环境化学最新版本

.,二、光化学photochemistry反应基础,1、光子photon的能量爱因斯坦-普朗克（Einstein-Planck）关系式：=h=hc/(J)E=N0h=N0hc/(KJ/mol)式中hPlanck常数，6.621034J.s；光子的频率，Hz；c光速，2.9981010cm/s；光子的波长，cm；N0阿佛加德罗常数，6.021023/mol。,.,随着波长的增加，光子的能量减小。,不同波长光的能量,高能光，能引起光化学反应（光离解）,低能光，不能引起光化学反应,例1计算波长为200nm紫外光的能量。,一般化学鍵的键能大于167.44KJ/mol,.,2、光化学反应原理光化学反应：由一个原子、分子、自由基或离子吸收一个光子后所引发的反应。初级过程：引发：A(分子)hA*(激发态分子)次级过程：离解：A*C+与其他分子反应生成新的物种：A*+BD+与惰性inertia分子碰撞失活(返回基态)：A*+MA+M发光而失活(返回基态)：A*Ah,.,3、大气中重要吸光物质的光离解吸光物质高层大气：N2、O2、O3（290nm）低层大气：NO2、SO2等,.,氧和氮的光离解氧分子键能：493.8kJ/mol（240nm以下紫外光可引发）：O2hO+O氮分子键能：939.4kJ/mol（127nm，仅限于臭氧层以上）：N2hN+N,当入射波长低于79.6nm(1391kJ/mol)时，N2将电离成N2。,.,臭氧和过氧化物的光离解臭氧分子键能：101.2kJ/mol220290nm强吸收（254nm最强吸收）290320nm少量吸收450700nm微弱吸收离解反应：O3hO2+O烷基过氧化物在300700nm范围有微弱吸收，光离解反应：ROORhRO+RO,.,NO2的光离解键能：300.5kJ/mol（300400nm吸光），光离解反应：NO2hNO+OO2+OMO3M,NO2是污染大气中最重要的吸光物质,在低层大气中可以吸收全部来自太阳的紫外光和部分可见光。,O3的唯一人为来源,.,OXIDIZINGNATUREOFTHEATMOSPHERE,EarthsatmosphereisoxidizingduetopresenceofO2SO2-SO42-;CH4-CO;CO-CO2;NO2-HNO3RadicalsareoxidizingagentsintheatmosphereOHisthecleansingagentoftheatmosphereKeytounderstandingatmosphericoxidantchemistryUnderstandradicalcyclingbutradicalcycleisintimatelyconnectedtooxidantchemistryofothertracecompoundsincludingO3StartwithO3O3isimportantfromchemical,climate,andhealthperspectives,.,ATMOSPHERICO3ABRIEFHISTORY,1840:Ozonediscoveredin1840byC.F.Schnbeinthoughtitwasmadeupofoxygenandhydrogen1848:Systematicmeasurementattemptscuriousity,growinginterestinenv.,healtheffects,economyofnature1861:OdlingsuggestedthatozonewasO31930:ChemicalmechanismforO3layerpostulated1952:O3identifiedascomponentofchemicalsmog,ChristianFrederichSchnbein,.,OZONEANDHEALTH,90%ofO3isinthestratosphere;O3layerwithmax9ppmAbsorptionof=200-320nm(UV-BandUV-C)bystrat.O3,Source:StratosphericOzone,NASA/GSFC,.,OZONEANDSTRATOSPHERICTEMPERATURE,LocalheatingofthestratosphereduetoUVabsorptionbyO3TroposphericO3isalsoanimportantgreenhousegas,Source:StratosphericOzone,NASA/GSFC,Source:EnvironmentalScience,Cunningham,P.W.andB.W.Saigo,2001,.,OZONEANDATMOSPHERICCHEMISTRY,O3istheprimarysourceoftroposphericOHOHisatmosphericdetergent,.,LATITUDINAL&TEMPORALVARIATIONOFTOTALO3,TotalO3inrangeof300-400DUPatternsduetostratosphericcirculationLowtotalO3athighsouthernlatinsouthernspringduetoozonehole,Dobsonunits1DU=2.69x1016moleculesO3cm-2,Source:StratosphericOzone,NASA/GSFC,.,STRATOSPHERICO3CHEMISTRY,.,THECHAPMANMECHANISMFORSTRATOSPHERICO3,CyclingbetweenO,O2,andO3,Source:StratosphericOzone,NASA/GSFC,.,MISSINGCHEMISTRYINCHAPMANMECHANISM,GlobalO3productionrate=5timesdestructionrateImbalancesuggestsoverest.ofprodn.orunderest.oflossO3productionwellconstrainedbygoodspectroscopicdataImpliesmissingchemicalsinksforOxReactionsofradicalswithOand/orO3Butradicalswillalsobeconsumedbyreaction,measured,calculated,Source:StratosphericOzone,NASA/GSFC,.,CATALYTICOXDESTRUCTIONINTHESTRATOSPHERE,RadicalchainreactionsX+O3XO+O2XO+OX+O2Net:O+O32O2XinthestratosphereH,OH,NO,ClHOx,NOx,andClxHOx=H+OH+HO2NOx=NO+NO2Clx=Cl+ClOReservoirstieupactiveradicalse.g.ClO+NO2ClONO2,StratosphericClxprecursors,Source:StratosphericOzone,NASA/GSFC,.,ColumnO3(DU),ANTARCTICTOTALOZONEDECREASE,DepletionoftotalcolumnO3startinginmid-tolate-70sduringSHspringGas-phasechemistrypredictedsmallerdecreases¬overAntarctica,O3,Source:StratosphericOzone,NASA/GSFC,Source:Farmannetal.,Nature,v.315,May1985,.,ALTITUDEDEPENDENCEOFANTARCTICO3DECREASE,Strongdepletionbetween12and20kmGasphasechemistrypredicteddecreasenear40km,Source:StratosphericOzone,NASA/GSFC,.,TEMPORALDEPENDENCEOFANTARCTICO3DECREASE,DepletionbeginsaroundSep1.&minimumisreachedaroundOct1,Source:NOAA/CMDL,.,REACTIONSONPOLARSTRATOSPHERICCLOUDS,ConversionofinactiveCltoactiveClandremovalofNOx,Source:StratosphericOzone,NASA/GSFC,.,ROLEOFMETEOROLOGY,Lowtemps.PSCformationreleaseofactiveClandremovalofNOxStrongvortexIsolatesairfrommid-lats.preventshighO3airinflux,Figureshowsstrongpolarvortex旋涡(asshownbysizeofwindvectors)&lowpolartemps.(asshownbycolors)atvariousaltitudesinthesouthernhemispherestratosphere,Source:StratosphericOzone,NASA/GSFC,.,NORTHERNvsSOUTHERNHEMISPHEREO3TRENDS,Vortexnotasstrongandtemps.notaslowinNH,Source:StratosphericOzone,NASA/GSFC,.,PROJECTEDCHANGESINSTRATOSPHERICClx,MontrealProtocolandsubsequentamendmentswillhavesignifcantimpactsonprojectedClxloadingofstratosphere,(ppb),Source:StratosphericOzone,NASA/GSFC,.,WMO1998ScientificAssessmentofOzoneDepletionOzonedepletionin2050wouldbeatleast50%atmidlatitudesintheNorthernHemisphereand70%atmidlatitudesintheSouthernHemisphere,about10timeslargerthantodaySurfaceUV-Bradiationin2050wouldatleastdoubleatmidlatitudesintheNorthernHemisphereandquadrupleatmidlatitudesintheSouthernHemispherecomparedwithanunperturbedatmosphere.Thiscomparestothecurrentincreasesof5%and8%intheNorthernandSouthernHemispheres,respectively,since1980,ESTIMATEDIMPACTSOFClxCONTROLS,.,TROPOSPHERICO3CHEMISTRY,Source:EPA,.,TroposphericO3generallylessthan100ppbawayfromurbanareas,TROPOSPHERICO3,Source:Wangetal.,1998,.,O3chemicalproductioninstratospherefollowedbydownwardtransporttothetroposphere,O2,O(3P),Solarradiation,(CO2+O2ChemicalO3destructionCouplingbetweenOHandHO2(HOx)viaO3,COOXIDATIONCYCLEO3DESTRUCTION,CO2,O3,2O2,.,O3+hvO2+O(1D)2.O(1D)+MO+M3.H2O+O(1D)2OH4.RH+