The Arctic ozone layer experiences conditions similar to those that created the Antarctic ozone hole, but an Arctic ozone hole is unlikely to form, a University professor said.

"The reason for a lot of concern is that now we see things starting to happen in the Arctic, which is a little closer to home," said William Brune, associate professor of meteorology. "That's the air that blows over Pennsylvania."

Brune, along with D. W. Toohey and J. G. Anderson, professor of earth and planetary science and professor of chemistry, both of Harvard University, studied the Arctic ozone layer in a NASA-sponsored mission based in Stavanger, Norway last winter.

Their research, as expected, showed no hole in the Arctic ozone layer, which screens the cancer-causing ultraviolet light from the sun, said Brune. However, the scientists discovered levels of reactive chlorine in the layer equal to levels in the Antarctic.

"We never expected this; we thought it would only be one-sixth as bad as in the Antarctic," said Brune.

Reactive chlorine destroys ozone, said Brune, noting one chlorine atom can destroy 100,000 ozone particles.

"The results were very surprising," added Anderson. "The strong prejudice going in was that the higher temperatures in the Arctic would preclude the existence of the very dangerous levels of chlorine."

"By saying chlorine is the cause, you're saying chloro-fluorocarbons are the cause," he said.

Ultraviolet light breaks up industrially produced chloro-fluorocarbons when they reach the upper atmosphere, releasing chlorine and bromine, Brune said. However, only a small portion of these gases is in the ozone-destroying reactive form, he said.

At this point, the stratospheric clouds over the cold polar regions come into play, he said. When the temperatures in those regions fall, clouds form at heights of 60,000 to 80,000 feet. These clouds convert relatively unreactive chlorine compounds into reactive compounds, Brune said.

The clouds work by capturing reactive nitrogen compounds and converting them to unreactive forms, he said. Reactive nitrogen compounds keep chlorine in unreactive forms, he added. Brune said the unreactive nitrogen compounds may be removed when the cloud particles grow large enough to fall.

Despite equal levels of reactive chlorine, Brune said it is unlikely a hole will form over the Arctic due to more moderate conditions there.

A vortex forms over each pole during the winter. Combined with the falling temperature, this swirling mass forms and maintains the chlorine-converting stratospheric clouds, Brune said.

The vortex in the Antarctic is stronger and the temperatures are colder, he said. Also, in that region, the stratospheric clouds are more frequent and last longer. This is a vital difference, Brune said.

"We don't think things will get out of control. The reactive chlorine doesn't have long enough in the Arctic. It takes six to eight weeks to destroy the ozone, and in the Arctic it only has two to three weeks," he said.

When the vortex breaks down, air from outside the vortex brings reactive nitrogen compounds, which then regulate the reactive chlorine compounds, Brune said.

Although no hole exists over the Arctic, Brune said the overall situation is cause for concern.

"The gases that were only released in the atmosphere in the last couple of decades have caused a 2 percent loss in the ozone," he said. "If we keep adding at present rates, by the year 2050 the amount of chlorine in the atmosphere will triple."

Anderson said their research has heightened interest in the ozone loss problem.

"It is now clear that the Northern Hemisphere is equally susceptible," he said.

Brune said the effects of increased exposure to ultraviolet light due to ozone loss include a higher rate of skin cancer, lower crop yields and destruction of the aquatic food chain.

"With skin cancer, the general rule is a 2 percent increase for every 1 percent decrease in ozone," he said.