Transcript Unit 5B Ch 13 S2- The Ozone Shieldx

ATMOSPHERE &
CLIMATE CHANGE
Chapter 13, Section 2: the ozone shield
Standards: SEV4f
WHAT IS THE OZONE LAYER?
• An area in the
stratosphere
where ozone is
highly
concentrated.
• Ozone (O 3 ) absorbs
most of the UV
light that comes
from the sun.
WHAT CHEMICAL IS ATTRIBUTED WITH
CAUSING OZONE DEPLETION?
Chlorofluorocarbons (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 Styrofoam
• Propellant in hair spray,
deodorant, insecticides & paint
• In 1970’s it was discovered they may
be damaging the ozone layer.
HOW DO CFC’S DEPLETE THE OZONE?
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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 (O 3 ) into an O 2 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.
Ultraviolet light hits a chlorofluorocarbon
(CFC) molecule, such as CFCl3, breaking
off a chlorine atom and leaving
CFCl2.
Sun
Cl Cl
C
Cl
F
UV radiation
Once free, the chlorine atom is off
to attack another ozone molecule
and begin the cycle again.
Cl
Cl
O
The chlorine atom attacks
an ozone (O3) molecule,
pulling an oxygen atom
off it and leaving
an oxygen
O
molecule (O2).
O
O
O
A free oxygen atom pulls
the oxygen atom off
the chlorine monoxide
molecule to form O2.
Cl
The chlorine
Cl
atom and the
O
oxygen atom join
to form a chlorine
O
O
monoxide molecule (ClO)
Cl
O
O
WHAT IS “THE OZONE HOLE”?
1980’s scientists
working in Antarctica
noticed a thinning of the
ozone by 50-98% that
was occurring each
spring.
HOW DOES THE OZONE HOLE FORM?
 During the dark winter
months, VERY cold
strong winds called
polar vortex winds trap
CFC’s and convert them
to molecular Cl 2
 In the spring, UV rays
split Cl 2 and the
individual Cl atoms
break ozone down
rapidly.
 The thinning lasts for
several months.
WHY CAN’T OZONE CREATED AT GROUND
LEVEL (AKA- BAD OZONE) HELP HEAL THE
OZONE THINNING?
Ozone at ground
level is highly
reactive and reacts
with other molecules
of air pollution
before it can even
enter the
stratosphere.
WHAT ARE THE EFFECTS OF OZONE
THINNING ON HUMANS?
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 ANIMALS & PLANTS?
 Oceans
 Kills phytoplankton which is
the bottom of the marine food
chain.
 Disrupts food chains
 Phytoplankton removes CO 2 so
if they die, CO 2 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
HOW CAN WE PROTECT THE OZONE
LAYER?
 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.
YOU SHOULD BE ABLE TO…
 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 ef fects 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.