F. Sherwood Rowland and Mario J. Molina warned that chlorofluorocarbon gases may be destroying the ozone layer of Earth’s stratosphere.
Ozone is an irritating bluish gas of pungent odor that is formed naturally in the upper atmosphere by a photochemical reaction with solar ultraviolet radiation. It is a rare gas that protects Earth from the most dangerous radiations of the Sun, such as ultraviolet radiation. Ozone can absorb ultraviolet rays efficiently even when it is present in very small amounts. Altogether, the ozone layer absorbs one-twentieth of the Sun’s radiation, including the dangerous shortwave rays that can do great damage to living things. All biological systems have evolved under the protection of the ozone shield in the stratosphere. Humanity, however, has for many years been depleting this ozone layer by releasing human-made chlorofluorocarbons (CFCs). One of these compounds in particular, dichlorodifluoromethane, carries the trademarked name Freon.
CFCs were discovered in 1928 by Thomas Midgley, Jr.
F. Sherwood Rowland, a physical chemist at the University of California at Irvine, first became interested in atmospheric chemistry in 1972. He was attending a meeting in Fort Lauderdale, Florida, that was organized by the U.S. Atomic Energy Commission. It was there that he heard that James Lovelock, an independent and creative English chemist, had invented an electron-capture gas chromatograph to detect atmospheric gases in minute amounts. With his invention, he had discovered a minute concentration of two commonly used CFCs in the atmosphere over Western Ireland. Rowland began to wonder what eventually became of the chemical.
Rowland later performed some calculations that showed that Lovelock’s concentrations were very close to the rough estimate of the total amount of CFCs being produced. Rowland reasoned that if all the CFCs ever released were present in the lowest layer of the atmosphere, the troposphere, that meant that nothing in this layer was destroying them. They had to go somewhere, however, and the only place for them to go was upward into the stratosphere, an upper portion of the atmosphere that is approximately 11 kilometers above the Earth. He believed that the CFCs would then decompose when exposed to ultraviolet radiation. Eighteen months later, Rowland turned this casual commentary into an elaborate study.
Mario J. Molina, a chemical engineer, was awarded the 1995 Nobel Prize in Chemistry, along with F. Sherwood Rowland and Paul Crutzen. All three were honored for their studies of the formation and decomposition of ozone in the stratosphere.
In the fall of 1973, Mario J. Molina had completed his doctorate in chemistry at the University of California, Berkeley, and came to work with Rowland. Together, they set out to determine what would happen to the CFCs in the atmosphere. By November, 1973, Molina had already established that nothing happened to them in the troposphere. CFCs do not react with living things, they do not dissolve in oceans, and they are not washed out of the air by rain—they do nothing except float around and gradually work their way upward into the stratosphere. It was a simple chemical deduction that they would be broken apart by the Sun’s ultraviolet radiation and that, as a result, chlorine atoms would be released into the stratosphere. At the time, a few chlorine atoms seemed unworthy of concern—that is, until Molina discovered that a single chlorine atom can scavenge and destroy many thousands of ozone molecules.
Using detailed calculations for chemical reactions, Molina concluded that each chlorine atom from CFCs would collide with a molecule of the highly unstable ozone. The reaction did not end there. Once chlorine was freed from the CFC, the by-product would be oxygen and a chemical fragment with an odd number of electrons called “chlorine monoxide.” The odd number of electrons, Molina knew, guaranteed that this fragment would react with a free oxygen atom to achieve an even number of electrons. He calculated that when the chlorine monoxide fragment met the free oxygen atom, the oxygen in chlorine monoxide would be attracted to the free oxygen atom and would split off to form a new oxygen molecule. Chlorine would then be freed and would collide with ozone, thus starting the cycle all over again.
In short, the breakdown of CFCs by sunlight would set off a chain reaction in which one chlorine atom could gobble up 100,000 molecules of ozone, turning them into ordinary oxygen with no power to absorb dangerous solar radiation. Rowland and Molina published their results in the June, 1974, issue of the journal Nature.
On September 26, 1974, the CFC/ozone story made the front page of The New York Times. In October, 1974, a government committee recommended that the National Academy of Sciences conduct a study on the validity of this theory. In June of 1975, Johnson Wax, the nation’s fifth-largest manufacturer of aerosol sprays, announced that it would stop using CFCs in its products. In June, 1975, Oregon became the first state to ban CFCs in aerosol sprays. In October, 1976, the Food and Drug Administration and the Environmental Protection Agency
In August, 1981, National Aeronautics and Space Administration (NASA) scientist Donald Heath announced that satellite records showed that the amount of ozone had declined 1 percent. In October, 1984, an English research group led by Joseph Charles Farman
Meanwhile, in 1987, many nations—including the United States—signed the Montreal Protocol
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Cook, J. Gordon. Our Astounding Atmosphere. New York: Dial Press, 1957. Written in the popular style and very easy to read. Takes the mystery out of the atmosphere and presents a difficult subject in an entertaining format. High school students should have no problem comprehending the subject matter. A few black-and-white photographs, but no graphics, mathematics, or tables. -
Gribbin, John. The Hole in the Sky: Man’s Threat to the Ozone Layer. New York: Bantam Books, 1988. An excellent paperback book that consists primarily of text, except for a few graphs and chemical equations. For the most part, should be used by the advanced high school and lower-level college student. Written by an acclaimed science writer and cosmologist. Focuses entirely on the ozone layer crisis. -
_______, ed. The Breathing Planet. New York: Basil Blackwell, 1986. A readable book; discusses climatic changes past and present, and looks at their effect on drought-stricken regions of the world. Two articles were written by Rowland: one on aerosol sprays and the other on chlorofluorocarbons in the stratosphere. Well illustrated; recommended as an excellent reference source for the upper-level high school student and the general public. -
Lutgens, Frederick K., and Edward J. Tarbuck. The Atmosphere: An Introduction to Meteorology. 10th ed. Upper Saddle River, N.J.: Prentice Hall, 2006. An introductory-level college textbook; copiously illustrated. Includes vocabulary and chapter reviews and contains seven appendixes and an extensive glossary. A good reference source on the atmosphere. -
Parson, Edward A. Protecting the Ozone Layer: Science and Strategy. New York: Oxford University Press, 2003. History of the successful international efforts to protect the ozone layer since the 1970’s. -
Roan, Sharon. Ozone Crisis: The Fifteen-Year Evolution of a Sudden Global Emergency. New York: John Wiley & Sons, 1989. An extremely interesting commentary on the ozone crisis in language the nonscientist can understand. Contains a few graphs and photographs and an extensive bibliography. Includes a chronology of events relative to the chlorofluorocarbon/ozone problem. Written by a staff science writer for the Orange County Register in Santa Clara, California, who has written extensively about the ozone crisis, the greenhouse effect, beach erosion, wildlife preservation, and other environmental issues. Highly recommended for readers of all levels.
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