AIR POLLUTION CONTROL L 11

L-11
OZONE DEPLETION
Air Pollution and Control
(Elective(Elective-I)

Earth’s Atmosphere

Prof S S Jahagirdar, NKOCET

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The ozone layer
•
•
•
•

Ozone is an unstable gas
It rapidly breaks down
The ozone layer is only a few cm thick
If the rate of breakdown is faster than
the rate of formation the ozone layer
thins
• This could develop into hole
• An ozone hole was first observed over
the Antarctic in 1985

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The Discovery
• In 1985, using satellites, balloons, and
surface stations, a team of researchers had
discovered a balding patch of ozone in the
upper stratosphere, the size of the United
States, over Antarctica.

British Atlantic Survey Research station,
Holly Bay, Antarctic coast
Team who discovered the hole 1985.
From left: Joe Farman, Brian Gardiner, and
Jonathan Shanklin


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What is ozone?
• Ozone forms a layer
in the stratosphere,
thinnest in the tropics
(around the equator)
and denser towards
the poles
• measured in Dobson
units (DU)
• ~260 DU near the
tropics


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What is a Dobson unit?
• 1 Dobson Unit
(DU) is defined to
be 0.01 mm
thickness at STP
- (00C and 1
atmos pressure).
• A slab 3mm thick
corresponds to
300 DU


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How is ozone formed?
UV radiation strikes the O2 molecule
and splits it, atomic oxygen
associates itself with another O2
molecule – simplistic version


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How ironic . . .
• At ground level, ozone is a health
hazardhazard-major constituent of
photochemical smog
• However, in the stratosphere, we
could not survive without it.
• It absorbs potentially harmful ultraultraviolet (UV – 240-320nm harmful)
240radiation
• Protects from skin cancer, etc
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The ozone layer is in the stratosphere

Good up
high! 

Bad
nearby! 

“Chapman Reactions”
• Ozone is formed by:
O2 + hv -> O + O

(1)

• Ozone can reform resulting in no net loss of
ozone:
O3 + hv -> O2 + O
O + O2 -> O3
• Ozone is also destroyed by the following
reaction:
O + O3 -> O2 + O2

(3)
(2)

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(4)

Comparison of reactions
• Reaction (2) slower with increasing
altitude
• Reaction (3) faster with increasing altitude
• Lower in stratosphere, atmosphere
denser, UV absorption increases – ozone
peaks 20km
• Closer to surface, UV level decreases,
ozone decreases

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The ozone layer

•Ozone is a triatomic form of oxygen
(O3) found in Earth’s upper and
lower atmosphere.
•The ozone layer, situated in the
stratosphere about 15 to 30 km above
the earth's surface.
•Ozone protects living organisms by
absorbing harmful ultraviolet
radiation (UVB) from the sun.

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ultraviolet A (long-wave) and
ultraviolet B (shortwave) rays


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• The ozone layer is being destroyed by
CFCs and other substances.
• Ozone depletion progressing globally
except in the tropical zone.
• Chlorofluoro carbons (CFC’s) and
other halogenated hydrocarbons
contribute to the destruction of
stratospheric ozone.
• Just one chlorine and bromine atom can
catalyze the destruction of 100,000 ozone
molecules
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What are CFCs?
• Used as propellants in aerosol spray
cans
• Used as refrigerants in fridges,
freezers and air conditioning units


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The ozone depletion process


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Too much ultra-violet light can result in:
ultrain:

•
•
•
•
•
•

Skin cancer
Eye damage such as cataracts
Immune system damage
Reduction in phytoplankton
Damage to the DNA in various life-forms
Possibly other things too that we don't
know about at the moment

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Effects on Plants
Physiological and developmental
processes of plants are affected by
UVB radiation, even by the amount of
UVB in present-day sunlight.


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• Effects on Marine Ecosystems
• Phytoplankton form the foundation of aquatic
food webs.
• Exposure to solar UVB radiation has been
shown to affect both orientation mechanisms
and motility in phytoplankton, resulting in
reduced survival rates for these organisms.


