1. Chapter 13, Section 2: the ozone shield
Standards: SEV4f
ATMOSPHERE &
CLIMATE CHANGE

2. • An area in the
stratosphere
where ozone is
highly
concentrated.
• Ozone (O3) absorbs
most of the UV
light that comes
from the sun.
WHAT IS THE OZONE LAYER?

3. Chlorofluorcarbons (CFCs)
• When first invented, were valued
because they are
• Nonpoisonous
• Nonflammable
• Do not corrode
• Were used for decades as
• Coolants in refrigerators & air
conditioners
• Component of Sytrofoam
• Propellant in hair spray,
deodorant, insecticides & paint
• In 1970’s it was discovered they may
be damaging the ozone layer.
WHAT CHEMICAL IS ATTRIBUTED WITH
CAUSING OZONE DEPLETION?

4. • At ground level, CFCs are
stable & do not cause
problems.
• When air currents carry them
to the stratosphere they can
deplete the ozone.
• Takes 10-20 years for the CFC’s to make
it to the stratosphere and they get
recycled while they are up there so they
are persistent for 60-120 years
• UV light from sun breaks CFC which
releases a chlorine atom.
• The chlorine atom breaks a molecule of
ozone (O3) into an O2 molecule and an
oxygen atom (O) which the chlorine
attaches to and creates chlorine
monoxide (ClO)
• Chlorine monoxide (ClO) hits another
ozone and the chlorine breaks off again
and attacks another ozone molecule.
• 1 chlorine from CFC can destroy
100,000 ozone molecules.
HOW DO CFC’S DEPLETE THE OZONE?

5. Ultraviolet light hits a chlorofluorocarbon
(CFC) molecule, such as CFCl3, breaking
off a chlorine atom and leaving
CFCl2.
UV radiation
Sun
Once free, the chlorine atom is off
to attack another ozone molecule
and begin the cycle again.
A free oxygen atom pulls
the oxygen atom off
the chlorine monoxide
molecule to form O2.
The chlorine
atom and the
oxygen atom join
to form a chlorine
monoxide molecule (ClO)
The chlorine atom attacks
an ozone (O3) molecule,
pulling an oxygen atom
off it and leaving
an oxygen
molecule (O2).
Cl
Cl
Cl
C
F
Cl
Cl
O
O
Cl
O
O
O
Cl
O
O
O
Cl
O
O

6. 1980’s scientists
working in Antarctica
noticed a thinning of the
ozone by 50-98% that
was occurring each
spring.
WHAT IS “THE OZONE HOLE”?

7.  During the dark winter
months, VERY cold
strong winds called
polar vortex winds trap
CFC’s and convert them
to molecular Cl2
 In the spring, UV rays
split Cl2 and the
individual Cl atoms
break ozone down
rapidly.
 The thinning lasts for
several months.
HOW DOES THE OZONE HOLE FORM?

8. Ozone at ground
level is highly
reactive and reacts
with other molecules
of air pollution
before it can even
enter the
stratosphere.
WHY CAN’T OZONE CREATED AT GROUND
LEVEL (AKA- BAD OZONE) HELP HEAL THE
OZONE THINNING?

9. UV light can
Damage DNA
Premature aging
Weakened immune
system
Increase chance of
developing cataracts
Increase susceptibility
to skin cancer
WHAT ARE THE EFFECTS OF OZONE
THINNING ON HUMANS?

10.  Oceans
 Kills phytoplankton which is
the bottom of the marine food
chain.
 Disrupts food chains
 Phytoplankton removes CO2 so
if they die, CO2 levels would go
up in atmosphere (global
climate change)
 Freshwater
 Kill amphibian eggs
 Survivors suffer birth defects
 Populations decline
 Land Plants
 Interferes with photosynthesis
 Reduces crop yield
WHAT ARE THE EFFECTS OF OZONE
THINNING ON ANIMALS & PLANTS?

11. Montreal Protocol
(1987)
 Meeting of several nations
calling for reduction or
elimination of CFCs in
products.
 Many manufacturers are
switching to non-CFC
propellants in aerosol
cans.
 You can help by:
 Not buying Styrofoam
products
 If air conditioner leaks, fix it
to prevent release to air.
HOW CAN WE PROTECT THE OZONE
LAYER?

12.  Describe the process by which chlorofluorcarbons destroy
ozone molecules in the stratosphere.
 Describe the process by which the ozone hole forms over
Antarctica in the spring.
 List five harmful effects that UV radiation could have on
plants or animals as a result of ozone thinning.
 Explain why it will take years for the ozone layer to recover,
even though the use of CFCs has declined significantly.
YOU SHOULD BE ABLE TO…