Chapter 13, Section 2: the ozone shieldStandards: SEV4f

ATMOSPHERE & CLIMATE CHANGE

• 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?

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?

• 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?

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breakingoff a chlorine atom and leaving CFCl2.

UV radiation

SunOnce free, the chlorine atom is off to attack another ozone moleculeand 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 attacksan ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2).

ClCl

ClC

F

ClCl

OO

Cl

OO O

ClO

OO

ClO

O

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”?

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?

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?

UV light canDamage DNAPremature agingWeakened immune system

Increase chance of developing cataracts

Increase susceptibility to skin cancer

WHAT ARE THE EFFECTS OF OZONE THINNING ON HUMANS?

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?

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?

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…