VOA Special English 慢速英语听力材料

This is the VOA Special English Environment Report.

Scientists in the United States have reported some good news about the ozone in the atmosphere. Recent findings suggest that the destruction of ozone by pollution is slowing. Ozone is a form of oxygen. Its presence above Earth protects us from radiation from the sun.

In one study, researchers examined information gathered by NASA space agency satellites and by equipment on Earth. The findings? In the words of Michael Newchurch of the University of Alabama: "This is the beginning of a recovery of the ozone layer."

Mister Newchurch led the study. He says the atmosphere was losing about eight percent of the ozone layer per ten-year period since the late nineteen-seventies. In the last five years, though, that rate of loss has dropped by half. He says the atmosphere should start to gain ozone before long. He says a full recovery, however, is about fifty years away, as long as the Montreal Protocol remains in place.

That is an international treaty from nineteen-eighty-seven to restore the ozone layer. The treaty restricts the use of a number of chemicals that destroy ozone, like chlorofluorocarbons, or C-F-C's.

Wide use of C-F-C's began in the nineteen-thirties. They became popular coolants in devices such as refrigerators and air conditioners. C-F-C's remain in the atmosphere for years.

Mister Newchurch says the study provides evidence that the Montreal Protocol is working by reducing C-F-C pollution. But the study found the ozone improvement only in the upper stratosphere. The scientists have not yet seen evidence of similar changes in the lower stratosphere. That holds most of the protective ozone.

The Montreal Protocol also restricts the use of methyl bromide, a chemical to kill insects. Farmers and shippers are the main users. Natural sources of methyl bromide include oceans and some plants. Scientists say the bromine gas it produces is fifty times more destructive to ozone than chlorine gas from C-F-C's.

Methyl bromide has never been used as widely as C-F-C's. But a separate study found a decrease in bromine gas levels in the atmosphere. Researchers at the National Oceanic and Atmospheric Administration did the study. They reported a thirteen percent drop since nineteen-ninety-eight. The report is based on eight years of measurements taken at ten stations around the world.

This VOA Special English Environment Report was written by Caty Weaver.