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• Effects on Biogeochemical Cycles
• Increases in solar UV radiation could affect
terrestrial and aquatic biogeochemical
cycles, thus altering both sources and sinks
of greenhouse and chemically-important
chemicallytrace gases.
• e.g., carbon dioxide (CO2), carbon monoxide
(CO), carbonyl sulfide (COS) and possibly other
gases, including ozone.
• These potential changes would contribute to
biospherebiosphere-atmosphere feedbacks that attenuate
or reinforce the atmospheric buildup of these
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gases.

• Effects on Materials
• Synthetic polymers, naturally occurring
biopolymers,
biopolymers, as well as some other materials
of commercial interest are adversely affected by
solar UV radiation.
• Today's materials are somewhat protected
from UVB by special additives.
• Therefore, any increase in solar UVB levels will
therefore accelerate their breakdown, limiting
the length of time for which they are useful
outdoors.

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Immune Suppression
•Scientists have found that
overexposure to UV radiation may
suppress proper functioning of the
body’s immune system and the skin’s
natural defenses.
• For example, the skin normally
mounts a defense against foreign
invaders such as cancers and
infections.

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• But overexposure to UV radiation can
weaken the immune system, reducing
the skin’s ability to protect against
these invaders.


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Effects on Human Health

Skin cancer
- Unprotected exposure Non-malignant
to UV radiation is the
most preventable risk
factor for skin cancer. malignant

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Over Exposure
• Accelerate aging of skin due high
exposure -The face, hands,
forearms, and the “V” of the neck
are especially susceptible to this
type of lesion.


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• Cataract
- Cataracts are a form of eye
damage in which a loss of
transparency in the lens of the eye
clouds vision.
- If left untreated, cataracts can lead
to blindness.
- Research has shown that UV
radiation increases the likelihood of
certain cataracts.
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What can be done?
• Reduce the use of CFCs
• They are already banned in aerosols
(1987)
• BUT they are still used as refrigerants
• Recycle fridges and air conditioning
plants

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Skin Protection
• Protect the skin against the solar radiation
using skin creams with SPF
• Use lip balm with SPF
• Cover up


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Protection
• Sunglasses with 100% UV
block
• Wrap around sunglasses
• Eye protection for children
• Hats


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What Is Being Done to Counter the Effects
of Ozone Depletion?

• Montreal Protocol (adopted in 1987) – panel
of experts was formed to investigate substances
responsible for hole formation
• Established policies that prevent future use of
certain types of chemicals
• Stipulated that the production and
consumption of compounds contributing
towards depletion of ozone in the stratosphere
were to be phased out by the year 2000 (2005
for methylchloroform)
methylchloroform)
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The current situation
• The holes developing over the pole suggest
that they may be show an improvement
• BUT CFC molecules take 30 years to rise up
to the stratosphere
• The chlorine radicals last a long time
• The peak ozone damage was supposed to
be in 2000
• Damage could go on another 50 years
© 2007 Paul Billiet ODWS

Signs of Recovery???

There have been some signs of recovery
• 1997 satellite showed a decline of
several known ozone-depleting gases
ozone• Satellite images show some slowing
down of ozone loss
However….
Antarctica - Dec. 2005

Recovery is slow

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Objective Questions
Q1. Ozone hole was first observed in ____.
Q2. The ozone layer, situated in the stratosphere
about __________km above the earth's
surface.
Q3. _______ is responsible for ozone depletion.
Q4. ___________ protocol was first step towards
reducing use of CFCs.
Q5.Breaking of ozone molecule takes place in
presence of ________________.

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Q6. Ozone layer thickness is measured in
____________ units.
Q7. Formation and destruction of ozone in the
atmosphere can be explained by ___________
reactions.
Q8. 1 Du = ____________________________.


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Theory Questions
Q1. Explain ‘Ozone depletion process with
respect to following points
- Sources/causes
- Chemical reactions
- Effects
- Remedies
Q2. Define Dobson unit.
Q3. Explain Chapman reactions.

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