环境化学4名师优质课获奖市赛课一等奖课件.ppt

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,本幻灯片资料仅供参考，不能作为科学依据，如有不当之处，请参考专业资料。,二、光化学photochemistry反应基础,1、光子,photon,能量,爱因斯坦-普朗克（Einstein-Planck）关系式：,=,h,=hc/,(J),E,=N,0,h=,N,0,hc/,(KJ/mol),式中,h,Planck常数，6.621034J.s；,光子频率，Hz；,c,光速，2.99810,10,cm/s；,光子波长，cm；,N,0,阿佛加德罗常数，6.0210,23,/mol。,第1页,伴随波长增加，光子能量减小。,波长（,nm,）,能量（,kJ/mol,）,光区域,200,300,597.2,398.4,紫外光,400,700,298.9,170.8,可见光,5000,59.7,23.9,红外线,不一样波长光能量,高能光，能引发光化学反应（光离解）,低能光，不能引发光化学反应,例1,计算波长为200nm紫外光能量。,普通化学鍵键能大于167.44KJ/mol,第2页,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反应。,初级过程：,引发：A(分子),h,A*(激发态分子),次级过程：,离解：A*,C+,与其它分子反应生成新物种：A*+B,D+,与惰性,inertia,分子碰撞失活(返回基态)：A*+M,A+M,发光而失活(返回基态)：A*,A,h,第3页,3、大气中主要吸光物质光离解,吸光物质,高层大气：N,2,、O,2,、O,3,（290nm）,低层大气：NO,2,、SO,2,等,第4页,氧和氮光离解,氧分子,键能：493.8kJ/mol（240nm以下紫外光可引发）：,O,2,h,O+O,氮分子,键能：939.4kJ/mol（127nm，仅限于臭氧层以上）：,N,2,h,N+N,当入射波长低于79.6nm(1391kJ/mol)时，N,2,将电离成N,2,。,第5页,臭氧和过氧化物光离解,臭氧,分子键能：101.2kJ/mol,220290nm 强吸收（254nm最强吸收）,290320nm 少许吸收,450700nm 微弱吸收,离解反应：,O,3,h,O,2,+O,烷基过氧化物,在300700nm范围有微弱吸收，光离解反应：,ROOR,h,RO+RO,第6页,NO,2,光离解,键能：300.5 kJ/mol（300400nm吸光），光离解反应：,NO,2,h,NO+O,O,2,+OM,O,3,M,NO,2,是污染大气中最主要吸光物质,在低层大气中能够吸收全部来自太阳紫外光和部分可见光。,O,3,唯一人为起源,第7页,OXIDIZING NATURE OF THE ATMOSPHERE,Earths atmosphere is,oxidizing,due to presence of O,2,SO,2,-SO,4,2-,;CH,4,-CO;CO-CO,2,;NO,2,-HNO,3,Radicals,are oxidizing agents in the atmosphere,OH is the cleansing agent of the atmosphere,Key to understanding atmospheric oxidant chemistry,Understand radical cycling but radical cycle is intimately connected to oxidant chemistry of other trace compounds including O,3,Start with O,3,O,3,is important from chemical,climate,and health perspectives,第8页,ATMOSPHERIC O,3,A BRIEF HISTORY,1840:,Ozone discovered in 1840 by C.F.Sch,nbein,thought it was made up of oxygen and hydrogen,1848:,Systematic measurement attempts curiousity,growing,interest in env.,health effects,economy of nature,1861:,Odling suggested that ozone was O,3,1930:,Chemical mechanism for O,3,layer postulated,1952:,O,3,identified as component of chemical smog,Christian Frederich Sch,nbein,第9页,OZONE AND HEALTH,90%of O,3,is in the stratosphere;O,3,layer with max 9 ppm,Absorption of,=200-320 nm,(UV-B and UV-C)by strat.O,3,Source:Stratospheric Ozone,NASA/GSFC,第10页,OZONE AND STRATOSPHERIC TEMPERATURE,Local heating of the stratosphere due to UV absorption by O,3,Tropospheric O,3,is also an important greenhouse gas,Source:Stratospheric Ozone,NASA/GSFC,Source:Environmental Science,Cunningham,P.W.and B.W.Saigo,第11页,O,3,O(,1,D),O(,3,P),2OH,Solar radiation,wavelength 290-320 nm,H,2,O,O,2,N,2,O,2,OZONE AND ATMOSPHERIC CHEMISTRY,O,3,is the primary source of tropospheric OH,OH is atmospheric detergent,第12页,LATITUDINAL&TEMPORAL VARIATION OF TOTAL O,3,Total O,3,in range of 300-400 DU,Patterns due to