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 user 2005-12-07 at 10:30:00 am Views: 110
  • #13349

    Delay expected in ozone recovery

    It could take far longer than expected for the ozone “hole” over Antarctica to repair itself, scientists have said.

    New research from the US and Canada indicates ozone-eating chemicals
    are still being released into the atmosphere in large quantities.

    The latest modelling predicts the protective gas layer
    found in the stratosphere will not now recover its health until about
    the year 2065.

    This is a more than a decade later than previous forecasts.

    “The reservoirs of ozone-depleting chemicals found in old fridges and
    air-conditioning systems may be greater than anticipated, and if this
    continues into the future then the projection of ozone hole recovery in
    2050 may have to be extended,” said Dale Hurst, from the US National
    Oceanic and Atmospheric Administration (Noaa).

    He was speaking here at the Fall Meeting of the American Geophysical Union.

    Dr Hurst was reporting the results of scientific flights through US and
    Canadian airspace which sampled the atmosphere for the presence of
    chlorine- and bromine-containing chemicals.

    CFC curbs

    The production of these halocarbons, as they are known, was restricted
    by the Montreal Protocol which became effective in 1987 – and it has
    been very successful.

    But the sharp falls in global emissions seen in the
    early years of the treaty are now levelling off; and it is becoming
    clear that some chlorofluorocarbons (CFCs), for example, which should
    have been exhausted in developed countries by now, are still in wide

    “It should be noted of course that CFCs have extremely long lifetimes
    in the atmosphere,” explained Paul Newman, from the US space agency’s
    Goddard Space Flight Center.

    “CFC-11 (a foam-blowing agent) has a lifetime of 11
    years and CFC-12 (a refrigerant) has a lifetime of 100 years, so they
    are in the atmosphere for a very long time.”

    Ozone is a molecule that is composed of three oxygen
    atoms. It is responsible for filtering out harmful ultra-violet
    radiation (less than 290 nanometres) from the Sun.

    The gas is constantly being made and destroyed in the
    stratosphere, about 30 km above the Earth. In an unpolluted atmosphere,
    this cycle of production and decomposition is in equilibrium.

    But CFCs and the other Montreal-restricted chemicals
    will rise into the stratosphere where they are broken down by the Sun’s
    rays. Chlorine and bromine atoms released from the man-made products
    then act as catalysts to decompose ozone.

    This year’s Antarctic ozone hole was among the biggest ever recorded, extending over an area of about 26 million square km.

    The thinning that occurs over the Arctic has never matched that in the
    southern polar region and it is expected to recover sooner, sometime
    between 2030 and 2040