Section 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 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? GM Chemist discovered Chlorofluorocarbons in 1930 (CFCs) …also known as freon Very stable Nontoxic Noncorrosive Inexpensive “Dream Chemical”

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 CFCs Air Conditioners Refrigerators Spray cans Cleaners for electronic parts Sterilizing medical instruments Fumigants for granaries and cargo ships

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? CFCs remain stable in troposphere due to unreactivity Over 11-20 years they get lifted into stratosphere by convection and drift 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? 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 Stratosphere Fig. 21-21 p. 484

Ozone Depletion: What Causes Depletion? CFCs are not the only culprit Halons (fire extinguishers) Hydrogen chloride (space shuttle) Some natural chemicals

Ozone Depleting Chemicals Chlorofluorocarbons (CFCs) Halons Methyl bromide Carbon tetrachloride Methyl chloroform Hydrogen chloride

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” 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” 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 Concern Increased incidence and severity of sunburn Increase in eye cataracts Increased incidence of skin cancer Immune system suppression Refer to Fig. 21-23 p. 486 Increase in acid deposition Lower crop yields and decline in productivity

Skin Cancers Fig. 21-25 p. 487

Solutions: 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.

Solutions: Protecting the Ozone Layer CFC substitutes Montreal Protocol Copenhagen Protocol Fig. 21-27 p. 489