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Hope at last!

Hope at last! ALL the diatribe and deliberations about protecting the ozone layer have not been just a lot of talk. Recently scientists reported that the concentration of ozone-depleting chemicals in the lower atmosphere began decreasing for the first time last year since their introduction in the early '60s. The discovery has revived hopes of bringing the ozone layer back to its original state. Experts have predicted that the depleted layer could start recovering within 10 years.

The latest finding implies that the ban on the production of the ozonedamaging compounds in the West following a 1987 international treaty, "is making a difference," said S A Montzka, one of researchers and an atmospheric chemist at the National Oceanic and Atmospheric Administration in Boulder, Colorado. It also implies that most countries were conforming to the treaty. "This is the beginning of a change," he declared, adding that it was the first step towards the goal of closing the hole in the ozone layer.

The ozone layer found in the stratosphere forms a natural screen against the ultraviolet rays of the sun which cause skin cancer in humans and also harm many plants and animals. The ozone-depleting compounds have been broadly categorised as chlorofluorocarbons, or CFCs, halons and chlorine-based solvents that have been in use for over three decades as refrigerants, cleaning agents, spray propellants, foams and fire extinguishers. These compounds contain chlorine and bromine. In the '80s, scientists discovered that these two reactive molecules drift into the upper atmosphere and cause the thinning of the ozone layer.

The predictions of mending the hole in the ozone layer are based on ground-level measurements taken by scientists on three continents and two Pacific Ocean islands, which showed a reduction in the concentration of ozone-layer damaging chemicals. "A detectable signal for ozone recovery is expected around 2005 or 2010," said Montzka. The rate of recovery, he said, will also depend on stratospheric temperature and chemical emissions from volcanoes. If there are no unusual changes in the temperature and emissiohs, it is estimated that it will take 50 to 60 years before the layer is restored to the levels before 1970.

However, Montzka warned that the years between 1997 and 1999 would be the worst for the ozone layer. That is the period when chlorine and bromine, which reached their highest levels in 1994 in the lower atmosphere, will reach the stratosphere. But, the high point, as Montzka said is that "we have turned the corner".

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