Largest Ever Hole In Ozone Layer Over Antarctica (All text below directly quoted from the NASA Web site.) From NASA'S Visible Earth Section Credit: Image courtesy the TOMS science team and the Scientific   Visualization Studio, NASA GSFC Satellite: TOMS Image Date: 09-06-2000 Ozone creation: Fifteen to thirty kilometers up in the atmosphere, in the layer called the stratosphere, ozone is created and destroyed primarily by ultraviolet radiation. The air in the stratosphere is bombarded continuously by ultraviolet radiation from the sun. When high-energy ultraviolet rays strike molecules of ordinary oxygen (O2), they split the molecule into two single oxygen atoms, known as atomic oxygen (O). A freed oxygen atom then can combine with an oxygen molecule to form a molecule of ozone (O3). Ozone destruction: Once in the stratosphere, the chlorofluorocarbon (CFC) molecules are no longer shielded from ultraviolet radiation by the ozone layer. Bombarded by the Sun's ultraviolet energy, CFC molecules break up and release their chlorine atoms. The free chlorine atoms then can react with ozone molecules, taking one oxygen atom to form chlorine monoxide and leaving an ordinary oxygen molecule. Description: A NASA instrument has detected an Antarctic ozone "hole" (what scientists call an "ozone depletion area") that is three times larger than the entire land mass of the United States—the largest such area ever observed. The "hole" expanded to a record size of approximately 11 million square miles (28.3 million square kilometers) on Sept. 3, 2000. The previous record was approximately 10.5 million square miles (27.2 million square km) on Sept. 19, 1998. The ozone hole's size currently has stabilized, but the low levels in its interior continue to fall. The lowest readings in the ozone hole are typically observed in late September or early October each year. Historically, the Antarctic ozone hole is largest during the month of October. Values below 150 Dobson Units (bright blue) are considered extremely low. "These observations reinforce concerns about the frailty of Earth's ozone layer. Although production of ozone-destroying gases has been curtailed under international agreements, concentrations of the gases in the stratosphere are only now reaching their peak. Due to their long persistence in the atmosphere, it will be many decades before the ozone hole is no longer an annual occurrence," said Dr. Michael J. Kurylo, manager of the Upper Atmosphere Research Program, NASA Headquarters, Washington, DC. Ozone molecules, made up of three atoms of oxygen, comprise a thin layer of the atmosphere that absorbs harmful ultraviolet radiation from the Sun. Most atmospheric ozone is found between approximately six miles (9.5 km) and 18 miles (29 km) above the Earth's surface. Scientists continuing to investigate this enormous hole are somewhat surprised by its size. The reasons behind the dimensions involve both early-spring conditions, and an extremely intense Antarctic vortex. The Antarctic vortex is an upper-altitude stratospheric air current that sweeps around the Antarctic continent, confining the Antarctic ozone hole. "Variations in the size of the ozone hole and of ozone depletion accompanying it from one year to the next are not unexpected," said Dr. Jack Kaye, Office of Earth Sciences Research Director, NASA Headquarters. "At this point we can only wait to see how the ozone hole will evolve in the coming few months and see how the year's hole compares in all respects to those of previous years." "Discoveries like these demonstrate the value of our long-term commitment to providing key observations to the scientific community," said Dr. Ghassem Asrar, Associate Administrator for NASA's Office of Earth Sciences at Headquarters. "We will soon launch QuickTOMS and Aura, two spacecraft that will continue to gather these important data." The measurements released today were obtained using the Total Ozone Mapping Spectrometer (TOMS) instrument aboard NASA's Earth Probe (TOMS-EP) satellite. NASA instruments have been measuring Antarctic ozone levels since the early 1970s. Since the discovery of the ozone "hole" in 1985, TOMS has been a key instrument for monitoring ozone levels over the Earth. TOMS ozone data and more pictures are available at: http://jwocky.gsfc.nasa.gov/TOMSmain.html  TOMS-EP and other ozone-measurement programs are important parts of a global environmental effort of NASA's Earth Science enterprise, a long-term research program designed to study Earth's land, oceans, atmosphere, ice and life as a total integrated system. The images from the Total Ozone Mapping Spectrometer (TOMS) show the progressive depletion of ozone over Antarctica from 1979 to 1999. This "ozone hole" has extended to cover an area as large as 10.5 million square miles in September 1998. The previous record of 10.0 million square miles was set in 1996. The Antarctic ozone hole develops each year between late August and early October. Regions with higher levels of ozone are shown in red. NASA and NOAA instruments have been measuring Antarctic ozone levels since the early 1970s. Large regions of depleted ozone began to develop over Antarctica in the early 1980s. While ozone holes of substantial size and depth are likely to continue to form during the next few years, scientists hope to see a reduction in ozone loss as levels of ozone-destroying CFCs (chlorofluorocarbons) are gradually reduced.

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