Scientists say that volcanic eruptions spew huge amounts of hydrochloric acid and hydrofluoric acid into the atmosphere where they can join industrial chemicals to eat away at the Earth's diminishing ozone layer.

Two volcanologists from the Michigan Technological University in Houghton and a geochemist from the University of Oregon in Eugene reported the results of the new volcano study in the current issue of the British journal Nature.While the scientists were unable to study the direct effects of an erupting volcano, they were able to simulate the conditions in a computer program called SOLVGAS, which examined simulated emissions consisting of approximately 40 fluorine and chlorine compounds.

"If they're ejected high enough into the atmosphere," said University of Oregon geochemist Mark Reed, "they can cause ozone destruction. This has been going on throughout Earth's history.

"This is not the only factor and certainly not the major factor," of ozone destruction, he said. "But volcano emissions constitute an additional significant source, perhaps an additional straw that could break the camel's back."

Reed said he and his colleagues examined major volcanic eruptions dating back 75,000 years and studied the effects of such degassing volcanoes as Kilauea in Hawaii, which erupted in 1984.

While volcanic acids apparently damage the ozone layer, they do not cause a fraction of the threat posed by the millions of tons of industrial chemicals that drift annually into Earth's ozone layer, Reed said.

Ozone is an oxygen molecule with an extra oxygen atom.

New evidence suggests that 12 million tons of hydrochloric acid and 6 million tons of hydrofluoric acid are produced annually by volcanoes.

In big eruptions, like the violent explosion of St. Augustine two years ago off the coast of Alaska, or Mt. St. Helens eight years ago in Washington, these ozone-damaging acids are shot directly into the upper atmosphere.

There they join industrial chemicals 15 to 30 miles above Earth's surface in the stratosphere where they eat away the gaseous layer that blocks out harmful ultraviolet rays from the sun.

These compounds are also being driven aloft by degassing volcanoes which spew the acids into Earth's lower atmosphere.

In such cases, the compounds never get farther than the troposphere, about 5 miles above Earth's surface, and usually are washed back in rainwater, contributing to the salt content of the seas.

Industrial compounds, particularly the chlorofluorocarbons (known as CFBs) used commercially in air conditioners and refrigerators, escape into the upper atmosphere and react with ozone, converting it into plain oxygen.