Sources and Emissions of Air Pollutantssamples.jbpub.com/9780763780449/80449_Ch02_021_rev2.pdf ·...

21

2ND REVISE

Chapter 2

Sources and Emissions of Air Pollutants

LEArning ObjECtivES

By the end of this chapter the reader will be able to:

• distinguishthe“troposphere”fromthe“stratosphere”• define“pollutedair”inrelationtovariousscientificdisciplines• describe“anthropogenic”sourcesofairpollutantsanddistinguishthemfrom“natural”

sources• list10sourcesofindooraircontaminants• identifythreemeteorologicalfactorsthataffectthedispersalofairpollutants

ChAPtEr OutLinE

I. Introduction II. MeasurementBasics III. Unpollutedvs.PollutedAir IV. AirPollutantSourcesandTheirEmissions V. PollutantTransport VI. SummaryofMajorPointsVII. QuizandProblemsVIII. DiscussionTopicsReferencesandRecommendedReading

21

© Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION

9955

22 Chapter 2 SourCeS and emiSSionS of air pollutantS

2ND REVISE 2ND REVISE

i. intrOduCtiOn

Structure of the Earth’s Atmosphere

TheEarth,alongwithMercury,Venus,andMars,isaterrestrial(asopposedtogaseous)planetwithaper-manent atmosphere.The Earth is an oblate (slightlyflattened)spherewithameandiameterof12,700km(about8,000statutemiles).Thehighestsurfacefeature,Mt.Everest,reachesabout8.87km(5.5miles)abovesea

level.Mt.Everestisthusaminutebumpontheglobethataddsonly0.06percenttotheEarth’sdiameter.

TheEarth’satmosphereconsistsofseveraldefinedlayers(Figure 2–1).Thetroposphere,inwhichalllifeexists,andfromwhichwebreathe,reachesanaltitudeofabout7–8kmatthepolestojustover13kmattheequa-tor:themeanthicknessbeing9.1km(5.7miles).Thus,thetroposphererepresentsaverythincoverovertheEarth,barelyhigherthanMt.Everest.IftheEarthisrepresentedbyaballwithadiameterof2m,thethickness

Figure 2–1 A:Layersoftheearth’satmosphere(notdrawntoscale);B:To-scaledepictionoflayersofearth’satmosphere. Source:TheUniversityofCaliforniaAirPollutionHealthEffectsLaboratory,withkindpermission.

Troposphere

Ozonosphere Stratosphere

Chemosphere

Ionosphere

Outer space

Mesosphere

Earth

(A)

Mt. Everest

Troposphere

Chemosphere

Stratosphere

Earth’s surface

(B)


9955


II. Measurement Basics 23

ofthetropospherewouldbeabout1.3mm(Figure 2–1).Themainpointisthatsurfaceairpollutantsarereleasedintoathinatmosphericskin.

GravitationalattractionbindstheatmospheretotheEarth.Theoutermosttracesoftheatmospherereachtoover100km(60miles)abovethesurface.Theprotec-tiveozonelayerisabovethetroposphereatavariablealtitudeofabout20to30km.

vertical Mixing and inversions

Fromourknowledgeofthermodynamicsandhotairballoonobservations,weknowthatheatingtheaircausesittoexpandandrise.Becausethetemperatureoftheairinthetropospherenormallydecreaseswithincreasingaltitude,warmersurfaceairrisesverticallyuntilitcoolssufficiently.Thisverticalairmovementandsubsequentmixingdilutesaircontaminantsgeneratednearthesur-face,thuspreventingtheiraccumulationintheairwenormallybreathe.However,thesituationischangedbyair temperature inversions,inwhichverticalairmove-mentisimpeded.Inversionsarecharacterizedbylocalparcelsofwarmairovercoolerair,whichpreventsthenormalverticalmixing.InversionscantrapairpollutantsveryclosetotheEarth’ssurface.Inversionsmaybelow,lessthan100mhigh,insomecases.Insuchcases,clearairmaybeseenaboveasharplydefinedsmoggyyellow-brownairlayerthatextendsdowntothesurface.

Inversionsarecausedbymanyphenomena,including(1)movementofawarmfrontintoaregion;(2)solarheatingoftheairaboveashadedvalley;(3)down-wardflowofcoldmountainairintoawarmvalley;and(4)nighttimecoolingof theEarth’s surfaceby theradiationofsurfaceheattospace.Severaltypesofaircontaminants(e.g.,blackcarbonparticles)absorbsolarenergyandheatthesurroundingair,thusitisalsopos-siblethatthetrappingofsolarheatintheupperlayersofaheavilypollutedairmasscanproduceorsustainanairinversion(i.e.,asmog inversion).Whenalow-levelinversioniscoupledwithstagnantwindsandheavylocalemissionsofaircontaminants,theconditionsarerightforanairpollutionepisode.Themajorhistoricalairpollutionepisodesalloccurredduringstagnantinversionsinregionsthathadsignificantsourcesofcombustion-relatedairpollutants(seeChapter1).AlthoughlocaldifferencesinairtemperatureandtheEarth’srotationnormallydrivewindsthattransportanddiluteairpol-lutants,airstagnationandlowwind-speedconditionsarecommoninmanyregions.

tropospheric vs. Stratospheric Pollutant Effects

Justabovethetroposphere,thestratospherereachestoanaltitudeofabout50km(30miles).Theboundarybetweenthetroposphereandthestratosphereiscalledthetropopause.Abovethetropopausethetemperaturerises,creatinganaturalglobalinversionthattrapspol-lutantsinthetroposphere.Largemeteorologicevents,suchasmajorstorms,volcaniceruptions,andnuclearbomb detonations, can penetrate the tropopause andlocallymixtroposphericandstratosphericair.Also,thetropopause does not represent an absolute barrier togaseousmoleculesthatrisethroughit,whichisafactorin the stratosphericozone depletion caused from theriseofchlorofluorocarbons(CFCs)andotherreactivesubstancesfromthetroposphere.

Pollutantsinthetropospherecanhavedirect effectsonlivingthingsandphysicalobjectsonthesurfaceoftheEarth.Thephysicalandchemicalpropertiesofthepollutants,thetimeofcontact,andotherfactorswilldeterminethetypesandmagnitudesofthesedirecteffects.Incontrast,pollutantsinthestratospheredonotusuallycontactthesurfaceorinteractwithlife,buttheycanproduce indirect effects.These indirecteffects relateprimarilytoabsorptionandscatteringofsolarradiation(visiblelight,infrared,andultravioletrays)andcosmicionizingradiation.Thestratosphereprovidesimportantprotectionforlifebyshieldingthesurfacefromsuchdamagingradiations.ItalsoinfluencesandstabilizesthetemperatureoftheEarth,whichhassignificantimplica-tionsforthesustainabilityoflifeonEarth(seeChapter5).Similarly,troposphericpollutantscanaffectsurfacetemperaturesbyscatteringandbyabsorbing thermalenergyfromthesunandbytrappingnighttimeheatthatradiatesfromthesurface.

ii. MEASurEMEnt bASiCS

Quantitation and Scale

Quantitative measurementsareamongtheindispens-abletoolsofscience.Withoutsuchmeasurementsoneonlyhasgeneralitiesandpersonalstatements,suchas“it’stoocold”;“theairisclean”;and“visibilityispoor.”Suchgeneralitiesconveysomeinformation,but theyareimpreciseandoflittleuseinairpollutionscience.Quantitative measurements are based on acceptedunits of measurementthatarepreciselydefined.Suchunitsdonotvaryfromtime-to-time,place-to-place,or


9955



Onecouldalsoexpressratiosonaweight-to-volumebasis.Forexample,1cubiccmofsulfurdioxidegas(SO2)atstandardlaboratoryconditionshasamassof2.6mg,thusthemeasureofmassofsulfurdioxidetoa1m3volumeofairwouldbe2.6mgper1millioncubiccm(or2.6mg/m3).Suchweightperunitvolumemeasuresarecommonlyreportedforsolidorliquidcontaminantssuspendedintheair.However,thismeasurecanstillbeusedwithgaseouscomponentsinair.Insomecasestheaircontaminantmayexistinboththegaseousandsolidorliquidphaseswithintheair.Theweightpervolumemeasureisoftenusedintheseinstances.

