Scientists Find Ozone Hole May Exist Over North Pole
THE Antarctic ozone hole is a well-established effect. But what about the Arctic?
There have been indications that the kind of chemistry that destroys ozone in the south is also at work in the north. A paper published yesterday in Nature magazine confirms this phenomenon.
Peter von der Gathen of the University of Bremen in Germany and colleagues from 10 other countries explain how they traced ozone particles in individual air parcels during the 1991-1992 Arctic winter. They found chemically caused ozone loss in the stratosphere. They conclude the loss is ''consistent with existing understanding of photochemical ozone-depletion processes.''
These are the chemical processes that break down chlorofluorcarbon (CFC) compounds to release ozone-destroying chlorine in the stratosphere, letting dangerous solar ultraviolet radiation through to the planet's surface.
CFCs have been widely used as air- conditioner coolants, cleaning agents, and spray-can propellants. Their manufacture is to be phased out next year under the Montreal Protocol, an international treaty. But it will take the better part of a century for the atmosphere to cleanse itself of the CFC burden it already has acquired.
Asked if the public should be concerned about an Arctic ozone hole, meteorologist Gloria Manney of the National Aeronautics and Space Administration Jet Propulsion Laboratory in Pasadena, Calif., called this ''a difficult question.'' She explained that it has been shown ''pretty conclusively that there is ozone destruction ... in the Arctic.'' But, she adds that ''it isn't yet clear that we are seeing a decrease in [the total] ozone'' overhead in the Arctic. The ozone loss seen may be short-lived and confined to a certain altitude.
''People shouldn't be too concerned'' right now, Dr. Manney says. But, she adds, the new findings highlight the need to closely monitor the Arctic.
The reason for this need is meteorological rather than strictly chemical. The complex process in which CFCs breakdown into ozone-destroying chemicals speeds up in the presence of cold clouds in the normally cloud-free stratosphere. Cloud particles provide surfaces that facilitate key steps in those processes.
Stratospheric clouds form during the Antarctic polar night. As the sun returns, the chemical processes get under way and ozone disappears. The research team now confirms that this chemical scenario also occurs in the Arctic stratosphere. But the meteorology is quite different. The Antarctic is a frozen continent surrounded by ocean. During the winter and spring, winds encircling it form a ''polar vortex,'' which confines the ozone-destroying region within the Antarctic stratosphere, forming what amounts to a confined chemical reactor.
THE Arctic is a frozen ocean surrounded by land. But its polar vortex is less stable than the Antarctic's. It doesn't confine the ozone- destroying region for an extended period and allows more mixing with air to the south. And the warmer northern stratosphere has fewer cloud formations.
Mario Molina of the Massachusetts Institute of Technology in Cambridge -- one of those who first warned about CFCs and ozone loss -- agrees that there is no cause for immediate alarm. But he notes that the Arctic is ''not too far from a situation where more ozone depletion could occur.''
If climate change brought colder winters in the Arctic stratosphere -- as global-warming studies forecast -- then enough cold stratospheric clouds could form to cause concern. Also, a more tightly confined polar vortex could develop. The fact that the Arctic air mixes south would spread ozone-depleted air over populated regions. As Dr. Molina puts it: ''We would not see ozone depletion as severe as in Antarctica. But ... we could see it over a larger area.''