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DESCRIPTIO N

OF TH E OAQP S RIS KPROGRA M AND TH E

ONGOINGLEAD NAAQ S RIS KASSESSMEN T PROJEC T

Thoma s McCurd y

Harve y M . Richmon d

U.S . Environmenta l Protectio nAgenc y Researc hTriangl e Park , Nort hCarolin a

Fo r presentatio na t th e 76t hAnnua l Meetin g o f th e

Ai r Pollutio nContro l Associatio n

Atlanta , Georgi a Jun e 19-24 , 198 3P. 3

DESCRIPTIO N

O F TH E OAQP S RIS KPROGRA M AND TH E ONGOINGLEAD NAAQ S RIS KASSESS PROJECT , T . McCurdy

an dH . M . Richmond , U.S . Environmenta l Protectio nAgency , Researc hTriangl e Park , N.C . 2771 1

EPA' s Offic e o f Ai r Qualit y Plannin g an

dStandards ' effort s t o develo pforma l quantitativ e ris k assessmen t method s t o ai di nmakin g futur e decision s o nalternativ e nationa l ambien t ai r qualit y standard s (NAAQS ) ar e briefl y described . Th e multi-year , ongoin g ris k analysi s program i s separate dint o two mai ndivisions : ris k assessmen t an dris k evaluation . Emphasi s o f th e program t o dat e ha s bee nondevelopin g an d applyin g alternativ e ris k assessmen t methods , two o f whic har e mor e full y describe d i ncompanio npaper s presente di nthi s session . EP A i s considerin g utilizin g a forma l ris k assessmen t metho di nth e ongoin g revie w o f th e lea d(Pb ) NAAQS . EPA' s initia l thinkin g o nth e focu s an dstructur e o f th e P bris k assessmen t projec t ar e briefl y described . Th e projec t plan s wil l b e reviewe db

y a Clea nAi r Scientifi c Advisor y Committe e Subcommitte e onHealt hRis k Assessment .

83-7. 1

DESCRIPTIO N

O F TH E OAQP S RIS KPROGRA M AN D TH E ONGOINGLEAD NAAQ S RIS KASSESS PROJECT , T . McCurd y

an dH . M . Richmond , U.S . Environmenta l Protectio nAgency , Researc hTriangl e Park , N.C . 2771 1

EPA' s Offic e o f Ai r Qualit y Plannin g an

dStandards ' effort s t o develo pforma l quantitativ e ris k assessmen t method s t o ai di nmakin g futur e decision s o nalternativ e nationa l ambien t ai r qualit y standard s (NAAQS ) ar e briefl y described . Th e multi-year , ongoin g ris k analysi s program i s separate dint o two mai ndivisions : ris k assessmen t andris k evaluation . Emphasi s o f th e program t o dat e ha s bee no ndevelopin g an d applyin g alternativ e ris k assessmen t methods , two o f whic har e mor e full y describe d i ncompanio npaper s presente di nthi s session . EP A i s considerin g utilizin g a forma l ris k assessmen t metho di nth e ongoin g revie w o f th e lea d(Pb ) NAAQS . EPA' s initia l thinkin g onth e focu s an dstructur e o f th e P bris k assessmen t projec t ar e briefl y described . Th e projec t plan s wil l b e reviewe db

y a Clea nAi r Scientifi c Advisor y Committe e Subcommitte e onHealt hRis k Assessment .P. 4
83-7.. 1

DESCRIPTIO NO F TH E OAQP S RIS K PROGRAM AN D TH E ONGOIN G LEA D NAAQ S RIS K ASSESSMEN T PROJEC T

Introductio n Th e Clea n Ai r Act , a s amende d i n 1977 , require s periodi c revie wand revision , i f needed , o f al l nationa l ambien t ai r qualit ystandard s (NAAQS ) t o ensur e tha t the yar e base d o n th e lates t scientifi c knowledge

