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Volcanic
Ozone Hole
NASA March 04,
2002 -An "ozone hole" could form over the North Pole after future
major volcanic eruptions, according to the cover story by a NASA scientist in
tomorrow's edition of the Proceedings of the National Academy of Sciences.
Since the
1980s a seasonal ozone hole, characterized by severe loss of ozone, has appeared
over the continent of Antarctica. However, scientists have not yet observed, on
an annual basis, as severe a thinning of the protective ozone layer in the
atmosphere over the Arctic. The ozone layer shields life on Earth from harmful
ultraviolet radiation. A northern ozone hole could be significant since more
people live in Arctic regions than near the South Pole.
Azadeh
Tabazadeh
"A
'volcanic ozone hole' is likely to occur over the Arctic within the next 30
years," said Azadeh Tabazadeh, lead author of the paper and a scientist at
NASA's Ames Research Center, Moffett Field, Calif. Her co-authors are: Katja
Drdla, also of Ames; Mark R. Schoeberl of NASA's Goddard Space Flight Center,
Greenbelt, Md.; Patrick Hamill of San Jose State University, Calif.; and O.
Brian Toon from the University of Colorado, Boulder.
"If a
period of high volcanic activity coincides with a series of cold Arctic winters,
then a springtime Arctic ozone hole may reappear for a number of consecutive
years, resembling the pattern seen in the Antarctic every spring since the
1980s," Tabazadeh said.
Unlike the
Antarctic where it is cold every winter, the winter in the Arctic stratosphere
is highly variable," Tabazadeh said. NASA satellite and airborne
observations show that significant Arctic ozone loss occurs only following very
cold winters, according to Tabazadeh.
Large
volcanic eruptions pump sulfur compounds into the Earth's atmosphere. These
compounds form sulfuric acid clouds similar to polar stratospheric clouds made
of nitric acid and water. The clouds of nitric acid and water form in the upper
atmosphere during very cold conditions and play a major part in the destruction
of ozone over Earth's poles. Following eruptions, volcanic sulfuric acid clouds
would greatly add to the ozone-destroying power of polar stratospheric clouds,
researchers said.
"Volcanic
aerosols also can cause ozone destruction at warmer temperatures than polar
stratospheric clouds, and this would expand the area of ozone destruction over
more populated areas," Tabazadeh said. "Nearly one-third of the total
ozone depletion could be a result of volcanic aerosol effects at altitudes below
about 17 kilometers (11.5 miles)," said the researchers.
"Volcanic
emissions can spread worldwide," said Schoeberl. "Our Mt. Pinatubo
computer simulation shows that the volcanic plume spread as far north as the
North Pole in the lowest part of the stratosphere within a few months after the
eruption."
Between
about 15 and 25 kilometers (9 to 16 miles) in altitude, volcanic Arctic clouds
could increase springtime ozone loss over the Arctic by as much as 70 percent,
according to Drdla. "The combination of thick volcanic aerosols at lower
altitudes and natural polar stratospheric clouds at higher altitudes could
greatly increase the potential for ozone destruction over the North Pole in a
cold year," Tabazadeh said.
Mt.
Pinatubo
"Both
the 1982 El Chichon and 1991 Mt. Pinatubo eruptions were sulfur-rich, producing
volcanic clouds that lasted a number of years in the stratosphere,"
Tabazadeh said. The Pinatubo eruption, as observed by NASA spacecraft, widely
expanded the area of ozone loss over the Arctic.
Mount
Pinatubo Sulfur Dioxide Cloud (NASA TOMS)
Both of
these eruptions did have an effect, however, over the South Pole, expanding the
area and the depth of the ozone hole over the Antarctic, according to Tabazadeh.
Computer simulations have shown that the early and rapid growth of the Antarctic
ozone hole in the early 1980s may have been influenced in part by a number of
large volcanic eruptions, she added.
"In
1993 the Arctic winter was not one of the coldest winters on record, and yet the
ozone loss was one of the greatest that we've seen," Tabazadeh said.
"This was due to the sulfurous Pinatubo clouds facilitating the destruction
of additional ozone at lower altitudes where polar stratospheric clouds cannot
form."
"Climate
change combined with aftereffects of large volcanic eruptions will contribute to
more ozone loss over both poles," Tabazadeh said. "This research
proves that ozone recovery is more complex than originally thought."
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