Ozone levels dropped as much as 97 percent at some altitudes over Antarctica last month, raising concerns about the safety of researchers stationed there, a congressional panel was told yesterday.
National Science Foundation official Peter E. Wilkniss told the Senate Environment and Public Works Committee that scientists working from McMurdo Station on Antarctica during this year's expedition found some of the lowest atmospheric ozone levels ever measured. By September, a strip of the stratosphere about nine miles high contained only 3 percent of the ozone considered normal.
The depletion was so dramatic, Wilkniss said, that expedition leaders have become worried about eye damage caused by increased ultraviolet radiation in Antarctica. Ozone screens the Earth from the most damaging ultraviolet rays, which can cause skin cancer, cataracts and suppression of the immune system.
"We got concerned about the health and safety of our workers in Antarctica, who may be exposed to as much as four times the amount of ultraviolet radiation as you would get in summer at the beach in Miami," he said.
The report was the first from ground crews who this year monitored the seasonal "hole" in the ozone layer over Antarctica. Late last month, scientists there reported an overall 50 percent decrease in ozone, a sharper decline than has been recorded in previous years.
The Antarctic ozone hole has riveted the attention of atmospheric scientists since it was first disclosed by British researchers two years ago. Experts who testified yesterday said the latest expedition provided the strongest evidence yet that chlorofluorocarbons (CFCs) are to blame for the seasonal depletion, which begins in the depth of the Antarctic winter and gradually disappears in the spring.
CFCs are Freon-type gases that are used as refrigerants, foam-blowing agents and, in some nations, as aerosol propellants.
"The results from this year indicate that it is time to take a stand," said Michael B. McElroy of Harvard University, who identified himself as a former advocate of a "cautious approach" toward regulating CFCs. "There is no longer reason to doubt that industrial gases containing chlorine are responsible for a dramatic large-scale change in the stratosphere."
"I'm getting worried," said Sen. John H. Chafee (R-R.I.).
"I think you should be worried," responded Robert T. Watson of the National Aeronautics and Space Administration. "If the goal were to return the Antarctic atmosphere to its pristine state, the only hope would be to stop production of CFCs immediately. And then it would take several hundred years."
But Watson said some of the ozone depletion in Antarctica is the result of unusual weather conditions in the area, where winter winds create a kind of whirlpool of frigid air that traps chlorine atoms and creates a fertile atmosphere for chemical reactions.
"I'm not yet convinced whether there will or will not be global ramifications," he said.
University of California scientist F. Sherwood Rowland said monitoring stations in Switzerland, Maine and North Dakota have recorded wintertime ozone drops of as high as 9 percent.
"It would be very risky and foolhardy to assume that similar chemistry won't occur over temperate zones and the tropics," he said.
Rowland also criticized a recent international agreement to reduce CFC use. The agreement, signed by 45 nations, including the United States, last month, would freeze CFC production at current levels by 1990 and reduce the chemicals' use 50 percent by 2000.
In the meantime, Rowland said, chlorine concentrations in the stratosphere will increase about 35 percent. "I don't think the global community can afford to wait for another dozen years before applying stringent controls on CFC emissions," he said.