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O. O. O. © NOAA. The ozone hole. © 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

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the ozone hole

O

O

O

© NOAA

The ozone hole

© 2007 Paul Billiet ODWS

ultra violet light
Ultra Violet light

© 2007 Paul Billiet ODWS

uv light and life
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 life4
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

ACGCTGGCTTAGT

TGCGACCGAATGA

ACGCTGGCT=TAGT

TGCGACCGAATGA

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

DNA

© 2007 Paul Billiet ODWS

specific damage by uv light
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 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

the ozone layer
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
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
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
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 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