1. The ozone hole
O
O O
© 2007 Paul Billiet ODWS
© NOAA

2. Ultra Violet light
© 2007 Paul Billiet ODWS

3. 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

4. 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

5. 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
ACGCTGGCTTAGT ACGCTGGCT=TAGT
DNA
TGCGACCGAATGA TGCGACCGAATGA
© 2007 Paul Billiet ODWS

6. 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

7. 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

8. Ozone pollution in the troposphere
Atmospheric O3 Paris 6eme arr 2006-2007
Data Airparif
160
150
140
130 Safety
120
110 limit
100
-3
O3 / µg m
90
80
70
60
50
40
30
20
10
0
02/07/2006 10/10/2006 18/01/2007 28/04/2007 06/08/2007 14/11/2007 22/02/2008
© Airparif

9. 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

10. 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

11. What are CFCs?
 Used as propellants in aerosol spray cans
 Used as refrigerants in fridges, freezers
and air conditioning units
© 2007 Paul Billiet ODWS

12. 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

13. 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

14. The biggest yet September 2006
© NASA