Additionalratiosofmeasurecanalsobeused.Forexample,asam3ofairhasamassofabout1.2kg,theweight-to-weightratioforthesulfurdioxideexampleabovewouldbeabout2.2ppmw.Onecouldalsoexpresstheratioofthenumberofsulfurdioxidemoleculestoairmolecules,butthisisseldomdoneinairpollutionscience.Theweightofanaircontaminantinacubicmeterofair(mg/m3)andthevolumeratio(ppmv,orjustppm)arenormallyused.table 2–2showssomeusefulcon-versionfactorsforchangingmg/m3toppmv.

variations in units of Measurement

Airpollutionscienceinvolvesseveraldisciplinesincludingmeteorology,chemistry,physics,ecology,biology,physiology, toxicology, andmedicine.Eachdisciplineusesitsownmeasuresforpollutantparticles,gases,orvapors.Meteorologistsareinterestedinemis-sionsmeasuredinmassorweightunits,soconcentra-tionsaremeasuredinunitssuchasmg/m3ofairorpartspermillionppmv.Chemiststendtouseunitssuchasmolespercubicmeterandatomsormoleculesperunitvolume.Physicistsmayusethenumber,mass,orsurfaceareaofparticlespercubiccentimeterand thepartialpressureofagas.Biologistsandphysiologists,whoareinterestedintheeffectsofairpollutantsonlivingsystems,usemeasuressuchasmassperunitvolumeofairandpartial pressureforgasesandvapors.Physiciansarefrequentlyinterestedindoses,sotheconcentrationsinorgansandtissues(e.g.,microgramspergramoftissueormassofpollutantdeliveredtoanindividualsubject)areofinterest.Althoughmanymoreexamplescouldbegiven,theimportantpointscanbemade:(1)anumberofmeasuresofpollutantsareincommonuse;(2)convert-ingunitsfromonemeasuretoanotherisoftenrequired.Thisintroductorytextwillusethosespecificunitsthatbestsuitthetopicathand.

observer-to-observer.Theyquantifytime,size,location,temperature,pressure,altitude,mass(orweight,whichismasstimestheaccelerationduetogravity),humidity,particlecount,andmanyothermeasurablefactors.Ratiossuchaspartspermillion(ppm)ormilligramspercubicmeter(mg/m3)arequantitative,andalsofrequentlyusedinairpollutionscience.

Todemonstratetheuseofmeasurementunits,con-sidersulfur.Thetotalmassof10billion,trillionsulfuratomsisonlyabout0.5grams.Incontrast,themassofsulfurreleasedinavolcaniceruptioncanbeseveralbilliongrams.Inordertoexpresssuchwiderangesofscale,powersof10(i.e.,exponents)areused.table 2–1providesthescientificnomenclatureassociatedwithpowersof10.Suchexponentsarecommonplace inairpollutionscience.

Powersof10arealsousedforexpressingratios.Forexample,1cubiccm(cm3)ofagasdispersedin1millioncubiccmofairis1partpermillion(ppmv,volume-to-volumeratio).Theconcentrationsofgas-eouscontaminantsintheairaretypicallyreportedasppmvvalues(usuallywithoutthesubscript,v).Toavoidconfusion, thinkofppmassimilar toapercentage.Insteadofaratioof1/100aswithapercent,ppmisaratioof1/1,000,000.Thescaleisdifferentbyseveralpowersof10.

Table 2–1 Powers of ten, using the International System of Units (SI) nomenclature.

Numerical Equivalent Prefix/Name Symbol

10-12 0.000000000001 pico/trillionth p10-9 0.000000001 nano/billionth n10-6 0.000001 micro/millionth µ10-3 0.001 milli/thousandth m10-2 0.01 centi/hundredth c10-1 0.1 deci/tenth d100 1 unity none101 10 deca/ten da102 100 hecto/hundred h103 1,000 kilo/thousand k106 1,000,000 mega/million M109 1,000,000,000 giga/billion G1012 1,000,000,000,000 tera/trillion T

Note: In the United Kingdom, 1 billion = 1012 (i.e. a million million), and 1 trillion = 1018 (i.e. a billion billion).


9955


III. Unpolluted vs. Polluted Air 25

iii. unPOLLutEd vS. POLLutEd Air

Clean Air, Can it be harmful?

Unpolluted (clean) tropospheric air isdefined intable 2–3.Ofthetwomajoratmosphericgases,N2andO2,oneisconsideredtobechemically inert(N2),andtheotheroxidizing (O2).However,N2 isnotalwaysbio-logicallyinert.Indeep-seadiving,wherethepressure

isseveralatmospheres,diversbreathingcompressedaircanbecomedisorientedduetothenarcoticeffectsofN2dissolvedinthefattytissueofthebrain.SoN2isbiologicallyinertatatmosphericpressure,buttoxicatelevatedpressures.Theuseof80percentheliumgasplus20percentO2indivingairpreventsgastoxicityproblemsatelevatedpressures.Similarly,O2isbenefi-cialatnormalpartialpressure(20.9percentof1atmo-sphere),buttoxicwhenbreathedforaprolongedtimeat

Table 2–2 When converting mg/m3 (mass of gas/volume of air) to ppm (volume gas/volume of air) multiply by k. Valid for 25°C and 760 mm Hg pressure.

PollutantGas ChemicalFormula GasMol.Wt.(g/mole) k=24.45/MW(ppm/[mg/m3])

Ammonia NH3 17.03 1.44Carbon dioxide CO2 44.01 0.556Carbon monoxide CO 28.01 0.873Chlorine Cl2 70.91 0.345Formaldehyde HCHO 30.03 0.814Hydrogen sulfide H2S 34.08 0.717Methane CH4 16.04 1.52Nitric oxide NO 30.01 0.815Nitrogen N2 28.02 0.873Nitrogen dioxide NO2 46.01 0.531Nitrous oxide N2O 44.02 0.555Oxygen O2 32.00 0.764Ozone O3 48.00 0.509Sulfur dioxide SO2 64.07 0.382

Table 2–3 The gaseous composition of dry and wet (100% RH) unpolluted air.

Substance ppmbyVolume,DryAir µgperm3,DryAir ppmbyVolume,WetAir

Nitrogen 781,000 9 × 108 757,000Oxygen 209,000 2.7 × 108 203,000Water 0 0 31,200Argon 9,300 1.5 × 107 9,000Carbon dioxide 315 5.7 × 105 305Neon 18 1.5 × 104 17Helium 5.2 8.5 × 102 5.0Methane 1.0–1.2 7.0 × 102 1.0Krypton 1.0 3.4 × 103 1.0Nitrous oxide trace trace traceHydrogen trace trace traceXenon trace trace traceOrganic vapors trace trace trace


9955



100percentconcentrationatapressureof1atmosphere.Intoxicology(thestudyofadverseeffectsofchemicals),notonlymustgasconcentrationsbeconsidered,butalsothegaspressures(orpartialpressuresofeachgasinamixture)mustbetakenintoaccount.Thus,thetoxicologyofagasorvaporinaspacecraft(lowambientpressure)orasubmarine(highambientpressure)maynotapplytootherenvironmentswithdifferentatmosphericpressures.

defining Air Pollutants

Air contaminants(alsoair pollutants)aredifficulttoconciselydefine.Theyexistinseveralformsincludingsolids,liquids,vapors(vaporsaregasesformedbyvol-atileliquids/solids),gases,ions,andmixturesoftheseprimarystatesofmatter.Pollutantsmaypersistintheaironlybriefly(e.g.,short-livedreactivechemicalspecieswithlifetimeslessthan1second),orforseveralyears(e.g.,verysmallparticlesandnonreactivegases).

