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RTD info logoMagazine on European Research Special issue - May 2005   
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Title  Ozone story

The discovery of a hole in the ozone layer goes back to the 1980s. It was in the Antarctic that the first ground measurements of ozone levels produced some surprising results. As early as 1985, Joseph Farman, from the British Antarctic Survey (BAS), published the results of his observations in Nature. A "hole", or a drop in concentration, albeit temporary but very marked, appeared each spring in the stratospheric ozone layer above the Antarctic. This phenomenon mainly occurred in the lower stratosphere. What is the situation today?

The Antarctic ozone hole was discovered in 1985 by British Antarctic Survey scientists, from left: Joe Farman, Brian Gardiner and Jon Shanklin.
The Antarctic ozone hole was discovered in 1985 by British Antarctic Survey scientists, from left: Joe Farman, Brian Gardiner and Jon Shanklin.
© BAS
"What is astonishing about this discovery is that the first measurements indicating a seasonal depletion in the Antarctic resulted from work on the ground," comments Dominique Fonteyn, from the Belgian Institute for Space Aeronomy (BISA), "even though the Americans had a satellite in orbit which was devoted to studying ozone.”

Interpreting the data…
Why did the Americans miss this discovery? In fact, the TOMS had indeed measured very low concentrations of ozone above the Antarctic region. But the values were so low that the American researchers decided initially that they should not be taken into account. In their opinion, the data did not reflect the actual situation, but indicated a technical problem affecting the orbiting instrument.

In 1987, various hypotheses were put forward as to how this hole had formed in the ozone layer (of the lower stratosphere). Two schools of thought emerged: on the one hand, those who considered that depletion of the ozone levels originated from dynamic effects (winds, etc.) in the upper atmosphere, while others preferred the idea of unsuspected or lesser known effects in the atmospheric chemistry.

CFC: guilty!
The next year, this phenomenon was investigated by NASA, the American Space Agency. A report drawn up with the help of some hundred or so experts from all over the world suggested that stratospheric ozone concentrations had fallen on average by 1.7 to 3% in the northern hemisphere between 1969 and 1986, despite major annual variations.

However, by the end of the 1980s, the scientific community had reached agreement about the cause of this depletion in both the Antarctic and Arctic regions: halogenated hydrocarbons, and particularly the notorious CFCs (chlorofluorocarbons). Further observational and laboratory studies showed that the ozone’s seasonal disappearance was indeed linked to chemical reactions in the upper atmosphere which were being triggered by the very low temperatures existing above the Antarctic in winter.

"The 1990s saw the gaps in our knowledge about the mechanisms involved filled in, explains Dominique Fonteyn," thanks in particular to the eruption of the Pinatubo volcano in the Philippines in 1992, which injected large quantities of particles into the upper atmosphere. Study of these particles helped us to better understand some of the chemical phenomena occurring in the stratosphere, and particularly the catalysing effect they played in the release of different chemical compounds which then attacked the ozone. Parallels could then be drawn with the depletion of the ozone layer outside these major volcanic events, following the emission of different pollutants, including CFCs, into our atmosphere."

The Arctic is less vulnerable
In the Arctic, depletion of the ozone layer has also been observed, but it is less marked. This can be explained by the fact that the temperatures in the lower stratosphere above the Arctic usually remain higher than those recorded in the Antarctic. The northern hemisphere has greater land mass and more continents, which play a role in its climatic instability. Even when it is very cold in the region around the North Pole, this does not last very long. So a "hole" does exist in the stratospheric ozone layer. Though still a cause for concern, it is neither as extensive nor as severe as in the Antarctic.

Perpetually evolving depletion
The Arctic ozone hole is less pronounced due to less severe conditions at the stratospheric level than in Antarctica. This image shows a low-ozone event over the northern hemisphere on 31 January 2002. The central white area was not covered by the satellite observations. Processed by DLR - Data provision by ESA.
The Arctic ozone hole is less pronounced due to less severe conditions at the stratospheric level than in Antarctica. This image shows a low-ozone event over the northern hemisphere on 31 January 2002. The central white area was not covered by the satellite observations. Processed by DLR - Data provision by ESA.
© ESA
The size of the hole in the ozone layer above the Antarctic oscillates wildly. An absolute record was attained in 2000, when the hole covered an area of 29.2 million km². In 2001 and 2002, the trend seemed to be downwards, but this respite was of short duration. By the autumn of 2003, the hole had reached more than 28 million km², before shrinking again last year. On September 22, 2004, at the peak of the phenomenon, a hole of 24.2 million km² was recorded above the Antarctic.

