Culprits of The Stratosphere

By MICHAEL D. LEMONICK

Representatives from 35 countries met in Montreal last week to hammer out an agreement that would limit man-made damage to the atmosphere's protective ozone layer. As they deliberated, the British journal Nature published a study offering the strongest evidence so far that man-made compounds called chlorofluorocarbons (CFCs) are the culprits. Crofton Farmer, principal author of the study and an atmospheric physicist at the Jet Propulsion Laboratory in Pasadena, Calif., reported that data gathered last year in the Antarctic are "entirely consistent" with the premise that CFCs -- used in refrigeration devices and as ingredients in plastic foams -- are destroying the ozone. "The evidence isn't final," he told TIME last week, "but it's strong enough."

Farmer and others have concentrated their research on the so-called Antarctic ozone hole. Though world ozone levels have dropped by an estimated 3% to 7% in the past several decades, south polar levels plunge by as much as 50% each September, then rebound. The discovery of the hole was announced in 1985 by a team led by Joseph Farman, a scientist with the British Antarctic Survey. Since then, researchers have flocked south to study the phenomenon.

Their interest is hardly academic. The ozone-enriched air, which stretches from six to 30 miles up, protects life on earth from dangerous solar ultraviolet radiation (UV). Although ozone, whose molecules are made of three oxygen atoms, absorbs UV radiation, even the amount that now penetrates the ozone layer can cause skin cancers and has been linked to cataracts. With less ozone, these disorders will increase; with no ozone at all, the UV could be deadly. Scientists have long suspected that decomposing CFCs in the stratosphere release chlorine, which acts as a catalyst, breaking ozone molecules apart. But it was all theory: Could the chemicals rise so high into the atmosphere? Might not the chlorine have come from such natural sources as volcanic eruptions?

Farmer discovered that chlorine compounds bloom as the hole appears each year. His theory: the compounds condense onto ice crystals during the polar winter; then, as spring nears in early September, the chlorine is warmed by the sun and converted into a reactive form that can destroy ozone. The presence of fluorine in the atmosphere supports the view that these chlorine compounds are of man-made origin. "There isn't any fluorine in the upper atmosphere from any natural source," says Farmer. This suggests that the source of the accompanying chlorine is chlorofluorocarbons.

$ Some experts remain cautious. Says William Brennan of the National Oceanic and Atmospheric Administration: "It would be dumb to make up my mind before the results from the field are all in." He should not have long to wait. Last month a DC-8 and a converted U-2 spyplane began flights under and through the hole in the most intensive attempt to date to pin down a detailed model of the ozone depletion process. Preliminary results should be announced later this month.

The Montreal conference, sponsored by the United Nations Environment Program, was convened to approve a proposal to freeze CFC production worldwide, initially at 1986 levels, then progressively reduce it over ten years. According to Farman, the delegates would do well to approve the measure. Along with other scientists, he is worried that the problem, if it remains uncorrected for the next two decades, will be "possibly beyond redemption."

With reporting by Edwin M. Reingold/Los Angeles