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CFC's and Ozone Depletion

Key Concepts

Ozone in the Atmosphere

Ozone in the Lower Atmosphere (troposphere)

About 10% of all ozone (O3) in the atmosphere is found in the troposhere (up to 16km above the earth's surface).

Ozone in the troposhere has harmful effects on many living things because it is toxic.

In humans, ozone causes eye irritation, compromised lung functions, aggrevation of respiratory conditions like asthma, and increases the susceptibility to infection.

Ozone pollution in the troposphere is often linked to photochemical smog.

Ozone in the lower atmosphere is formed during electrical discharge from high voltage appliances as shown in the equations below:

O2(g) → 2O(g)

O2(g) + O(g) → O3(g)

Ozone in the Upper Atmosphere (stratosphere)

About 90% of all ozone (O3) in the atmosphere is found in the stratosphere (16 to 32 km above the earth's surface).

In the stratosphere ozone acts as the primary UV radiation shield, short wavelength UV radiation from the sun (<240nm) provides the energy to split oxygen molecules into oxygen atoms:

O2(g)UV radiation
2O(g)

Oxygen atoms then react with oxygen molecules to form ozone:

O(g) + O2(g) → O3(g)

Ozone can absorb harmful UV-B and UV-C radiation, preventing it from reaching the earth's surface:

O3(g)UV radiation
O2(g) + O(g)

The constant formation and destruction of ozone maintains a balance over time.

Human acitivities, such as the release of chlorofluorocarbons in to the atmosphere, have disturbed this balance.

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Chlorofluorocarbons (CFCs) and Halons

CFC Name Formula Code Uses
trichlorofluoromethane
freon-11
CCl3F CFC-11 refigeration,
aerosols,
foams

dichlorofluoromethane
freon-12
CCl2F2 CFC-12 refigeration,
aerosols,
foams,
air conditioning

1,1,2-trichloro-1,2,2-trifluoroethane
freon-13
CCl2FCClF2 CFC-13 electronics,
dry cleaning,
fire extinguishers

1,2-dichloro-1,1,2,2-tetrafluoroethane
freon-14
CClF2CClF2 CFC-14 aerosols

1,2,2-trichloro-1,1,2-trifluoroethane
freon-113
CClF2CCl2F CFC-113 degreasing and
cleaning printed
circuit boards

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Chemistry of Ozone Depletion by CFCs

CCl3F(g)u.v radiation
CCl2F(g)+Cl(g)

Cl(g)+O3(g)ClO(g)+O2(g)

ClO(g)+O(g)O2(g)+Cl(g)

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Substitutes for CFCs

Name Formula Code Uses
chlorodifluoromethane CHClF2 HCFC-22 air conditioning,
refrigeration,
foams

1-chloro-1,1-difluoroethane CClF2CH3 HCFC-142b aerosols

1,1-difluoroethane CHF2CH3 HCFC-152a aerosols,
refrigeration

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