Indoor-Air-Pollution-上海交通大学环境科学与工程学院

IndoorAirPollution——RadioactivityfromRadonGasGroupmembers:刘佳颖，叶秋雯，裴伟Outline IntroductionWheredoesradoncomefrom?Howdoesradongetinsidebuildings?ThelevelanddistributionofradonTheRiskofLivingWithRadonReducingRadonRisksIntroductionAlthoughpollutantconcentrationsvarysignificantlyfrombuildingtobuilding,thelevelsofsomecommonairpollutantsoftenaregreaterindoorsthanoutdoors.Sincemostpeoplespendmoretimeindoorsthanoutdoors,exposuretoindoorairpollutantsisanimportantenvironmentalproblem.What’sindoorairpollution?

IndoorAirPollutionisthetermusedtodescribetheamountofcontaminantsintheairinsideabuildingfromsourcessuchascigarettesmoking,fuelcombustionforheatingorcooking,certainwallboards,carpets,orinsulationaswellasthegeologyofthearea(radoninsoilorrocksbeneaththestructure).What’sradon(氡)?Radonisanaturally-occurringradioactive(放射性的)butinert(惰性的)gaspartofthedecaychainthatstartswithuranium(铀)andendswithplumbum(铅).

Uranium-238DecayChainPropertyofRadonSingleatomgasInert,colorless,odorlessatordinarytemperaturesMeltingpoint:202degreesKBoilingpoint:211degreesKAtomicradius:1.34angstroms(theheaviestknowngas)Half-life:3.8daysWheredoesradoncomefrom?Naturalsource:Earthandrockbeneathhome;Wellwater;Outdoorair;Artificialsource:Dailylifematerials:leather;lowdensityplastic(likeplasticbags,etc.);paintsBuildingmaterials:gypsumboard(sheetrock),concreteblock,mortar,sheathingpaper(tarpaper),woodpaneling,andmostinsulation.Someuraniumispresentinallearthmaterials.Oncontinentalsurfacestherocks,sedimentsandsoilstypicallycontainbetween1and3partspermillion(abbreviatedppm)ofuranium.Someearthmaterialsmayhavemore.Howdoesradongetinsidebuildings?

CracksinsolidfloorsConstructionjointsCracksinwallsGapsinsuspendedfloorsGapsaroundservicepipesCavitiesinsidewallsThewatersupplyRadonfromsoilgasisthemaincauseofradonproblems.Howmuchofradonreachesthesurfacedependsontheuraniumcontentoftheunderlyingearthmaterialstogetherwiththeirdepthandpermeability(thatis,thepresenceoffracturesandinterconnectedporespacesthatactasconduitsforradon).Enterthelowestlevelofabuildingusingwhateverpathwaysareavailable.SoilForstructureswithbasementsorslab-on-gradefoundations,theentrypointsincludeCracksandporesinfloorslabs,walls,andfloor-walljoints;Openingsaroundsumppumps,floordrains,andpipespenetratingfloorsandwalls.Structureswithacrawlspacebetweenthegroundandlowestfloorlevelmaybelessvulnerabletoradon,whichtendstoescapetotheoutsideairwhenappropriateventsareinstalled,butcanstilladmitsomeofthegasthroughcracksintheflooring.

WaterRadoncanalsoenterintohomesthroughthewatersystem.Thisismainlytrueforhousesinwhichgroundwaterisusedasthemainwatersupply.Smallpublicwaterworksandprivatedomesticwellsoftenhaveclosedsystemsandshorttransittimesthatdonotallowradontodecaytoharmlessby-productsbeforeenteringahome.Onceinside,radonescapesfromthewatertotheindoorairaspeopletakeshowers,washclothesordishes,orotherwiseusewater.Theareasmostlikelytohaveproblemswithradoningroundwaterarethosewithhavehighlevelsofuraniumintheunderlyingrocks.Waterinriversandreservoirsusuallycontainsverylittleradon,becauseitescapesintotheair.Thushomesthatrelyonsurfacewaterusuallydonothavearadonproblemfromtheirwater.Inbigcities,waterprocessinginlargemunicipalsystemsaeratesthewater,whichallowsradontoescape,andalsodelaystheuseofwateruntilmostoftheremainingradonhasdecayed.TheAverageLevelofRadonFoundinaHomeBasedonanationalresidentialradonsurveycompletedin1991,theaverageindoorradonlevelisabout1.3picocuries(皮居里=10-12Ci)perliter(pCi/L)intheUnitedStates.Theaverageoutdoorlevelisabout0.4pCi/L.

ThesafelevelofradonThereisnosafelevelofradon--anyexposureposessomeriskofcancer.

Zone1countieshaveapredictedaverageindoorradonscreeninglevelgreaterthan4pCi/L(picocuriesperliter)(redzones)Zone2countieshaveapredictedaverageindoorradonscreeninglevelbetween2and4pCi/L(orangezones)Zone3countieshaveapredictedaverageindoorradonscreeninglevellessthan2pCi/L(yellowzones)TheRiskofLivingWithRadonRadongasdecaysintoradioactiveparticlesthatcangettrappedinyourlungswhenyoubreathe.Astheybreakdownfurther,theseparticlesreleasesmallburstsofenergy.Thiscandamagelungtissueandleadtolungcanceroverthecourseofyourlifetime.Smokingcombinedwithradonisanespeciallyserioushealthrisk.Childrenhavebeenreportedtohavegreaterriskthanadultsofcertaintypesofcancerfromradiation,buttherearecurrentlynoconclusivedataonwhetherchildrenareatgreaterriskthanadultsfromradon.RadonRiskIfYouSmoke/NeverSmokeRadonLevelIf1,000peoplewhosmokedwereexposedtothisleveloveralifetime*...If1,000peoplewhoneversmokedwereexposedtothisleveloveralifetime*...WHATTODO:

Stopsmokingand...20pCi/LAbout260peoplecouldgetlungcancerAbout36peoplecouldgetlungcancerFixyourhome10pCi/LAbout150peoplecouldgetlungcancerAbout18peoplecouldgetlungcancerFixyourhome8pCi/LAbout120peoplecouldgetlungcancerAbout15peoplecouldgetlungcancerFixyourhome4pCi/LAbout62peoplecouldgetlungcancerAbout7peoplecouldgetlungcancerFixyourhome2pCi/LAbout32peoplecouldgetlungcancerAbout4personcouldgetlungcancerConsiderfixingbetween2and4pCi/L1.3pCi/LAbout20peoplecouldgetlungcancerAbout2peoplecouldgetlungcancer(Reducingradon

evelsbelow2pCi/Lisdifficult.)0.4pCi/LAbout3peoplecouldgetlungcancerNote:Ifyouareaformersmoker,yourriskmaybelower.

*LifetimeriskoflungcancerdeathsfromEPAAssessmentofRisksfromRadoninHomes(EPA402-R-03-003).

**ComparisondatacalculatedusingtheCentersforDiseaseControlandPrevention's1999-2001NationalCenterforInjuryPreventionandControlReports.EPA(EnvironmentalProtectionAgency美国环保署)estimatesthatradoncausesthousandsofcancerdeathsintheU.S.eachyear.ReducingRadonRisksTherearetwowaystoprotectyourfa