Low Ozone Level Found Above Antarctica
"Low Ozone Level Found Above Antarctica"
Newspaper article
By: Walter Sullivan
Date: November 7, 1985
Source: Sullivan, Walter. "Low Ozone Level Found Above Antarctica." New York Times (November 7, 1985).
About the Author: Walter Sullivan was a prolific science writer and editor at The New York Times. He also wrote several popular science books, including We Are Not Alone: The Continuing Search for Extraterrestrial Intelligence and Black Holes: Edge of Space, Edge of Time. In 1978 he won an award for distinguished public service from the National Science Foundation. The American Geophysical Union dedicated an award for excellence in scientific journalism in his name.
INTRODUCTION
The ozone hole is a large area over the continent of Antarctica where concentrations of the gas ozone in the stratosphere typically fall in the Antarctic spring between August and November of each year. Concentrations are usually about 70 percent of those found during the rest of the year.
Ozone is generally found both in the troposphere, which extends 5 to 9 miles (8 to 14.5 kilometers) above sea level, and in the stratosphere, which extends between 10 and 31 miles (17 and 50 kilometers) in altitude. In the troposphere, ozone is considered a pollutant because it contributes to the formation of smog. In the stratosphere, ozone occurs naturally and acts as an important protective shield against harmful radiation from the sun. Stratospheric ozone absorbs much of the ultraviolet energy at wavelengths between 240 and 320 nanometers that impinge on the Earth. This ultraviolet radiation is responsible for sunburn, skin cancer, damage to vegetation, and higher rates of genetic mutation in many invertebrate animals.
Ozone is formed in the stratosphere by the energy of sunlight. Oxygen molecules are generally found as two oxygen atoms joined together, symbolized O2. When ultraviolet energy from the sun strikes an oxygen molecule, it can dissociate the two atoms of oxygen, O. The oxygen atoms are extremely reactive and quickly join with a third molecule of oxygen to form O3, which is ozone.
Ozone can be destroyed naturally when an atom of oxygen joins with ozone to form O4. The O4 molecule then splits to form two molecules of oxygen, O2. However, this reaction occurs too slowly to account for the concentrations of ozone that are actually found in the stratosphere. Research has shown that other gases have the ability to destroy ozone as well. In particular, manmade chemicals that contain chlorine, known as chlorofluorocarbons or CFCs, are particularly effective at destroying ozone. CFCs are used in refrigeration and cooling systems, aerosols and solvents. Also, gases containing bromine and nitrogen oxides are involved in the breakdown of ozone. Nitrogen oxides result from the burning of fossil fuels.
Between 1955 and 1978, the average monthly measurements of the ozone in the stratosphere over Antarctica in October were between about 275 and 350 Dobson Units (DU). In the late 1970s the concentrations of ozone began to sharply decline. In 1985, the average measurement of ozone in the month of October had decreased to around 170 DU.
PRIMARY SOURCE
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SIGNIFICANCE
Since the 1980s, a significant amount of scientific research has been devoted to understanding the formation of the ozone hole. Scientists discovered that the ozone hole is the result of particular conditions, which coalesce to cause a severe depletion in the concentration of ozone over Antarctica in the winter. First, a polar vortex, or circular weather pattern, forms over the continent in the winter. This isolates the air in the stratosphere from interacting with the stratosphere in the rest of the planet. Second, the temperatures inside the vortex become extremely cold. This allows for the formation of special clouds of water and nitric acid ice crystals known as Polar Stratospheric Clouds, or PSCs. The PSCs act as a substrate on which chemical reactions can occur. In particular, inactive chlorine and bromine compounds are converted to forms which are much more reactive. Finally, when the sun returns to Antarctica in the spring, it initiates a series of reactions that rapidly destroys ozone. During these cycles the chlorine compounds are not destroyed and can react again and again with ozone. This process continues until the vortex warms up and eventually dissipates. The size and timing of the ozone hole varies each year because it is dependent on the size and duration of the polar vortex.
Many of the compounds responsible for the conditions that result in the ozone hole are industrial products. In particular, CFCs, halons, carbon tetrachloride, methyl chloroform and methyl bromide all play important roles in the destruction of ozone and are classified as class I ozone-depleting substances.
A global agreement to limit the production of class I substances was part of the Montreal Protocol of 1987. In this agreement, the signatory Parties proposed to cut the production of CFCs in half by 2000. Given the large amount of public attention focused on the ozone hole and the interest placed on the situation by environmental groups, the Parties met again in 1992 in Copenhagen. At this meeting, they proposed an accelerated phase-out of class I substances. Under the revised schedule, all class I substances except methyl bromide were completely phased out by 1995 and production and consumption of methyl bromide ceased as of 2005. The United States agreed to the accelerated schedule and it was enforced under the Clean Air Act.
Subsequent to the agreement on class I ozone-depleting substances, hydrochlorofluorocarbons (HCFCs), which were used to replace CFCs in industrial uses, were found to have ozone-reducing potential. The production and consumption of these substances will be phased out by 2030.
FURTHER RESOURCES
Web sites
NASA. "Stratospheric Ozone Depletion." 〈http://www.nas.nasa.gov/About/Education/Ozone/ozone.html〉 (accessed January 6, 2006).
The Ozone Hole. 〈http://www.theozonehole.com〉 (accessed January 6, 2006).
United States Environmental Protection Agency. "The Antarctic Ozone Hole." 〈http://www.epa.gov/ozone/science/hole/index.html〉 (accessed January 6, 2006).
University of Cambridge Centre for Atmospheric Science. "The Ozone Hole Tour." 〈http://www.atm.ch.cam.ac.uk/tour/index.html〉 (accessed January 6, 2006).