The document discusses ozone depletion and the importance of the ozone layer. It describes how CFCs released into the atmosphere were depleting the stratospheric ozone layer. The ozone layer protects life on Earth by absorbing harmful ultraviolet radiation from the sun. CFCs were initially widely used but are now known to release chlorine atoms that destroy ozone molecules. The consequences of ozone layer depletion include increased UV radiation reaching the Earth's surface, which can harm humans through higher rates of skin cancer and cataracts, and harm ecosystems and food supplies. International agreements like the Montreal Protocol have led to bans on CFCs and their replacement with more ozone-friendly substances to help restore the ozone layer

1. Course: LLB
Subject : Environment Laws
Unit: 3
Course: LLB
Subject : Environment Laws
Unit: 3

2. Ozone Depletion

3. 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 Ultra-violet
radiation from the sun.

5. 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

6. Formation of ozone layer
O2 + sunlight  O + O
O + O2  O3

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

8. 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

9. 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

10. 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

11. What is CFCs? [2]
CFCs are used in aerosol sprays
(Sources: http://www.yahoo.com) CFCs were used as refrigerants in the
past (Sources: http://www.yahoo.com )

12. 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

14. 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

15. 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

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

17. Health
• Sunburn, eye diseases (cataract),
skin cancer.
• Reduce our immune system 
other diseases

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

19. Food supply
• Reduce photosynthesis - crops
affected.
• Kills plankton  fish 

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

21. What has been done? [1]
 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.
International cooperation:

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

23. 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

24. 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/Assessment94
.html)
 Hong Kong Cyber Campus (http:/www.hkcampus.net/main.phtml)
– Ozone depletion (http://cwc.hkcampus.net/~cwc-
fkc/Ozone%20Depletion.files/frame.htm)
– Chemistry Summer Project Work
(http://ucc.hkcampus.net/~ucc-ckt/ozone/first.htm)
http://archive.greenpeace.org/~ozone/gallery/sshow/sshow.html

25. Thank You