Scientists probe the ozone hole for clues to its cause

AUGUST is miserable at the end of the earth. While cities north of the equator swelter under the late summer sun, this community of 100,000 at the southern tip of South America shudders through the last stages of another harsh winter. Some days, the biting wind and the cold, driving rain blow so fiercely off the Strait of Magellan that merely crossing the street requires meticulous preparation. Then, late in the month, the skies clear, and by early September the winds die down to a tolerable bluster. And in recent years, something else happens to the air at the bottom of the world: In the stratosphere high above the Antarctic, the earth's protective layer of ozone begins to disappear, creating an irregular ``hole'' roughly the size of the United States. In about three weeks, much of the ozone in this area is destroyed, stripping away the planet's best defense against damage caused by the sun's ultraviolet rays.

More of this protective shield disappeared last month than has been recorded before - a 50 percent loss between mid-August and mid-September, according to Robert Watson, chief of NASA's high-altitude research program. Ozone levels fell to 35 percent last year during the same period, and to 40 percent in 1985.

Scientists have been talking about ozone depletion since the mid-1970s, but the ultimate threat posed by the Antarctic hole - destruction of ozone globally - has given the problem a new sense of urgency. Scientists fear that a major loss of ozone could lead to dramatic increases in skin cancer and cause crop failures and climate changes.

This year, a team of 150 scientists, engineers, NASA technicians, and pilots set up shop in a chilly military hangar here in the most ambitious examination of the ozone hole to date. They brought several tons of scientific equipment to conduct some 21 experiments, collecting extensive data from two specially equipped jets, ground measurements in Antarctica, and satellites passing overhead. The magnitude of the NASA expedition has raised expectations that the scientists will come up with some definitive answers to explain the cause of the mysterious hole.

So far, the preliminary findings announced by Dr. Watson last Wednesday point to the combined effect of man-made chemicals, principally chlorofluorocarbons (CFCs), and the extreme cold over Antarctica at the beginning of the Southern Hemisphere spring as the cause of the ozone hole. Scientists will study the data for another six months before issuing a final report. ``This is the most important earth science experiment of the decade,'' said Watson.

Threatened by the results is the $100 billion worldwide CFC industry, which has balked at developing alternatives for the chemical compounds, made primarily of chlorine, fluorine, and carbon. Ironically, what has made CFCs so useful - their stability - may be the very reason they now threaten the environment. The compounds are so safe - they aren't toxic, flammable, or water-soluble - that they survive for decades. Eventually they reach the stratosphere, where they are broken down by the sun's ultraviolet rays. Once released from its chemical bond, the chlorine in CFCs attacks ozone.

The ozone hole was first confirmed in 1985 by British scientists stationed on the Antarctic coast. The British team had noticed a dramatic drop in ozone levels 10 years ago, but the measurements were so abnormal that they were attributed to computer or human error. But the measurements were later corroborated by a second British station 1,000 miles away, and last October American scientists at McMurdo Station on the Antarctic Peninsula concluded that chemicals, primarily CFCs, were responsible for the hole.

That announcement set off a storm of controversy and pushed ahead plans for this seven-week, $10 million expedition. Funded primarily by NASA, it also included scientific teams from other federal agencies, universities, and the Chemical Manufacturers' Association, plus meteorological support from Britain, Chile, and the United States.

The focal point of the expedition was a $20 million single-engine jet called the ER-2, the newest generation of high-altitude planes developed after the U-2 ``spy'' planes. Loaded with 14 sophisticated instruments tucked into ``pods'' under each wing, the ER-2 penetrated the ozone hole at upwards of 67,000 feet. A second jet, a modified DC-8 jetliner with seven experiments on board, flew at 33,000 to 34,000 feet at the lower end of the ozone hole. Unlike the ER-2, the DC-8 carried scientists who operated their own experiments during the 12-hour flights.

The stratosphere above the Antarctic is like no other, said Ron Williams, one of three ER-2 pilots assigned to the expedition. ``We've reached temperatures of -90 degrees centigrade [-130 degrees F.]. And the winds are up to 150 knots. There were even clouds at 64,000 feet. I've never seen clouds at that altitude.''

Scientists worked around the clock to ensure that their experiments would perform flawlessly. On flight days, scientists on the DC-8 took off at 5:30 a.m. for the rigorous 12-hour flight. Those with experiments on the ER-2 arrived at about 4 a.m. to prepare their instruments for the 9:30 takeoff. After each seven-hour flight, they spent the next six hours analyzing their valuable data. The data were converted to diskettes and transferred to a central computer, allowing all the scientists to review the information and make adjustments for the next flight.

Because so much was at stake, the scientists agreed to release the Sept. 30 statement at the conclusion of the expedition, describing, as Watson said, ``all we know for sure.''

``The scientific community will say that's not wise, but the mission is so significant to society that we have to do it,'' he said. James Anderson, a Harvard University atmospheric scientist, agreed. ``This isn't usually the way science is done. But the potential results are devastating for a $100 billion industry.''

[According to an Associated Press report, Dr. Anderson said at a news conference in Santiago, Chile, last Wednesday that the preliminary findings did not indicate a need for new, more dramatic measures to curb production of CFCs. Referring to the agreement reached last month by more than 55 nations to reduce CFC use by 50 percent in the next decade, he said, ``The Montreal accords ... are properly cast to handle our present understanding and adjust to advances in our future understanding. The variation that this year represents over previous years is not yet sufficiently dramatic to change the approach.''

[Rafe Pomerance, a staff member of the World Resources Institute, a Washington-based environmental and policy research group that avocates stricter controls on CFC emissions, said of the report: ``It's a dramatic finding, and we'll increase pressure for faster reductions [in emissions], faster ratifications [of the Montreal agreement], and more research.'']