. Thi s pape r briefl yreview s th e histor yo f th e Offic e o f Ai r Qualit yPlannin g an d Standards ' (OAQPS ) effort s t o develo p forma l quantitativ e ris k assessmen t method s t o ai d i n makin g futur e decision s o n NAAQS

. Afte r th e OAQP S ris k progra mi s described , th e pape r focuse s o n th e ongoin g ris k assessmen t projec t fo r th e lea d NAAQ S review

. Apropose d conceptua l framewor k describin g th e role s o f scientifi c knowledge , ris k assessment , and ris k evaluatio n i n settin g futur e NAAQ S an d th e relationshi p o f thi s framewor k t o th e existin g Clea n Ai r Ac t an d curren t standard-settin g procedure s hav e bee n describe d elsewhere.1' 2 OAQP S Ris k Analysi s Progra m Sinc e 1977 , OAQP S ha s bee n developin g an d explorin g th e potentia l futur e us e o f quantitativ e healt h ris k assessmen t approache s t o ai d i n makin g decision s o n primar y(health-based ) NAAQS

. EPA' s effor t t o develo p a ris k assessmen t approac h fo r NAAQ S decision s bega n durin g th e revie wo f th e photochemica l oxidan t (late r redesignate d ozone ) ambien t standard

. I n 1977 , Thoma s Feagans , a n OAQP S analyst , an d Dr

. Willia mBiller , a n OAQP S contractor , develope d a healt h ris k assessmen t approac h fo r analyzin g alternativ e ozon e NAAQS

. Incorporatin g som e o f th e technique s and principle s develope d i n th e fiel d o f decisio n analysis , th e approac h involve d elicitin g judgmenta l probabilitie s fro mhealt h and ai r qualit yexpert s t o represen t th e majo r uncertaintie s whi.c h giv e ris e t o healt h risk s associate d wit h attainmen t o f alternativ e NAAQS

. Result s o f th e ozon e ris k assessmen t wer e summarize d i n th e propose d rulemakin g notic e an d a documen t describin g th e applicatio n o f th e metho d t o ozon e wa s issue d i n Jul y1978.3> 4 I n th e proposa l notic e EP Aacknowledge d tha t th e metho d ha d no t receive d adequat e peer-revie wan d EP Aconclude d i n th e promulgatio n notic e tha t th e metho d require d furthe r stud yan d development.* ^

A t OAQPS' s request , EPA' s Scienc e Advisor yBoar d (SAB ) establishe d a Subcommitte e o n Healt h Ris k Assessmen t t o revie wth e ozon e an d othe r ris k assessmen t method s bein g use d o r develope d withi n th e Agency

. Afte r it s firs t meetin g i n Apri l 1979 , th e Subcommitte e commende d EP Afo r recognizin g th e nee d fo r and undertakin g developmen t o f quantitativ e subjectiv e decisio n aid s fo r us e i n assessin g healt h risk s associate d wit h NAAQS. ' Th e Subcommittee , however , strongl yrecommende d tha t EP Ano t appl yth e ris k assessmen t metho d develope d durin g th e ozon e revie wunti l th e approac h wa s furthe r developed , bette r explained , and publishe d i n peer-reviewe d journals

. Th e Subcommitte e als o recommende d tha t OAQP S develo p an d evaluat e othe r ris k assessmen t method s i n additio n t o th e approac h use d i n ozone .P. 5 83-7. 1

