What is ozone ?? and how it is getting depleted....!

1. Ozone Depletion
Vishal Shukla
India

2. Importance of the ozone layer
Near ground level (trochosphere) pollution
Form photochemical smog and acid
rain
In the stratosphere (15 - 50 km) ozone layer screen out harmful Ultraviolet radiation from the sun.

4. Our atmosphere
[1]

Troposphere:
-
The lowest layer (about 15 km from the ground)
Contains normal air composed of N2, O2, water vapour, CO2, etc.
Temperature decreases with altitude
-

Stratosphere:
-
Above the troposphere
Temperature increases with altitude
Contains a lot of ozone (ozone layer):
-
•
•
•
Found in the stratosphere between 10 - 50km above the ground
Protects us from the harmful effects of UV of certain wavelengths
Decrease in ozone concentration  Increase in UV-B radiation
reaching the earth surface

5. Formation of ozone layer
O2 + sunlight  O + O
O + O2  O 3

6. Ozone formation
[2]
Ozone (O3)
Chemically forms when UV hits on stratosphere
Oxygen molecules dissociate into atomic oxygen
O2

O+O
Atomic oxygen quickly combines with other oxygen molecules
to form ozone
O + O2
O3

7. Ozone formation
[3]
Ozone (O3)
A pollutant on ground level
–
A component of photochemical smog
Important for our survival
–
Absorbs some of the potentially harmful UV radiation
which can cause skin cancer and damage to vegetation
Split and regenerate repeatedly
Highest concentration in the upper atmosphere
Concentration decreases at lower altitudes

8. Ozone formation
[1]
Ozone (O3)
Made up of three oxygen atoms
Occurs naturally as a layer in the stratosphere
The layer is thinnest around the equator and the
concentration increases towards the poles
The amount of ozone above a point on the earth’s
surface is measured in Dobson units (DU)
–
–
~ 260 DU near the Tropics
higher elsewhere

9. What is CFCs?
[1]
Chlorofluorocarbons (CFCs)
Composed of elements chlorine, fluorine, and
carbon
Developed in 1930 by DuPont
CFCs were welcomed by industries:
–
–
–
Low toxicity
Chemical stability
Cheap
Usage:
–
–
–
–
–
As refrigerants
As blowing agents
For making flexible foam
As cleaning agents
As propellants

10. CFCs are used in aerosol sprays
CFCs were used as refrigerants in the
past

11. Present situation
Stratospheric ozone over Antarctica:
– Has been depleted over the last 15 years
– The ozone hole:
enlarging
large enough to cover most of the North America
would take at least 50 years to restore

13. Destruction of ozone layer
Chlorine atoms from CFCs attack the
ozone, taking away ozone and
forming chlorine monoxide (ClO).
O3 + Cl  O2 + ClO
Chlorine monoxide then combines with
another oxygen atom to form a new
oxygen molecule and a chlorine atom.
ClO + O  Cl + O2
The chlorine atom is free to destroy up to 100,000 ozone molecules

14. Causes of ozone depletion
Details are not fully understood
Catalyzed by halocarbons (carbon compounds
containing fluorine, chlorine, bromine and iodine)
–
Examples: CFCs and ClONO2
Halogen atoms catalyze ozone layer depletion by
destroying ozone molecules and forming oxygen
molecules.
Much more serious in Antarctica than other regions
on the planet

15. Consequences of less ozone
Because CFCs has long life span
and very stable, it continuous to
attack the ozone layer and more
UV reach our earth.

16. Impacts on human health
Skin Cancer
Cataracts and Other Eye Damages
Suppression of Immunity

17. Food supply
Reduce photosynthesis - crops
affected.
Kills plankton  fish ↓

18. Impacts on other animals
Reduces plankton population
Reduces penguin population
Reduces the percentage of hatching of
frog eggs

19. What has been done?
[1]
International cooperation:
Ban the use of CFCs as aerosol propellants
The Vienna Convention on the Protection of the
Ozone Layer in 1985
–
Governments committed themselves to protect the ozone
layer and to co-operate with each other to improve
understanding of ozone crisis.
The Montreal Protocol on Substances that deplete
the Ozone Layer
–
–
Adopted by Governments in 1987
Aims to reduce and eventually eliminate the emissions of
man-made ozone-depleting substances.

20. What has been done?
[2]
SunWise School Program by EPA of
the US
Phaseout of production of CFCs
Substitutes for CFCs

21. 1. How do scientists monitor the ozone level in the
stratosphere? Are the measurements accurate?
Monitoring
a. 1970s - 67 measuring stations at ground level
- uneven distribution
- too short to identify statistically
significant trends.
- calculations contain inherent
uncertainties  incomplete scientific
description built in the computer
programme.
b. 1979 - Total Ozone Mapping Spectrometer on
satellites (TOMS)

22. 2. How serious is the problem Of ozone
depletion?
Seriousness of ozone depletion:
1992 - average ozone concentration
is 2-3% lower than before
Northern parts of Europe and
Canada 20% lower in 93 winter
Antarctic - 50-90% lower every
winter

23. 3. Are there any proofs that CFCs cause
the depletion of ozone?
Chlorine monoxide which is an
intermediate formed in the destruction
of ozone.

