SAN FRANCISCO -- The ozone hole over Antarctica might persist two decades longer than predicted, until 2065, because ozone-destroying chemicals are still being released by developed nations a decade after their production and importation were banned.
The Montreal Protocol, ratified in 1987, banned the creation of chemicals such as chlorofluorocarbons used as coolant by developed nations. It followed the discovery that such chemicals ripped apart ozone molecules and severely thinned the layer of ozone that sits about 20 miles above Earth's surface and shields the planet from harsh ultraviolet radiation that causes cancer and cataracts and can harm wildlife.
Developing countries were allowed to continue using the substances for several decades to avoid the higher cost of replacement chemicals. Scientists had predicted that the phasing out of the chemicals by developed nations would allow the ozone hole over Antarctica to recover by 2040 or 2050.
But measurements taken in 2003 and released yesterday show that emissions of the chemicals from the United States and Canada made up about 15 percent of the world total even though the nations are no longer producing the compounds, said Dale Hurst, an atmospheric chemist from the National Oceanic and Atmospheric Administration who made the measurements.
He estimated that developed countries now account for about half of the world's total.
"These fractions are surprisingly high," Hurst said at a briefing on the issue held at the American Geophysical Union, a scientific meeting of 11,000 earth scientists. "We would have expected them to be exhausted by 2003."
Hurst says he believes the compounds are not new ones but are left over from old fire extinguishers, refrigerators and air-conditioning systems that were created before the ban went into effect but are being legally recycled and slowly leaking out into the atmosphere.
Hurst said in an interview that he doubted that there was much illicit production of two major chlorofluorocarbons in the U.S. or Canada because his measurements showed no traces of a chemical used in their production.
The overall rates of two major ozone-destroying chemicals, chlorine and bromine, peaked in 2002 and are now in decline, he said.
But scientists greatly underestimated the amount of already produced chemicals that remained and were still in use, Hurst said.
The ozone hole over the Antarctic is now not expected to recover until 2065, said John Austin, another NOAA scientist who runs computer models of how the ozone layer will respond in the future.
The ozone hole over Antarctica was first detected 20 years ago. This year's hole was one of the largest ever recorded and was 9.4 million square miles, about the size of North America. That rivaled the record in 1998, when the hole was 10.1 million square miles, according to the National Aeronautics and Space Administration. Before 1985, ozone holes measured less than 4 million square miles.
Hurst's measurements, taken by low-flying aircraft, of ozone-destroying chemicals near the planet's surface have been confirmed by satellite, said Michelle Santee, an atmospheric scientist at the Jet Propulsion Laboratory.
Total levels of chlorine in the stratosphere have declined in recent years, but they are still five times as high as natural levels, she said. In addition, the particular chlorine molecule that destroys ozone - chlorine oxide - is still forming in high amounts during winter months over the Antarctic.
"As a result, the ozone has been eaten away," Santee said.
Some of the chemicals involved persist for 40 years, others for 100 and can continually tear apart ozone through chemical reactions, she said.
Chlorofluorocarbons are allowed to be recycled. Moving them from one place to another does allow some of the chemicals to leak out. But the alternative to recycling would be to vent them to the atmosphere all at once, which would raise levels even more suddenly, the scientists said.
Usha Lee McFarling writes for the Los Angeles Times.