By
The Associated Press
WELLINGTON, New Zealand - The hole in the ozone layer over Antarctica stretched over a Chilean city when it ballooned to a record size last month, the first time it has reached a population center, scientists said yesterday.
Previously, the hole had only opened over Antarctica and the surrounding ocean.
Citing data from the U.S. space agency NASA, atmospheric research scientist Stephen Wood said the hole covered 11.4 million square miles - an area more than three times the size of the United States - on Sept. 9 and 10.
For those two days, the hole extended over Punta Arenas, a southern Chile city of about 120,000 people, exposing residents to very high levels of ultraviolet radiation. Too much UV radiation can cause skin cancer and destroy tiny plants at the beginning of the food chain.
Wood is a researcher with New Zealand's respected National Institute of Water and Atmospheric Research.
Dr. Dean Peterson, science strategy manager of the Antarctica New Zealand research group, said Wood's findings showed a city being exposed to the ozone hole for the first time.
"The longer it gets, the greater the chances of populated areas being hit by low ozone levels," said Peterson, who was not involved in the study.
Peterson said smaller spots of low ozone could affect Argentina and even the tip of South Africa, Australia or New Zealand.
"The hole won't grow to that size," he said. "But as it breaks apart, fingers of low ozone, or filaments as we call them, will go over major land mass areas. Those filaments will be over the land mass for a few weeks."
Last month, scientists expressed surprise when NASA data from Sept. 3 showed the hole at just under 11 million square miles - the biggest it had ever been. It continued to grow in the days afterward, according to the data cited by Wood.
Record-low temperatures in the stratosphere are believed to have helped the expansion of the ozone hole during the southern hemisphere's spring season.
Antarctic ozone depletion starts in July, when sunlight triggers chemical reactions in cold air trapped over the South Pole during the Antarctic winter. It intensifies during August and September before tailing off as temperatures rise in late November or early December.
Depletion of the ozone layer over Antarctica and the Arctic is being monitored because ozone protects Earth from harmful ultraviolet radiation.
Human-made chlorine compounds used in refrigerants, aerosol sprays, solvents, foam-blowing agents and bromine compounds used in firefighting halogens cause most ozone depletion. The temperature over Antarctica also significantly affects the size of each year's hole. Starting in October, warmer temperatures reduce the ability of chlorine and other gases to destroy ozone.
Experts agree that the man-made chemicals are leveling off thanks to the 1989 Montreal Protocol, which commits countries to eliminating production and use of ozone-depleting substances. But it could be 20 years before ozone levels recover noticeably.