24. 4. Why was there such a great difference in
terms of the attitudes of policy makers in
the US and Europe towards the warning
of scientists about CFCs in the 70's?
Attitudes of policy makers
US - NAS and EPA support scientists
warning of the problem and recommend
banning  wide coverage in the media 
increased public concern

25. Britain - Environmental Depths report
with a cautious tone, against the
need for precipitate action 
public debate of lower profile

26. 5. Will the Montreal Protocol save the
ozone layer?
Montreal Protocol
-- came too late
-- countries which had signed the Protocol had not
taken any immediate and practical action.
-- the chemicals already produced will continue to
seep into the atmosphere and attack the ozone
layer.
-- Many countries refused to cut down the use of
CFCs (e.g. China / India) unless they get some
financial help in meeting their demand.

27. 6. What do you think make policy
makers
sign
the
Montreal
Protocol?
Public pressure because of growing public,
scientific and political concern.

28. 7. Why are there exceptions for
developing countries for the
Protocol?
Exceptions for developing countries
- because they do not have the technology
to switch to alternatives, refuse to sign
the protocol.
- to encourage them to participate in the
protocol.
- growing domestic needs and potential
markets for CFCs.

29. 8. Why don't developing countries agree to
the standards of the Protocol? What can
be done to make them cut their use of
CFCs?
Financial and technological aids can help
LDCs to cut CFCs use

30. 9. What are the reactions of business to the
Montreal Protocol?
Reactions of business
- finding substitutes
- developing new technologies
- surprising results: save money & improve
performance

31. 10. Other than stopping CFC production,
what other remedial work should be
done? Are there any obstacles to these?
Other remedial work
- to develop systems for recovery &
recycling the chemicals already used.
Obstacles
- technical challenge, diplomatic challenge

32. 11. What are the alternatives for CFCs?
Are they expensive? Who will promote
the use of these alternatives?
Alternatives for CFCs
- ammonia, propane, water
- cheap because abundant and not patented
- scientists and business which foresee the
advantage of using such alternatives
(energy saving, cheap), but not chemical
companies

33. 12. Are there any relationships between the
Greenhouse
Effect
and
ozone
depletion?
Similarities between GHE and Ozone
Depletion issue
- long-term environmental impact which
affect future generations, e.g. food supply
- prediction of future impact involves
scientific uncertainties

34. - global problem
- difficult to impose environmental regulations
- clash with economic interests or conflicts
among countries
- no immediate action to deal with the problem
although many conference concerning about
this problem.

35. 13. Contrast the reactions of policy makers
towards the issue of global warming and
ozone depletion. Why do you think
there's such a difference in attitudes?
- Policy makers have taken action for the ozone
issue before there is scientific proof (1985:
Vienna Convention; proof came in 1987) but
not GHE - reasons:
- image of a hole in the sky, through which pour
deadly cancer-causing rays exerted a powerful
hold on the public imagination  great
pressure on policy makers to do something

36. - effect of ozone depletion already felt with
reports of increase in cancer risk e.g. in Australia
- effects of GHE do not create so much
disturbance among average citizens; melting of
ice, flooding, species extinction: seem not to be
direct effects on individuals' well-being

37. Discussion
Naturally, there is a balance of ozone
formation and depletion. What disturb this
balance?
What are the functions of the ozone layer?
How to reduce emission of ozone depleting
substances?
Do you agree that people living in the
southern hemisphere are more prone to skin
cancer than those living in the northern
hemisphere? Why?

38. Relevant websites
[1]
US Environmental Protection Agency
(http://www.epa.gov)
–
–
The Science of Ozone Depletion
(http://www.epa.gov/students/ozone_depletion.htm)
United States Environmental Protection Agency: Ozone
Depletion Home Page (http://www.epa.gov/docs/ozone/)
USA NASA (http://www.nasa.gov)
–
NASA-Stratospheric Ozone Depletion Tutorial
(http://www.nas.nasa.gov/About/Education/Ozone)
Union of Concerned Scientists (http://www.ucsusa.org)
–
Ozone Depletion
(http://www.ucsusa.org/ozonedepletion/ozone.sciupdate.html
)

39. Relevant websites
[2]
The National Oceanic and Atmospheric
Administration (NOAA) (http://www.al.noaa.gov)
–
WMO/UNEP Scientific Assessment of Ozone Depletion
1994
(http://www.al.noaa.gov/WWWHD/pubdocs/Assessment9
4.html)
Hong Kong Cyber Campus
(http:/www.hkcampus.net/main.phtml)
–
–
Ozone depletion (http://cwc.hkcampus.net/~cwcfkc/Ozone%20Depletion.files/frame.htm)
Chemistry Summer Project Work
(http://ucc.hkcampus.net/~ucc-ckt/ozone/first.htm)