stratospheric ozone depletion

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Stratospheric Ozone Depletion. IB syllabus: 5.6.1-5.6.6 AP syllabus Ch 17, 18 Video The Hole Story. Syllabus Statements. 5.6.1: Outline the overall structure and composition of the atmosphere 5.6.2: Describe the role of ozone in the absorption of UV radiation. - PowerPoint PPT Presentation


Ozone Depletion

Stratospheric Ozone DepletionIB syllabus: 5.6.1-5.6.6AP syllabusCh 17, 18Video The Hole StorySyllabus Statements5.6.1: Outline the overall structure and composition of the atmosphere5.6.2: Describe the role of ozone in the absorption of UV radiation.5.6.3: Explain the interaction between ozone and halogenated organic gasses.5.6.4: State the effects of UV radiation on living tissues and biological productivity.5.6.5: Describe three methods of reducing the manufacture and release of ozone-depleting substances5.6.6: Describe and evaluate the role of national and international organizations in reducing the emissions of ozone-depleting substancesvocabularyHalogenated organic gasesPollutionNon-point source pollutionReplenishable natural capitalAtmospheric StructureLayered structure Troposphere, Stratosphere, Mesosphere, ThermosphereTroposphere is layer next to earths surface 75-80% of mass of earths airAtmospheric composition 78% nitrogen, 21% oxygen, trace amounts of water, argon, carbon dioxideLapse rate rate at which temperature declines with increasing altitude in the troposphereLayers of the Atmosphere

Atmospheric pressure (millibars)02004006008001,0001201101009080706050403020100(SeaLevel)804004080120Pressure = 1,000millibars atground levelTemperature (C)Altitude (kilometers)Altitude (miles)756555453525155ThermosphereHeating via ozoneMesosphereStratosphereOzone layer

Heating from the earthTroposphereTemperaturePressureMesopauseStratopauseTropopauseOzoneOzone is O3 formed from O + O2Found in the lower Stratosphere as the ozone layer good protective qualitiesFound in the Troposphere as a result of human pollution bad qualities photochemical oxidantOzone FormationO3 + UV O + O2

O + O O2

O + O2 O3

Its ReplenishableOzone absorbs UV radiationWhen UV strikes O3 it is absorbed and its energy used to break the chemical bondO3 + UV O + O2So UV doesnt make it to the earths surfaceOzone LayerLayer in the lower stratosphereKeeps 95% of harmful UV radiation awaySeasonal depletion of ozone layer above Arctic & Antarctic, overall thinning everywhere but tropicsDepletion is serious long term threat to (1) humans, (2) other animals, (3) sun driven producers (plants) supporting food webs

CFCs (Freons)Discovered in 1930Chemically stable, odorless, nonflamable, nontoxic, noncorrosive dream chemical in the troposphereCoolants, Propellants, Sterilants, Fumigants1974 discovered to be lowering concentrations of stratospheric ozoneImmediate ban called forCFCs IILarge quantities being released use, leaks, production of plasticsRemain in troposphere unreactive, insoluble very stable11-20 years to rise to stratosphereRelease high energy Cl atoms when exposed to UV which speed up breakdown of ozoneEach CFC lasts 65-385 years in stratosphereCan break down up to 100,000 molecules of ozone

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breakingoff a chlorine atom and leaving CFCl2.UV radiationSunOnce 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).ClClClCFClClOOClOOOClOOOClOOSummary of ReactionsCCl3F + UV Cl + CCl2FCl + O3 ClO + O2Cl + O Cl + O2Repeated many timesSummary of ReactionsCCl3F + UV Cl + CCl2F

Cl + O3 ClO + O2

ClO + O Cl + O2

Steps 2 + 3 are repeated many times causing massive destruction of ozoneMethyl BromideOther major ODCUsed as a pesticide and fumigant on cropsKills nematodes, fungi, weedsRemember that ozone breaks down naturally when it absorbs UVThis speeds up that process and limits the regeneration of O3 Pollutants enhance O3 destruction disturbing the equilibrium of the O3 production system

Year19701975199020002005198519551960196519801995400350300250200150100Total ozone (Dobson units)October monthly meansDecreasing ozone volume in fall over the polesSeasonal Polar ThinningSeasonal loss of ozone in summers over polesOzone hole is actually ozone thinningSunless winters, polar vortex causes swirling winds isolated from rest of atmosphereIce crystals in clouds collect CFCs and speed release of ClSun returns in spring / summer and frees large volumes of free ClOzone thinning travels north to effect Aus, NZ, S. Am., S. Af.

August 7, 2001October 10, 20013530252015105051015Ozone partial pressure (milipascals)Altitude (kilometers)Year1979198219851988199119941997200020032006051015202530Million square kilometersFigure 18-29Page 474

Area of North AmericaSize of Ozone thinning



Human Health

Worse sunburn

More eye cataracts

More skin cancers

Immune system suppression

Food and Forests

Reduced yields for some crops

Reduced seafood supplies from reduced phytoplankton

Decreased forest productivity for UV-sensitive tree species


Increased eye cataracts in some species

Decreased population of aquatic species sensitive to UV radiation

Reduced population of surface phytoplankton

Disrupted aquatic food webs from reduced phytoplankton

Air Pollution and Materials

Increased acid deposition

Increased photochemical smog

Degradation of outdoor paints and plastics

Global Warming

Accelerated warming because of decreased ocean uptake of CO2 from atmosphere by phytoplankton and CFCs acting as greenhouse gasesWhat are the effects?

Effects on Humans, Plants, Animals & Global climate

A 1% loss of stratospheric ozone equals a 2% increase in skin cancers & 1% increase in cataracts worldwide.

Humans make cultural changes, others cannot

Ultraviolet AUltraviolet BThin layer ofdead cellsSquamouscellsBasallayerMelanocytecellsBasalmembraneBloodvesselsHairEpidermisSweatglandDermisSquamous Cell CarcinomaBasal Cell CarcinomaMelanomaSolutions & ProtectionMust immediately stop using ozone depleting chemicalsLong recovery time afterwards due to persistence in the atmosphereSubstitutes are available for most CFC usesHydrocarbons seem to be best for futureHow can the manufacture and release of ODC be reduced?Refrigerants can be recycledAlternatives to gas blown plastics can be usedAlternative propellents hydroflourocarbons better but a potent greenhouse gasAlternatives to methyl bromide can be used for fumigation and pesticidesProblemsExisting stockpiles were ok to use after the phase outOld CFCs continue to leak out of junked cars and fridgesBlack market trade in CFCs increasing because they are not made but still usefulChina, India, Mexico have increased use and production of CFCsFull recovery expected by 2050 if current decline continues

Montreal Protocol1987, 36 nations in MontrealCut emissions of CFCs by 30% between 1989 and 2000After 1989 ozone thinning info new meetings in 1990, 1992 formed new Copenhagen protocol, 177 nations more stringent reductions requiredUNEP involved in these agreements as well as an accelerated phase out for Korea, China, IndiaMontreal Multilateral Fund estd for aiding transitionAlso studying the relative effectiveness of the measures being taken


Year19501975200020252050207521003,00006,0009,00012,00015,000Abundance (parts per trillion)No protocol1987MontrealProtocol1992CopenhagenProtocolOzone depleting chemical concentration Predictions in stratosphereIn the USGovernment ratified Montreal Protocol agreeing stop production of CFC propellentsTaxes levied on CFC production and useCorporations changing their waysMcDonalds (1987) stopped use of styrofoam packaging Caused foam packaging industry to stop use of all CFCs by 1988NextReturn to 1980 levels by 2050Assume countries follow agreement and dont produce new ODCOzone loss has been cooling troposphere masking global warmings real effectsGood precedent for global cooperation


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