stratospheric circulation,Low total O,3,at high southern lat in southern spring,due to ozone hole,Dobson units,1 DU=2.69 x 10,16,molecules O,3,cm,-2,Source:Stratospheric Ozone,NASA/GSFC,第13页,STRATOSPHERIC O,3,CHEMISTRY,第14页,THE CHAPMAN MECHANISM FOR STRATOSPHERIC O,3,Cycling between O,O,2,and O,3,Source:Stratospheric Ozone,NASA/GSFC,第15页,MISSING CHEMISTRY IN CHAPMAN MECHANISM,Global O,3,production rate=5 times destruction rate,Imbalance suggests overest.of prodn.or underest.of loss,O,3,production well constrained by good spectroscopic data,Implies missing chemical sinks for O,x,Reactions of radicals with O and/or O,3,But radicals will also be consumed by reaction,measured,calculated,Source:Stratospheric Ozone,NASA/GSFC,第16页,CATALYTIC O,X,DESTRUCTION IN THE STRATOSPHERE,Radical chain reactions,X+O,3,XO+O,2,XO+O X+O,2,Net:O+O,3,2O,2,X in the stratosphere,H,OH,NO,Cl,HO,x,NO,x,and Cl,x,HO,x,=H+OH+HO,2,NO,x,=NO+NO,2,Cl,x,=Cl+ClO,Reservoirs tie up active radicals,e.g.,ClO+NO,2,ClONO,2,Stratospheric Cl,x,precursors,Source:Stratospheric Ozone,NASA/GSFC,第17页,Column O,3,(DU),ANTARCTIC TOTAL OZONE DECREASE,Depletion of total column O,3,starting in mid-to late-70s,during SH spring,Gas-phase chemistry predicted smaller decreases&not,over Antarctica,O,3,Source:Stratospheric Ozone,NASA/GSFC,Source:Farmann et al.,Nature,v.315,May 1985,第18页,ALTITUDE DEPENDENCE OF ANTARCTIC O,3,DECREASE,Strong depletion between 12 and 20 km,Gas phase chemistry predicted decrease near 40 km,Source:Stratospheric Ozone,NASA/GSFC,第19页,TEMPORAL DEPENDENCE OF ANTARCTIC O,3,DECREASE,Depletion begins around Sep 1.&minimum is reached around,Oct 1,Source:NOAA/CMDL,第20页,REACTIONS ON POLAR STRATOSPHERIC CLOUDS,Conversion of inactive Cl to active Cl and removal of NO,x,Source:Stratospheric Ozone,NASA/GSFC,第21页,ROLE OF METEOROLOGY,Low temps.,PSC formation,release of active Cl,and removal of NO,x,Strong vortex,Isolates air from mid-lats.,prevents high O,3,air influx,Figure shows strong polar vortex,旋涡,(as shown by size of wind,vectors)&low polar temps.(as shown by colors)at various,altitudes in the southern hemisphere stratosphere,Source:Stratospheric Ozone,NASA/GSFC,第22页,NORTHERN vs SOUTHERN HEMISPHERE O,3,TRENDS,Vortex not as strong and temps.not as low in NH,Source:Stratospheric Ozone,NASA/GSFC,第23页,PROJECTED CHANGES IN STRATOSPHERIC Cl,x,Montreal Protocol and subsequent amendments will have,signifcant impacts on projected Cl,x,loading of stratosphere,(ppb),Source:Stratospheric Ozone,NASA/GSFC,第24页,WMO 1998 Scientific Assessment of Ozone Depletion,Ozone depletion in 2050 would be at least 50%at,midlatitudes in the Northern Hemisphere and 70%,at midlatitudes in the Southern Hemisphere,about,10 times larger than today,Surface UV-B radiation in 2050 would at least double,at midlatitudes in the Northern