Early data show that the ozone hole that develops each year over Antarctica has reached about the same magnitude as those of the past several years, according to scientists from the Commerce Department's National Oceanic and Atmospheric Administration and NASA.

Last year, the geographic area covered by the ozone hole was one of the largest on record. By early October, additional data will provide a more complete picture of the extent and intensity of this year's ozone hole in Antarctica.

The primary cause of the ozone hole, which has occurred each year over Antarctica since the early—to mid—1980s, is the chemical reactions that release chlorine and bromine into the atmosphere. The source of these chemicals is human-produced chlorofluorocarbons and bromine containing compounds used in a variety of industrial and commercial applications.

"While chlorine has started to decline in the atmosphere, very high concentrations still remain at the altitude of the ozone layer. " NOAA researcher Sam Oltmans. The amounts are more than sufficient to cause the ozone hole we observe each year."

These chemicals—in combination with very cold temperatures that form high- altitude clouds during the polar night, and a confined circumpolar wind system, produce potent conditions for ozone destruction. These ozone-destroying chemicals are no longer increasing because of the regulations put in place by the Montreal Protocol. However, they break down very slowly in the earth's atmosphere, and a recurring annual ozone hole will be present for several more decades. Year-to-year fluctuations in the area of the ozone hole can be expected due to variations in upper atmospheric weather patterns.

NASA and NOAA use satellites to measure the extent and depth of the ozone hole. NASA's Total Ozone Mapping Spectrometer (TOMS), currently aboard the Earth Probe satellite, and NOAA's Solar Backscattering Ultra-Violet (SBUV/2) instrument aboard the Polar-orbiting Operational Environmental Satellites, have been measuring Antarctic ozone levels for more than 20 years. NOAA also monitors the ozone hole at the South Pole using instrumented balloons that take vertical profiles of the atmosphere and measure the amount of total ozone present.

The ozone hole is defined as area of the region with total ozone below 220 Dobson units. A Dobson unit describes the thickness of the ozone layer in a column directly above the location being measured.

"This year preliminary satellite data show that as of early September, ozone hole area was in excess of 20 million square kilometers (8 million square miles), about twice the size of the contiguous United States," said Lawrence Flynn, a research scientist with NOAA's National Environmental Satellite, Data, and Information Service.

The hole's size similar to last year at this time and about 50 percent larger than the 10 year (1991-2000) average for early September. With very cold temperatures over Antarctica and with the circumpolar wind currents (the polar vortex) in a stable pattern, a large ozone hole, similar to the past several years has already developed.

The global ozone layer has also suffered from depletion because of an increase in stratospheric chlorine and bromine but not to the degree that is observed each spring in Antarctica. Ozone forms a layer that surrounds and protects the earth from the harmful effects of the sun's ultraviolet radiation. Excessive amounts of UV radiation can damage important plant and animal life on earth and in the oceans as well as contribute to increases in skin cancer and cataracts in humans.

Video File Feed: A B-roll of imagery and other materials will be broadcast during NASA TV video file feed scheduled for Sept. 17 at 3 p.m., 6 p.m., 9 p.m. and midnight EDT. NASA TV is broadcast on GE-2, transponder 9C, C-band, located at 85 degrees West Longitude. The frequency is 3880 MHz. Polarization is vertical and audio is monaural at 6.8 MHz.

Additional information on the science and on measurements of the ozone hole and of atmospheric ozone depletion in general can be found at http://www.ozonelayer.noaa.gov. and http://toms.gsfc.nasa.gov. Links available on these sites will let you follow the development of this year's ozone hole.

A link under the Data menu (Current/Antarctic) on the first site gives a plot tracking the area of the ozone hole estimated from SBUV/2 data and another plot tracking the ozone amount at the South Pole as measured by balloon sondes. A link on the second site uses information from Earth Probe TOMS to estimate the minimum total ozone column within the polar vortex as well as to track the area.