臭氧破坏的危害.ppt

OzoneLayerandExtinctionofSpecies Contents OzonelayerdepletionExtinctionofspeciesandlossofbiodiversity OzoneLayerDepletion Sourceofozone Consistedof3oxygenatoms unlikeordinaryoxygenmolecule whichhas2atoms Ithasabluishcolour DualroleofOzone Atneargroundlevel ozoneisanairpollutant Evenatalowconcentration ppm itisirritatingtorespiratorysystem Itisstronglyoxidizing andisnowcommonlyusedinsterilizationofwater ItspresenceinthestratosphereisvitaltolifeonEarthasitcanabsorbharmfulultra violetradiation knownasUVB wavelength270 315nm fromsunlight StructureofAtmosphere Source NASA FormationofOzoneinstratosphere O2 radiation 240nm 2OO2 O M O3 MMoleculeMcarriestheenergyofthereactionbutremainunchanged DestructionofOzone I Ozonecanbedestroyedbyanumberoffreeradicalcatalysts themostimportantofwhicharethehydroxylradical OH thenitricoxideradical NO andatomicchlorine Cl andbromine Br Humanactivityhasdramaticallyincreasedthechlorineandbromine Theseelementsarefoundincertainstableorganiccompounds especiallychlorofluorocarbons CFCs whichmayfindtheirwaytothestratospherewithoutbeingdestroyedinthetroposphereduetolowreactivity Onceinthestratosphere theClandBratomsareliberatedfromtheparentcompoundsbytheactionofultravioletlight andcandestroyozonemoleculesthroughavarietyofcatalyticcycles DestructionofOzone II Cl O3 ClO O2ClO O Cl O2InsumO3 O O2 O2 Increaserateofrecombinationofoxygen leadingtoanoveralldecreaseintheamountofozone OzoneholeinSeptember2006 Largestholeintherecord SizeofNorthAmerica Source NASA ConcentrationOzoneinAntarcticregion ConsequencesofOzonedepletion SincetheozonelayerabsorbsUVBultravioletlightfromtheSun ozonelayerdepletionisexpectedtoincreasesurfaceUVBlevels Possiblelinkedtohigherincidenceofskincancer Leadtodecreaseofcropyield MontrealProtocol TheMontrealProtocolonSubstancesThatDepletetheOzoneLayerisaninternationaltreatydesignedtoprotecttheozonelayerbyphasingouttheproductionofanumberofsubstancesbelievedtoberesponsibleforozonedepletion ThetreatyenteredintoforceonJanuary1 1989 Duetoitswidespreadadoptionandimplementationithasbeenhailedasanexampleofexceptionalinternationalcooperation Perhapsthesinglemostsuccessfulinternationalagreementtodate OzoneDepletingSubstances Chlorofluorocarbons CFCs wereusedinairconditioning coolingunits asaerosolspraypropellantspriortothe1980s andinthecleaningprocessesofdelicateelectronicequipment ItiscalculatedthataCFCmoleculetakesanaverageof15yearstogofromthegroundleveluptotheupperatmosphere anditcanstaythereforaboutacentury destroyingupto100 000ozonemoleculesduringthattime Currentsituation CFCshavebeenreplacedtosomeextentbythelessdamaginghydro chloro fluoro carbons HCFCs althoughconcernsremainregardingHCFCsalso Insomeapplications hydro fluoro carbons HFCs havebeenusedtoreplaceCFCs HFCs whichcontainnochlorineorbromine donotcontributeatalltoozonedepletionalthoughtheyarepotentgreenhousegases RecoveryofOzoneLayer SincetheadoptionandstrengtheningoftheMontrealProtocolhasledtoreductionsintheemissionsofCFCs atmosphericconcentrationsofthemostsignificantcompoundshavebeendeclining Thesesubstancesarebeinggraduallyremovedfromtheatmosphere By2015 theAntarcticozoneholewouldhavereducedbyonly1millionkm outof25CompleterecoveryoftheAntarcticozonelayerwillnotoccuruntiltheyear2050orlater Adetectablerecoverywillnotoccuruntilaround2024 withozonelevelsrecoveringto1980levelsbyaround2068 ExtinctionandLossofBiodiversity Earth sSixthMassExtinction Since1500AD 784extinctionshavebeendocumentedbytheInternationalUnionforConservationofNatureandNaturalResources However sincemostextinctionsarelikelytogoundocumented scientistsestimatethatduringthelastcentury between20 000andtwomillionspecieshavebecomeextinct buttheprecisetotalcannotbedeterminedmoreaccuratelywithinthelimitsofpresentknowledge TheWorldConservationUnion sIUCNRedListcontains15 589speciesthreatenedwithextinctionin2004 Accordingtoa1998surveyof400biologistsconductedbyNewYork sAmericanMuseumofNaturalHistory nearly70percentofbiologistsbelievethatwearecurrentlyintheearlystagesofahuman causedmassextinctionThesameproportionofrespondentsagreedwiththepredictionthatupto20percentofalllivingspeciescouldbecomeextinctwithin30years by2028 Causeofextinctionofspecies DeforestationHabitatdestruction degradationorfragmentationOver exploitation huntingHumanpopulationgrowthPollutionIntroductionofexoticspeciesClimatechange Someexamplesofextinctspecies DodoonaflightlessbirdlivingonAsmallislandinIndianOcean TheyArehuntedtoextinctioninlate17thCenturybysailorsanddogsbroughtBythemasfood Baiji ChineseRiverDolphinDeclaredfunctionalyextinctin2006 BaliTigergoneextinctin1937 Link ExtinctionofSpeciesandBiodiversity Extinctionofspeciescauseairreversiblelossofbiodiversity Importanceofbiodiversity Possiblenewsourcesoffoodanddr