Ultraviolet alert
Because of the enormous proportions the Antarctic hole in the ozone layer has reached in recent years, its first direct effects on human populations in Latin America are now starting to be felt. Higher levels of ultraviolet rays emitted by the sun, which are filtered less by the stratospheric ozone, reach the ground, increasing the risks of skin cancer and cataracts.

Thus, in Punta Arenas, in southern Chile, the authorities are now recommending a sort of curfew in the middle of the day. When the sun is at its highest height, between 11.00 and 15.00, the ultraviolet rays are at their most powerful. And in this region, which suffers from depletion of the Antarctic ozone layer, going outdoors without good protection causes sunburn within minutes.


Printable version

Features 1 2 3 4 5 6 7
  The polar regions: sentinels of major climate change 
  Polar flora and fauna facing up to major climate warming
  The peoples of the Arctic, the first victims of global warming
  And what would happen if the Gulf Stream stopped?
  Ozone story
  Satellites at the service of polar research
  Permanent monitoring of the atmosphere from the Svalbard

  READ MORE  
  What is ozone?

Ozone is an unstable molecule made up of three oxygen atoms (O3). It is found at two levels in the atmosphere. Near the ground (tropospheric ozone), it is toxic, notably for the respiratory tract and mucosa. This ozone is generated by pollution, mainly from motor vehicles. Ozone is also found ...
 
  The Montreal Protocol

The Montreal Protocol is an international convention which regulates the production and use of substances which harm the ozone layer, such as CFCs, chlorine and bromine, which mainly result from the halogenated hydrocarbons generated by human activities.

Ozone depletion in the upper stratosphere ...
 

  TO FIND OUT MORE  
 
  • United Nations Environment Programme
  • University of Cambridge, Centre for Atmospheric Science
  • TheOzoneHole
  •  


       
      Top
    Features 1 2 3 4 5 6 7
      What is ozone?

    Ozone is an unstable molecule made up of three oxygen atoms (O3). It is found at two levels in the atmosphere. Near the ground (tropospheric ozone), it is toxic, notably for the respiratory tract and mucosa. This ozone is generated by pollution, mainly from motor vehicles. Ozone is also found at high altitude in the stratosphere. Here, there is a "layer" some 20 to 25 km above the Earth, which is formed through equilibrium between from its formation and destruction under the effect of solar radiation, from temperature changes and from the presence of other chemical substances. This layer protects us from some of the harmful rays of the sun, such as ultraviolet radiation. When we talk about the hole in the ozone layer it is in this stratospheric ozone.

      The Montreal Protocol

    The Montreal Protocol is an international convention which regulates the production and use of substances which harm the ozone layer, such as CFCs, chlorine and bromine, which mainly result from the halogenated hydrocarbons generated by human activities.

    Ozone depletion in the upper stratosphere was recognised as early as the 1970s. It concerned the ozone throughout the world, and not specifically at the poles. Studies carried out after 1970 already incriminated CFCs and halogens as the cause of this depletion. This explains why, in 1987, the Montreal Protocol recommended reducing emissions of these chemical substances which affect both the upper and lower stratospheres.

    Since it came into force in 1989, the Protocol has been ratified by more than 180 countries, and amended four times. It has prohibited the use of these substances (particularly in refrigeration) since 1996 in developed countries, and envisages their prohibition in developing countries between now and 2010.

    In the long term (because of the momentum of this phenomenon) it should reduce the quantities of chlorinated compounds in the stratosphere and allow the ozone to return to normal levels sometime between now and the end of this century.

    The Montreal Protocol has reduced CFC emissions greatly but it will be some decades before existing CFCs in the stratosphere have decayed and present no further harm to the ozone layer.
    The Montreal Protocol has reduced CFC emissions greatly but it will be some decades before existing CFCs in the stratosphere have decayed and present no further harm to the ozone layer.

    TO FIND OUT MORE

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