13EnergyandEnvironment.docx

13EnergyandEnvironment.docx

《13EnergyandEnvironment.docx》由会员分享，可在线阅读，更多相关《13EnergyandEnvironment.docx（15页珍藏版）》请在冰豆网上搜索。

13EnergyandEnvironment

Chapter13EnergyandEnvironment

13.1EnergyandEnvironment

Theconversionofenergyfromoneformtoanotheroftenaffectstheenvironmentandtheairwebreatheinmanyways,andthusthestudyofenergyisnotcompletewithoutconsideringitsimpactontheenvironment.Fossilfuelssuchascoal,oilandnaturalgashavebeenpoweringtheindustrialdevelopmentandtheamenitiesofmodernlifethatweenjoysince1700s,butthishasnotbeenwithoutanyundesirablesideeffects.Fromthesoilwefarmandthewaterwedrinktotheairwebreathe,theenvironmenthasbeenpayingaheavytollforit.Pollutantsemittedduringthecombustionoffossilfuelsareresponsibleforsmog,acidrainandglobalwarmingandclimatechange.Theenvironmentalpollutionhasreachedsuchhighlevelsthatitbecameaseriousthreattovegetation,wildlife,andhumanhealth.Airpollutionhasbeenthecauseofnumeroushealthproblemsincludingasthmaandcancer.Itisestimatedthatover60,000peopleintheUnitedStatesalonedieeachyearduetoheartandlungdiseasesrelatedtoairpollution.

Hundredsofelementsandcompoundssuchasbenzeneandformaldehydeareknowntobeemittedduringthecombustionofcoal,oil,naturalgas,andwoodinelectricpowerplants,enginesofvehicles,furnacesandevenfireplaces.Somecompoundsareaddedtoliquidfuelsforvariousreasons（suchasMTBEtoraisetheoctanenumberofthefuelandalsotooxygenatethefuelinwintermonthstoreduceurbansmog）.Thelargestsourceofairpollutionisthemotorvehicles,andthepollutantsreleasedbythevehiclesareusuallygroupedashydrocarbons（HC）,nitrogenoxides（NOx）,andcarbonmonoxide（CO）.TheHCemissionsarealargecomponentofvolatileorganiccompounds（VOC）emissions,andthetwotermsaregenerallyusedinterchangeablyformotorvehicleemissions.AsignificantportionoftheVOCorHCemissionsarecausedbytheevaporationoffuelsduringrefuelingorspillageduringspitbackorbyevaporationfromgastankswithfaultycapsthatdonotclosetightly.Thesolvents,propellants,andhouseholdcleaningproductsthatcontainbenzene,butane,orotherHCproductsarealsosignificantsourcesofHCemissions.

Theincreaseofenvironmentalpollutionatalarmingratesandtherisingawarenessofitsdangersmadeitnecessarytocontrolitbylegislationandinternationaltreaties.IntheUnitedStates,theCleanAirActof1970（whosepassagewasaidedbythe14-daysmogalertinWashingtonthatyear）setlimitsonpollutantsemittedbylargeplantsandvehicles.Theseearlystandardsfocusedonemissionsofhydrocarbons,nitrogenoxides,andcarbonmonoxide.ThenewcarswererequiredtohavecatalyticconvertersintheirexhaustsystemstoreduceHCandCOemissions.Asasidebenefit,theremovalofleadfromgasolinetopermittheuseofcatalyticconvertersledtoasignificantreductionintoxicleademission.

EmissionlimitsforHC,NOxandCOfromcarshavebeendecliningsteadilysince1970.TheCleanAirActof1990madetherequirementsonemissionseventougher,primarilyforozone,CO,nitrogendioxide,andparticulatematter（PM）.Asaresult,today’sindustrialfacilitiesandvehiclesemitafractionofthepollutantstheyusedtoemitafewdecadesago.TheHCemissionsofcars,forexample,decreasedfromabout8gpm（gramspermile）in1970to0.4gpmin1980andabout0.1gpmin1999.Thisisasignificantreductionsincemanyofthegaseoustoxicsfrommotorvehiclesandliquidfuelsarehydrocarbons.

Childrenaremostsusceptibletothedamagescausedbyairpollutantssincetheirorgansarestilldeveloping.Theyarealsoexposedtomorepollutionsincetheyaremoreactive,andthustheybreathefaster.Peoplewithheartandlungproblems,especiallythosewithasthma,aremostaffectedbyairpollutants.Thisbecomesapparentwhentheairpollutionlevelsintheirneighborhoodsrisetohighlevels.

13.1.1OzoneandSmog

IfyouliveinametropolitanareasuchasLosAngeles,youareprobablyfamiliarwithurbansmog—thedarkyelloworbrownhazethatbuildsupinalargestagnantairmassandhangsoverpopulatedareasoncalmhotsummerdays.Smogismadeupmostlyofground-levelozone（O3）,butitalsocontainsnumerousotherchemicals,includingcarbonmonoxide（CO）,particulatemattersuchassootanddust,volatileorganiccompounds（VOC）suchasbenzene,butane,andotherhydrocarbons.Theharmfulground-levelozoneshouldnotbeconfusedwiththeusefulozonelayerhighinthestratospherethatprotectstheearthfromthesun’sharmfulultravioletrays.Ozoneatgroundlevelisapollutantwithseveraladversehealtheffects.

