Web edition: June 3, 2011
Print edition: June 18, 2011; Vol.179 #13 (p. 32)
September 21, 1974 | Vol. 106 | No. 12
Freon: Destroying the ozone layer?
A fascinating paradox has surfaced regarding man, ozone and the atmosphere that adds an ironic twist to the story of technological advancement. Researchers have noted during the past two decades that nitrous oxides and hydrocarbon pollutants building up in the lower atmosphere are acted upon by sunlight to produce ozone (O3). High levels of ozone, in turn, cause respiratory problems and kill plants.
Now, it seems, Freon and other fluorocarbon pollutants in the upper atmosphere may be removing ozone, which acts as a protective layer against harmful ultraviolet light. (Freon is a DuPont tradename but is used as a generic term by many scientists.) By polluting his own air, man may be creating too much ozone below, too little above and possibly deleterious effects from both conditions . . .
Frank S. Rowland and Mario J. Molina, physical chemists at the University of California at Irvine, have proposed a model for freon breakdown and ozone destruction. It is based on a similar reaction between nitrous oxide and ozone in the lower atmosphere. First, they propose, freons in the stratosphere absorb ultraviolet light in the 1,750 to 2,200 angstrom range, and chlorine is liberated. The liberated chlorine atom in turn attacks ozone, breaking it into oxygen. Each chlorine atom can remove thousands of ozone molecules from the stratosphere in this way, Rowland predicts.
Concentrations of fluorocarbons can be expected to reach 10 to 30 times their present levels if production continues to increase at the current nine percent per year. The result would be the destruction of 10 percent of the stratospheric ozone layer within 50 years, Rowland says. He has already calculated a one percent reduction in stratospheric ozone – a reduction that could result in about 8,000 additional cases of skin cancer this year, according to National Academy of Sciences statistics on skin cancer.
UPDATE | June 18, 2011
CFCs go from craze, to controversy, to congé
In the mid-1970s, a domestic craze became an environmental enemy. For more than two decades, aerosols had been praised as handy household helpers: “Merely by waving science’s newest gadget, you will be able to apply leg paint, extrude whipped cream, squirt shaving lather, waft a perfume, distribute insect killers … and fill the waffle iron” (SNL: 4/7/51, p. 218).
But these “aerosol bombs” relied on chlorofluorocarbons. In 1974, scientists proposed that these compounds could deplete ozone in the stratosphere. In 1985, researchers reported an ozone hole over Antarctica, bolstering the idea. International efforts to phase out CFCs have been highly successful, and the Antarctic ozone hole now appears to be on the mend (SN: 6/4/11, p. 15).
Though leg paint is no longer a cheap fashion solution, people still use non-CFC–based aerosols widely. Today’s propellants don’t destroy ozone but do pose other problems. Hydrocarbons can contribute to ground-level ozone formation, a health threat. And some hydrofluorocarbons belong among another class of environmental enemies: the atmosphere-warming greenhouse gases. – Elizabeth Quill
Credit: Maps courtesy of the GSFC Scientific Visualization Studio; Paper: paphia/Istockphoto