What makes something an air pollutant? From aregulatory perspective,anairpollutantisasubstancethatis,ormaybe,presentataconcentrationthatexceedsitssafeconcentration.Also,fromaregulatorypointofviewtheairisnotnecessarilypollutedifnoneofitscon-stituentsareoutofcompliancewithanairqualitystan-dard.Notethattheairmayquicklygofrom“unpolluted”to“polluted”ifanairstandardistightened.Regulatoryagenciesmayrefertocriteria pollutants, air toxics,orhazardous air pollutants(HAPs)thathavepublishedstandardsthatareintendedtoprotectsusceptiblepopu-lationsorthegeneralpublic.CriteriaairstandardsarereviewedbytheU.S.EnvironmentalProtectionAgency(U.S.EPA)abouteveryfiveyears.HAPsarereviewedonlywhendeemednecessary.Workersareusuallyper-mittedexposuretohigherlevelsofairpollutantsthanthepublic,asworkersarehealthier(asagroup).Fortheprotectionofworkersfromairbornehazards,essentiallyanysubstancemayaddedatanytimetoliststhatproviderecommended(e.g.,ACGIH®,2010)airconcentrations.

Fromapractical perspective,anairpollutantcanbedefinedasanysubstance,regulatedornot,thatinter-fereswithaperson,process,oranobjectthathasvalue.Thus,forananalyticalchemistatraceofwatervaporintheairmaybeaninterferingpollutant.Foradeepseadiver,N2gasintankairmaybeapollutant.Andforamanufacturerofcomputerchips,verytinyamountsofparticlesintheairareseriouspollutantsthatmayaffectproductquality.Asthepracticalperspectivecan

includeessentiallyanyknownsubstanceasapollutant,it isimpracticaltoconsideritinthecontextofthistextbook:specialtypublicationsshouldbeconsultedasneeded.

Anairpollutantisasubstancethat,atrealisticenviron-mentalconcentrations,isknowntohaveadverseeffectsonhumans,otheranimals,vegetation,visibility,thecli-mate,orotherassets(suchasobjectsofart,machinery,orbuildings).

Becauseregulatedpollutantshavebeensubjectedtothemostintensiveresearch,theyareaprimaryfocusinthistextbook.IftheU.S.EPA,theOccupationalSafetyandHealthAdministration(OSHA),oranothermajorregulatorybodydeemssomethingtobeanairpollutant,sowill the authorsof thisbook.However, themainpointisthatboththesubstanceanditsconcentration,alongwithasubject’sexposureandsensitivity,arewhatactuallyproduceahealthproblem.

iv. Air POLLutAnt SOurCES And thEir EMiSSiOnS

terminology and Pollutant Source Categories

Thesourcesofairpollutantsarenumerousandvaried.Threecategoriesofsourcesmaybedefined:(1)natural(i.e.,thosethatarenotassociatedwithhumanactivities);(2)anthropogenic(i.e.,thoseproducedbyhumanactiv-ities);and(3)secondary(i.e.,thoseformedintheatmo-spherefromnaturalandanthropogenicairpollutants).Eachofthesethreecategoriesofairpollutantscanbefurthersubdivided.Forexample,anthropogenicpollutantsourcescanbeclassifiedasstationary,(e.g.,factories,farms,homes,etc.)vs.mobile(e.g.,cars,trucks,boats,aircraft,etc.).Othersubcategories,suchasindoorvs.outdoor, organicvs.inorganic,orlocalvs.regional,arealsoused.Thefollowingsectionswillprovideanover-viewofthesourcesandemissionsassociatedwiththeseandothercategoriesandclassesofairpollutants.

natural vs. Anthropogenic

table 2–4listssomemajorsourcesandannualnationalemissionestimates(inthousandsoftons)forsomeoftheairpollutantsthatareregulatedbytheU.S.EPA.Thenaturalsourcesofselectedairpollutantsareshownintable 2–5.Severalpointscanbemaderelatedtothesetables.Naturalsourcesaredifficult,ifnotimpossibleto


9955


IV. Air Pollutant Sources and Their Emissions 27

Table 2–4 Some major anthropogenic sources and emissions of ambient air pollutants in the United States in 1993, including primary particle sources and sources of precursor gases (sulfur and nitrogen oxides) and volatile organic compounds (VOCs) (EPA, 1996). PM10 refers to particles with diameters under 10 micro meters. SOx and NOx are oxides of sulfur and nitrogen, respectively. One ton equals 907 kg.

ThousandsofTons/Year

Source PM10 SOx NOx VOCs

Fuel Combustion Utilities 270 15,836 7,782 36 Industrial 219 2,830 3,176 271 Other sources 723 600 732 341Industrial Processes 553 1,862 905 3,091Solvent Utilization 305 43 90 10,381On-road Vehicles 197 438 7,437 6,094Off-road Vehicles 395 278 2,996 2,207Fugitive Dust Roads 22,568 Construction/Mining 11,368 Agriculture 7,236

Table 2–5 Some major global natural sources and emissions of air pollutants.

MillionsTons/Year

Source Particles Sulfur NOx CO

Dust & Soil 90–450 24Sea Spray 800 48Biological 70–180 108 3–30 40–400

ActionVolcanic * 5.5

EruptionsLightning 24Fires & Other * 35 100–5,700

Oxidation

Note:* = extremely large amounts are released.Data, in short tons (2,000 lbs, 907 kg), are from various

sources including: Finlayson–Pitts and Pitts (1986); U.S. EPA (2000).

control.Naturalemissionsareoftengeneratedatlocationsthatareunpopulated,orsparselypopulatedbypeople.Fortheseandotherreasons,theprimaryfocusofregula-torsisonstudyingandcontrollinganthropogenicsources.However,aproblemariseswhensecondarypollutants(formedintheair)areconsidered.Forexample,anthro-

pogenic(ornatural)SO2isaprecursorofH2SO4(sulfuricacid)andotheracidicsulfates.Butthenatural(andanthropogenic)pollutant,NH3(ammonia)reactswithH2SO4,andneutralizesitsstrongacidity.Proposednetreactionsinclude:

SO2 + H2O + ½O2 → H2SO4 (Eq. 2–1)

H2SO4 + NH3 ↔ (NH4) HSO4 (Eq. 2–2)

2H2SO4 + 3NH3 ↔ (NH4)3 H(SO4)2 (Eq. 2–3)

H2SO4 + 2NH3 ↔ (NH4)2 SO4 (Eq. 2–4)

Equations2–1to2–4representtheformation(andbackreactions)ofgases/vaporstosolidorliquidprod-ucts,inthiscasesulfatesalts.Thesesaltsaretypicallysecondarypollutantsformedbythereactionsofanthro-pogenicandnaturalemissions.Sometimes,itisdiffi-culttoisolatetherolesofhumanactivitiesinproducingpoorairquality.

The foregoingexample,which representsonly afewof essentially countless atmospheric reactions,demonstratestheimportanceofairchemistrymodelingtosupportregulations.AirchemistryiscoveredmorecompletelyinChapter3.


9955



particulatematterincludestationary-sourcefuelcom-bustion(includingmanagedburning),mobilesources,andindustrialprocesses(whichareresponsibleforabout10percentofthetotal).Sourcesthatarehighly-localized,suchaselectricpowerplantsandindustrialplants,areoftenclassifiedaspoint sources,whileagriculturaloper-ations andurbancenters aredistributed sources.Allsourcescanhaveasignificantimpactonlocalairquality.Thedistinction,pointvs.distributed,isimportantformodelinglocalairconcentrationsofpollutants.Ingen-eral,pointsourcesareeasiertoquantifyandtocontrolthanaredistributedsources.

Enclosed Settings and Workplaces

Overview

Airpollutionisnotjustanoutdoorproblem.Infact,theairinmanyenclosed environmentsismorecontaminated

Stationary vs. Mobile and Point vs. Distributed Sources

Anthropogenicpollutantsourcesareclassifiedasstationaryormobile.ThemajorstationarysourcesasdefinedbytheU.S.EPA(2000)include:

• electricutilitiesthatburnorganicfuels(notethatnuclear,hydroelectric,andwind-poweredutilitiesusuallydonotproduceairpollutants);

• industrialplantsthatburnorganicfuels;• chemicalmanufacturing;• metalsprocessing;• petroleumindustries;• otherindustries(agriculture,textile,wood,rubber,

electronic,construction,etc.);• solventusers(degreasing,graphicarts,drycleaning,

etc.);• storage(terminals,servicestations,chemicalstorage,

etc.);• wastehandling(incinerators,openburning,land-

fills,etc.);and• miscellaneous sources (forestry,health services,

accidentalreleases,repairshops,coolingtowers,etc.).

