz, with audio on 6.8
megahertz.