I nrespons e t o th e SA B Subcommitte e recommendations , OAQP S develope d a n expande dris k analysi s program inth e fal l o f 1979. 8 Th e ris k analysi s program involve s bot hris k assessmen t an dris k evaluatio nprojects . However , th e majo r emphasi s o f th e program t o dat e ha s bee nonris k assessment , whic hi s define da s th e proces s o f makin g ris k estimate s an ddescribin g th e severit y o f harm associate dwit hadvers e events . Ris k evaluatio ni s define da s th e proces s o f evaluatin g how

muc hris k i s acceptabl e i nligh t o f al l relevan t circumstances . Th e firs t projec t undertake ni ndevelopin g alternativ e ris k assessmen t approache s wa s a highl y interactiv e effor t involvin g si xgroup s o f distinguishe d researcher s fro

m a variet y

o f disciplines , includin g decisio nanalysis , biostatistics , an

dbehaviora l psychology . Th e objective s o f thi s projec t wer e t o (1 ) develo pconceptua l ris k assessmen t approache s suitabl e fo r us e b y EP A i n reviewin g ambien t ai r standards , an d(2 ) narrow

dow nthes e alternative s t o 2 - 3 approache s fo r furthe r development . A two-da y

kick-of f publi c meetin g wa s hel di nApri l 198 0 a t whic hinformatio n an dview s wer e exchange donth e problem o f developin g a suitabl e ris k assessmen t approac hfo r NAAQS . At th e conclusio no f th e project , th e SAB Subcommitte e reviewe dth e si xconceptua l approache s an dconclude dtha t two approache s particularl y

warrante dfurthe r development.9«1 0

Inparalle l wit hth e alternativ e conceptua l approache s project , Feagan s andBille r develope dfurthe r th e metho dtha t hadbee nuse dfo r th e ozon e ris k assessmen t (hereafte r "F/ B Ris k Assessmen t Method"). 1 1 I nMa y 198 1 th e SA B Subcommitte e reviewe da repor t describin g th e F/ B Ris k Assessmen t Metho dand conclude dthat , "while th e F/ B approac hma y hav e commendabl e aspect s a s a researc heffort , i t i s not , init s presen t form , a nimplementabl e too l fo r publi c polic y

decisio nmakin g . . ." 1 2 Th e Subcommitte e als o recommende d tha t th e author s publis hthei r wor k i npeer-reviewe djournal s s o tha t other s i nth e professiona l communit y coul djudg e th e merit s o f thei r viewpoint . Th e author s ar e followin g th e Subcommittee' s recommendation s t o publis hthei r work , bu t onl y

th e firs t o f a planne dserie s o f paper s ha s bee npublishe ds o far. 1 3

Ina neffor t t o furthe r develo pth e two promisin g alternativ e conceptua l approache s recommende db y th e SAB , OAQP S awarde dseparat e contract s t o SR I Internationa l an

dWoodward-Clyd e Consultant s i nJun e 1981 . Thes e developmenta l project s wer e oriente dtowar da nillustrativ e applicatio no f th e tw o conceptua l approache s usin g carbo nmonoxid e (CO ) a s th e pollutan t o f interest , on e o f th e si xpollutant s fo r whic hNAAQ S exist . Report s describin g th e two illustrativ e applicatio nproject s hav e bee ncomplete dan dwil l b e reviewe db y a Subcommitte e recentl y create db

y th e Clea nAi r Scientifi c Advisor y Committe e (CASAC). 1 4,1 5 Th e two project s ar e summarize di ntwo othe r paper s inthi s session. 1 6 * 1 7
OAQP S ha s undertake na ninteragenc y agreemen t wit hArgonn e Nationa l Laborator y

t o conduc t a ris k assessmen t fo r alternativ e lead(Pb ) ambien t standards . Th e approac huse db y Argonn e wil l b e base do nth e bes t feature s o f th e developmenta l effort s discusse dabov e an dth e recommendation s o f th e CASA C Subcommittee . Th e nex t sectio no f thi s pape r discusse s i nmor e detai l th e PbNAAQ S ris k assessmen t project .P. 6 83-7. 1

