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PD0RDD > NASA 08.10.98 18:05l 157 Lines 7078 Bytes #-10047 (0) @ WW
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Onderwerp: ANTARCTIC OZONE DEPLETION SETS NEW SIZE RECORD
David E. Steitz
Headquarters, Washington, DC October 6, 1998
(Phone: 202/358-1730)
Lynn Chandler
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/614-5562)
Stephanie Kenitzer
NOAA/NCEP, Silver Spring, MD
(Phone: 301/763-8000, ext. 7007)
RELEASE: 98-178
ANTARCTIC OZONE DEPLETION SETS NEW SIZE RECORD
NASA and NOAA satellites show that the Antarctic ozone
thinning covers the largest expanse of territory since the
depletion developed in the early 1980s. The measurements
were obtained this year between mid-August and early October
using the Total Ozone Mapping Spectrometer (TOMS) instrument
aboard NASA's Earth Probe (TOMS-EP) satellite and the Solar
Backscatter Ultraviolet Instrument (SBUV) aboard the NOAA-14
satellite.
"This is the largest Antarctic ozone hole we've ever
observed, and it's nearly the deepest," said Dr. Richard
McPeters, Principal Investigator for Earth Probe TOMS.
Preliminary data from the satellites show that this
year's ozone depletion reached a record size of 10.5 million
square miles (27.3 million square kilometers) on Sept. 19,
1998. The previous record of 10.0 million square miles was
set on Sept. 7, 1996.
The ozone level fell to 90 Dobson units on Sept. 30,
1998. This nearly equals the lowest value ever recorded of
88 Dobson Units seen on Sept. 28, 1994, over Antarctica.
Scientists are not concerned that the hole might be
growing because they know it is a direct result of unusually
cold stratospheric temperatures, though they do not know why
it is colder this year. The decrease in ozone, however,
could result in more acute solar or ultraviolet radiation
exposure in southern Chile and Argentina if the ozone hole
were to pass over that region. One of the primary concerns
with an ozone hole of this size is that as the hole "breaks
up," the ozone-depleted air will diffuse and reduce the
overall ozone levels in the mid-latitudes of the southern
hemisphere.
These ozone losses are caused by chlorine and bromine
compounds released by chlorofluorocarbons (CFCs) and halons.
Year-to-year variations of size and depth of the ozone hole
depend on the variations in meteorological conditions.
Scientists believe that the decrease in Antarctic ozone is
attributed to unusually cold (by 5-9 degrees Fahrenheit)
temperatures in the southern middle and polar latitudes.
"This year was colder than normal and therefore enables
greater activation of reactive chlorine that ultimately
causes more ozone loss and lower ozone levels," said Dr.
Alvin J. Miller of the National Centers for Environmental
Prediction (NCEP).
This decrease in ozone was observed earlier than usual
with the hole opening in mid-August about two weeks before a
typical year. This is consistent with expectations, since
chlorine levels have slightly increased since the early
1990s.
As a result of international agreements known as the
Montreal Protocol on ozone-depleting substances (and its
amendments), chlorine levels from CFCs already have peaked in
the lower atmosphere and should peak in the Antarctic
stratosphere within a few years. As we move into the next
century, chlorine-catalyzed ozone losses resulting from CFCs
and other chlorine-containing species will be reduced.
"An ozone hole of substantial depth and size is likely
to continue to form for the next few years or until the
stratospheric chlorine amount drops to its pre-ozone hole
values," said Dr. Paul Newman at NASA's Goddard Space Flight
Center (GSFC), Greenbelt, MD. "The decrease in chlorine in
our atmosphere is analogous to using a small air cleaner to
recycle all of the air in a large indoor sports stadium -- it
will take a very, very long time."
Scientists and others have a keen interest in ozone
depletion, given that the increased amounts of ultraviolet
radiation that reach the Earth's surface because of ozone
loss have the potential to increase the incidence of skin
cancer and cataracts in humans, harm some crops, and
interfere with marine life.
NASA and NOAA instruments have been measuring Antarctic
ozone levels since the early 1970s. Since the discovery of
the ozone hole in 1985, TOMS and SBUV have been key
instruments for monitoring ozone levels over the Earth.
Analysis of TOMS and SBUV data have traced in detail the
annual development of the Antarctic "ozone hole," a large
area of intense ozone depletion that occurs between late
August and early October. Analysis of the historical data
indicated that the hole has existed since at least 1979.
A Dobson unit measures the physical thickness of the
ozone layer at the pressure of the Earth's surface. The
global average ozone layer thickness is 300 Dobson units,
which equals three millimeters or 1/8th of an inch, and while
not uniform, averages the thickness of two stacked pennies.
In contrast during these annual occurrences, the ozone layer
thickness in the ozone hole is about 100 Dobson units (1/25th
of an inch or 1 millimeter thick), approximately the
thickness of a single dime.
Ozone shields life on Earth from the harmful effects of
the Sun's ultraviolet radiation. The ozone molecule is made
up of three atoms of oxygen; ozone comprises a thin layer of
the atmosphere which absorbs harmful ultraviolet radiation
from the Sun. Most atmospheric ozone is found in a thin
layer between 6-18 miles up.
TOMS ozone data and pictures are available on the
Internet at the following URL:
http://toms.gsfc.nasa.gov
or through links at URL:
http://pao.gsfc.nasa.gov/
TOMS-EP and other ozone-measurement programs are key
parts of a global environmental effort of NASA's Earth
Science enterprise, a long-term research program designed to
study Earth's land, oceans, atmosphere, ice and life as a
total integrated system. Goddard developed and manages the
operation of the TOMS-EP for NASA's Office of Earth Science,
Washington, DC.
-end-
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