Earth’s Changing Earth’s Changing EnvironmentEnvironment

Lecture 5Lecture 5

Depletion of the Ozone LayerDepletion of the Ozone Layer

The Stratospheric Ozone LayerThe Stratospheric Ozone Layer

Begins where the Begins where the tropospheretroposphere ends at 50,000 ends at 50,000 feet (10 miles) above the Earth’s surface. feet (10 miles) above the Earth’s surface.

The lower stratosphere is the location of most The lower stratosphere is the location of most atmospheric ozone. atmospheric ozone.

Solar UV RadiationSolar UV Radiation

UV Radiation is blocked by the ozone layerUV Radiation is blocked by the ozone layer But UV Radiation also forms the ozone But UV Radiation also forms the ozone

layer. layer.

Solar SpectrumSolar Spectrum

Regions of the Solar Regions of the Solar SpectrumSpectrum

Regions of the Solar UV Regions of the Solar UV SpectrumSpectrum

Chapman Reactions form O3 in Chapman Reactions form O3 in the Stratospherethe Stratosphere

O3 absorbs most of the UVB O3 absorbs most of the UVB radiationradiation

These two processes form the These two processes form the Ozone CycleOzone Cycle

Depletion of the Ozone Depletion of the Ozone LayerLayer

Chlorine acts as a catalyst to Chlorine acts as a catalyst to destroy the Ozone layerdestroy the Ozone layer

How does Chlorine get into the How does Chlorine get into the Stratosphere?Stratosphere?

chlorofluorocarbons (CFCs). chlorofluorocarbons (CFCs). CFC-12 (CF2Cl2) (freon)CFC-12 (CF2Cl2) (freon) CFC-11 (CFCl3)CFC-11 (CFCl3)

Have 100 year atmospheric lifetimesHave 100 year atmospheric lifetimes

Mario MolinaMario Molina

• Born in Mexico City• Won Nobel Prize in 1995• In 1974 with Sherry Roland, he predicted that CFCs could destroy ozone layer

Antarctic Ozone HoleAntarctic Ozone Hole

Normally, stratospheric reactions put Normally, stratospheric reactions put chlorine from CFCs into chlorine from CFCs into inertinert forms forms (HCL and ClONO2)(HCL and ClONO2)

Ice crystals in these antarctic Ice crystals in these antarctic polar polar stratospheric clouds stratospheric clouds ((PSCsPSCs) act as ) act as sites for the conversion of the inert sites for the conversion of the inert form of chlorine to the active form of form of chlorine to the active form of chlorine. chlorine.

Antarctic Ozone HoleAntarctic Ozone Hole Every spring, UVC radiation breaks CLEvery spring, UVC radiation breaks CL2 2 formed on formed on

the PSCs into atomic chlorine. This active CL the PSCs into atomic chlorine. This active CL causes a very sharp decrease in the causes a very sharp decrease in the concentration of ozone in the Antarctic concentration of ozone in the Antarctic

stratosphere, an ozone hole.stratosphere, an ozone hole.

                                                                                 

US Ozone DepletionUS Ozone Depletion

Health and Environmental Health and Environmental EffectsEffects

The Montreal ProtocolThe Montreal Protocol

International treaty for the International treaty for the control on the production and control on the production and consumption of ozone-consumption of ozone-depleting substances agreed depleting substances agreed on in 1987.on in 1987.

President Reagan signed the President Reagan signed the ratified Protocol in 1988.ratified Protocol in 1988.

1994 Copenhagen 1994 Copenhagen Amendment and Vienna Amendment and Vienna Adjustments called for a more Adjustments called for a more rapid phase out of certain ODP rapid phase out of certain ODP chemicals. chemicals.

Montreal ProtocolMontreal Protocol

29 countries plus the 29 countries plus the European Union signed European Union signed initiallyinitially

All have agreed to a All have agreed to a phase-out schedulephase-out schedule

Globally emission of Globally emission of ODPs has been ODPs has been drastically reduced to drastically reduced to around 10% of original around 10% of original levels.levels.

EPA – Ozone Depletion EPA – Ozone Depletion ProgramProgram

Command and Control StrategyCommand and Control Strategy Halt the production of ozone-depleting Halt the production of ozone-depleting

substances (ODS) substances (ODS) Ensure refrigerants and halon fire Ensure refrigerants and halon fire

extinguishing agents are recycled extinguishing agents are recycled properly properly

identifying alternative to ODSidentifying alternative to ODS banning the release of OD refrigerantsbanning the release of OD refrigerants

US Phase-out of high ODP US Phase-out of high ODP chemicalschemicals

chlorofluorocarbonchlorofluorocarbons (CFCs)s (CFCs)

carbon tetrachloridcarbon tetrachloridee

methyl chloroformmethyl chloroform halonshalons

Will take 50 years to Will take 50 years to RecoverRecover