Acid Clouds Destroy Arctic Ozone, NASA Says...05/31/00

WASHINGTON, (Reuters) - Icy clouds filled with nitric acid helped eat away the protective ozone layer over the Arctic last winter, NASA scientists said on Tuesday.

Global warming could help the long-lived clouds last even longer, despite efforts by industry to reduce the amount of chlorine spewing out, the researchers told a conference.

"We found that the clouds lasted longer during the 1999/2000 winter than during past winters, allowing greater ozone depletion over the Arctic," Eric Jensen of NASA's Ames Research Centre told a meeting of the American Geophysical Union.

They said it was possible the Arctic could suffer from an ozone hole like one that has appeared over the Antarctic.

"With the clouds persisting longer, we are seeing greater ozone losses, even though the amount of chlorine in the atmosphere has declined slightly," added Owen Toon, a professor at the University of Colorado who helped lead the study.

The ozone hole over the Antarctic is better known but it is remote. Toon noted that ozone-depleted air from the Arctic drifts south toward North America, Europe and Russia each spring. This could mean more ultraviolet light reaching populated areas and farms.

In an attempt to preserve the ozone layer, which protects people, animals and crops from dangerous ultraviolet rays from the sun, governments agreed to ban the use of chlorofluorocarbons (CFCs) and other ozone-destroying chemicals in 1996.

But observations by aircraft, balloons and ground-based instruments show that clouds in the stratosphere were helping to destroy the Arctic's ozone layer.

Nitrogen, which can help moderate the destructive work of chlorine compounds, is drizzling out of the clouds, the researchers said. "This was a real surprise," said Toon.

He said ozone loss over the Arctic has been worsening since 1995. If the warming of the Earth's atmosphere adds to this, it could take decades for the ozone layer to recover.

NASA reported last month that ozone concentrations declined as much as 60 percent from November through March in some parts of the Arctic stratosphere, which lies between 10 and 30 miles (16 and 50 kms) above the Earth.

DC-8 aircraft from NASA made about 25 flights over the region over the winter, and U.S., British, Japanese, Russian, Swedish and other scientists measured information from weather balloons and observations made at Kiruna, Sweden, which is north of the Arctic Circle.

The ozone layer is fairly hardy, but if there are high levels of inorganic chlorine, temperatures cold enough for the formation of polar stratospheric clouds and plenty of sunlight, as is seen in late winter and early spring, chemical reactions can take place that will destroy it.

Consequences of ozone loss can be severe, scientists say. People will suffer higher rates of sunburn and skin cancer and crops and livestock will be damaged as ultraviolet rays that are usually filtered out hit the Earth's service.