Douglas Isbell
Headquarters, Washington, DC           October 25, 1996
(Phone:  202/358-1753)

Allen Kenitzer
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-8955)

RELEASE: 96-217

1996 ANTARCTIC OZONE HOLE BELOW RECORD AVERAGE SIZE 

     Two NASA instruments again have detected substantial 
depletion of ozone levels over Antarctica, commonly referred 
to as the Antarctic ozone hole. 

     The average size of the Antarctic ozone hole during 1996 
has been almost as large as in the peak year of 1993, 
although ozone values are higher than the record lows seen in 
September 1994, according to preliminary analysis of 
satellite data by scientists at NASA's Goddard Space Flight 
Center in Greenbelt, MD.   During the current year, the ozone 
hole covered a surface area over the South Pole roughly equal 
in size to the North American continent.

     These data were recorded by two of NASA's Total Ozone 
Mapping Spectrometer instruments (TOMS) launched this year, 
one on board the NASA Earth Probe satellite and another on 
the Japanese Advanced Earth-Observing Satellite (ADEOS) 
satellite.  Low ozone amounts over the Antarctic continent 
consistent with these TOMS data also have been validated by 
ground-based instruments and other satellite-based 
instruments. 

     The average size of the ozone hole during this year was 
8.3 million square miles, similar to observations in the last 
four years.  The largest observed average size of the ozone 
hole was in 1993, at 8.5 million square miles.

     The hole started to form in mid-August of this year and 
reached a one-day peak size on Sept. 7, 1996, of about 10 
million square miles, then quickly shrunk to values of less 
than 8.5 million square miles.  The previous largest one-day 
peak size hole was 9.4 million square-miles on Sept. 27, 
1992.  In comparison, the surface area of North America is 
8.1 million square-miles while Antarctica has a surface area 
of 5.4 million square-miles. 

     Since the mid-1980s, the region covered by low total 
ozone begins to grow each year in early August.  This region 
reaches its maximum extent in September, while the lowest 
ozone values are typically seen in late September and early 
October.  The ozone hole usually disappears by early 
December.  The ozone hole in 1996 opened up slightly earlier 
than in previous years, but had begun to decrease in surface 
area below 7.7 million square-miles by Oct. 16, 1996. 

     "This ozone hole is very similar to those seen in recent 
years," said Dr. Paul Newman, research scientist in the 
Laboratory for Atmospheres at Goddard.  "Although its area 
climbed briefly over that of the previous peak, that is not 
as great a concern as the average size, because 
meteorological conditions can cause large day-to-day 
fluctuations.  This is similar to winter temperatures, where 
one really cold day is not as important as the average 
temperature over the whole winter season."

     The ozone amounts measured by TOMS/ADEOS and TOMS/Earth 
Probe dropped to 111 Dobson units on Oct. 5 near the center 
of the Antarctic continent, with values below 220 Dobson 
units measured over a wide area.  Total ozone values less 
than 100 Dobson units were measured in both 1993 and 1994, 
with the record low value of 88 Dobson units measured on 
Sept. 28, 1994.

     Ozone, a molecule made up of three atoms of oxygen, 
comprises a thin layer of the atmosphere which absorbs 
harmful ultraviolet radiation from the Sun.  A Dobson unit is 
related to the physical thickness of the ozone layer if it 
were brought to the Earth's surface.  The global average 
ozone layer thickness is 300 Dobson units, which equals 1/8th 
of an inch, approximately the thickness of two stacked 
pennies.  In contrast, the ozone layer thickness in the ozone 
hole is about 100 Dobson units (1/25th of an inch), 
approximately the thickness of a single dime. 

     Scientists at the South Pole from the National Oceanic 
and Atmospheric Administration (NOAA), working with balloon-
borne measurements, have found low total ozone values similar 
to those seen in 1995.  "However, in the central region of 
the ozone hole, from 7.5 to 12.5 miles altitude, ozone 
depletion was more severe than in the past," said Dr. Dave 
Hofmann of the NOAA Climate Monitoring and Diagnostics Lab in 
Boulder, CO.  The NOAA measurements showed that complete 
destruction of ozone at an altitude of 10 miles was observed 
over the period from Sept. 24 to Oct. 14.  "Total ozone did 
not reach record lows because of unusually high ozone above 
the ozone hole at 15 miles which compensated for the low 
values in the ozone hole," Hofmann said.

     "These deep and large ozone holes are likely to continue 
to form annually until the stratospheric chlorine amount 
drops to its pre-ozone hole values," said Dr. Richard 
Stolarski, also a research scientist at Goddard.  "The 
slightly earlier ozone hole this year probably resulted from 
the continued increase of Antarctic stratospheric total 
chlorine levels." 

     Since the discovery of the ozone hole in 1985, TOMS has 
been a key instrument for monitoring ozone levels throughout 
the southern hemisphere.  The first TOMS aboard NASA's 
Nimbus-7 satellite measured Antarctic ozone levels from 
November 1978 to May 1993, and it helped make ozone a 
household word through pictures of the Antarctic ozone hole.  
It was followed by a TOMS sensor on a Russian satellite.

     TOMS data also provided part of the scientific 
underpinning for the Montreal Protocol, under which many of 
the world's nations have agreed to phase out the use of 
ozone-depleting chemicals.  As a result of restrictions in 
the Montreal Protocol, chlorine levels have already peaked in 
the lower atmosphere, and should peak in the Antarctic 
stratosphere in about three to five years. 

     The size and depth of the ozone hole, and global ozone 
levels, depend on meteorological conditions and on the amount 
of chlorine present in the atmosphere, and may be affected by 
the presence of sulfate aerosols produced by volcanic 
eruptions.  Scientists speculate that ozone values over 
Antarctica were low in 1993 and 1994 because of the enhanced 
presence of sulfuric acid aerosols in the stratosphere due to 
the June 1991 Mount Pinatubo eruption in the Philippines. 

     TOMS-Earth Probe, launched in July of this year, is the 
third in the series of TOMS instruments.  Operating from a 
312-mile orbit, TOMS-Earth Probe is principally dedicated to 
collecting ozone and aerosol data in the lower atmosphere.  
The fourth TOMS instrument was launched in August aboard 
ADEOS into a 500-mile orbit.  ADEOS is an international 
climate change research mission that includes instruments 
from the U.S., Japan, and France, with investigators from 
many countries around the world.

     Both TOMS-EP and ADEOS are key parts of a global 
environmental effort which includes NASA's Mission to Planet 
Earth, a long term, coordinated research effort to study the 
Earth as a global environmental system. 

     TOMS ozone data and pictures are available to anyone 
with a computer connection to the Internet World Wide Web at:

              http://jwocky.gsfc.nasa.gov

     The TOMS instruments are managed by the Goddard Space 
Flight Center for NASA's Office of Mission to Planet Earth, 
Washington, DC.