Theprimarysourceofbothnitrogenoxidesandhydrocarbonsisthemotorvehicles.Hydrocarbonsandnitrogenoxidesreactinthepresenceofsunlightinhotcalmdaystoformground-levelozone,whichistheprimarycomponentofsmog（Fig.13.1）.Thesmogformationusuallypeaksinlateafternoonswhenthetemperaturesarehighestandthereisplentyofsunlight.Althoughground-levelsmogandozoneforminurbanareaswithheavytrafficorindustry,theprevailingwindscantransportthemseveralhundredmilestoothercities.Thisshowsthatpollutionknowsofnoboundaries,anditisaglobalproblem.

Figure13.1Groundlevelozone,whichistheprimarycomponentofsmogformswhenHCandNOxreactinthepresenceofsunlightinhotcalmdays

Ozoneirritateseyesanddamagestheairsacsinthelungswhereoxygenandcarbondioxideareexchanged,causingeventualhardeningofthissoftandspongytissue.Italsocausesshortnessofbreath,wheezing,fatigue,headaches,andnausea,andaggravatesrespiratoryproblemssuchasasthma.Everyexposuretoozonedoesalittledamagetothelungs,justlikecigarettesmoke,eventuallyreducingtheindividual’slungcapacity.Stayingindoorsandminimizingphysicalactivityduringheavysmogwillminimizedamage.Ozonealsoharmsvegetationbydamagingleaftissues.Toimprovetheairqualityinareaswiththeworstozoneproblems,reformulatedgasoline（RFG）thatcontainsatleast2percentoxygenwasintroduced.TheuseofRFGhasresultedinsignificantreductionintheemissionofozoneandotherpollutants,anditsuseismandatoryinmanysmog-proneareas.

Theotherseriouspollutantinsmogiscarbonmonoxide,whichisacolorless,odorless,poisonousgas.Itismostlyemittedbymotorvehicles,anditcanbuildtodangerouslevelsinareaswithheavycongestedtraffic.Itdeprives剥夺thebody’sorgansfromgettingenoughoxygenbybindingwiththeredbloodcellsthatwouldotherwisecarryoxygen.Atlowlevels,carbonmonoxidedecreasestheamountofoxygensuppliedtothebrainandotherorgansandmuscles,slowsbodyreactionsandreflexes,andimpairs削弱judgment.Itposesaseriousthreattopeoplewithheartdiseasebecauseofthefragile脆弱的conditionofthecirculatorysystemandtofetuses胎儿becauseoftheoxygenneedsofthedevelopingbrain.Athighlevels,itcanbefatal,asevidencedbynumerousdeathscausedbycarsthatarewarmedupinclosedgaragesorbyexhaustgasesleakingintothecars.

Smogalsocontainssuspendedparticulatemattersuchasdustandsootemittedbyvehiclesandindustrialfacilities.Suchparticlesirritatetheeyesandthelungssincetheymaycarrycompoundssuchasacidsandmetals.

13.1.2AcidRain

Fossilfuelsaremixturesofvariouschemicals,includingsmallamountsofsulfur.Thesulfurinthefuelreactswithoxygentoformsulfurdioxide（SO2）,whichisanairpollutant.ThemainsourceofSO2istheelectricpowerplantsthatburnhigh-sulfurcoal.TheCleanAirActof1970haslimitedtheSO2emissionsseverely,whichforcedtheplantstoinstallSO2scrubbers,toswitchtolow-sulfurcoal,ortogasifythecoalandrecoverthesulfur.MotorvehiclesalsocontributetoSO2emissionssincegasolineanddieselfuelsalsocontainsmallamountsofsulfur.Volcaniceruptionsandhotspringsalsoreleasesulfuroxides（thecauseoftherotteneggsmell）.

Thesulfuroxidesandnitricoxidesreactwithwatervaporandotherchemicalshighintheatmosphereinthepresenceofsunlighttoformsulfuricandnitricacids.Theacidsformedusuallydissolveinthesuspendedwaterdropletsincloudsorfog.Theseacid-laden装满的droplets,whichcanbeasacidicaslemonjuice,arewashedfromtheairontothesoilbyrainorsnow.Thisisknownasacidrain.Thesoiliscapableofneutralizingacertainamountofacid,buttheamountsproducedbythepowerplantsusinginexpensivehigh-sulfurcoalhasexceededthiscapability,andasaresultmanylakesandriversinindustrialareassuchasNewYork,Pennsylvania,andMichiganhavebecometooacidicforfishtogrow.Forestsinthoseareasalsoexperienceaslowdeathduetoabsorbingtheacidsthroughtheirleaves,needles,androots.Evenmarblestructuresdeteriorateduetoacidrain.Themagnitudeoftheproblemwasnotrecognizeduntiltheearly1970s,andseriousmeasuresaretakensincethentoreducethesulfurdioxideemissiondrasticallybyinstallingscrubbersinplantsandbydesulfurizingcoalbeforecombustion.

13.1.3TheGreenhouseEffect:

GlobalWarmingandClimateChange

Youhaveprobablynoticedthatwhenyouleaveyourcarunderdirectsunlightonasunnyday,theinteriorofthecargetsmuchwarmerthantheairoutside,andyoumayhavewonderedwhythecaractslikeaheattrap.Thisisbecauseglassatthicknessencounteredinpracticetransmitsover90percentofradiationinthevisiblerangeandispracticallyopaque（nontransparent）toradiationinthelongerwavelengthinfrared红外线的regions.Therefore,glassallowsthesolarradiationtoenterfreelybutblockstheinfraredradiationemittedbytheinteriorsurfaces.Thiscausesariseintheinteriortem