1. THE OZONE HOLE
NOAA O
© 2016 Paul Billiet ODWS

2. Ultra Violet light
© 2016 Paul Billiet ODWS

3. UV light and life UV light is high energy radiation
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.
© 2016 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.
© 2016 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
TGCGACCGAATCA
ACGCTGGCT=TAGT
TGCGACCGAATGA
DNA
© 2016 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.
© 2016 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.
© 2016 Paul Billiet ODWS

8. Ozone pollution in the troposphere
Airparif
Safety
limit
© 2016 Paul Billiet ODWS

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.
© 2016 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)
2Cl + 2O3  2ClO + 2O2
2ClO + M  Cl2O2 + M
Cl2O2 + sunlight  2Cl + O2
2O3  3O2
© 2016 Paul Billiet ODWS

11. What are CFCs? Used as propellants in aerosol spray cans
Used as refrigerants in fridges, freezers and air conditioning units.
© 2016 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.
© 2016 Paul Billiet ODWS

13. The current situation
The holes developing over the pole suggest that they may be showing 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 70 years.
© 2016 Paul Billiet ODWS

14. The biggest yet September 2006
NASA
© 2016 Paul Billiet ODWS