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. J

Th e Estimatio n o f Commutin g Pattern s i n Application s o f th e Hazardou s Ai r Pollutan t Exposur e Mode l (HAPEM )

Te d R
. Johnso n an

d Jame s E
. Cape l I T Corporatio n Sout h Squar e corporat e Centr e On e 371 0 Universit yDrive , Suit e 20 1 Durham , Nort h Carolin a 27707-620 8

Diann e M
. Byrn e Pollutan t Assessmen t Branc h Offic e o f Ai r Qualit yPlanning an d standard s U.S
. Environmenta l Protectio n Agenc y Researc h Triangl e Park , Nort h Carolin a 2771 1

Fo r Presentatio n a t th e 84t h Annua l Meetin g o f th e Ai r an d Wast e Managemen t Associatio n Vancouver , Britis h Columbi a

Jun e 16-21 , 199 1

Disclaimer : Th e statement s an d analytica l conclusion s presente d i n thi s pape r ar e thos e o f th e authors
. The yd o no t necessaril y reflec t U.S
. Environmenta l Protectio n Agenc ypolicy

.P. 3

91-172. 6 The Offic e o f Ai r Quality Plannin

g an dstandard s (OAQPS ) o f th e U.S . Environmenta l Protectio nAgenc y (EPA ) i s responsibl e fo r developin

g nationa l standard s t o reduc e emission s o f hazardou s ai r pollutants . Withi nOAQPS , th e Pollutan t Assessmen t Branc h (PAB ) i s responsibl e fo r assessin

g th e healt hrisk s associated wit hexposur e t o thes e emissions . I naccordanc e wit hthi s responsibility , th e PA B continuall y

evaluate s an

dupdate s it s exposur e an

dris k assessmen t capabilitie s t o reflec t th e curren t stat e o f knowledge . Inth e past , th

e PAB' s exposur e assessment s assumedtha t th e population-at-ris k wa s continuousl y expose dt o the outdoo r concentratio

nestimatedat th

e plac e o f residence . Thi s simplifyin

g assumptio

ndoe s not conside r th e effect s o

nexposur e of tim e spent indoor s or awa y fro m home . A

mor e sophisticated methodolog

y fo r estimatin

g populatio

nexposur e i s currentl y bein g developed . Thi s methodolog y i s incorporate

di na population exposur e mode l developedb y I T Corporatio

n(formerly

PE I Associates , inc.) , unde r contrac t t o EPA . Th e mode l i s noteworth

y i ntha t i t combine s feature s fro m tw o exposur e model s use db y EP A fo r ris k assessment , th e Nationa l Ambient Ai r Quality Standard s Exposur e Mode l (NEM ) an dth e Huma nExposur e Mode l (HEM) . Thi s repor t present s a brie f overvie w o f NE M an dHEM , a mor e detaileddescriptio no f th

e ne w mode l referredt o a s th e Hazardou s Ai r Pollutan t Exposur e Mode l (HAPEM) , an da summar

y of researcheffort s t o developa nalgorith

m capabl e o f estimatin g commutin

g pattern s i

narea s wher e HAPE

M i s applied . TH E EP A EXPOSURE MODEL S The EP A routinel y

use s NE

M an dHE M t o evaluat e populatio n exposur e t o ai r pollution . Historically , NE M ha s beenapplie

d t o th e criteri a pollutant s (e.g. , ozon e an dcarbo nmonoxide) , where a s HE M ha s bee

napplie

dt o toxi c pollutant s (e.g. , benzene) . Th e structur e of eac

hmode l reflect s th e differenc e i

napplication . The NE M i s typicall y

applie dt o a larg

e urba nare a whichha s bee nsubdividedint o contiguou s districts . The mode l simulate s th e movement s of smal l populatio ngroup s calle

dcohort s throug

h zone s o f varyin

g ai r quality . Th e mode l account s for th e short ter m effect s o

nexposur e o f geographi c locatio n(i.e. , distric t occupied) , microenvironment , an dbreathin

