Slides in this set
CFCs are used as working fluids in refrigerators
and air conditioners because they are gases at
room temperature which can be easily liquefied
by compression and because they are stable and
r a n ts
fri g e
CFCs are used as foaming
agents in the production
of polystyrene and foam
plastics used for
Foaming agents in insulation and packing
plastics production materials
ros CFCs are used as
ol' a propellant in
spray cans for
Ozone in the Lower Atmosphere (troposphere)
About 10% of all ozone (O3) in the atmosphere is found in the troposphere (up
to 16km above the earth's surface).
Ozone in the troposphere has harmful effects on many living things because it
In humans, ozone causes eye irritation, compromised lung functions,
aggravation 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)…read more
Gases are removed from the lower atmosphere in two general ways:
-They either dissolve in the clouds and are rained out,
-Or they react chemically to be converted into other substances.
Neither of these mechanisms are particularly relevant for CFCs.
Chlorofluorocarbons are insoluble in water, and they are so stable that they can
exist in the lower atmosphere for years.…read more
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
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 activities, such as the release of chlorofluorocarbons in to the atmosphere, have disturbed
this balance.…read more
During the life time in the atmosphere, the CFC molecules wander around
moving wherever the air currents take them.
They can eventually make their way up into the stratosphere
where for the first time they come into contact with (UV) radiation
of high enough energy to cause them to break down.
For example, energy of wavelength less than 215 nm will break
the covalent bond between one of the chlorine atoms and the
carbon atom in CF2Cl2.…read more