Lea dNAAQ S Ris k Assessmen t Projec t OAQP S believe s tha t th e ris k assessmen t program i s now a t a stag e wher e a napplicatio nprojec t fo r anon-lin e standard-settin g effor t i s desirable . Th e NAAQ S pollutan t selecte dt o appl y th e OAQP S ris k assessmen t metho di s lea d (Pb) . Th e existin g P bstandar dwa s se t i n197 8 an di s now

u pfo r revie w

unde r §109(d)(l ) o f th e Clea nAi r Act . A Subcommitte e o f CASA C i s assistin g th e ful l Committe e i nreviewin g th e Pbris k assessmen t project . Th e Subcommittee' s view s an

dguidanc e wil l b e ver y importan t i nth e conduc t o f th e Pbproject . Fo r thi s reason , th e idea s an dapproac hdescribe dbelo w ar e tentativ e an

dma y b e altered . I

nfact , whethe r o r no t th e ris k estimate s derive da s par t o f th e projec t wil l b e use di nth e PbNAAQ S revie w depend s upo nCASAC' s review , publi c comment s regardin g th e technica l adequac y o f th e approach , andEP A management' s evaluatio no f th e usefulnes s o f th e technique .
Focu s o f th e P bRis k Projec t Fina l judgment s o

nth e scop e an

dfocu s o f th e ris k assessmen t wil l b e base d o na revie w

o f th e scientifi c evidenc e presente dan devaluate dinth e revise d Pbcriteri a document . Base dona preliminar y revie w o f th e scientifi c evidence , OAQP S i s considerin g narrowin g th e scop e o f th e P bris k projec t i nth e manne r describe dbelow . 

### 1 . Exposur e an

dris k extimate s wil l be obtaine dfo r onl y 1 0 citie s (due t o limitation s o navailabilit y

o f Pbai r qualit y

dat a fo r urbanize dareas ) an

dfo r a representativ e sampl e o f area s surroundin g selecte dmajo r poin t source s o f Pbemission s (primar y an dsecondar y smelters , batter y

manufacturin g plants , etc.) . Thus , exposur e and ris k estimate s wil l no t b e applicabl e t o th e natio na s a whole . 2 . Exposur e an

dris k estimate s wil l b e provide dfo r two potentiall y sensitiv e populatio ngroups : childre n6 year s ol dan dyounge r and pregnan t women . 3 . Ris k estimate s wil l b e provide dfo r u pt o eigh t genera l healt heffect s indicators : hem e biosynthesis , cognitive/behaviora l effects , electrophysiologica l effects , rena l function , reproductiv e and developmenta l effects , deliver y complications , erythropoieti c effects , andcardiovascula r an dimmunologica l functiona l impacts . Th e Pbris k projec t wil l investigat e al l significan t environmenta l pathway s o f P bexposure , includin g wate r andfoo dingestion , othe r ingestio n (sucha s pic a fo r paint) , an dinhalation . Finally , th e impac t o f varyin g th e averagin g time s fo r th e standar dwil l b e investigated . Th e curren t averagin g tim e i s a calenda r quarter . Structur e o f th e PbRis k Projec t
Th e overal l structur e o f th e P bris k projec t i s depicte di nFigur e 1 . Ther e ar e fiv e majo r component s o f th e project . Th e firs t tw o componen t model s ar e focuse do npredictin g tota l P bexposur e fo r th e sensitiv e group s o f concer n i nth e geographica l area s o f interes t (se e above) . Input s t o th e firs t componen t mode l includ e alternativ e Pbai r qualit y standard s unde r consideration , existin g< Alternate P bAmbien t Standard s Poin t

Sourc e Modelin g

Componen t Mode l 1 . Ambien t ai r qualit y model .

Tim e Serie s Analysi s o f Ambien t Ai r Dat a /Predicte d \

- XP bAmbien t V J \ Level s / Huma n

Activit y Dat a

" S * Componen t Mode l 2 . Urba narea specifi c human exposur e mode l (NEM) .

