Experiments show ice factor in polar ozone depletion

Press, 3 December 1987, Page 38

Experiments show ice factor in polar ozone depletion

By

GLENNDA CHUI

of Knight-Ridder Newspapers San Jose, California

Two groups of United States scientists have said they had demonstrated in the laboratory, the process by which chlorine is thought to be eating up the ozone layer over Antarctica, creating the infamous ozone hole.

Although their results did not prove chlorine was the culprit, they did show such chemical reactions were plausible, said David Golden of SRI International in Menlo Park, who led one of the research groups. The results add to growing evidence that man-made chemicals are partly to blame for the ozone hole, which this year was deeper than ever.

“They fit in very nicely with our current theories for the Antarctic ozone hole” and provide a "key

missing link” in the chemical explanation for it, said Richard Turco, an atmospheric scientist in Los Angeles. The reports, by scientists at SRI and at the Jet Propulsion Laboratory in Pasadena, were published in the journal “Science.” Ozone, a deep-blue gas whose molecules consist of three atoms of oxygen, forms a protective blanket high above the earth, where It screens out ultraviolet rays which could cause cancer and eye damage. Scientists worry chemicals called chlorofluorocarbons, used in refrigeration, industry foam packaging and spray cans, are eating away at this ozone layer.

Two years ago, British researchers reported the ozone layer above Antarctica had been thinning briefly but dramatically every spring since 1977. And last spring, re-

searchers found ozone levels above Antarctica fell by 50 per cent — the biggest drop since measurements have been made.

They said the evidence strongly suggested the ozone was being destroyed by a combination of chlorofluorocarbons and harsh Antarctic weather.

The studies just reported lend weight to theories of how this could happen. Most chlorine in the atmosphere is tied up in lazy compounds which don’t like to react with, others.

But in Antarctica, these harmless compounds are somehow converted to highly active chemicals which quickly destroy ozone.

Scientists have speculated this conversion took place within the icy clouds which hovered over Antarctica every spring.

The two Californian groups said they had recreated these reactions in the laboratory. In one set of experiments, Mario Molina and his colleagues at the Jet Propulsion Laboratory created a thin film of ice inside a narrow glass tube and then blew harmless chlorine compounds into the tube to see whether they would react. Sure enough, they did, he said.

They formed molecules which easily broke up in sunlight and turned into ozone “eaters”. “We have studied that reaction also extensively without ice, and it’s just too slow to matter,” Molina said.

“But in the presence of ice it’s enormously accelerated.”

The SRI group got similar results using a different method. Brian Toon, an atmospheric physicist at N.A.S.A.’s Ames Research

Centre in Mountain View, said the new data supported the idea chlorine was destroying the ozone.

“There were a zillion theories around,” he said.

“But theories don’t amount to anything in science — all that really counts is data.” He said the. results also indicated rapid depletion of ozone happened only in very cold conditions, “which means this isn’t going to start occurring over the rest of the earth.” But the new studies fell short of proving chlorine was indeed to blame, scientists said.

It would take more study, in the field and in the laboratory, to settle the question.

“Even with all this, we are still stumped at what causes the ozone depletion,” Turco said. “This is not by any means the final answer.”