CyberDodo and the Ozone Layer (1-35)
This is a zone of our atmosphere situated at a high altitude of between 20 and 50 kilometres, in which this gas is concentrated. Take note, although it is indispensable for life on Earth – what we will study together – it is not very abundant, because if it were possible to compact this naturally very diluted ozone in a very compact, pure layer, it will only have a density of 3 millimetres.
What is the ozone layer for?
Very simply to help life exist on Earth! By filtering the ultra-violet rays of the sun (The UV-b and UV-c) which have a destructive effect on living cells (Cancers, DNA damage, burning, disturbed photosynthesis of vegetation, etc.). The ozone layer is an intelligent shield, since it protects us from damaging solar rays while letting those which are beneficial to us pass through.
What are the origins of the ozone which constitutes this layer?
At high altitude, this is a natural process initiated by ultra-violet rays that break dioxygen particles that will recombine to create the ozone. This chemical reaction is called the "Chapman Cycle ".
The quantity of ozone has remained remarkably stable for hundreds of millions of years, because this process of creation and destruction of the ozone balances itself out.
Why do we talk of the hole in the ozone layer?
Because in the 80s, a hole was discovered in the ozone layer below the antarctic regions (South Pole) during springtime in the southern hemisphere (attaining maximum levels in September/October). The term ‘hole’ is actually inappropriate, because it was really a high reduction in the ozone concentration; almost 50% had disappeared.
Scientists have been focusing on the study of this phenomenon and have confirmed that it will recur every year at increasingly worrying proportions. For example, if we were to consider that the ozone would altogether represent 3 millimetre thick layer, only half of it will remain in 2006!
Thanks to NASA, it is easy to visualise the annual appearance and disappearance of the hole in the ozone layer:
Why does this phenomenon occur?
You have guessed the answer: man! More precisely, due to CFC gases (chloro-fluoro-carbons), HCFC (hydro- chloro-fluoro-carbons) and halons. These gases are particularly used by machines which produce cold (Air conditioning, refrigeration, etc.), such as aerosols and solvants or halon fire extinguishers.
They have dramatic effects on the stability and chlorine content of the ozone layer. In some years, they attain a high altitude where they are ‘broken’ by ultraviolet rays and then free their chlorine atoms, which will in turn destroy the ozone.
Which initiatives have been taken to fight against CFCs?
In September 1987, an agreement was signed to reduce CFC emissions. This initial agreement has been regularly revised to lead to the total prohibition of CFC gases wotjom a few years time.
The scientific community estimates that this awareness and drastic associated measures should enable the ozone layer to be re-established from here until the end of the 21st century, which is excellent news.
Has this environmental danger therefore been eliminated?
If the countries respect their commitments, particularly where the ozone layer is concerned: yes.
But an even more serious risk arises from this good news, because CFCs and other HCFCs have been replaced by HFCs (hydro-fluoro-carbons) which, although they do not attack the ozone layer, are terrible greenhouse gases which contribute strongly towards global warming.
The new challenge we are faced with is therefore to attain elimination of all utilisation of HFCs as quickly as possible... On this subject, see the cartoon, the case file and the quiz on greenhouse gas effects.
To see the cartoon on the ozone layer, click here
To see the quiz, click here
For the game, click here
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