Post on 11-Jul-2020
Ozone layer Depletion
TheAtmosphere• Thisisourprotectiveblanketofgasses.
– 78%Nitrogen(N2)– 21%Oxygen(O2)– Proportionallysmallamountsofcarbondioxide,watervaporandothertracesubstances
AtmosphericGases
TheAtmosphere-Layers• Troposphere– Layerinwhichwelive– Mostweatheroccurshere
• Cloudsformherecontributingtothealbedoeffect
– 90%ofthegassesarehere– 78%nitrogen,21%oxygen– Temperaturedecreaseswithaltitudeuntilthenextlayerisreached
• Stratosphere– 6-31milesinaltitude– Calm– Airtrafficduetolackofweather
– Temperatureincreaseswithaltitude
– Ozonelayer(oxygenisconvertedtoO3bylightningand/orsunlight)
– 99%ofultravioletradiation(especiallyUV-B)isabsorbedbythestratosphere
TheAtmosphere-Layers
OzoneLayer• Presentinthestratosphere• AbsorbsUVradiation(99%)• Comprisedofahighconcentrationof03molecules.– Oxygenexistsin3formsintheatmosphere:O3,O2,andO.
– OzoneisbeingcontinuouslyformedanddecomposedduetotheenergyfromUVrays.O3+UVàO2+OàO3
Ozone• OzoneisO3• Naturallyoccurringinthestratosphere.• TheabsorptionofenergyfromUVrayscausestheformationanddeformationofO3.
• Withoutanthropogenicinputsthesystemisinequilibrium
O3O2+O
OzoneStratosphericOzone• Naturallyoccurring.• BeneficialtolifeonEarth
• Createsaprotectivelayerthatabsorbs99%ofUVradiationinsunlight
TroposphericOzone• Alsocalledground-levelozone
• Anthropogenic• DoesNOTmigratetotheatmosphere
• SecondaryAirpollutant• Respiratoryirritant,eyeirritant,damagesplants
DestructionofAtmosphericOzone
• ThegroupofmoleculesthatareinthiscategoryareoftenreferredtoasODS(OzoneDepletingSubstances)
• Anthropogenicsources:– CFCs– Halocarbons/Halons
• Usedinfireretardants• Foam-blowinginsulation
• 1chlorinecandestroy100,000ozonemolecules
CFCs• Chlorofluorocarbon• TrademarknameisFreon• CFCshavestablestructureswhichallowthemtomigratethroughthetroposphere
• TheyarebrokendownwhenexposedtostrongUVradiation
• Usedin– Refridgerants– Propellants/aerosols– Gasblownplastics(Styrofoam)– Pesticides– Flameretardants
CCl3F+UVàCl+CCl2F
Cl+O3àClO+O2
ClO+0àCl+O2
Repeatedmanytimes
SummaryofCFCReactions
VideoofOzoneDepletion
• https://www.youtube.com/watch?v=V7eDjqJ7vsY
Thinningozone
EffectsofThinningOzoneLayer
EnvironmentalEffects• GreaterUVradiation
damagesphotosyntheticorganisms(especiallyphytoplankton)decreasingprimaryproductivity
• Sunburnsanimals• Cataracts/blindnessin
animals
HumanHealthEffects• Sunburn/skincancer• Cataracts(eyedamage)• Wrinkles• Decreasedimmune
response
PollutionManagement
• Recyclingrefrigerants• Findingalternativestogas-blownplastics,halogenatedpesticides,propellantsandaerosols
• Developingnon-propellantalternatives
MontrealProtocol• Internationaltreatytoprotecttheozonelayerbyphasingoutmaterialsbelievedtocausethedepletionofstratosphericozone
• HasbeenVERYsuccessful.Ozonelayerisshowingsignsofrecovery
• BansCFCsandhalons• Includesseveralgroupsofsubstances,allofthemincludingchlorineorbromine.