Mobilesources,whicharevehicles,include:

• on-road gasoline powered trucks, automobiles,andmotorcycles;

• on-roaddiesels;and• off-road vehicles (gasoline and diesel powered

automobilesandtrucks,aircraft,marinevehicles,andrailroadengines).

Foreachsource,dataaregatheredonpollutantssuchascarbonmonoxide;sulfurdioxide;ammonia;volatileorganiccompounds;nitrogenoxides;lead;particulatematter; and hazardous air pollutants. Figures 2–2 through 2–9depict2008U.S.emissionsforseveralairpollutants.Themajorsourceofcarbonmonoxideison-roadvehicles(about60percentofthetotal).Non-roadvehiclesemitanother20percent,andothersourcesemittheremainder.Vehiclesarealsomajoremissionsourcesfornitrogenoxidesandvolatileorganiccom-pounds.Electricutilitiesaremajoremittersofsulfurdioxide.Mostof the leademissionsare frommetalsprocessing,followedbywastedisposal/recycling,vehi-cles,andstationaryfuelcombustionsources.Mostoftheammoniaisemittedbylivestock,organicdecay,andfertilizer-related sources. Sources of anthropogenic

Highway vehicles,57%

Stationary fuelcombustion, 8%

Industrial and othersources, 9%

Non-road mobilesources, 26%

2008 U.S. carbon monoxide emissions

Figure 2–2 U.S.1998COemissions Source:U.S.EPA(2010).

2008 U.S. nitrogen oxides emissionsNon-road mobile

sources, 26%

Stationary fuelcombustion, 33%Industrial and other

sources, 9%


Figure 2–3 U.S.1998NOxemissions Source:U.S.EPA(2010).


9955



Figure 2–4 U.S.2008Volatileorganiccompoundemissions. Source:U.S.EPA(2010).

2008 U.S. volatile organic compounds emissions





Figure 2–5 U.S.2008SO2emissions. Source:U.S.EPA(2010).

2008 U.S. sulfur dioxide emissions



Highway vehicles,1%


Figure 2–6 U.S.2008PM10(particlesunder10μmdiameter)emissionsfromnonfugitivedustsources.

Source:U.S.EPA(2010).

2008 U.S. non-fugative PM10 emissions



Highway vehicles,9%


Figure 2–7 U.S.2008PM2.5(particlesunder2.5μmdiam-eter)fromnonfugitivedustsources.

Source:U.S.EPA(2010).



2008 U.S. non-fugative PM2.5 emissions



Figure 2–8 U.S.2008Leademissions. Source:U.S.EPA(2010).




2008 U.S. lead emissions

Figure 2–9 U.S.2008Ammoniaemissions. Source:U.S.EPA(2010).


2008 U.S. ammonia emissions

Highway vehicles,8%



9955



than the localoutdoorenvironment.The reasons forthisare(1)thelimitedvolumesofdilutionair;(2)thelowwindspeedsindoors;and(3)thesometimesintenseindoorsources(e.g.,smoking,cooking,andcleaning).Althoughonemightthinkofresidencesasthemajoroccupiedenclosedsettings,workplaces,publicbuild-ings,andvehiclesarealsoplacesinwhichindoorexpo-suresoccur.

Time-activity patterns(howlongandwherepeopleare exposed) areused to estimatehumanexposures.Peoplespendabout90percentoftheirtimeinenclosedenvironments.Eachtypeofindoorsettinghasitsuniquecharacteristics,andimportantvariationsinsourcesandemissionsoccurwithineach.Considertwoworkplaces,anofficeandametalfoundry;theyhaveverylittleincommon.Similarly,theairqualityforanairconditioned,gas-heatedresidencewilldifferconsiderablyfromonethathasnoairconditioningandwherethesourceofheatcomesfromburningcoalorwoodindoors.Asimilarcontrastcouldbedrawnbetweenairqualityinanupscaleautomobileandanold“clunker.”Becauseenclosedsettingsaresovariable,thischapterwillcoveronlyafewspecificexamplesinordertoexplorebasicprinciples.

Residences

Incontrast tooutdoorairpollution,which isbothsource-dominated and meteorology-dominated, resi-dentialairpollutionissource-dominated.Pollutantsgeneratedinthehomearenotrapidlydispersedbythewind,andresidentialaircleanerscanseldomoverpoweruncontrolledpollutantsources.table 2–6listssomeofthemostcommonsourcesofresidentialaircon-taminants.Figure 2–10illustratessomeindoorsources.

Whetherornotthesesourcesproducehealthproblemsdependsontheaircontaminantconcentrations,whetherco-stresses (suchasexcessiveheat,cold,orextremehumidity)arepresent,andthesensitivityandgeneralhealthstatusoftheoccupants.

Allergensandirritants(table 2–7)canposeasignifi-cantresidentialproblem,especiallyforsensitive indi-viduals.Such“sensitives”includepeoplewithallergies,asthma,bronchitis,emphysema,respiratory-tractinfec-tions,andcardiovasculardiseases.These,andotherhealth-related conditions, may both impair normalrespiratorytractdefensesandleadtoexaggerated(evenlife-threatening) responses to modest levels of aircontaminants.Suchvulnerableindividualsmayrequireaverycleanairenvironment.Insomecases,medicaladviceandtreatmentbyaqualifiedallergistand/orapulmonaryphysicianisneeded.

Itiswisetocontrolindoorsourcesofaircontaminants,bothforthesakeofthehealthyresidentsandanysensitiveorotherwisecompromisedindividuals.table 2–8hasachecklistthatcanbeusedinthehome(alsotheschool,office,etc.)forreducingindoorsources.Inaddition,commercialaircleanerscanbeeffectiveifthemajorpollutantsourceshavebeencontrolled.Suchaircleanersshouldbeselectedfortheirair throughput rateandtheircleaning efficiency.Anaircleanerthatprocessesonlyafewcubicfeetofairperminutemaybetotallyineffec-tiveinaroomwithanairvolumeof3,000cubicfeet(8.5cubicmeters).Similarly,anaircleanerthatisnotcapable of removing fine particles (e.g., those fromsmokingorcooking)ororganicvapors,mayprovidelittlerelieftoindooroccupants.Anuncontrolledsourcewithina poorly ventilated and/or poorly filtered residence

Table 2–6 Common sources of residential air pollutants.

Pollutant Sources

Asbestos and other fibers Old insulation in/on ceilings, walls, stoves, pipes, floor tiles, heaters, etc.Lead Old paint, toys, and other commercial productsBiological aerosols Mold, pets, insects, rodents, people, humidifiers, indoor plants, etc.Volatile organic compounds

(including formaldehyde)Air fresheners, spray products, solvents, glues, new building-materials, paints,

printers, ink, etc.Combustion products Smoking, cooking, wood and gas fireplaces, water heaters, candles, incense, etc.Dust Vacuuming/cleaning, plants, dirt, outdoor air, etc.Gases Off-gassing from water and various products, electrical discharges, combustion,

outdoor air, gas appliances, etc.Radon Intrusion from soil, masonry, and underground water


9955



GAS

1

2

3

4 8

7

9

10

12

13

13

1415

16

17

18

19

20

21

5

6

11

Figure 2–10 Somecommonsourcesofresidentialaircontaminantsinclude:(1)fireplace,candles,andincense;(2)vacuumingandcleaning;(3)smoking;(4)indoorpets;(5)pottedplants;(6)insects,radon,andmethane;(7)foodprepara-tion;(8)gasappliances;(9)storedfuel;(10)vehicles;(11)paint,thinner,etc;(12)humidifier;(13)carpetanddrapes; (14) bedding and furniture; (15) computer/printer; (16) air conditioner; (17) hobbies; (18) fish tank;(19)shower;(20)outdoorair;and(21)insulation.

Source:TheUniversityofCaliforniaAirPollutionHealthEffectsLaboratory,withkindpermission.

Table 2–7 Irritants and allergens in residences.

A.Irritants(examplesonly) Sources

Solvents, alcohols, etc. Cleaning and polishing agents, plastics, liquid fuels, hobbies that involve glue, paint and/or solvents, etc.

Formaldehyde Air fresheners, other spray products, solvents, glues, new building- materials, paints, printers, ink, etc.