Hemisphere and quadruple,at midlatitudes in the Southern Hemisphere compared with,an unperturbed atmosphere.This compares to the current,increases of 5%and 8%in the Northern and Southern,Hemispheres,respectively,since 1980,ESTIMATED IMPACTS OF Cl,x,CONTROLS,第25页,TROPOSPHERIC O,3,CHEMISTRY,Source:EPA,第26页,Tropospheric O,3,generally less than 100 ppb away,from urban areas,TROPOSPHERIC O,3,Source:Wang et al.,1998,第27页,O,3,chemical production in stratosphere followed,by downward transport to the troposphere,O,2,O(,3,P),Solar radiation,(240 nm),O,3,O2,Solar radiation(CO,2,+O,3,Catalytic role of NO,x,(NO+NO,2,)in recycling HO,2,to OH,Coupling between OH and HO,2,(HO,x,)via NO,CO OXIDATION CYCLE O,3,PRODUCTION,CO,2,O,3,第29页,NO or,O,3,OH,HO,2,CO,O,2,Net:CO+O,3,-CO,2,+O,2,Chemical O,3,destruction,Coupling between OH and HO,2,(HO,x,)via O,3,CO OXIDATION CYCLE O,3,DESTRUCTION,CO,2,O,3,2O,2,第30页,O,3,+hv,O,2,+O(,1,D),2.O(,1,D)+M,O+M,3.H,2,O+O(,1,D)2OH,4.RH+OH RO,2,+H,2,O,5.RO,2,+NO RO+NO,2,6.RO+O,2,RCHO+HO,2,7.HO,2,+NO OH+NO,2,8.HO,2,+HO,2,H,2,O,2,+O,2,9.OH+NO,2,+M HNO,3,+M,SCHEMATIC OF HYDROCARBON CHEMISRY,O,2,Net rxns 1-7:,RH+4O,2,RCHO+2O,3,+H,2,O,Source:Introduction to Atmospheric Chemistry,Jacob,D.J.,1999,can produce more O,3,第31页,ROLE OF NO,X,IN O,3,CHEMICAL PRODUCTION,Cycling of HO,x,(OH+HO,2,)by NO,x,vs.radical termination reactions,Too little NO,x,:Radical termination(e.g.HO,2,+HO,2,)rather than radical cycling(e.g.HO,2,+NO)leading to O,3,chemical destruction,Too much NO,x,:Radical termination by alternate route(e.g.OH+NO,2,)as well as short-term O,3,destruction by NO+O,3,-NO,2,=implications for O,3,peak downwind of strong NO,X,sources,第32页,NO,x,-AND HYDROCARBON-LIMITED REGIMES,NO,x,limited,Hydrocarbon limited,Complications:,Natural emissions of hydrocarbons are important,Transport of pollutants into and out of region,Source:Introduction to Atmospheric Chemistry,Jacob,D.J.,1999,第33页,Questions:,NO,x,or HC emission controls or combination,Degree of emission controls,Uncertainties,Reliability of emission inventories,清单,(e.g.natural hydrocarbon inventories),Reliability of air quality models(e.g.local vs transported NO,x,/HC/O,3,),ISSUES IN O,3,POLLUTION CONTROL,第34页,1998 MEASURED SURFACE OZONE CONCENTRATIONS,2nd highest daily max 1-hr(ppb),65,65-124,125-164,65-84,205-404,Source:1998 EPA National Trends Report,118,153,169,36,141,155,167,165-204,4th highest daily max 8-hr(ppb),50 ppbv,and 10-20%of crops in areas with growing-season mean O3 50 ppbv,Potentially large impact in future years:Year 2100 IPCC scenario from HARVARD model gives,50%of population in areas with max.monthly-mean O3 85 ppbv,and 50%of crops in areas,with growing season mean O3 70 ppbv,第36页,ATMOSPHERIC AEROSOLS AND ACID RAIN,Combustion,generated,Aerosols and acid rain can effect natural&managed ecosystems,第37页,硝酸和烷基硝酸酯光离解,RO-NO,2,键能：199.4kJ/mol（吸收120335nm）：,硝酸：,HNO,3,（HONO,2,）,h,HO+NO,2,烷基硝酸酯：,RONO,2,h,RO+NO,2,对于300nm以上光吸收速度很小,第38页,亚硝酸和烷基亚硝酸酯光离解,HO-NO键能：201.1kJ/mol,H-ONO键能：324.0kJ/mol,HNO,2,对200400nm光有吸收，发生光离解：,HONO,h,HO+NO,HNO,2,h,H+NO,2,RONO,h,NO+RO,仅次于NO,2,光离解最主要光离解初级反应。