Boston — While East-West negotiators discuss arms control in Geneva, another group of delegates is meeting there to talk about controlling the use of chemicals that may threaten Earth's protective ozone layer. Representatives from some 40 nations are following up the March 1985 conference at which 28 countries signed the Vienna Convention for the Protection of the Ozone Layer. Signers included the United States and the Soviet Union.
That convention established the diplomatic machinery to develop an international action plan by next April. The current meeting, which runs Dec. 1-5, is considering what to do.
US representatives are urging fellow delegates to freeze production of the chemicals at current levels while planning to cut back sharply on their long-term use. But any decision on this or other action has to be taken against a background of scientific uncertainty.
The chemicals in question belong to the chlorofluorocarbon (CFC) family. We use them as the working fluid in air conditioners and refrigerators, in making plastic foams, and as propellants in spray cans. This latter use is banned in Canada, Sweden, and the United States. When CFCs escape and migrate to the stratosphere, they can take part in complex chemical reactions that lead to ozone destruction.
Ozone is a form of oxygen that has three atoms per molecule. Formed by action of sunlight in the high stratosphere, it absorbs biologically harmful ultraviolet (UV) solar radiation. Natural processes form and destroy this ozone all the time. It's a balance of processes that, on average, maintain the ozone shield.
There's little doubt that CFC pollution has added a new, ozone-destroying factor to this chemical equation. The key question, which scientists can't yet answer, asks whether this tips the balance toward net ozone loss.
The so-called Antarctic ozone hole illustrates the problem.
During Antarctic spring -- August through November -- ozone concentrations drop over the South Pole region and increase in a surrounding latitude band. Considering a zone from the pole to south latitude 44 degrees, there's no net loss of ozone in any given year. There's only a rearrangement of its distribution. The hole fills in again when summer comes in November.
Scientists have known this for some time. What has caught their attention is a recent year-to-year drop in the total ozone within the springtime maximum and minimum regions.
At the same time, Antarctic CFC concentrations, measured at ground level, have been rising. The National Ozone Expedition, sent to study the situation, reported in an Oct. 20 statement that it had no definite explanation for the occurence. Nevertheless, its members concluded that chemical processes involving CFCs probably are thinning Antarctic ozone.
Scientists who wonder about natural causes challenge this conclusion. The November issue of Geophysical Research Letters is devoted to the problem. Its editors -- Mark B. Schoeberi and Arlin J. Krueger of the NASA Goddard Space Flight Center -- note that chemical processes can't explain all the facts. For example, they can't account for seasonal ozone redistribution. Also, the year-to-year ozone decline correlates with a decline in average seasonal temperature, so a slight climate change may be involved. Finally, this year's ozone totals exceed those of 1985, suggesting that the decline has at least paused if not ended.
``Despite the number of public pronouncements, no clear link between man-made pollutants and ozone depletion over the Antarctic has been established,'' editors Schoeberi and Kruger say.
The degree of danger people might face also is uncertain. A US Environmental Protection Agency study projects a substantial rise in skin cancer rates if CFC use isn't curbed. John R. Wiesenfeld, chairman of Cornell University's chemistry department, has challenged this study, which was released to the press before receiving formal scientific review. In a statement issued by Cornell, he calls it a ``snap judgment.'' ``There is not even a qualitative understanding of what causes ozone-layer behavior,'' he says. ``How can the EPA make a quantitative statement?'' he asks.
He also notes that the growing popularity of sunbathing may be a bigger threat than ozone depletion. He points out that just moving south from Baltimore to Washington increases UV exposure as much as would a one percent ozone drop.
What is needed, Wiesenfeld says, is a stepped-up, global research effort to better understand the atmospheric chemistry involved and learn more about ozone depletion.
The United States position at Geneva is that it would be prudent to curb CFC use now in spite of the scientific uncertainties.