Catalyst 5/4Should developed countries bear the brunt of

the responsibility for reducing CO2 emissions because they produce more?

Developed countries can more easily adapt to global warming. Should they be responsible for offering assistance to developing countries?

Structure of the AtmosphereMade up of several vertical layers

Troposphere - bottom layer Where weather occurs Temperature decrease with elevation At the top is tropopause - acts as a lid

Stratosphere - above the troposphere Stratospheric ozone layer just above the tropopause Protects again UV radiation

Ultraviolet Radiation and OzoneOzone layer in the stratosphere called the

ozone shieldAbsorbs most of the potentially hazardous

ultraviolet radiation from the sun

Ultraviolet radiation consists of wavelengths between 0.1 and 0.4 μm Ultraviolet A (UVA)Ultraviolet B (UVB)Ultraviolet C (UVC).

Ultraviolet Radiation and OzoneOzone layer in the stratosphere called the

ozone shieldAbsorbs most of the potentially hazardous

ultraviolet radiation from the sun

Ultraviolet radiation consists of wavelengths between 0.1 and 0.4 μm Ultraviolet A (UVA)Ultraviolet B (UVB)Ultraviolet C (UVC).

Ultraviolet Radiation and OzoneUltraviolet C (UVC)

Shortest wavelength and most energetic of the types of ultraviolet radiation

Sufficient energy to break apart diatomic oxygen (O2)

Each of these oxygen atoms may combine with an O2 molecule to create ozone

UVC strongly absorbed in the stratosphere, and negligible amounts reach the Earth’s surface

Ultraviolet Radiation and OzoneUltraviolet A (UVA)

Longest wavelengthLeast energy of the three types of ultraviolet

radiationUVA can cause some damage to living cellsNot affected by stratospheric ozone, and is

transmitted to the Earth’s surface

Ultraviolet Radiation and OzoneUltraviolet B (UVB)

Energetic and strongly absorbed by stratospheric ozone

Ozone is the only known gas that absorbs UVB Depletion of ozone in the stratosphere results

in an increase in the UVB that reaches the surface of the Earth

Ultraviolet Radiation and OzoneApproximately 99% of all ultraviolet solar

radiation (all UVC and most UVB) is absorbed by the ozone layer Natural service function Protects us from the potentially harmful effects

of ultraviolet radiation

Measurement of Stratospheric OzoneFirst measured in 1920s using Dobson

ultraviolet spectrometer.Dobson unit (DU) - 1DU = 1 ppb O3

Now have measurements from all over the world for 30 years

Ground based measurements first identified ozone depletion over the AntarcticConcentrations have been decreasing since the

mid-1970s“Ozone hole”

Ozone Depletion: CausesChloroflurocarbons

(CFCs): Family of organic compounds made up of carbon, chlorine, and fluorine

Example: Freon-12 (CCl2F2)

Gaseous CFCs deplete the ozone

Discovered through research done by Rowland and Molina

Ozone Depletion: EffectsHuman Health

SunburnsMore eye cataracts and skin cancerImmune system suppression

Food and ForestsReduced yields for some cropsReduced seafood supplies from reduced phytoplanktonDecreased forest productivity for UV-sensitive tree

speciesClimate Change

CFCs act as a greenhouse gases

Ozone Depletion: EffectsWildlife

Increased eye cataracts in some speciesDecreased populations of aquatic species sensitive

to UV radiationReduced populations of surface phytoplanktonDisrupted aquatic food webs from reduced

phytoplanktonAir Pollution and Materials

Increased acid depositionIncreased photochemical smogDegradation of outdoor paints and plastics

Think BoxWhich of these effects do you think are most

threatening? Why?

Ozone Depletion: SolutionsMontreal Protocol (1987)

36 nationsGoal: Cut CFC emissions by about 35%

between 1989 and 2000. Copenhagen Protocol (1992)

An amendment that accelerated the phase-out of key ozone-depleting chemicals

These agreements have been signed by all 196 of the world’s countriesOzone levels should return to 1980 levels by

2036 (18 years earlier than projected)

Ozone Depletion: SolutionsPrevention to solve an environmental issueFirst time nations and governments worked

together to solve a global issueConvincing and dramatic scientific evidenceCFCs produced by a small number of

international companiesPrivate sector forced to find more profitable

substitute chemicals

Ozone Depletion: SolutionsCFC substitutes

Hydroflourocarbons (HFCs) Acts as a greenhouse gas

U.S. government asked the UN to enact mandatory reductions in HFC emissions through the Montreal ProtocolWould like to do the same for N2O

Think BoxWhat lessons do you think we can learn from

ozone depletion in trying to solve the problem with global warming?

Objectives for practice1. Describe the evidence for ozone depletion2. Discuss the process that leads to ozone

depletion3. Identify and describe the effects of ozone

depletion 4. Construct strategies to deal with ozone

depletion