Tests Show Aerosol Gases May Pose Threat to Earth

Two scientists have calculated that gases released by aerosol cans have already accumulated sufficiently in the upper air to begin depleting the ozone that prOtects the earth from lethal ultraviolet radiation

The calculations, culations, by scientists at Harvard University, follow the recent discovery that these gases, used as aerosol propellants for hair sprays, insecticides and the like, ‘while inert chemically, are highly efficient in promoting ozone breakdown.

The finding has posed a new, and ominous threat to stability of the ozone layer that lies primarily between 10 and 30 miles aloft. There has also been con cern that the layer would be depleted by exhaust gases from a large fleet of supersonic transport planes or by extensive explosions of nuclear weapons.

On Sept. 5 Dr. Fred C: 1kle, director of the Arms Control and Disarmament Agency, said that nitric oxides injected into the stratosphere by a nuclear war could wipe out the ozone layer entirely.

Because certain wavelengths of ultraviolet light from the sun break down molecules essential to life, it is believed that land life did not emerge until the development of the ozone layer late in the earth's history. The lethal wavelengths cannot penetrate water.

The most prevalent concern, however, is not for total loss of the ozone. which is broken down and restored in a complex sequence of day and night chemical reactions. Rather, it is a fear of sufficient depletion to cause widespread skin cancer and other effects.

Furthermore; because ultraviolet absorption by ozone contributes substantially to upper air heating, radical reduction of such heating could alter climates.

Ozone is a gas whose molecules are formed of three oxygen atoms instead of the two that are paired in ordinary oxygen, providing individual atoms that can merge to convert twoatom molecules into the threeatom ozone molecule.

The Harvard calculations were made by Dr. Michael B. McElroy, professor of atmospheric science, and Dr. Steven C. Wofsy, an atmospheric physicist. They found that, even if dispersal of aerosol propellants and other ‘:such. gases; ‘widely known under the trade name Freon, is halted as soon as. practicable, depletion of the ozone layer by 1990 could reach 5 per cent.

They consider a halt by the end of this decade to be the earliest plausible time, in view of political and commercial considerations. As others have pointed out in a number of recent discussions of the danger, the effect will continue for some time after a cutoff because the gas at sea level must work its way up into the stratosphere.

If according to the Harvard scientists, the cutoff is delayed until its effect on the ozone layer, having reached 10 per cent, becomes indisputable, the consequences could be more severe.

Basing their calculations on a relatively conservative estimate of an annual increase of 10 per cent in release of the gases, they predict that the depletion will not level off until the year 2000,.By then they helm, the ozone layer will have been red duced 14 to 15 per cent.

Slow Recovery Foreseen

If releases of Freon continue to increase 21 per cent a year, as has recently been the case for the aerosol propellants, the ozone level will be down 7 per centby 1984 and 30 per cent by 1994. A cutoff in 1987 would modify the effect to a maximum depletion, in 1995 of 21 per cent.

In all cases recovery would. be slow since there are no chemical reactions that remove such gases from the air.

In an independent analysis, three University of. Michigan scientists have concluded that; by 1985 or 1990, chlorine derived from the atmosphere's Freon content will have become the dominant factor in ozone breakdown.

This report, by Drs. Ralph J. Cicerone, Richard S. Stolarski and’ Stacy Walters, appears in tomorrow's issue of the journal Science.

The Freon gases In question’ are chlorbfluoromethanes, one of which, marketed as Freon 11, isused. as the propellant in aerosol cans since it is inert chemically and does not react with the _substance. being ejected. The other, Freon 12, is used as a refrigerant.

As recently as last year the release of these gases into the atmosphere was considered a boon rather than a hazard: In the British journal Nature on Jan. 19, 1973, it was noted that these gases, being released into the air at a rate growing rapidly, could be used as harmless traces of air movements.

As of 1971, it.was estimated, one million tons of each kind of Freon, was being released yearly into the atmosphere. Furthermore, almost all such gas produced to date by world industry is still in residence ‘within the air, the report said.

However, wrote the authors, “the presence of these compounds constitutes no conceivable hazard.”

But last June,’ Drs. Mario J. Molina and F. S. Rowland of the University of California at Irvine reported in Nature that the Freons, far from being innocuous constituents, are six times more effective in breaking down ozone than the oxides of nitrogen that had been the chief focus of attention.

Supersonic transports and nuclear explosions release oxides of nitrogen into the upper air, and it is known that they act as catalysts both in promoting the breakdown of ozone and in “stealing” free oxygen atoms that might otherwise mate with oxygen gas to form new ozone.

Hence, there has been concern regarding the effect of such transports and such explosions on the ozone layer. The Harvard group has calculated that the exhaust from 400 Concordetype supersonic transports operating seven hours day would deplete the ozone layer by about 1 per cent.

Now it appears that sunlight breaks down the Freon, releasing chlorine, which has an even more powerful catalytic effort. The Harvard scientists had begun a year ago to look into the possible role of chlorine introduced into the stratosphere by passage of the projected space shuttle, whose exhaust would contain hydrogen chloride.

This. enabled them to apply the same calculations to the freon problem.

That the accumulation of Freon in the world's atmoSphere is increasing rapidly was confirmed earlier this month by Dr. John W. Swinner‘ton of the Naval Research Laboratory ‘at a meeting of the American Chemical Society.

In 1972, measurements on a cruise from Los Angeles to ntarctica, he said, showed an verage level of 61 parts per rillion. A year later, over the Atlantic, it was 85 parts per trillion, and in January of this year measurements in the Arctic showed it to have reached 120 parts per trillion.

On June 14 of this year A. B. Pittock, a government atmospheric physicist in Australia, reported that balloon measurements of ozone over Australia showed a general decline in the amount of that gas over the eight year s prior to 1973. Whether this was a global effect was uncertain.

As noted yesterday by Dr. McElroy of Harvard, there is a variation in ozone content of about 1 per cent, apparently related to the 11‐year sunspot cycle, and a suggestion of a slight, 20‐year cycle of unknown origin.

While Freon is the trade name of du Pont de Nemours & Co., similar gases are manufactured in this country by Allied Chemical. Union Carbide, Pennwalt, Kaiser Chemical and Racon. They are extensively used in airconditioning as well as in refrigeration systems.

In response to recent reports of possible ozone effects, the Manufacturing Chemists Association in Washington, on behalf of producers of the gases in various parts of the world, has initiated its own program of laboratory studies.

Last night Charles S. Booz, spokesman for du Pont's Freon products division in Wilmington, Del., termed the assessments of ozone effects “largely hypothesis.” He added that “very little is known” of chemical reactions in the special environment of the upper atmosphere.

Dr. McElroy, in a telephone interview, himself emphasized that the analysis, which is being submitted to the journal Science, is obviously theoretical. He expressed the hope that there would now be extensive measurements of Freon levels and of upper air contamination by hydrogen chloride.

He said he assumed that others would take a hard look at the Harvard calculations. The surest way to ‘assess the predictions would be to wait and see what happens, he added, but that is hardly acceptable.

“It is,” he said, “a very unusual situation for science.”