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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