/• » Populatio n& Trave l Dat a /Tot a



### - X Expo \Esti i Tota l P b sur e mate s

Figur e 1 . Flo

w Char t o f th e Lead NAAQ S Ris k Assessmen t Project . EXPOSUR E REPOR T 

# S- >

RIS K REPOR T Componen t Mode l 3 . Physiologica l uptak e model . 

# H 'Estimate d

Physiologi c ^Indicator ;

Healt h Exper t Encodin g Componen t

Mode l 4 . Dose-effec t relationshi p models .

Componen t Mode l 5 . Area-specifi c ris k assessmen t model . 

### XL

ead Coun t Ris k Estimate s >

•>!P. 8
83-7. 1

ai r qualit y

distribution s (a s supplemente db y tim e serie s analysi s t o obtai na complet e dat a set) , an dpoin t sourc e modelin g outputs . Th e prime produc t o f Componen t Mode l 1 i s estimate ddail y ai r qualit y

concentration s a t specifie d geographica l area s (calle dneighborhoo dtypes ) fo r eac ho f th e te ncitie s an d majo r poin t source s bein g analyzed . Componen t Mode l 2 develop s area-specifi c tota l exposur e estimate s fo r subjec t populatio ngroups . Bot hai r an dnon-ai r exposure s wil l b e accounte d for , an dth e outpu t o f th e mode l wil l b e inth e for m o f (1 ) distribution s o f exposure s experience db y sensitiv e groups , an d(2 ) th e expecte dnumbe r o f peopl e expose dt o variou s concentratio nlevels . Th e prim e input s t o Mode l 2 ar e th e ai r qualit y

estimate s fro

m Mode l 1 , informatio no npeople' s activit y patterns , an

dprobablisiti c "additiv e factors " o f Pbcontribution s fo r eac h environmenta l pathwa y o f Pbtha t wil l b e modeled . Fo r a mor e thoroug hdiscussio n o f th e exposur e component s o f th e OAQP S ris k assessmen t procedure , se e Bille r e t al . (198 1 ). 1 8

Componen t Mode l 3 tranform s tota l Pbexposur e estimate s int o distribution s o f bloo dan

ddentin e Pbinsensitiv e populatio ngroup s i nth e analyze dareas . Thi s "uptake " physiologica l mode l itsel f contain s two submodels : (1 ) anabsorptio n mode l relatin g P bexposur e estimates , disaggregate db y environmenta l pathway , t o Pbretaine dinth e body , an d(2 ) an

equilibriu

m mode l relatin g th e interchang e o f P bamon g body

organisms . Th e absorptio nmode l provide s a dail y estimat e o f Pbretaine dinth e body . Th e equilibriu m mode l produce s dail y an dtime-average d estimate s o f bloo dPban ddentin e Pb(inshe dteeth) . T o accomplis hthi s require s tha t th e interactio namon g bone , tissue , blood , andothe r pool s o f bod y Pbb e explicit y

modeled . Componen t Mode l 3 output s wil l b e i nth e form o f distribution s o f bloo dand/o r dentin e Pbi nsensitiv e populatio ngroups , an dinth e form

o f expecte dnumber s o f peopl e havin g a specifie dleve l o f bloo d o r dentin e Pbconcentrations . Th e prime output s o f componen t model s 4 and5 ar e probabilisti c estimate s o f healt hris k t o sensitiv e populatio ngroup s associate dwit halternativ e P b NAAQ S i nth e geographica l area s bein g analyzed . (Fo r a mor e thoroug hdiscussio n o f probablisti c ris k estimates , als o calle dbenchmar k an dhea dcoun t risk , se e reference s 1 9 and20) . Mode l 4 i s primaril y focuse dupo ndevelopin g dose respons e relationship s fo r th e healt heffect s categorie s note dabove . A n importan t par t o f thi s tas k pertain s t o th e probabilisti c encodin g o f healt h exper t judgment s regardin g uncertai nfunctiona l linkage s an dvariable s o f th e dose-respons e relationship . Mode l 5 integrate s th e output s o f Mode l 4 wit h th e exposure/uptak e modelin g result s fro m Mode l 3 t o produc e th e neede d ris k estimates . Result s o f th e projec t wil l b e describe di ntwo reports . Th e firs t repor t wil l b e focuse donexposur e modelin g results , whil e th e secon dwil l summariz e th e exposur e informatio nan ddescrib e output s o f th e uptake an dris k assessmen t models . Thes e report s wil l b e submitte dt o th e CASA C Subcommitte e andth e publi c fo r review . I f thes e review s ar e favorabl e from a scientifi c an

