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The ozone hole
© NOAA
O OO
© 2007 Paul Billiet ODWS
Ultra Violet light
© 2007 Paul Billiet ODWS
UV light and life UV light is high energy light When it strikes molecules it can cause
them to beak into ions or free radicals The free radicals in turn damage large
molecules such as proteins and DNA Damage to DNA causes mutations It is a mutagen Mutations can lead to cancer
© 2007 Paul Billiet ODWS
UV light and life UV light can have beneficial effects too It stimulates the transformation dietary
steroids into Vit D (calciferol) UV light is used to sterilise foods and
medical equipment Some animals can see UV light Insects use it to guide them to nectar
sources in flowers
© 2007 Paul Billiet ODWS
UV light & DNA UV-B has a direct effect on DNA DNA absorbs UV light of 260nm The action of UV forms thymine dimers This can cause a gene mutation when the
DNA replicates
UV-B Thymine dimer
ACGCTGGCTTAGTTGCGACCGAATGA
ACGCTGGCT=TAGTTGCGACCGAATGA
DNA
© 2007 Paul Billiet ODWS
Specific damage by UV light Sunburn Clouding of the cornea and formation of
cataract Skin cancer (melanoma) Reduced rates of photosynthesis
© 2007 Paul Billiet ODWS
Ozone in the atmosphere Ozone (O3) forms under the effect of UV
light in the stratosphere Ozone can also form in the troposphere Naturally it forms from volcanic activity It is produced by motor vehicules so it is a
pollutant Sunlight acts on NOx to produce O3
© 2007 Paul Billiet ODWS
Atmospheric O3 Paris 6eme arr 2006-2007Data Airparif
0102030405060708090
100110120130140150160
02/07/2006 10/10/2006 18/01/2007 28/04/2007 06/08/2007 14/11/2007 22/02/2008
O3
/ µg
m-3
© Airparif
Ozone pollution in the troposphere
Safety limit
The ozone layer Ozone is an unstable gas It rapidly breaks down The ozone layer is only a few cm thick If the rate of breakdown is faster than the
rate of formation the ozone layer thins This could develop into hole An ozone hole was first observed over the
Antarctic in 1985
© 2007 Paul Billiet ODWS
The cause of the hole Chlorofluorocarbons (CFCs) The breakdown under the effect of UV
light to release chlorine radicals (Cl) Especially under cold conditions The chlorine radicals react with O3
converting it to O2 and more radicals ClO
© 2007 Paul Billiet ODWS
What are CFCs? Used as propellants in aerosol spray cans Used as refrigerants in fridges, freezers
and air conditioning units
© 2007 Paul Billiet ODWS
What can be done? Reduce the use of CFCs They are already banned in aerosols
(1987) BUT they are still used as refrigerants Recycle fridges and air conditioning plants
© 2007 Paul Billiet ODWS
The current situation The holes developing over the pole
suggest that they may be show an improvement
BUT CFC molecules take 30 years to rise up to the stratosphere
The chlorine radicals last a long time The peak ozone damage was supposed to
be in 2000 Damage could go on another 50 years
© 2007 Paul Billiet ODWS
The biggest yet September 2006
© NASA