Dust Vacuuming/cleaning, plants, dirt, outdoor air, etc.

B.Allergens(examplesonly)

Insect products (droppings, body parts) Dust mites, cockroaches, other insect infestationsPet-related Cat, dog, and rodent allergens from saliva, fur, droppings, bedding,

food, water dishesPlant-related Pollens, molds (from dead plant material and soil), volatile fragrances, etc.


9955



couldresultinarapidbuildupofcontaminantswithinthelivingspace.Thus,eliminationoreffectivecontrolofacontaminantsourceisoftenmorecriticaltoairqualitythanitsdilutionormechanicalremovalfromtheair.

Workplaces

Thevarietyofairpollutantsandtheirsourcesinwork-placesisgreatenoughtodefyanysuccinctsummary.Officesmayhavesolvents,ozone(fromprintersandcopiers),allergensfrominsectinfestations,dust,micro-organisms from ducts and air conditioners, carbonmonoxidefromair intakesnear truck loadingzones,andavarietyofaircontaminantsfromnearbyindustrial

operations. In addition, crowded offices will havehuman-generatedaircontaminantsfromclothingfibers,dander,coughing,andsometimesbody-generatedodors.Manufacturingoperationsmayproduceairbornesolvents,organicand inorganicdusts, exoticchemicals,metalfumes,andmanyothersubstances.Inaddition,heat,noise,vibration,andextremesinhumiditycanexacer-batethedirecteffectsofairpollutantsonworkers.

Manufacturingandotherheavyindustrialoperationsusually require theparticipationof trainedIndustrialHygieniststocontrolthepotentialrisks.Itisessentialthatworkplacesconformtomodernairqualitycriteriaaswellasstandardsforheat,noise,vibration,andother

Table 2–8 Indoor air pollutant control checklist.

_____ 1. House dust

_____ 2. Deteriorating cloth, rubber, wood, plastic, paper

_____ 3. Indoor animals (birds, dogs, cats, rodents, fish tank bubblers, etc.)

_____ 4. Pet bedding, food, water, and litter boxes

_____ 5. Sprays (air fresheners, paints, insecticides, cleaners, cosmetics)

_____ 6. Smoking (cigarettes, cigars, pipes) and burning incense and candles

_____ 7. Fireplaces, wood, coal, and kerosene stoves

_____ 8. Smoke from cooking food

_____ 9. Poorly-vented or broken ovens, stoves, heaters, clothes dryers, and water heaters

_____10. Dusty or soiled carpets, drapes, blankets, pillows, sheets, or mattresses

_____11. Dirty air filters, soiled or dusty air ducts

_____12. Dirty humidifier and dehumidifier water tanks

_____13. Standing water or evidence of mold

_____14. Damp cloth, paper, wood, carpets, walls, etc.

_____15. Indoor plants with pollen or mold growth on container or soil

_____16. Dust-catching decorations, stuffed toys, and drapery

_____17. Hobby-associated activities and materials

_____18. Paints and solvents that are not tightly sealed

_____19. Insects, including mites, ants, fleas, roaches, spiders, and flies

_____20. Poorly-ventilated rooms

_____21. Garbage and spills

_____22. Odorous building materials, insulation, carpets, drapes or furniture

Note: If completing this checklist does not resolve a residential air problem, air cleaners with sufficient throughput and efficiency should be used. Use of an air cleaner in the bedroom may be particularly effective, if the contaminant sources have been removed. When sensitive or ill residents are present, or when symptoms persist, professional medical help is needed.

Source:The University of California Air Pollution Health Effects Laboratory, with kind permission.


9955



hazards.IntheUnitedStates,privateprofessionalorgani-zations, suchas theAmerican Conference of Govern-mental Industrial Hygienists(ACGIH®)andtheAmerican Industrial Hygiene Association(AIHA)publishvolun-taryguidelinesthatareapplicabletoworkplaces.Also,governmental organizations, such as the National Institute for Occupational Safety and Health(NIOSH),the Occu pational Safety and Health Administration(OSHA),theCenters for Disease Control and Prevention(CDC), the Mine Safety and Health Administration(MSHA),andnumerousstateagenciespublishimportantreports,guidelines,andregulations.Althoughthecostofmaintainingahealthfulworkplacemaybesubstantial,itisusuallynegligibletothealternative(i.e.,significantworker illnesses).A good example of air quality andotherworkplacerecommendationscanbefoundintheACGIH®publicationTLVs® and BEIs®(2010).TLVs®are8-houraveragedthreshold limitvalues(airconcentra-tions)nottobeexceededforaircontaminants,andBEIs®arebiological exposure indices,whichareconcentrationsinblood,urine,etc.,thatcanbemeasuredinworkerstodeterminetheiractualexposures.TheACGIH®publica-tionalsocoversother“agents”suchas(1)noise;(2)elec-tromagnetic radiation and fields (including lasers,ultravioletlight,andionizingradiation);(3)thermal(heatandcold)stress;and(4)ergonomics(lifting,vibration,etc.).Theseotheragents,ifnotcontrolled,canproducedirectharmandincreasetherisksassociatedwithexpo-suretoairpollutants.

Evenifalloftherecommendationsforworkplaceairarefollowed,someworkersmaynotbeadequatelyprotected.TheTLVs®andBEIs®acknowledgeandcau-tionthattherecommendationsaredesignedtoprotect“healthy”workingadults,andthattheymaynotprotectallworkers.Sensitiveindividualsmayrequirereassign-mentofduties,stringentlocalengineeringcontrols,andifallelsefails,additionalpersonalprotectiveequipment(e.g.,respiratoryprotection)toreduceexposures.

Criteria Air Pollutants vs. hazardous Air Pollutants

Criteria air pollutants (CAPs) and hazardous air pollutants (HAPs)arespecificagents thathavebeendefinedbylegislationsuchastheU.S.Clean Air Act,orsimilar international standards. In theUnitedStates,therearesevencriteriaairpollutants(seeExhibit6–1,Chapter6).EachonehasassociatedNational Ambient Air Quality Standards(NAAQS)thataretoberevisited

andpossiblyrevisedbytheU.S.EPAatleasteveryfiveyears.TheNAAQSincludeprimary pollutant criteriaforprotectinghumanhealthandsecondary pollutant criteriaforothereffectssuchasreducedvisibility,and/ordamagetomonuments,crops,orlivestock.PrimaryNAAQSmustprotect sensitive subpopulationsandincludeamargin of safety.ConsiderationsofthecostandfeasibilityofattainmentforprimaryandsecondaryNAAQSarecurrentlyprohibitedbylaw.

Hazardous air pollutants(HAPs),alsodesignatedbytheU.S.EPA,currentlycompriseabout200substances,includingbothspecificagents(suchasasbestos,benzene,andformaldehyde)andchemicalclasses(suchasarseniccompounds,cokeovenemissions,nickelcompounds,andradionuclides).ThedistinctionbetweenCAPsandHAPsistwofold:(1)CAPshavebeendeterminedtopresentageneralrisktothehealthofthepublic,andHAPsarebelievedtocauseadversehealthand/orenvi-ronmentaleffects;and(2)unlikeCAPs,HAPsmaybeaddedtoordeletedfromtheirlistings,andtheydonothavethemandatedfive-yearreviewcycle.

SimilarapproachestolistingairpollutantshavebeenestablishedbyCanada,theUnitedKingdom,andtheWorldHealthOrganization,tonameafew.However,nations differ in their standards, often significantly.Twomainpointsare(1)thatairstandardsareconstantlyevolving; and (2) that different approaches are usedthroughouttheworld.

Accidents and disasters

Anaccidentalreleaseofairpollutantscanproducea major health catastrophe for a local community.Explosions,fires,industrialcontainmentfailures,rail-roadcarderailments,andtruckingaccidentscanreleasesubstantial quantities of fuels, solvents, combustionproducts,radionuclides,and/ortoxicaircontaminants.Similarly,naturalaccidents,suchasvolcaniceruptions,earthquakes,forestfires,andhurricanescangeneratehighlevelsofairpollutants.Suchaccidentscantakehundredsto thousandsof lives.Warfareandterroristattacksmustalsobeincludedinthelistofcausesofairpollutiondisasters.Poisongases(e.g.,sulfurandnitro-genmustards,phosgene,chlorine,hydrogencyanideand nerve agents), biological aerosols (e.g., botulin,ricin,anthraxbacteria,andviruses),andradionuclides(fromatomic,hydrogenandso-called“dirty”bombs)areamongthepotentialairpollutants.Warfareagentsaresoughtbyterroristsinordertoachievetheirends.


