ANTARCTICA
NEWS ARCHIVES
Preparing
Ozonesondes |
Ozone
Hole Breaks Two Records
Posted:
October 31, 2006
Courtesy:
Antarctic
Sun
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By Peter Rejcek
It’s not the sort of record you like to see
broken, particularly if you live in the Southern Hemisphere.
Scientists from various agencies and universities measuring
ozone depletion over Antarctica say this year’s annual
ozone hole not only matches the largest hole in area on
record, but it is also the deepest that’s ever formed.
On Sept. 24 of this year, the Antarctic ozone hole reached
a one-day record of 29.5 million square kilometers, an area
that spans the entire continent and spills over into parts
of Australia and South America. That’s roughly the
same size as the record-setting hole that appeared over
the region in 2000.
But the vertical disappearance of ozone is even more pronounced
than in previous years, particularly between about 14 and
22 kilometers above the Earth in the mid-section of the
atmosphere known as the stratosphere, according to researchers.
“There is a huge section this year that is completely
depleted to zero,” said Jennifer Mercer, co-principal
investigator (PI) from the University of Wyoming, who is
leading the group carrying out balloon-borne and laser measurements
of the annual ozone depletion event. The ozone hole, a region
in the lower stratosphere centered more or less over the
Antarctic continent, has suffered nearly total depletion
in previous years but never to this vertical extent.
Terry Deshler, also from the University of Wyoming, is the
PI for the team, which deploys each year to McMurdo Station
from roughly mid-August to early November. The group will
launch between 25 and 30 balloons with instruments to take
ozone and aerosol profiles, and other measurements.
The University of Wyoming was one of two universities, in
addition to NASA and the National Oceanographic and Atmospheric
Administration (NOAA), which first came to Antarctica 20
years ago to find the cause behind the ozone hole after
its initial discovery in 1985. State University of New York
at Stoneybrook rounded out the team.
That group — the National Ozone Expedition eventually
determined through balloon-borne, surface-based and laboratory
measurements that chlorine released from chlorofluorocarbons
(CFCs) was the main culprit responsible for stealing ozone
from the atmosphere.
David Hofmann was the PI for the University of Wyoming in
1986. Today, he’s the director of the Global Monitoring
Division at NOAA’s Earth System Research Laboratory
in Boulder, Colo. In that role, he’s the PI for a South
Pole project that measures atmosphere constituents, including
ozone-depleting chemicals. Balloon-borne instruments are
launched from South Pole station year-long.
During a phone interview from his office in Boulder, Hofmann
said that he never expected to still be involved in ozone
depletion studies and research two decades later. Back in
1986, when he and colleagues arrived at McMurdo and South
Pole stations to begin their measurements, the process causing
the ozone hole was not understood very well. In fact, there
was some doubt whether a chemical or dynamic process, such
as a meteorological event, caused the hole. However, it
soon became apparent that a chemical reaction was to blame.
Ozone refresher
Ozone is a somewhat unstable molecule made up of three oxygen
atoms instead of two. It’s found throughout the Earth’s
atmosphere, with the highest levels occurring in the lower
stratosphere, a region commonly referred to as the ozone
layer, between about 10 and 30 kilometers above the planet’s
surface. (The layer just below that is the troposphere,
where we live and breathe.) The ozone layer blocks harmful
ultraviolet rays that have been linked to skin cancer.
The ozone hole over the Antarctic waxes and wanes every
year between August and November as the Antarctic summer
begins. (A similar but far smaller hole occurs above the
Arctic during springtime there.) The hole is the result
of the input of CFCs and other chlorine- and bromine-containing
gases that interact with two naturally occurring events.
One is the polar vortex, a sort of atmospheric cyclone that
is strongest in winter when temperatures are below negative
80 degrees Celsius. The other is polar stratospheric clouds
(PSCs), or nacreous clouds when visible, that also form
in the extreme polar winter.
The vortex is a closed system that can circulate the ozone-destroying
chemicals quickly. The PSCs provide an excellent surface
for setting chlorine and bromine free to run amok and destroy
ozone in the presence of sunlight. So, the returning sun
serves as the match to set this whole chemical pyre ablaze,
beginning in August, breaking the free-floating chlorine
molecules into their most reactive state.
The ozone hole eventually “closes” as the vortex
weakens and dissipates by November with the warming temperatures.
The atmospheric mixing that ensues then consumes the harmful
chlorine and bromine in other reactions, but also causes
a small percentage of ozone depletion throughout the southern
hemisphere as the depleted Antarctic air mixes with mid-latitude
air.
Recovery
Scientists say they expect these monstrous-sized ozone holes
to continue for at least the next several years. Real improvements
may not come until the year 2010, and continued variability
may mask the healing process for quite some time. Estimates
for recovery range from 2040 to 2080, though NOAA and NASA
anticipate recovery by 2065.
Researchers are measuring slightly less ozone-destroying
chemicals despite this year’s record ozone hole.
“The chlorine maximum [in the stratosphere] was reached
about the year 2000, so we should start to see improvements,”
Mercer said.
Hofmann said chlorine and bromine levels reached their maximum
concentration at the Earth’s surface around 1994. “It
takes a long time for these gases to get into the stratosphere,
especially to get into the Antarctic stratosphere,”
he said, adding that these molecules can take six years
to travel here from the northern hemisphere.
… And regression
Whether the ozone layer can make a full recovery to pre-1980s
levels when CFCs and other chemicals first started their
assault is uncertain at this time. That’s partly because
not all production of ozone-destroying chemicals has ceased.
In fact, United States chemical companies have more than
20 million pounds of methyl bromide, a pesticide, stockpiled.
In addition, the U.S. Environmental Protection Agency allowed
production of another 15 million pounds this year, according
to a Los Angeles Times article.
Hofmann noted that atmospheric measurements, such as those
NOAA conducts at the South Pole, have found declining levels
of these pesticide compounds in the last five or six years.
Global warming, while unrelated to ozone destruction, may
play a role in the severity of the annual ozone hole and
the ozone layer’s eventual recovery. That’s because
greenhouse gases that trap heat in the troposphere slow
the heat transfer to the stratosphere, causing it to remain
colder for longer periods of time.
“If you have a colder stratosphere, then you could
have much longer, colder polar vortices every year,”
Mercer explained. “This would allow for [a] larger
or longer ozone hole because the ozone hole area is controlled
by the size of that vortex.”
The variability in climate change models makes it hard to
predict how the greenhouse effect may impede ozone hole
recovery, the scientists say.
A model solution?
Despite these apparent setbacks, scientists remain optimistic
that the ozone layer will eventually heal. They credit the
quick reaction of the international community, which adopted
the 1987 Montreal Protocol. The agreement, and its subsequent
amendments, provided for the protection of the ozone layer
by phasing out the substances causing depletion.
The protocol is an example of how nations could cooperate
on tackling a potentially more serious problem: global warming
and the pervasive use of technologies that emit carbon dioxide,
the key greenhouse gas, according to Hofmann.
“It’s a good model for the global warming issue,
that the international community can put together a set
of regulations everybody can get along with,” he said.
“The world economy is running on things that emit CO2
now. Realization of a non-carbon economy is a long way off,”
he said.
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Antarctic
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