Ozone layer depletion occurs when ozone-depleting substances like CFCs break down ozone molecules in the stratosphere. This allows more ultraviolet radiation to reach the Earth's surface, increasing health and environmental risks. The ozone hole was first detected in 1975 and grew substantially in size through the 1980s and 1990s before stabilizing due to the Montreal Protocol banning CFCs. Global warming occurs when greenhouse gases like carbon dioxide trap heat in the lower atmosphere, increasing average surface and lower atmospheric temperatures globally over long periods of time. Both phenomena pose risks but international agreements have led to reductions in their drivers.

1. Ozone layer depletion and
Global warming
Part 1

2. Ozone layer
Ozone and Ozone layer:
• Ozone gas is found on the lower portion of the
stratosphere at the height of about 20km
above the earth in the form of a layer called
ozonosphere.
• Stratospheric ozone is typically measured
in Dobson Units (DU), which is the number of
molecules required to create a layer of pure
ozone 0.01 millimeters thick at a temperature
of 0 degrees Celsius and an air pressure of 1
atmosphere (the pressure at the surface of
the Earth).

3. Ozone hole
• The ozone layer was discovered in 1913 by the
French physicists Charles Fabry and Henri
Buisson.
• Ozone hole was detected at first in 1975.
• Some British scientists noticed effects of O3 hole
in 1985.
• Ozone hole can caused by some green house
gases (GHGs).

4. Ozone hole
• In 1979—when scientists were just coming to
understand that atmospheric ozone could be
depleted—the area of ozone depletion over
Antarctica
grew
to
1.1
million
square
kilometers,
with
a
minimum
ozone
concentration of 194 Dobson Units.
• In 1987, as the Montreal Protocol was being
signed, the area of the hole reached 22.4 million
square kilometers and ozone concentrations
dropped to 109 DU.

5. Ozone hole
• By 2006, the worst year for ozone depletion to
date, the numbers were 29.6 million square
kilometers and just 84 DU.
• By 2011, the most recent year with a complete
data set, the hole stretched 26 million square
kilometers and dropped to 95 DU.

6. Characteristics of Ozone layer
Function:
• It regulates the weather and climate of the
earth.
• It filters away the ultraviolet radiation and
protects the earth as protective layer.
Photochemical reaction:
Ozone is an unstable gas and for its
formation destruction (photochemical
reaction) process; UV ray is essential
which come from the sun.

7. Characteristics of Ozone layer
Photochemical reaction:
O + O2
O3
UV
O3
O + O2
In these processes a part of the harmful UV
rays is converted in to infra-red (IFinfrared - wavelength is longer thas
visible light) rays, which is not lethal to
man however has heating effect.

8. Cause of O3 depletion:
When ozone destruction is being greater then
the formation known as ozone depletion.
CFCs, CCl4, CH4 etc. are main chemicals called
halocarbons that used to check the ozone
formation. These carbon compounds
produce the chlorine, which breaks the O3
molecules and reduces O3 content in the
atmosphere.
Reaction:
Cl +O3
ClO + O2
ClO
Cl + O
By this way; one atom of Cl is sufficient to
destroy a lakh of ozone molecules.

9. Cause of O3 depletion:
• Destruction of ozone molecules lead the
destruction of ozone layer. Therefore,
harmful UV (ultra violate radiation) got
chance to come through the ozone layer
and fall on the earth surface.
• UV is lethal to all living being.

10. Form of UV coming from sun:
We know that the visible light range is about differ
than the UV or IF rays.
Earth receives UV radiation in 3 forms:
– UVA in the wavelength range 315-400 NM
– UVB in the wavelength range 289-314 NM
– UVC in the wavelength range 100-280 NM
Among these UV-B is most dangerous.

11. Effects of UV rays
Presence of UV (estimated)
The effects of O3 depletion eventually increase the
UV rays penetration to the surface of the earth.
• 1% drops in stratospheric O3 increase 2-3 % UV.
• In this century (21st) UV rays may be increase 34% at the tropics and 10-12 % at high altitude.
Effects on Agricultural crops:
• Agricultural crop losses.
• Increase food production costs because of physical
damages of growing plant.
• Damage is also spread in other plants of the
earth’s physical ecosystem.

