While problems persist, a new survey of air samples from the Point Barrow Observatory and other sampling sites indicates that global agreements to curb the manufacture and use of chemicals that attack the ozone layer are working. Colo. The others are in Hawaii, American Samoa, and at the South Pole. The recent review, led by CMDL chemist Stephen Montzka, shows that overall, ozone-depleting compounds in the lower atmosphere fell by about 3 percent between 1994, when they were at their peak, and 1997, the latest figures used for the study. Breaking Down the Ozone These compounds eventually work their way into the stratosphere, where they break down the ozone that protects the Earth's surface from excessive amounts of the sun's ultraviolet radiation. Such reactions have led to the ozone hole that appears over Antarctica each spring and to a more recent thinning of the ozone layer over parts of the Arctic, researchers say.
Sunlight breaks down CFCs into components that destroy ozone molecules high in the atmosphere.
Based on the provisions of the 1987 Montreal Protocol and subsequent amendments, the ozone layer is expected to recover to pre-1980 levels by 2050, with the first evidence of recovery likely to show up in about 10 years. But several factors could delay the recovery, researchers say. Still Rising One is the increasing level of a chlorine-based compound known as chlorofluorocarbon 12. Used in refrigerators and air conditioners, CFC-12 is no longer produced in developed countries, although large amounts of the gas lie in junked appliances, which leak as they age. But Prather adds that CFC-12 is still being produced in developing nations, such as China, Mexico, and India, which were given an extra 10 years to begin phasing out production.