Section 9 and 10 Ozone DepletionSection 9 and 10 Ozone Depletion

• What is the threat from ozone depletion? Good versus bad ozone.

• What causes ozone depletion?

• What happens to ozone levels over Earth’s poles?

• Why should we be worried about ozone depletion?

• What are solutions to this problem?

Ozone DepletionOzone Depletion

What is ozone?

“Good” versus “bad” ozone

Where is the “ozone layer”

Keeps out about 95% of UV rays

Layer has been thinning

Ozone Depletion: What Causes Depletion?Ozone Depletion: What Causes Depletion?

GM Chemist discovered Chlorofluorocarbons in 1930 (CFCs)

…also known as freon

• Very stable• Nontoxic• Noncorrosive• Inexpensive

“Dream Chemical”

Ozone Depletion: What Causes Depletion?Ozone Depletion: What Causes Depletion?

CFCs used for:

• Coolant in refrigerators and air conditioners

• Propellant in aerosol sprays

• Cleaner for electronics

• Bubbles in plastic foams

• Insulations

Former Uses of CFCsFormer Uses of CFCs

Air Conditioners

Refrigerators

Spray cans

Cleaners for electronic parts

Sterilizing medical instruments

Fumigants for granaries and cargo ships

Air Conditioners

Refrigerators

Spray cans

Cleaners for electronic parts

Sterilizing medical instruments

Fumigants for granaries and cargo ships

Ozone Depletion: What Causes Depletion?Ozone Depletion: What Causes Depletion?

Too good to be true:

1974 study at UC Irvine indicated threat to ozone layer from CFCs

Shock to the $28 billion per year CFC industry –DuPont and other chemical companies

Ozone Depletion: What Causes Depletion?Ozone Depletion: What Causes Depletion?

1) CFCs remain stable in troposphere due to unreactivity

2) Over 11-20 years they get lifted into stratosphere by convection and drift

3) Once in stratosphere they break down by UV rays releasing highly reactive chlorine atoms (with others) that in a chain reaction break apart ozone

Ozone Depletion: What Causes Depletion?Ozone Depletion: What Causes Depletion?4) Each CFC molecule lasts

in stratosphere for 65-385 years

Can convert 100,000 of O3 to O2 during that time.

DuPont and others fought findings until 1988 when they admitted problems.

1995 Nobel Prize Chemistry

Ozone Depletion in the StratosphereOzone Depletion in the Stratosphere

Fig. 21-21 p. 484

Ozone Depletion: What Causes Depletion?Ozone Depletion: What Causes Depletion?

CFCs are not the only culprit

• Halons (fire extinguishers)

• Hydrogen chloride (space shuttle)

• Some natural chemicals

Ozone Depleting ChemicalsOzone Depleting Chemicals

Chlorofluorocarbons (CFCs)Chlorofluorocarbons (CFCs)HalonsHalonsMethyl bromideMethyl bromideCarbon tetrachlorideCarbon tetrachlorideMethyl chloroformMethyl chloroformHydrogen chlorideHydrogen chloride

Ozone “Hole”Ozone “Hole”

During 4 months each year half of the ozone layer above Antarctica is depleted

1984 researchers discovered 40-50% reductions in later winter (August – November)

Ozone “Hole”Ozone “Hole”

“Ozone Hole” more accurate “ozone thinning”

Polar Vortex: circular winds blowing around poles during winter isolates atmosphere.

Warming at end of winter releases frozen chemicals destroying ozone

Ozone “Hole”Ozone “Hole”Huge problem for parts of

New Zealand, Australia South American and South Africa

Similar “hole” but less severe over Arctic during late winter early spring

Loss of the Ozone Layer: Reasons for ConcernLoss of the Ozone Layer: Reasons for Concern

Increased incidence and severity of sunburn Increased incidence and severity of sunburn

Increase in eye cataracts Increase in eye cataracts

Increased incidence of skin cancer Increased incidence of skin cancer

Immune system suppression Immune system suppression

Increase in acid deposition Increase in acid deposition

Lower crop yields and decline in productivity Lower crop yields and decline in productivity

Refer to Fig. 21-23 p. 486Refer to Fig. 21-23 p. 486

Skin CancersSkin Cancers

Fig. 21-25 p. 487

Solutions: Protecting the Ozone LayerSolutions: Protecting the Ozone Layer

1987 Montreal Protocol 36 nations:

Goal: reduce CFCs by 35% by 2000

1992 Copenhagen Protocol accelerated phase out

Good news: substitutes do exist

If all of the ozone-depleting substances were banned tomorrow, it would take about 90-150

years for Earth to recover to pre-1975 levels.

If all of the ozone-depleting substances were banned tomorrow, it would take about 90-150

years for Earth to recover to pre-1975 levels.

Solutions: Protecting the Ozone LayerSolutions: Protecting the Ozone Layer

CFC substitutes CFC substitutes

Montreal Protocol Montreal Protocol

Copenhagen ProtocolCopenhagen Protocol

Fig. 21-27 p. 489Fig. 21-27 p. 489