d technica l perspective , OAQP S wil l integrat e th e ris k assessmen t result s wit h it s othe r on-goin g P bstandard-settin g activities , suc ha s th e OAQP S "staf f paper. " (Th

e OAQP S "staf f paper " reflect s th e staff' s interpretatio n o f th e ke y

studie s an

dscientifi c evidenc e describe di nth e criteri a documen tP. 9 83-7. 1

an didentifie s critica l uncertaintie s an djudgment s tha t mus t b e addresse di n th e standard-settin g process.*^ 1 ) I f tha t occurs , th e ris k assessmen t output s wil l b e a forma l par t o f th e P bNAAQ S revie w

proces s andth e ful l CASA C wil l als o revie w

th e ris k report s an dresult s a s par t o f th e overal l revie w o f th e OAQP S staf f paper . I naddition , th e report s wil l b e submitte dt o th e publi c fo r revie w

an dcomment . Thus , ther e wil l b e numerou s opportunitie s fo r intereste dpartie s t o revie w an dcommen t onOAQPS' s Pbris k assessmen t approac h andresults . Thi s hopefull y wil l ensur e anope nandtechnicall y vali dprojec t a s OAQP S furthe r improve s it s technique s t o ai dstandard-settin g decisions .P.1 0 83-7. 1

REFERENCE S

1 . T.B . Feagan s an

d W.F . Biller , A

Genera l Metho d fo r Assessin g Healt h Risk s Associate d wit hPrimar y Nationa l Ambien t Ai r Qualit y Standards , U.S . EPA , Researc hTriangl e Park , N.C , Ma y 1981 . 2 . H.M . Richmond , " A framewor k fo r assessin g healt hrisk s associate d wit h nationa l ambien t ai r qualit y standards. " Th e Environmenta l Professiona l 3_(3):22 5 (1981) . 3 . 4 3 Federa l Registe r 2696 2 (Jun e 22 , 1978) . 4 . U.S . Environmenta l Protectio nAgency , Offic e o f Ai r Qualit y Plannin g an

d Standards , A

Metho d o f Assessin g th e Healt hRisk s Associate d wit hAlternativ e Ai r Qualit y

Standard s fo r Ozone , U.S . EPA , Researc hTriangl e Park , N.C , Jun e 1978 . 5 . 4 3 Federa l Registe r 2696 2 (June 22 , 1978) . 6 . 4 0 Federa l Registe r 820 2 (February 8 , 1979) . 7 . U.S . Environmenta l Protectio nAgency , Scienc e Advisor y Board , Subcommitte e o nHealt hRis k Assessment , Revie w o f " A Metho d o f Assessin g th e Healt h Risk s Associate d wit hAlternativ e Ai r Qualit y Standard s fo r Ozone, " U.S . EPA , Washington , D.C , Septembe r 1979 . 8 . U.S . Environmenta l Protectio nAgency , Offic e o f Ai r Qualit y Plannin g an d Standards , Ris k Analysi s Program Pla nan

