# Depletion of stratospheric ozone A by liwenting

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```									Depletion of stratospheric ozone Name:__________ Period:__score: _/20

Structure and composition of the atmosphere (only review page 1 as needed)                 (5.6.1)
1. Draw the following axes on the grid:
 Vertical (y) axis: Altitude from 0 to 150 km above ground.
 Horizontal (x) axis: temperatures -100 to +200°C
2. Now add horizontal lines to divide the atmosphere into layers and boundaries
(pauses):
The troposphere extends from the ground to the tropopause at 15 km. The
stratosphere then extends to the stratopause at 55 km, followed by the
mesosphere which ends with the mesopause at 80km.
3. Plot the average annual temperatures as a smooth curve:
Altitude / km Temperature / °C Pressure / mb
0               15                1000
15              -60                 100
55                0                    .1
80              -80                    .01
150             200                    0
4. Shade in ozone layer: 15-50 km. The ozone layer is located within the
stratosphere. The ozone absorbs uv light from the sun.

5. Use the top of the graph for a second horizontal axis for pressure from 0 to 1000
millibars. Plot the pressure change data.

6. Why does the temperature decrease with altitude in the troposphere and then
increase again in the stratosphere?

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The role of ozone      (5.6.2) Name: ____________ score:___/20

Ozone is found in the stratosphere in the so-called ozone layer 15 – 50 km above the
Earth’s surface. It plays a critical role in maintaining the health of the biosphere as it
intercepts much of the sun’s ultra-violet radiation.

Ozone is formed by the reaction between oxygen and ultra-violet radiation. UVB
radiation (280-320nm) is absorbed both during oxygen splitting (I) and
destruction of ozone (III).
O2 + UV radiation  O ° + O°                (I)
O° + O2  O3                                (II)
O3 + UV radiation  O2 + O° + heat          (III)
There is a balance between ozone formation (II) and destruction (III).
Heat released from (III) warms up the stratosphere (see your diagram of atmospheric
structure). You do not need to memorise these equations.

Ozone depletion                                                                              (5.6.3)
Halogenated organic gases of which chlorofluorocarbons or CFCs are the most well
known are very stable under normal conditions but can liberate halogen atoms
(chlorine, bromine, fluorine) when exposed to ultraviolet radiation in the stratosphere
(I). These atoms (Cl°) react with ozone (II) and monatomic oxygen atoms (III).
CFCl3 + UV radiation  CFCl2 + Cl°           (I)
Cl° + O3  O2 + ClO                          (II)
ClO + O°  Cl° + O2                          (III)
CFCs therefore both destroy ozone and slow the rate of ozone reformation.

These pollutants enhance the destruction of ozone thereby disturbing the equilibrium
of the ozone production system. Furthermore the release of chlorine atoms (Cl°) in
reaction III can then go on to destroy more ozone molecules by reaction II. One
chlorine atom can catalyze the destruction of 100, 000 molecules of ozone.

1. What is the chemical formula for ozone? How is it different than oxygen?

2. Where is the ozone layer?

3. What are the reactions that occur naturally in the formation and depletion of
ozone? Why do they only occur in the stratosphere?

4. Describe the role of ozone in the absorption of ultraviolet radiation. Explain why
this is important.

5. Why is ozone depletion an example of positive feedback?

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The effects of ultra-violet radiation on living tissues and productivity                     (5.6.4)
Without the ozone layer planktonic life is harmed and life would not be possible on
land.

7 . List the effects of ultraviolet radiation on living tissues. Describe what is meant by
mutations.

8. List the effects of uv radiation on biological productivity.

9. What does uv radiation do to phytoplankton? What could happen to the food chain
in the ocean if the ozone layer continued to become depleted?

Reducing ozone-depleting substances                                                          (5.6.5)
10. Describe three methods of reducing the manufacture and release of ozone-
depleting substances.

11. Use the replace, regulate and restore model of pollution management strategy to
suggest some actions for reducing ozone-depleting substances.
You should be familiar with three examples.

Strategy for reducing pollution         Example of action
Altering the human activity
producing pollution

Regulating and reducing the
pollutants at the point of
emission

Clean up and restoration                At this point, chlorine atoms cannot be removed
from the atmosphere.

It is also impossible to run a hose up to the
stratosphere and put ozone up there.

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Role of national and international organizations in reducing CFC emissions                 (5.6.6)
The reduction of emissions of CFCs and other ozone-depleting substances has been
one of the most successful international cooperative ventures to date.

Timeline in CFC reduction:
1970s Ozone depleting properties of CFCs recognised. In 1974, USA and Sweden
banned them from non-essential aerosol uses. Concerns continued to mount
through 1980s.
1985 British Antarctic Survey reports the ozone hole.
1987 Montreal Protocol organised by the United Nations Environmental Program
(UNEP). Over 30 countries agree to cut CFC emissions by half by 2000.
1990 London Protocol: The Montreal Protocol was amended because the CFC
emissions were still too high. Industrialised countries would eliminate CFC
production by 2000 and developing countries by 2010.

Effectiveness of CFC reduction agreements                                                  (5.6.6)
As stated above this has been a good example of international cooperation. However
this is not the end of the story. Due to long life of CFCs in atmosphere, chlorine will
not reach its peak in the stratosphere until 2005 nor return to normal levels much
before 2050. Developing countries are still allowed to make and use CFCs and there

Role of national governments and other organisations in CFC reduction
12. Describe and evaluate the role of national and international organizations in
reducing the emissions of ozone-depleting substances.

13. Examine the role of the United Nations Environmental Programme (UNEP) in
reducing CFC’s.

14. What is the Montreal Protocol? When did it occur? Has it been effective?

15. What is the prognosis for the ozone depletion?

16. What steps are (your) national governments are taking to comply with these
agreements?

17. Name local or non-governmental organizations concerned with CFC reduction.
Example: Greenpeace, Friends of the Earth

18. What actions are they taking to persuade governments to comply?

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Role of individuals in CFC reduction.
19. What can individuals, such as yourself, do to help protect the ozone layer?

20. Past paper question
The chart shows the percentage CFC use in 1986.
a.     Comment on the significance of the data in
relation to more and less developed regions.

b.     Discuss the success of the UNEP and other international bodies in dealing
with the CFC problem

c.     State one change in the data that the pie chart for the year 2000 might show.

21. Evaluate the success of the Montreal Protocol

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5.6     Depletion of Stratospheric Ozone (3h)
5.6.1      Outline the overall structure and composition of the atmosphere.              2
5.6.2      Describe the role of ozone in the absorption of ultraviolet radiation.        2
5.6.3      Explain the interaction between ozone and halogenated organic gases.          3
5.6.4      State the effects of ultraviolet radiation on living tissues and biological
productivity.                                                                 1
5.6.5      Describe three methods of reducing the manufacture and release of
ozone-depleting substances.                                                   2
5.6.6      Describe and evaluate the role of national and international organizations
in reducing the emissions of ozone-depleting substances.                      2, 3

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