Halting worldwide loss of ozone shield

While the Antarctic ozone hole has gripped public attention, atmospheric chemists have been looking for signs of ozone loss elsewhere. Research teams may have found one such indication in the Arctic. According to reports at the Polar Ozone Workshop held in Aspen, Colo., last month, the same kind of pollution-related chemistry thought to destroy ozone over Antarctica seems to be at work over the north polar region as well.

This follows the NASA report in March that, on a global average, the ozone layer has thinned by 2.5 percent over the past decade. Here again, pollution by chlorofluocarbons is a suspected culprit. CFCs are chemicals used as working fluids in refrigerators and air conditioners, as agents in blowing bubbles in plastic foam, and as cleaning agents for electronic components.

Such mounting evidence of a CFC threat to the ozone layer puts pressure on the signers of the Montreal Protocol on Substances That Deplete the Ozone Layer to toughen CFC restrictions.

The agreement that 24 nations and the European Community signed in Montreal last September would freeze CFC consumption at 1986 levels beginning July 1, 1989. It would ultimately cut CFC use in half by mid-1998. It would also freeze use of halons (bromine-containing fluorocarbons used for fire extinction) at 1986 levels. Mexico and the United States have already ratified the protocol. At least nine more signatories must also ratify it this year if it is to go into effect next January as scheduled.

Many experts now suspect that we may be losing ozone faster than has been believed. In that case, the protocol's CFC phase-out may be too slow. Thus when - and if - the protocol goes into effect in January, the United Nations Environment Program will organize a reassessment of the ozone situation. This will give signatory governments the knowledge with which to consider tightening up CFC use. The agreement provides for such reassessment.

To recapitulate briefly, ozone is a form of oxygen with three atoms per molecule. It forms in the stratosphere under action of solar ultraviolet radiation. Once formed, it absorbs this type of radiation and shields earth's life forms from these biologically damaging rays.

Ozone forms and disappears all the time in chemical reactions that occur naturally in the stratosphere. This results in an equilibrium between formation and loss that maintains the ozone shield at its natural strength. When CFCs migrate to the stratosphere, however, they also take part in a complex chemical process that liberates chlorine, which then destroys ozone. Thus, CFC pollution can tip the balance toward increased ozone destruction.

Without the ozone shield to absorb it, solar ultraviolet radiation would make it dangerous to walk in the sunshine. The Montreal Protocol signatories should ratify their agreement promptly. Then they should urgently consider tighter CFC controls.

A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.

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