By Sid Perkins
From San Francisco, at a meeting of the American Geophysical Union
The ozone-free zone that develops high in the atmosphere over Antarctica each summer was a result of the presence of chlorine- and bromine-containing chemicals may not heal until 2065, about 15 years later than previously projected.
Over most of the world, an ozone layer blocks much of the sun’s ultraviolet radiation from reaching Earth’s surface. However, in the extremely cold air over Antarctica, the combination of sunlight and certain gases, such as the chlorofluorocarbons used in refrigeration, readily destroys ozone.
At its yearly peak in early October, the ozone hole covered about 24.3 million square kilometers, an area about the size of North America. That’s down from the hole’s largest extent of 26.2 million km2 in 1998 but not by as much as scientists had expected, says Dale F. Hurst, an atmospheric chemist with the National Oceanic and Atmospheric Administration in Boulder, Colo.
The production of many ozone-destroying chemicals was banned by international agreement in 1995, says Hurst. But concentrations of some of those chemicals low in the atmosphere over the United States and Canada—parcels of air that end up high over Antarctica 5 to 6 years later—hint that the chemicals are still used in significant quantities.
The recent measurements suggest that stockpiles of such gases may be larger than scientists had estimated. Recycling and reuse of those chemicals may be extending the life of such stockpiles, Hurst notes.
Using estimates of the atmospheric lifetimes of the ozone-destroying chemicals, researchers had projected that by 2050 the ozone hole over Antarctica would shrink to the size it was in 1980, the year that it was first noted. The atmospheric data gathered over the United States and Canada now suggest a 15-year delay in recovery, says Hurst.