,第39页,醛光离解,（,CH,2,O和CH,3,CHO,）,H-CHO键能：365.5kJ/mol（吸收240360nm），光离解反应：,甲醛H,2,CO,h,H+HCO,H,2,CO,h,H,2,+CO,乙醛CH,3,CHO,h,H+CH,3,CO,CH,3,CHO,h,CH,3,+HCO,CH3CHO,h,CH,4,+CO,第40页,卤代烃光离解,卤代甲烷光解：,CH,3,X,h,CH,3,+X,式中X代表,Cl,Br,I,F,。,键强次序：CH,3,FCH,3,HCH,3,ClCH,3,BrCH,3,I,第41页,SO,2,光吸收,SO,2,键能：545.1 kJ/mol（200nm），吸收三个波段：,340400nm（极弱）,240330nm（较强）,280240nm（很强）,SO,2,不能光离解，只能形成激发态分子：,SO,2,h,SO,2,活性粒子：,HO、RO、RO,2,、H、HCO、CH,3,、CH,3,CO等自由基被称为大气中“活性粒子”，它们性质尤其活泼，能够引发一系列反应，参加很多污染物化学转化过程，造成生成各种各样二次污染物。,第42页,三、大气中主要自由基起源,键断裂与自由基（free radical）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,含有强烈夺取电子倾向和结协力。,自由基,含有很强氧化能力和化学活性。,第43页,1、HO起源,HO,H,2,O,O+O,2,O,3,315nm,HNO,2,400nm,H,2,O,2,370nm,NO,HO,2,O,2,H+HCO,HCHO,313nm,HO基形成路径,（1）HONO,HONO,（400nm）,（2）H,2,O,2,2HO,（300nm）,（3）OH,2,O,2HO,（O来自O,3,光离解）,（4）HO,2,NO,HONO,2,（HO,2,来自HCHO光离解，,产生H与O,2,作用）,HO基,形成路径,第44页,大气中HO浓度测算,：,用数学模拟算出大气中HO基全球平均浓度约为710,5,个分子/cm,3,；,用激光共振荧光光谱法测定HO基浓度范围为3510,4,个分子/cm,3,，,浓度数值随纬度、高度及地域不一样而改变，与季节相关。,第45页,HO在对流层中随高度和纬度分布,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。,HO和HO,2,自由基日改变曲线,光化学生成产率白天高于夜间，峰值出现在阳光最强时间。,夏季高于冬季。,第46页,2、HO,2,起源,由CH,2,O、CH,3,ONO以及H,2,O,2,形成：,（1）HCHO,H,HCO,（313nm）,H,O,2,HO,2,HCO,O,2,HO,2,CO,（2）CH,3,ONO,NO,CH,3,O,（300,400nm）,CH,3,O,O,2,HO,2,CH,2,O,（3）H,2,O,2,2,HO,（370nm）,2,HO,2H,2,O,2,2,HO,2,2H,2,O,2,HO,2CO,2CO,2,2,H,2,H,O,2,2,HO,2,第47页,3、CH,3,、CH,3,O、RO,2,起源,CH,3,：,CH,3,CHO,h,CH,3,+HCO,CH,3,COCH,3,h,CH,3,+CH,3,CO,CH,3,O,：,CH,3,ONO,h,CH,3,O +NO,CH,3,O,2,和RO,2,：,CH,3,+O,2,CH,3,O,2,R O,2,RO,2,第48页,四、氮氧化物转化transform,1、NOx光化学反应,NO(nitric oxide)、NO,2,(nitrogen dioxide)与O,3,(ozone)之间存在着化学循环chemical cycling是大气光化学过程基础。,当阳光照射到含有NO和NO,2,空气时，反应：,NO,2,h,NO+O,O,2,+OM,O,3,M,O,3,NO,NO,2,+O,2,第49页,2、,NOx气相转化,N,2,O,光解,photolysis：N,2,O,h,N,2,+O,去除,elimination：N,2,O O,N,2,+O,2,N,2,O O,NO+NO,第50页,2、,NOx气相转化,NO,NO,O,3,NO,2,+O,2,HO+NO,HONO,RO+NO,RONO,RO,2,+NO,RO+NO,2,HO,2,+NO,HO+NO,2,RCOO,2,+NO,RO+CO+NO,2,第51页,NO,2,HO+NO,2,HNO,3,O,3,+NO,2,NO,3,+O,2,NO,3,能够和NO反应或光解作用再生成NO,2,，或者再与NO,2,深入反应生成N,2,O,5,。,N,2,O,5,与H,2,O作用形成HNO,3,。,PAN（过氧乙酰基硝酸酯,peroxy acetyl nitrate,）,CH,3,CO+O,2,CH,3,COO,2,CH,3,COO,2,NO,2,CH,3,COO,2,NO,2,PAN含有热不稳定性，遇热会分解回到CH,3,COO,2,和NO,2,。,第52页,3、,NOx液相转化,NOx可溶于大气水中，组成一个液相平衡体系。,NOx液相平衡,NO(g),NO(aq),aquatic,NO,2,(g),NO,2,(aq),2NO,2,(aq),N,2,O,4,NO(aq)+NO,2,(aq),N,2,O,8,(aq),对于NO-NO,2,体系，存在液相平衡：,2 NO,2,(g)+H,2,O,2H,+,+NO,2,-,+NO,3,-,NO(g)+NO,2,(g)+H,2,O,2H,+,+2NO,2,-,第53页,NH,3,和HNO,3,液相平衡,aquatic balance,NH,3,(g)+H,2,O,NH,3,H,2,O,NH,3,H,2,O,NH,4,+,+OH,-,HNO,3,(g)+H,2,O,HNO,3,H,2,O,HNO,3,H,2,O,H,+,+NO,3,-,第54页,