This year’s Antarctic ozone hole is the second largest
ever observed, according to scientists from NASA, the
National Oceanic and Atmospheric Administration (NOAA), and
the Naval Research Laboratory.

The Antarctic ozone hole is defined as thinning of the ozone
layer over the continent to levels significantly below pre-
1979 levels. Ozone blocks harmful ultraviolet “B” rays. Loss
of stratospheric ozone has been linked to skin cancer in
humans and other adverse biological effects on plants and

The size of this year’s hole reached 10.9 million square
miles on September 11, 2003. It was slightly larger than the
North American continent, but smaller than the largest hole
ever recorded, on September 10, 2000, when it covered 11.5
million square miles. Last year the ozone hole was smaller,
covering 8.1 million square miles.

NASA’s Earth Probe Total Ozone Mapping Spectrometer and the
NOAA-16 Solar Backscatter Ultraviolet instrument provided
ozone measurements from space. These data were coupled with
data collected by NOAA’s Climate Monitoring and Diagnostics
Laboratory (CMDL) from balloon-borne instruments, which
measure the ozone hole’s vertical structure.

NASA’s own scientist Paul Newman said, “While chlorine and
bromine chemicals cause the ozone hole, extremely cold
temperatures, especially near the edge of Antarctica, are
also key factors in ozone loss.”

Given the leveling or slowly declining atmospheric abundance
of ozone-destroying gases, the year-to-year changes in the
size and depth of the ozone hole are dominated by the year-
to-year variations in temperature in this part of the
atmosphere. The fact this year’s ozone loss is much greater
than last year’s reflects the very different meteorological
conditions between these two years.

NASA scientist Rich McPeters said ozone observations showed
the total amount of ozone from surface to space was 106
Dobson Units (DU) on September 14, 2003, the minimum value
reached this year. “Dobson units” measure the “thickness” of
protective ozone in the stratosphere. They range from 100 DU
to 500 DU, which translate to about 1 millimeter (1/25 inch)
to 5 millimeters (1/5 inch) of ozone in a layer.

Bryan Johnson of CMDL said the ozone depletion region, from
7-to-14 miles above the Earth, has large losses, similar to
losses seen in the 1990s. If the stratospheric temperature
remains cold over the pole, then we should see complete
ozone loss in the 9-13 mile layer, with total column ozone
reaching 100 DU by early October.

The Montreal Protocol and its amendments banned chlorine-
containing chlorofluorocarbons (CFCs) and bromine-containing
halons in 1995, because of their destructive effect on the
ozone. However, CFCs and halons are extremely long-lived and
still linger at high concentrations in the atmosphere.
However, the atmospheric abundances of ozone destroying
chemicals are beginning to decline. As a result, the
Antarctic ozone hole should disappear in about 50 years.

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