12. Effects of UV rays:
Effects on health:
• Sunburn, Ageing, Wrinkling of skin.
• Destruction of protein, Mutation of genes.
• EPA ( Environmental Protection Agency)
said– By increasing of 1% UVB rays increases basal
cell cancer1% and squamous cell cancer 2%.
– It may caused melanoma skin cancer
– Cataracts disease in eye by about 0.2%.

13. Ozone hole improvement
• The average size of the 2012 ozone hole
was 6.9 million square miles (17.9 million
square kilometers).
• Argentine scientists agree that there are
signs of recovery of the ozone layer that
protects life on earth by filtering out the
sun’s harmful ultraviolet radiation.

14. Importance of CFCs at the
beginning
• CFCs-11 and CFCs-12 developed in 1930s
as a refrigerants (refrigeration, building and
mobile air conditioning). Because it is:
–
–
–
–
Extremely stable,
Nontoxic
Inert
Relative to the electrical and mechanical
machinery.
• By 1970s, it had been used as- Aerosol
propellant in the hair spray, deodorants,
insecticide etc.

15. Importance of CFCs at the
beginning
• Later on it was started to use in various
industries as an industrial blowing agent
for manufacturing:
– flexible, rigid plastic foams.
– polyurethane and polystyrene foams and
– industrial cleaning agents and solvents
• CFC-113 was started to use as a solvent,
especially for microelectronic production.

16. CFCs are one of the important
causes for ozone layer depletion.
People start thinking about the
alternatives to way out of this
risk!!

17. Alternative sources of CFCs
Two viable substances in the form of HCFC and
HFC-34 are considered to be harmless for ozone.
Out of these two HFC-34 is the less harmful
because, absence of chlorine in it but it has some
problem:
– It is expensive.
– Inflammable.
– Toxic in nature.
So, we can use instead of these Butane, Propane
because it is—
–
–
–
Less expensive.
Less harmful.
Freely available.

18. Today’s Propellants:
• Hydro-fluoro carbons (HFCs)
• Hydrofluoralkanes (HFA)
- Used in inhaler.
• Chloro-methyl carbons (CMCs)
- Disadvantage: Expensive
• Ammonia
- Disadvantage(s): pungent, toxic, and
flammable
• Hydrocarbons
- Disadvantage(s): flammable
• Carbon Dioxide
- Disadvantage: greenhouse gas

19. Global warming
A green house effect and Global
warming
Part 2

20. How does the Global worming take
place??
When the solar radiation first fall on the top of the
atmosphere the harmful UV radiations are
absorbed by the O3. In this process some part of
the UVs are reflected to the atmosphere and
some are converted in to IF rays which is not
lethal to man.
IF radiations coming to earth from the sun are of
short wavelengths but the IF rays reflected from
the earth are of long wavelengths. The IF
radiation reflected from the earth cannot escape
out from the carbon dioxide layer present in the
atmosphere. CO2 gas has the ability to absorb IF
radiation reflected from the earth surface.

21. How does the Global worming take
place??
The heating up of earth’s atmosphere due to trapping
of IF rays; that has reflected from the earth surface
by the CO2 layer (in the atmosphere) called Green
house effect which caused global warming.
It
•
•
•
has been observed that
CO2 (a GHG) can increase temperature by 50% .
CFCs can increase temperature by20%.
Other air pollutants can increase temperature by
30%

22. Greenhouse gases
Greenhouse gases are made out of:
– water vapor
– carbon dioxide
– methane
– nitrous oxide
– ozone
– chlorofluorocarbons (CFCs)(halocarbons)
They are all natural gases, but extra
greenhouses gases can be made from the
anthropogenic activities.

23. GHGs influenced by human activities

24. Impacts of Global Warming
•
•
•
•
•
•
•
•
Increase in the flow of rivers and change in
rainfall pattern.
Chances of submersion of islands.
Occurrence of more cyclones and hurricanes.
This will cause damage of agricultural crops.
Fresh water will be contaminated with the salty
water of sea.
Human population will be displaced.
The forest vegetation will not be able to adapt
with the changing temperature and may face
destruction.
As a result of global warming, the temperature
of southern Europe and Central America will rise
and affect the rain fall in these areas.

25. • Dobson Units (DU): The number of
molecules required to create a layer
of pure ozone 0.01 millimeters thick
at a temperature of 0 degrees
Celsius and an air pressure of 1
atmosphere (the pressure at the
surface of the Earth).