OHRO2+H2O5.RO2+NORO+NO26.RO+O2RCHO+HO27.HO2+NOOH+NO28.HO2+HO2H2O2+O29.OH+NO2+MHNO3+M,SCHEMATICOFHYDROCARBONCHEMISRY,O2,Netrxns1-7:RH+4O2RCHO+2O3+H2O,Source:IntroductiontoAtmosphericChemistry,Jacob,D.J.,1999,canproducemoreO3,.,ROLEOFNOXINO3CHEMICALPRODUCTION,CyclingofHOx(OH+HO2)byNOxvs.radicalterminationreactionsToolittleNOx:Radicaltermination(e.g.HO2+HO2)ratherthanradicalcycling(e.g.HO2+NO)leadingtoO3chemicaldestructionToomuchNOx:Radicalterminationbyalternateroute(e.g.OH+NO2)aswellasshort-termO3destructionbyNO+O3-NO2=implicationsforO3peakdownwindofstrongNOXsources,.,NOx-ANDHYDROCARBON-LIMITEDREGIMES,NOxlimited,Hydrocarbonlimited,Complications:NaturalemissionsofhydrocarbonsareimportantTransportofpollutantsintoandoutofregion,Source:IntroductiontoAtmosphericChemistry,Jacob,D.J.,1999,.,Questions:NOxorHCemissioncontrolsorcombinationDegreeofemissioncontrolsUncertaintiesReliabilityofemissioninventories清单(e.g.naturalhydrocarboninventories)Reliabilityofairqualitymodels(e.g.localvstransportedNOx/HC/O3),ISSUESINO3POLLUTIONCONTROL,.,1998MEASUREDSURFACEOZONECONCENTRATIONS,2ndhighestdailymax1-hr(ppb),50ppbvPotentiallylargeimpactinfutureyears:Year2100IPCCscenariofromHARVARDmodelgives50%ofpopulationinareaswithmax.monthly-meanO385ppbv,and50%ofcropsinareaswithgrowingseasonmeanO370ppbv,.,ATMOSPHERICAEROSOLSANDACIDRAIN,Combustiongenerated,Aerosolsandacidraincaneffectnatural&managedecosystems,.,硝酸和烷基硝酸酯的光离解RO-NO2键能：199.4kJ/mol（吸收120335nm）：硝酸：HNO3（HONO2）hHO+NO2烷基硝酸酯：RONO2hRO+NO2,对于300nm以上的光的吸收速度很小,.,亚硝酸和烷基亚硝酸酯的光离解HO-NO键能：201.1kJ/molH-ONO键能：324.0kJ/molHNO2对200400nm的光有吸收，发生光离解：HONOhHO+NOHNO2hH+NO2RONOhNO+RO,仅次于NO2光离解的最重要的光离解初级反应。,.,醛的光离解（CH2O和CH3CHO）H-CHO键能：365.5kJ/mol（吸收240360nm），光离解反应：甲醛H2COhH+HCOH2COhH2+CO乙醛CH3CHOhH+CH3COCH3CHOhCH3+HCOCH3CHOhCH4+CO,.,卤代烃的光离解卤代甲烷的光解：CH3XhCH3+X式中X代表Cl,Br,I,F。,键强顺序：CH3FCH3HCH3ClCH3BrCH3I,.,SO2的光吸收SO2键能：545.1kJ/mol（200nm），吸收三个波段：340400nm（极弱）240330nm（较强）280240nm（很强）SO2不能光离解，只能形成激发态分子：SO2hSO2,活性粒子：HO、RO、RO2、H、HCO、CH3、CH3CO等自由基被称为大气中的“活性粒子”，它们性质特别活泼，能够引发一系列反应，参与很多的污染物的化学转化过程，导致生成各种各样的二次污染物。,.,三、大气中重要自由基的来源,键的断裂与自由基（freeradical）的形成：不对称裂解形成正、负离子；对称裂解形成自由基。自由基具有强烈的夺取电子倾向和结合力。自由基具有很强的氧化能力和化学活性。,.,1、HO的来源,HO基的形成途径（1）HONOHONO（400nm）（2）H2O22HO（300nm）（3）OH2O2HO（O来自O3的光离解）（4）HO2NOHONO2（HO2来自HCHO光离解，产生的H与O2作用）,HO基的形成途径,.,大气中HO的浓度测算：用数学模拟算出大气中HO基的全球平均浓度约为7105个分子/cm3；用激光共振荧光光谱法测定HO基的浓度范围为35104个分子/cm3，浓度数值随纬度、高度及地区的不同而变化，与季节有关。,.,HO在对流层中随高度和纬度的分布,HO最高浓度出现在热带（温度高，太阳辐射强）；在两半球间分布不对称。,.,2、HO2的来源,由CH2O、CH3ONO以及H2O2形成：（1）HCHOHHCO（313nm）HO2HO2HCOO2HO2CO（2）CH3ONONOCH3O（300400nm）CH3OO2HO2CH2O（3）H2O22HO（370nm）2HO2H2O22HO22H2O2HO2CO2CO22H2HO22HO2,.,3、CH3、CH3O