The potential of these chemicals to destroy ozone in the upper atmosphere has been recognized by scientists since the early 1970's.

Many of the chemicals linger in the upper atmosphere for a century or more, destroying ozone all the while.

These can destroy ozone when they reach the upper atmosphere.

Both classes of chemicals have been found to combine with and destroy ozone in the atmosphere.

This would remove chlorine from the chain of reactions which destroys ozone.

This means it would destroy less ozone in its lifetime.

At the same time, the forest vegetation itself destroys ozone near the ground, where it is a pollutant.

But there is less of them in the atmosphere, and they consequently destroy far less ozone.

It has been shown that human activity does destroy ozone at a faster rate than normal.

The chemicals are believed to destroy ozone, which blocks the sun's harmful rays.