9955



Airpollutionisnotsimplyaproblemcausedbyindustry,transportation,agriculture,andotheractivitiesthatareoftenessentialtomaintainingpublichealth.

Anespecially-tragicindustrialdisasteroccurredin1984inBhopal,India.Anexplosionatapesticidefacil-ityduringanatmosphericinversionreleasedtonsofmethylisocyanateintotheairofanearbycommunity,andabout200,000peoplewereexposed.Thehighly-irritantchemicalmostlikelyproducedover3,000deaths,includ-ingthoseatthetimeoftheexplosionandthoseoverthefollowingfouryears.ThousandsmoredelayedBhopalfatalitiesareprojectedintothefuture.Suchdisastersleadtopublicfear,andtheyresultinpressureongovern-mentstoprovidebetterprotection.

v. POLLutAnt trAnSPOrt

Overview

Thetransportofairpollutantsislargelydrivenbyweatherphenomena.Verticalairmotionsalongwithprevailingwindsbothdiluteanddisperseparticlesandgasesemittedfromanygivensource.Onaglobalscale,unequalsolarheatingcauseswarmairneartheequatortoriseandthendescendasitcoolsandtravelstowardthenorthandsouthpoles.Thiseffectalonewouldpro-ducewindcirculationtowardthepolesathighaltitudesandtowardtheequatoratlowaltitudes.Butseveralotherphenomenacomplicatetheglobalweatherpicture.TheEarth’srotationhastwoeffects,surfacefrictionthatdragssurfaceairinthedirectionofrotationandaCoriolis forcethat,ingeneral,turnsairmovementtotherightintheNorthernhemisphereandtowardstheleftintheSouthernhemisphere.TheCoriolis forceoccursasaconsequenceoftheEarth’srotation.Surfacecharacter-istics(e.g.,oceansandotherlargebodiesofwatervs.landareas) that modify the air temperature and moisturecontentalsoinfluencelargeairflowpatterns.Mountains,forests,andevencitiesaffectwindpatternsmorelocally;Figure 2–11depictsthemajorconvectivecellsandthegeneral climate systems.Although the principles ofweatherphenomenaareunderstood,long-rangeweatherpredictionsarehighlyuncertaindueto theeffectsofsmall-scalephenomena.Weatherisachaotic system,inthatsmallchangesininitialconditionscanproducelargelong-termconsequences.

Ifemittedparticlesandgasesstrictlyfollowedthewinds,concentrationsdownwindcouldbeaccuratelypredictedoverthetimescaleofafewdays.However,

suchpredictionsareriskybecauseairborneparticlesandgasescanseparatefromtheirairparcels(thevolumeofairintowhichtheywereemitted),duetodiffusionandsedimentation.Also,localmeteorologycaninfluencetheriseandtransportofaironalocalscale.Suchlocalmeteorology includes air inversions and convectivephenomena(asproducedbylocalheatingeffects,eddies,terraineffects,andotherphenomena).

Gasesandvaporsmorecloselyfollowwindpatterns,buttheyhavediffusionvelocitiesthatcancausethemtospreadbeyondtheairparcelintowhichtheyareemitted.

Particleswithlargeaerodynamicdiameters(20μmandabove;seeChapter3onaerodynamicdiameters)havebehaviorsstronglyinfluencedbygravityandbytheparticle’sinertia.Therefore,theyreadilysettleoutoftheairparcelsinwhichtheyareentrained.Particlesinthissizeregimesettleoutoftheairatvelocitiesthatexceed3mperhour.Thus,ifsuchparticlesareemitted

Subtropical high

Polar high

South pole

Subpolar low

Subtropical high

Intertropical convergence zone

Polar high

Subpolar low

Equator

30° N

30° S

60° S

60° N

North pole

Figure 2–11 The large-scale motion of the Earth’s atmo-sphere.Thismotion is influencedby thermalgradients,frictionbetweentheairandrotatingEarth,andtheCoriolisforce.

Source: The University of California AirPollutionHealthEffectsLaboratory,withkindpermission.


9955


V. Pollutant Transport 35

1mabovethesurfacetheywillsettletothegroundinabout 20 minutes, unless they encounter substantialupdraftsordescendingterrain.Smallparticles,e.g.,those1μmorsmallerindiameterhavesettlingvelocities(seeChapter3)oflessthanafewcmperhour.Suchparticlescantravelinthewindformorethanseveralkmbeforesettlingtotheground.Verysmallparticlescantravelthousandsofkmbeforesettlingoutoftheair.

Otherphenomenathatproducethelossofcontami-nantparticles,gases,andvaporsfromtheairinclude:

• evaporationofvolatileparticles;• chemicaltransformations;• capturebyvegetationandotherobjects(bothanthro-

pogenicandnatural);• capturebyprecipitation(rain,snow,etc.);and• attachmenttoparticlesthatsettleout.

gaussian Plume Model

TheGaussianplumemodel isused forestimatingdownwindpollutantconcentrationsemittedfrompointsources.Themodelisthree-dimensionalinthatdown-wind,crosswind,andverticaldispersingcomponentsareconsidered.Attheemissionpoint,pollutantdilutionoccursindirectproportionwiththewindspeed.TheplumeshapenearthesourceisGaussian(i.e.,bell-shapednormal-distributions)initscross-sections.Thestandarddeviationsofthenormaldistributionsincreasewithdistancefromtheemissionpointsource.Themodelisusefulforpredictingairpollutantconcentrationsdown-

windfromsmokestacks.However,thebasicmodeldoesnotincludepollutantlosses(orformations)intheplumecausedbychemicalreactionsandparticlesedimenta-tion.Chemicalreactionsinplumescanleadtosignifi-cantacidificationandhencedownwindaciddeposition(seeExhibit 2–1).

Plumes and Smokestacks

Plumesfromsmokestackspresentagoodcasestudyinwhichtoexamineairpollutanttransport.Increasingtheheightofasmokestackwillusuallydecreasethenear-stackgroundlevelconcentrationsofemittedparticlesandgasesandcauseemissionstodiluteanddepositfurtherdownwind,whichiswhysmokestackstendtobetall.Ambientairvelocityhaseffectsonstackemis-sions.Lowwindstendtoincreasenearbygroundlevelconcentrations,butathighwindspeedstheadditionaldilutionoftheemissionsdecreasesdownwindconcen-trations.Asanexample,ifthepollutantconcentrationdownwindfromapointemissionsourceis10mg/m3ofair,thendoublingthewindspeedshouldresultinaconcentrationof about5mg/m3,orhalf theoriginalconcentration.

Thebuoyancyofaplumeisafactorininitialplumerise.Awarmerorotherwiselower-densityplumewillrise toaheightwhereitmatches thedensityof theair.Interestingly,humidairhasalowerdensitythandryair.ThisisbecausethemolecularweightofH2Ovapor(18atomicmassunits)islessthanthatofboth

Exhibit 2–1 Aciddeposition(acidrain,snow,andaerosols).

Thedepositionofacidicairpollutioncanhaveadverseeffectsonsoilandfreshwaterlakesthataredownwindfromlargesourcesofsulfurdioxide,sulfuricacid,NO,NO2,andnitricacid.Aciddeposition,whichreferstothedepositionofrain,snow,fog,oracidaerosols,cancauseimmediateand/ordelayeddecreasesinthepHofwaterandsoil.Thedelayedeffectsaremainlyduetothemeltingofacidifiedsnowandthesubsequentrunoff.Theeffects,whichdependonthebufferingcapacityoflakesandsoil,includedecreases(orelimination)ofsensitivespeciesoffishanddecreasedgrowthofforests.TheEasternUnitedStatesandEasternEuropehavebeenmostheavilyimpactedbyaciddeposition,primarilyduetothepresenceofemissionsofacidsandacidprecursors.Emissioncontrols,e.g.,sulfurreductionsincoal,arepartiallydirectedtowardreducingtheadverseeffectsofaciddepositioninimpactedareas.

