Environmental Systems and Societies

1. Topic 5
Pollution Management
5.6 Depletion of Stratospheric Ozone
http://www.youtube.com/watch?v=
t5w9eIPYodg
http://edroness.blogspot.mx/2014/
02/ozone-depletion.html

2. Composition of Air
carbon dioxide; argon; 0.93%
0.038% other gases, 0%
oxygen; 20.9%
nitrogen; 78.1%

3. Structure of the Atmosphere
• It is a mixture of solids, liquids
and gases held in place by the
Earth’s gravity
• Close to the surface (first 15 km
the troposphere), the
composition is fairly constant. It
changes at higher altitudes
• Certain gases are characteristic
of different altitudes *
• A layer of ozone occurs at an
altitude between 10 – 15 km
(this is called the stratosphere)
Altitude
(km)
Most
Significant
Gas
10 - 50
ozone
100 - 200
nitrogen
200 - 1100
oxygen
1100 - 3500
helium
> 3500
hydrogen

4. Pressure (mb)
Structure of the Atmosphere
OZONE
LAYER

5. The Role of Ozone
• Ozone (O3) is produced by the action of sunlight on O2
molecules
• There are higher concentrations around the equator due
to higher levels of sunlight, but it concentrates near the
poles due to transportation by winds
• Ozone is a greenhouse gas but also absorbs incoming
(and some outgoing) UV light
• Ozone production and destruction is at equilibrium (but
it is destroyed by anthropogenic pollutants (e.g.
chlorofluorocarbons (CFCs) and NOx)
• Without the ozone layer, incoming UV radiation from the
sun would destroy all life

6. The Effect of CFCs
• CFCs are stable industrial products of byproducts that contain chlorine, fluorine or
bromine (halogens)
• They can persist for many years in the
troposphere, however when they travel to the
stratosphere, UV light breaks them down and
release their halogen atoms
• The halogens catalyse the breakdown of ozone
• A hole in the ozone layer was first reported over
Antarctica by the British Antarctic Survey in 1985
• The hole is seasonal – ozone thins during the
Antarctic winter, since colder temperatures
result in the formation of clouds of ice particles
provide catalytic surfaces to accelerate ozone
breakdown

7. •
The Effects of Increased UV(B)
Light
Humans and other animals
– Sunburn, skin cancer, immune deficiencies, eye damage and
cataracts
– Effects may be acute or chronic (chronic effects are often
irreversible)
– It may have effects on the success of vaccinations
– Reduction of fish stocks
– Fall in frog populations
– Due to the Antarctic Ozone hole Australia tried to increase
public awareness, but has seen an increase in skin cancer over
the last decade
• Plants
– Reduced yield (although GM is producing UV(B) tolerant
varieties)
– Reduction in natural plant productivity, particularly
phytoplankton

8. Regulation
• Reduction in the use of CFCs
– They have been discontinued as propellants in
aerosol cans
– They are being phased out as refrigerants
– There are now programmes for the collection of old
fridges and the recycling of the CFCs they contain
• Reduction in the use of methyl bromide
– Used as a soil insecticide, but phased out in Europe
and the US in 2005. Still used in many countries

9. Regulation
• There has been successful international cooperation,
largely organised by the United Nations Environment
Programme (UNEP) – Montreal Protocol (1987)
• Europe banned the use of CFCs in 2000
• Developing countries are phasing out their use, but this
will take considerably longer
• A total worldwide ban should be in place by 2030
• However CFCs are very persistent in the troposphere
and will continue to have effects well into the future
• Some of the chemicals used to replace CFCs (e.g.
HCFCs) are greenhouse gases

10. Questions
1.
2.
3.
4.
Describe the composition of the atmosphere
Describe the role of ozone
Explain the effect of ozone depleting substances
State the effects of increased UV(B) radiation on
humans, animals and plants
5. Describe the efforts of international
organisations in reducing the effects of ozone
depleting substances and evaluate their
effectiveness