|
Ozone
Hole 1991
Ozone Hole Area
|
Minimum Ozone
|
|
(million
km2) |
(DU) |
|
Maximum
Daily |
Minimum
Daily |
| Year |
Date |
Value |
Date |
Value |
| 1991 |
04
October |
22.6 |
06
October |
94 |
http://ozonewatch.gsfc.nasa.gov
The 1991 Antarctic Ozone Hole; TOMS observations
The 1991 Antarctic springtime ozone decline, as measured by the Total Ozone
Mapping Spectrometer (TOMS), was similar to those of earlier deep ozone hole
years, 1987, 1989, and 1990. The minimum total ozone value was recorded on
October 5, 1991 at 108 Dobson units near the South Pole. This was 8 DU lower
than in any of the earlier years. Four of the last five years have exhibited an
extensive, deep ozone hole. The area of the hole was about the same as in 1987,
1989, and 1990. The recovery of the low total ozone values occurred in
mid‐November as the polar vortex broke up.
Arlin Krueger NASA Goddard Space Flight Center, Code 916, Greenbelt, MD 20771
Mark Schoeberl NASA Goddard Space
Flight Center, Code 916, Greenbelt, MD 20771
Paul Newman NASA Goddard Space
Flight Center, Code 916, Greenbelt, MD 20771
Richard Stolarski NASA Goddard
Space Flight Center, Code 916, Greenbelt, MD 20771
WORST OZONE HOLE STIRS HEALTH FEAR
By MALCOLM W. BROWNE New York
Times
Published: October 10, 1991
The National Aeronautics and
Space Administration reported yesterday that a satellite passing over Antarctica
had measured the lowest stratospheric ozone level on record, an ominous
indication of potential global health risks.
Dolores Beasley, a spokeswoman
for the agency's Goddard Space Flight Center at Greenbelt, Md., said the
measurement was made Sunday by the total ozone mapping spectrometer, or TOMS, an
instrument aboard the Nimbus-7 satellite.
Dr. Arlin Krueger, a Goddard
scientist, said the ozone level in the Antarctic stratosphere was measured that
day as 110 Dobson units. Dobson units measure the atmosphere's ability to absorb
and block certain wavelengths of light coming from the Sun, notably ultraviolet
radiation. In normal times, the atmosphere above Antarctica measures about 500
Dobson units, but values far below this have been recorded in recent years when
seasonal "ozone holes" have developed over the southern continent.
The Antarctic ozone hole that has
just appeared is the fourth severe one to develop since 1986, the year that
significant ozone depletion of the stratosphere was first observed. Atmospheric
scientists regard seasonal ozone holes as part of a much larger potential
problem: a worldwide depletion of stratospheric ozone. Possible Health Problems
Public-health experts fear that
the increasing intensity of ultraviolet radiation that now penetrates the
atmosphere may greatly increase the incidence of skin cancer and cataracts, and
could significantly diminish global crops and the marine food chain.
"The minimum ozone on Oct.
6, 1991, is the lowest we have ever seen with the TOMS instrument in its 13-year
record of data," Dr. Krueger said. "Although the data are preliminary,
we expect that the final results will confirm this conclusion."
Space-agency scientists cautioned
that the record low for a single day did not in itself imply that the Antarctic
ozone hole would be more extensive and severe during the entire season than in
any previous year, but there are other indications that this year's hole will be
one of the worst seen so far. This is the third consecutive year that severe
ozone depletion has been observed over Antarctica.
Evidence has been rapidly
accumulating in the last few years that the main cause of stratospheric ozone
depletion has been the presence of chlorofluorocarbon chemicals released into
the atmosphere by human activity. These substances are widely used as
refrigerants, solvents and foaming agents in insulating plastics.
Because they are highly resistant
to chemical attack, chlorofluorocarbons remain in the atmosphere for many years,
eventually drifting up into the stratosphere where they are broken down by
ultraviolet radiation. The chlorine and oxygen compounds yielded by this
breakdown then destroy the natural stratospheric ozone.
Although the world's major
producers and users of chlorofluorocarbons agreed last year to phase out their
use by the end of the century, some scientists and conservationists argue that
ozone depletion has reached a crisis, and that a more urgent global ban against
these chemicals is essential.
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