Thechemistryofacidrain,snow,fog,andaerosolshasbeenextensivelystudied.TheneutralpHofpurewater,i.e.,neitheracidicnorbasic,is7.0.Evenpristinerainhasaslightly-acidicpHof5.0to5.65,duetothenaturalCO2andothersubstancesintheair.Downwindofsometypesofindustriesandelectricpowerplants,thepHofraincanbeaslowas4.2.Thisacidityformsover time inplumes. Interestingly, tallersmokestackscanproducemoreacidicconditionsdownwindbecauseof thelongertimesavailableforacidstoform.


9955



N2(28atomicmassunits)andO2(32atomicmassunits),whichmakeupmostoftheair;therefore,watervapordisplacestheseheaviergases.

Whenthesmokestackemitsaplumeatalowupwardvelocityandatatemperatureanddensitynearambientconditionsonecanobservetheinteractionoftheplumewiththewindandtheverticalairtemperatureprofile.Figure 2–12showstwolikelyverticaltemperaturepro-filesintheatmosphere.Thesolidlineshowsthestandardlapse rate,whichisthenormaldecreaseinairtemperaturewithaltitudeinthetroposphere.Thestandardlapserateis9.8°Cperkm,butitcanvary.Thedashedlinerepresentsthetemperatureprofileinalow-level(400m)inversioncondition.Suchinversions,whichcanbelowerorhigherthan400m,arenotuncommon.Figure 2–13showsatopviewofatypicalsmokestackplumecarriedbyawindmovingfromlefttoright.Notethattheplumespreadsoutwardandisdilutedasittravelswiththewind.Theconcentrationofpollutantsintheplumeisusuallygreat-estalongitscenterline,taperingtolowconcentrationsatitsperiphery,aspredictedbytheGaussianplumemodel.Similarly,ifviewedfromtheside,thecenter-lineoftheplumewillhavethehighestconcentrationofstackemissions.

Figure 2–14showstheeffectofwindonaplumeinthenormallapse-ratecase.Withnowind,thetypical

plumewillriseandspreadlaterally.Inawind,theplumewillalsospreadas it isblown.Thespreadingplumemaytouchthenearbygroundifthesmokestackisshort,whichcanproducehighlevelsofemissionsatgroundlevelnearthestack.

Figure 2–15 demonstrates plume behavior in aninversionconditionwhenthesmokestackisaboveorbelowtheinversionheight.Asfortheshortsmokestack,anemissionbelowtheinversionlayercanproducesub-stantiallocalground-levelconcentrations.Theconditionofalowinversionheightandanevenshortersmokestackiscalledtrapping.

0 2 4

Distance downwind (km)

Top view

6

Figure 2–13 Topviewofapoint-sourceplumeinalightwind. Source: The University of California Air

PollutionHealthEffectsLaboratory,withkindpermission.

Tall stack,no wind

Tall stack,light wind

Short stack,light wind

A. B. C.

Figure 2–14 Plumesfrom:A:tallstackwithnowind;B:tallstackwithalightwind;andC:shortstack,withalightwind.


0

500

1000

Alti

tude

in m

eter

s 1500

2000

5 10

Neutrallapse rate

15

Temperature �C

20 25 30

Inversion topat 400 m

Figure 2–12 Variationofairtemperaturevs.heightabovetheEarth’ssurface.Theslopeofthesolidlineistheneutrallapserateof9.8°Cperkm.Thedashedline depicts a hypothetical inversion layer at400mabovegroundlevel.



9955


VII. Quiz and Problems 37

dispersionalsoapplytootheremissionpointsources,suchasfactories,vehicles,andfires.

vi. SuMMAry OF MAjOr POintS

ThesurfaceoftheEarthhasalimitedairvolume,thetroposphere,whichsupportslife.Abovethetroposphere,the stratosphere is also essential to life because itshieldsthesurfacefromharmfulradiationsandhelpstostabilizethetemperatureoftheplanet.Severalscientificdisciplines,eachwiththeirownnomenclature,studyairpollutantsintheatmosphere.Airpollutionstudiesrequirequantitationandpreciseunitsofmeasurementinordertodevelopreliableknowledgeandtodeviseacceptableairqualitystandards.Thereareseveralwaystodefinetheterm“airpollution”dependingonone’sperspective.Regulated(e.g.,criteriaandtoxic)airpol-lutantsareamainfocusofmodernresearch.Airpol-lutantsareemittedbyavarietyofsources,whichmaybe“natural”or“anthropogenic,”“outdoor”or“indoor,”“stationary”or“mobile,”and“point”or“distributed.”Enclosedspacesandworkplacesarehighlyvariedwithrespect to sources and emissions of air pollutants.However,duetothelackofeffectivedilutionandwinddispersal,strictsourcecontrolisusuallyneededinordertoprotectoccupantsintheseenvironments.Althoughgovernmentalregulationhasbeeneffectiveincontrol-ling“normal”emissions,periodicaccidentsandnaturaldisastersaddtothecontinuinghealth-relatedtollofairpollution.

Thetransportofaircontaminantsmustbeconsideredinorder tounderstandtheirdownwindconcentrations,andthusexposuresofpeople,animals,andplants.Oneaspectoftransportthathasbeenwellstudiedisthedisper-sionofplumes.Smokestackplumesaredispersedundertheinfluenceofmeteorologicalconditions(e.g.,windspeedandverticalairtemperatureprofiles)andsmoke-stackdesign(specificallysmokestackheightabovethesurface).

vii. Quiz And PrObLEMS

Quiz Questions

(select the best answer)

1. The“troposphere”:a. isatermthatdescribestheuppermostregion

oftheEarth’sair.

Figure 2–16showstheeffectofthestrength(steepnessoftheairtemperatureprofile)oftheenvironmentallapserate.Ifthelapserateisstrong,loopingoftheplumecanoccur,whichcancausetheplumetodescendtothesurface, rise, and descend again. If the lapse rate isweak,theplumetendstoremainaloft.

Themostseriousconditions,suchasashortsmoke-stack,anemissionbelowalowinversion,andastronglapserate,havethepotentialforproducinghighground-levelconcentrationsofemissions.Intheidealcasethesmokestackwillbetallenoughtoallowsubstantialdilutionoftheplumebeforeitreachesthesurface.Theexamplesgivendemonstratejustsomeofthefatesofsmokestackplumes.Theprinciplesofsmokestackplume

Effect of stack height

Inversion layer

A. B.

Figure 2–15 Effectofstackheight:A:aboveinversionlayer;andB:belowinversionlayer.


Effect of lapse rate on a smokestack plume

A. B.

Figure 2–16 Effect of lapse rate on a smokestack plume:A:forastronglapserateinwhichthedecreaseintemperaturevs.altitudeismuchgreaterthannormal,producingloopingoftheplume;B:foranormallapse-ratecondition.



9955



c. negligible in comparison to outdoor airpollution.

d. independentoftheactivitiesofoccupants. 9. Theuseofaircleanersindoors:

a. isthebestwaytodealwithbuilding-relatedillnesses.

b. istheprimarymeansofcontrollingindoorairqualityinthehome.

c. isagoodmethodforcontrollingindoorcar-bonmonoxide,butnotindoorallergens.

d. areeffectiveifthemajorsourcesofairpollut-antshavebeenremovedandthefilteringrateandefficiencyaresufficient.

10. TheU.S.EPA’sdesignatedhazardousairpollut-ants(HAPs):a. arealsocalled“secondaryNAAQS.”b. isalistofsubstancesthatcanchangethrough

bothadditionsanddeletionsbytheU.S.EPA.c. includeclassesofairpollutants,butnotindi-

vidualsubstances.d. havebeendeterminedtocauseadverseenvi-

ronmental effects but not adverse humanhealtheffects.

11. Howdoestheheightofasmokestackinfluencethe ground-level concentrations of its emittedparticlesandgases?a. Itisnotanimportantfactor.b. It isonly important if there isan inversion

condition.c. It is only importantwhenwind speeds are

low.d. Noneoftheabovearetrue.

