This seminar presentation summarizes Ozone layer depletion. It introduces ozone and the ozone layer, how ozone depleting substances like CFCs react with ozone leading to its destruction. The consequences of ozone layer depletion include increased skin cancer and other health issues. International agreements like the Montreal Protocol were enacted to regulate ozone depleting substances and protect the ozone layer.

1. SEMINAR PRESENTATION
BY
OZOAGU CHIJIOKE PETER
ESUT/2009/100055
TOPIC: OZONE LAYER DEPLETION
DEPARTMENT OF INDUSTRIAL CHEMISTY
FACUTY OF APPLIED NATURAL SCIENCES
ENUGU STATE UNIVERSITY OF SCIENCE
AND TECHNOLOGY
MAY, 2013

2. OUTLINE
• INTRODUCTION
• OZONE
• OZONE LAYER
• OZONE LAYER DEPLETION
• OZONE DEPLETING PROCESS
• CONSEQUENCES OF OZONE LAYER
DEPLETION
• THE WORLD’S REACTION
• CONCLUSION

3. INTRODUCTION
Over the years, man appreciated the use of
most chemicals because of their quality and
economical values. Scientific evidence have
however proved that most of these
chemicals release free radicals such as; Cl,
Br, OH, NO and NO2, which when released
into the atmosphere reacts with the
stratospheric ozone thereby leading to ozone
layer depletion.
Ozone layer depletion leads to increased UV
radiation (especially UVB) reaching the
earth, thereby causing harm to plants,
animals and aquatic life.

4. OZONE
Ozone is a triatomic molecule consisting of
three oxygen atoms. It is an allotrope of
oxygen that is much less stable than the
diatomic allotrope. Ozone is a gas formed
from diaoxygen by the action of ultraviolet
light and also atmospheric electrical
discharge.
PHYSICAL PROPERTIES
A pale blue gas with a molar mass
48.00gmol-1
 Density: 2.144mgcm-3 (at 0oC).
 Melting Point: -192oC, 81K
 Boiling Point: -112oC, 161K
 Solubility in H2O: 1.05gL-1(at 0oC)
 Very soluble in: CCl4, Sulfuric acid, CFCs

5. Resonance Lewis Structure of the Ozone Molecule.

6. OZONE LAYER
The Ozone layer is a layer in the Earth’s atmosphere
containing relatively high concentration of ozone. The ozone
layer is mainly found in the lower portion of the
stratosphere from approximately 20 to 30 kilometer (12 to
19 miles) above earth.
It absorbs 97 – 99% of the sun’s medium frequency
(UVB) ultraviolet light (from about 200nm – 315nm) which
potentially damages exposed life forms on earth.
Ozone in the stratosphere is produced from short wave
UV rays (in the UVC band) reacting with O2
O2 + Photon (<240nm) 2O
O + O2 + M O3 + M
where "M" denotes the third body that carries off the
excess energy of the reaction. The thus produced ozone is
destroyed by the reaction with atomic oxygen
O3 + O → 2 O2

7. OZONE LAYER DEPLETION
This is the gradual thinning of the ozone
layer or reduction in the amount of
stratospheric ozone in the atmosphere,
caused by the catalytic destruction by
ozone depleting substances (ODS) which
release free radicals when it dissociates in
the atmosphere.
The most important of these free
radicals include;
Nitric oxide (NO)
Nitrous oxide (NO2)
Hydroxyl (OH)
Atomic Chloride (Cl)
Atomic Bromide (Br)

9. • CFCs + hv Cl*
• Cl* + O3 ClO* + O2
• O3 + hv O2 + O
• O + ClO* Cl* + O2
Overall reaction :
• 2O3 + hv 3O2 Ozone destruction
• NO + O3 NO2 + O2
• NO2 + O3 NO3 + O2
• NO3 + NO2 N2O5
• O + O3 2O2
uvc

11. CONSEQUENCES OF OZONE DEPLETION
Skin cancer (UVB)
Suppression of the immune system
Ocular damage
Global warming
Effects on terrestrial plants (yield
reduction)
Effects on aquatic eco-system.

12. THE WORLD’S REACTION
Depletion of the stratospheric ozone is a global
problem and hence stirred up an international debate
over the use of ODS. Efforts at negotiating an
international agreement controlling CFC use
culminated in the 1987 Montreal Protocol and Kyoto
Protocol.
Three major factors are important in
understanding the sources of such agreement:
 The evolving scientific understanding of the problem.
 Increasing public concern over the problem based on
the threat of skin cancer and the discovery of the
Antarctic ozone hole.
 The availability of acceptable substitutes for CFCs.

13. CONCLUSION
The threat posed by ozone layer
depletion is an unusual environmental
issue. Unlike many other environmental
problems, it potentially affects the well-
being of every individual in every
country. It is neither a developed
country problem nor a developing
country problem; it is a global problem.
As such, countries should regulate the
production or uses made of CFCs and
other ODS in order to reduce further
depletion of the ozone layer.