Technology News Daily  [Printer-friendly version]
October 23, 2006


[Rachel's introduction: The earth's ozone layer is what makes the
surface of the Earth habitable for humans. Without it, we would all
have to live indoors or below ground. A family of chemicals invented
by DuPont almost destroyed it. It was a close call. Now the ozone
layer is slowly -- slowly -- recovering.]

NASA and National Oceanic and Atmospheric Administration (NOAA)
scientists report this year's ozone hole in the polar region of the
Southern Hemisphere has broken records for area and depth.

The ozone layer acts to protect life on Earth by blocking harmful
ultraviolet rays from the sun. The "ozone hole" is a severe depletion
of the ozone layer high above Antarctica. It is primarily caused by
human-produced compounds that release chlorine and bromine gases in
the stratosphere.

"From September 21 to 30, the average area of the ozone hole was the
largest ever observed, at 10.6 million square miles," said Paul
Newman, atmospheric scientist at NASA's Goddard Space Flight Center,
Greenbelt, Md. If the stratospheric weather conditions had been
normal, the ozone hole would be expected to reach a size of about 8.9
to 9.3 million square miles, about the surface area of North America.

The Ozone Monitoring Instrument on NASA's Aura satellite measures the
total amount of ozone from the ground to the upper atmosphere over the
entire Antarctic continent. This instrument observed a low value of 85
Dobson Units (DU) on Oct. 8, in a region over the East Antarctic ice
sheet. Dobson Units are a measure of ozone amounts above a fixed point
in the atmosphere. The Ozone Monitoring Instrument was developed by
the Netherlands' Agency for Aerospace Programs, Delft, The
Netherlands, and the Finnish Meteorological Institute, Helsinki,

Scientists from NOAA's Earth System Research Laboratory in Boulder,
Colo., use balloon-borne instruments to measure ozone directly over
the South Pole. By Oct. 9, the total column ozone had plunged to 93 DU
from approximately 300 DU in mid-July. More importantly, nearly all of
the ozone in the layer between eight and 13 miles above the Earth's
surface had been destroyed. In this critical layer, the instrument
measured a record low of only 1.2 DU., having rapidly plunged from an
average non-hole reading of 125 DU in July and August.

"These numbers mean the ozone is virtually gone in this layer of the
atmosphere," said David Hofmann, director of the Global Monitoring
Division at the NOAA Earth System Research Laboratory. "The depleted
layer has an unusual vertical extent this year, so it appears that the
2006 ozone hole will go down as a record-setter."

Observations by Aura's Microwave Limb Sounder show extremely high
levels of ozone destroying chlorine chemicals in the lower
stratosphere (approximately 12.4 miles high). These high chlorine
values covered the entire Antarctic region in mid to late September.
The high chlorine levels were accompanied by extremely low values of

The temperature of the Antarctic stratosphere causes the severity of
the ozone hole to vary from year to year. Colder than average
temperatures result in larger and deeper ozone holes, while warmer
temperatures lead to smaller ones. The NOAA National Centers for
Environmental Prediction (NCEP) provided analyses of satellite and
balloon stratospheric temperature observations. The temperature
readings from NOAA satellites and balloons during late-September 2006
showed the lower stratosphere at the rim of Antarctica was
approximately nine degrees Fahrenheit colder than average, increasing
the size of this year's ozone hole by 1.2 to 1.5 million square miles.

The Antarctic stratosphere warms by the return of sunlight at the end
of the polar winter and by large-scale weather systems (planetary-
scale waves) that form in the troposphere and move upward into the
stratosphere. During the 2006 Antarctic winter and spring, these
planetary-scale wave systems were relatively weak, causing the
stratosphere to be colder than average.

As a result of the Montreal Protocol and its amendments, the
concentrations of ozone-depleting substances in the lower atmosphere
(troposphere) peaked around 1995 and are decreasing in both the
troposphere and stratosphere. It is estimated these gases reached peak
levels in the Antarctica stratosphere in 2001. However, these ozone-
depleting substances typically have very long lifetimes in the
atmosphere (more than 40 years).

As a result of this slow decline, the ozone hole is estimated to
annually very slowly decrease in area by about 0.1 to 0.2 percent for
the next five to 10 years. This slow decrease is masked by large year-
to-year variations caused by Antarctic stratosphere weather

The recently completed 2006 World Meteorological Organization/United
Nations Environment Programme Scientific Assessment of Ozone Depletion
concluded the ozone hole recovery would be masked by annual
variability for the near future and the ozone hole would fully recover
in approximately 2065.

"We now have the largest ozone hole on record for this time of year,"
said Craig Long of NCEP. As the sun rises higher in the sky during
October and November, this unusually large and persistent area may
allow much more ultraviolet light than usual to reach Earth's surface
in the southern latitudes.