12. Which meteorological factors are importantin influencing ground-level air pollutantconcentrations?a. precipitation.b. windspeed.c. inversions.d. Alloftheabovearetrue.

Problems

1. Convertthefollowingtoppm.10percent100percent1ppb

b. isover1,000kmthick.c. providestheairinwhichtheEarth’sliving

thingsexist.d. consistsof80percentoxygenand20percent

ozone. 2. Anairinversioniscausedby:

a. stagnantwinds.b. lowatmosphericpressure.c. coolerairontopofwarmerair.d. warmerairontopofcoolerair.

3. Thethreeaircontaminants,ozone,sulfurdioxide,andcarbonaceousfineparticles,are:a. onlynaturalaircontaminants.b. onlyanthropogenicaircontaminants.c. both natural and anthropogenic air con-

taminants.d. neithernaturalnoranthropogenicaircon-

taminants. 4. Howdoairpollutantconcentrationsof10-3and

10-6mg/m3comparetoeachother?a. 10-3isathousandtimesgreaterthan10-6.b. 10-6istwotimesgreaterthan10-3.c. 10-3istwotimesgreaterthan10-6.d. 10-6isthreetimesgreaterthan10-3.

5. Whatfactorscanclassifyasubstanceasanairpollutant?a. presenceintheair.b. interferencewithhumanhealthorwelfare,

damagetomaterialsorobjectsofvalue,orinterferencewithimportantscientificprocesses.

c. bothaandb.d. Noneoftheabovearetrue.

6. Howwouldoneclassifythepopulationofcross-countrymotorcyclesassourcesofairpollution?a. stationary,distributed,andnatural.b. mobile,distributed,andanthropogenic.c. mobile,point,andnatural.d. stationary,point,andanthropogenic.

7. Themajoranthropogenicsourcesofparticulateairpollutantsare:a. stationary-sourcefuelcombustion.b. mobile-sourcefuelcombustion.c. volcaniceruptionsandnaturalfires.d. bothaandb.

8. Indoorairpollutionis:a. source-dominated.b. meteorologydominated.


9955


VIII. Discussion Topics 39

references and recommended reading

ACGIH® (American Conference of GovernmentalIndustrialHygienists),ACGIH®, TLVs®, and BEIs®,American Conference of Governmental IndustrialHygienists,Cincinnati,OH,2010.

Costa,D.L.,“Airpollution,”inCasarett and Doull’s Essentials of Toxicology,Klaassen,C.D.,andWatkins,J.B., III, eds., McGraw–Hill, New York, 2003,Chapter28,pp.407–418.

Finlayson–Pitts,B.J.andPitts,J.N.Jr.,Atmospheric Chemistry: Fundamentals and Experimental Tech-niques,JohnWiley&Sons,NewYork,1986.

Gammage,R.B.andBerven,B.A.,eds.,Indoor Air and Human Health, 2nd Edition,LewisPublishers,BocaRaton,FL,1996.

Grant,L.D.,Shoaf,C.R.,andDavis,J.M.,“UnitedStatesandinternationalapproachestoestablishingair standardsandguidelines,” inAir Pollution and Health,Holgate,S.T.,Samet,J.M.,Koren,H.S.,andMaynard,R.L.,eds.,AcademicPress,SanDiego,CA,1999,Chapter42,pp.947–982.

HindsW.C.,Aerosol Technology: Properties, Behavior and Measurement of Airborne Particles, 2nd Edition,Wiley–Interscience,NewYork,1999.

Lippmann,M.andMaynard,R.L.,“Airqualityguide-linesandstandards,”inAir Pollution and Health,Holgate, S.T., Samet, J.M., Koren, H.S., andMaynard,R.L.,eds.,AcademicPress,SanDiego,CA,1999,Chapter43,pp.983–1017.

(NOAA)NationalOceanicandAtmosphericAdmin-istration,NationalAeronauticsandSpaceAdminis-trationandU.S.AirForce,U.S. Standard Atmosphere,1976,NOAA–S/T76–1562,WashingtonDC,1976.

Perkins, J.L., Modern Industrial Hygiene, Vol. I: Recognition and Evaluation of Chemical Agents, 2nd Edition,AmericanConferenceofGovernmentalIndustrialHygienists,Cincinnati,OH,2008.

Rom,W.N. andMarkowitz,S., eds.,Environmental and Occupational Medicine, 4th Edition,LippincottWilliams&Wilkins,Hagerstown,MD,2006.

Samet, J.M. and Spengler, J.D., eds., Indoor Air Pollution: A Health Perspective, Johns HopkinsUniversityPress,Baltimore,MD,1991.

Scaillet,B.,Arevolcanicgasesserialkillers?Science,319:1628–1629,2008.

Seinfeld,J.H.andPandis,S.N.,Atmospheric Chem-istry and Physics, 2nd Edition,Wiley–Interscience,NewYork,2006.

2. If the Earth and its atmosphere shrunk to thesize of an apple, how thick would the tropo-spherebe?

3. Howmuchtimeisrequiredforanaircleanerwithathroughputairrateof15cubicfeetperminute(1cubicfoot=0.0283m3)tofilterthevolumeofairinaroom20feetby20feetby10feet(1foot=0.305m)?

4. Using Table 2–4, estimate the percent of totalPM10emissionsthatcomefromvehicles.

5. Ifanasthmaticchildlivedinyourhome,namesixsourcesofairpollutantsthatshouldbeeliminatedorgreatlyreduced.

6. Recommendationsforchildrenatschoolincludeallowingthemtogooutsideduringrecesseveninsmoggycities.Howcanthisrecommendationbejustified?

7. If gasoline-powered cars were all replaced byelectric vehicles, what air pollutants would bereduced?Whatairpollutants,ifany,wouldnotbereduced?

viii. diSCuSSiOn tOPiCS

1. Whatarethemajorsourcesandemissionsofairpollutants in your community? Do the sourcesbenefitthecommunity?Howwouldonedecideon whether or not a specific pollutant sourceshould be shut down or required to reduce itsemissions?

2. What jobs/occupations expose workers to thepoorest air quality? Contrast the air quality-relatedhazardsforanelementaryschoolteacher,afarmer,aparamedic,andaconstructionworker.Whichoccupationismostlikelytodeveloplungdisease?

3. Shouldindoorpottedplantsberecommendedfortreatingpeoplewithasthma?Discusstheprosandconsassociatedwithyourselection.

4. Cantheairinacitybetooclean?5. You are charged with the task of designing a

smokestackforanewchemicalplantthatwillbebuilt somewhereneara largecity.Theadversepublichealtheffectsareaconcern.Whatfactorswouldyoutakeintoaccountthatwouldinfluenceyourdesign?


9955


2ND REVISE

U.S.EnvironmentalProtectionAgency,WashingtonDC,1991.

U.S. EPA (United States Environmental ProtectionAgency) National Air Pollutant Emission Trends,EPA–454/R–00–02,U.S.EnvironmentalProtectionAgency,officeofAirQualityPlanningandStandards,ResearchTrianglePark,NC,2000.

U.S. EPA (United States Environmental ProtectionAgency),Our Nation’s Air: Status and Trends Through 2008, EPA–454/R–09–002, U.S. EnvironmentalProtectionAgency,ResearchTrianglePark,NC,2010.

Sidel,V.W.,Onel,E.,Geiger,H.J.,Leaning,J.,andFoege,W.H.,“Publichealthresponsestonaturalandhuman-madedisasters,”inPublic Health and Pre-ventive Medicine, 13th Edition, Last, J.M., andWallace,R.B.,eds.,Appleton&Lange,Norwalk,CT,1992,Chapter74,pp.1173–1186.

Stern,A.C., ed., Air Pollution, Vol. I., 3rd Edition,AcademicPress,NewYork,1976.

U.S. EPA (United States Environmental ProtectionAgency)Building Air Quality: A Guide for Building Owners and Facility Managers,EPA/400/1–91/033,


9955

Sources and Emissions of Air Pollutantssamples.jbpub.com/9780763780449/80449_Ch02_021_rev2.pdf ·...

Documents

Transcript of Sources and Emissions of Air Pollutantssamples.jbpub.com/9780763780449/80449_Ch02_021_rev2.pdf ·...