d Accomplishments , U.S . EPA , Researc hTriangl e Park , N.C , Februar y 1981 . 9 . U.S . Environmenta l Protectio nAgency , Offic e o f Ai r Qualit y Plannin g and Standards , Conceptua l Approache s t o Healt hRis k Assessmen t fo r Alternativ e NAAQS , U.S . EPA , Researc hTriangl e Park , N.C , Ma y 1981 . 10 . U.S . Environmenta l Protectio nAgency , Scienc e Advisor y Boar d Subcommitte e onHealt hRis k Assessment , Approache s t o Healt hRis k Assessmen t fo r Alternativ e Nationa l Ambien t Ai r Qualit y Standards , U.S . EPA , Washington , D.C , Decembe r 1980 . 11 . T.B . Feagan s an

d W.F . Biller , A

Genera l Metho d fo r Assessin g Healt hRisk s Associate d wit hPrimar y Nationa l Ambien t Ai r Qualit y Standards , U.S . EPA , Researc hTriangl e Park , N.C , Ma y 1981 . 12 . U.S . Environmenta l Protectio nAgency , Scienc e Advisor y Boar d Subcommitte e o nHealt hRis k Assessment , Revie w o f " A Genera l Metho d fo r Assessin g Healt hRisk s Associate d wit hPrimar y Nationa l Ambien t Ai r Qualit y Standards, " U.S . EPA , Washington , D.C , Septembe r 1981 . 13 . T.B . Feagan s an

d W.F . Biller , "Ris k assessment : describin g th e protectio n provide d b

y ambien t ai r qualit y standards. " Th e Environmenta l Professiona l 3 . (3) : 23 5 (1981) .P.1 1

83-7.1 . r

14 . R.L . Keene y

e t al. , Developmen t an dApplicatio no f a Ris k Assessmen t Methodolog y

t o Stud y

Alternativ e Nationa l Ambien t Carbo nMonoxid e Standards , U.S . EPA , Researc hTriangl e Park , N.C , Marc h1982 . 15 . A.E . Smith , P.C . McNamee , an dM.W . Merkhofer , Developmen t o f Decisio n Analysi s Methodolog y fo r Healt hRis k Assessment : A nIllustrativ e Applicatio nt o Alternativ e Ai r Qualit y Standard s fo r Carbo nMonoxide , U.S . EPA , Researc hTriangl e Park , N.C , Marc h1982 . 16 . R.L . Keeney , R.K . Sarin , andR.L . Winkler , " A ris k assessmen t mode l fo r th e study

o f alternativ e nationa l ambien t carbo nmonoxid e standards, " pape r t o b e presente da t th e 76t hAnnua l Meetin g o f th e Ai r Pollutio n Contro l Association , Atlanta , 1983 . 17 . P.C . McNamee , M.W . Merkhofer , andA.E . Smith , "Illustrativ e applicatio n o f decisio nanalysi s methodolog y t o healt hris k assessmen t o f ambien t ai r qualit y

standard s fo r carbo nmonoxide, " pape r t o b e presente da t th e 76t hAnnua l Meetin g o f th e Ai r Pollutio nContro l Association , Atlanta , 1983 . 18 . W.F . Biller , e t al. , " A genera l mode l fo r estimatin g exposur e associate d wit halternativ e NAAQS, " pape r 81-18. 4 presente da t th e 74t hAnnua l Meetin g o f th e Ai r Pollutio nContro l Association , Philadelphia , 1981 . 19 . T.B . Feagan s an

dW.F . Biller . A

Genera l Metho dfo r Assessin g Healt h Risk s Associate dwit hPrimar y Nationa l Ambien t Ai r Qualit y Standards , U.S . EPA , Ma y

1981 . 20 . H.M . Richmond , T . McCurdy , an dB . Jordan , "Ris k analysi s i nth e contex t o f nationa l ambien t ai r qualit y standards, " pape r 82-9. 3 presente da t th e 75t hAnnua l Meetin g o f th e Ai r Pollutio nContro l Association , New

Orleans , 1982 . 21 . J . Padget t andH.M . Richmond . "Th e proces s o f establishin g an drevisin g nationa l ambien t ai r qualit y standards. " JAPC A

33(1) : 1 8 (1983) .