g rate . Ambien t concentration s in , eachdistric t are usuall y determinedfro

m fixed-sit e monitorin g dat a tha t hav

e bee nadjustedt o simulat e a particula r regulator y scenario . Cohor t movements , whichvar y wit hage an

doccupation , ar e base do nactivity

diar y studie s an

d loca l commutin

g data . Exposur e estimate s are providedfo r averagin

g time s rangin

g fro m 1 hou r t o 1 year . A

probabilisti c versiono f NE

M applicabl e t o ozon e (PNEM-03 ) ha s beendescribed b y Johnso ne t al .P. 4

91-172. 6 The HE M i s typicall y

use dt o estimat e annua l averag e exposure s an

dassociatedrisk s i na narea surroundin

g a particula r emissio nsource , A

pola r coordinat e gri di s establishedfo

r th e source , an

dpopulatio

ncentroid s identifie d fro m censu s dat a are locate do nth e gri dsystem . A

dispersion mode l i s use

dt o estimat e th

e annua l averag e ambient concentrationa t eac hreceptor point o nth e gri dan

da t th e centroi dlocations . Earl y version s o f HE

M assume dtha t person s residin g a t eachcentroi dlocatio nwer e constantl y

outdoor s an

d remaineda t the sam e location . Th

e PA B ha s recentl y

developed HE M II , a nimprove

dversio

nof HE M tha t account s fo

r th e effect a of microenvironment . Th e HAPE M i s a hybri dof NE M an dHEM . Consisten t wit hth e NE M approach , HAPE

M divide s th

e populatio

ninto cohort s tha t mov e throug hmicroenvironment s an dbetweenhom

e an dwork locations . Lik e HEM , HAPE

M use s a dispersio

nmode l (ISCLT ) t o estimat e annua l averag e pollutan t concentration s a t populatio nreceptor s an dfenceline location s surroundin g a source . Th

e HAPE M i s describedi

nmor e detai l i

nth e next section . METHODOLOG

Y A five-step methodolog y i s use dt o appl y

HAPE M t o a particula r facility . Thi s proces s ca nb e illustrate

d b y describin

g ho w HAPE M woul db

e use dt o estimat e pollutan t exposure s an

d risk s associate

dwit ha hypothetica l emission source . step 1 : Define Population-at-Risk , Exposur e Districts , an d Exposur e Period . The HAPE

M provide s estimate s of th e distributio

nof pollutan t exposur e an dassociate

dris k withi na defined populatio

n(th e "population-at-risk" ) fo r a specifie

dexposur e period . The exposur e perio di s usuall y

a recent calenda r yea r fo r whic hgoo

dmeteorologica l an dpopulatio

ndat a ar e available . Th e population-at-ris k i s usuall y define da s al l person s residin g withi na specifieddistanc e fror a a particula r emissio nsource . Thi s circula r area i s referre dt o a s th

e residentia l zone . Person s livin

g withi nth

e residentia l zon

e are assume

dt o wor

k withi na large r circula r area , th e commutin

g zone . The commutin g zon e als o ha s th

e emissio

nsourc e a s it s center . Radi i o f 1 0 kilometer s (km ) an d5 0 km , respectively , are typicall y use dt o define th

e residentia l an

dcommutin

g zones . The residentia l zon e i s divide

dint o a

nexhaustiv

e se t o f hom e districts . Eac

hhom e distric t i s define da s one or mor e geographi c unit s fo r whichBurea

uo f Censu s (BOC ) dat a are available . The commutin g are a i s divide

dinto a

nexhaustiv

e se tP. 5

91-172. 6

o f wor k districts

. Thes e ar e als o base d o n BO C units , bu t ar e generall ymuc h large r i n siz e tha n th e hom e districts

. Withi n th e residentia l zone , th e wor k district s ar e define d a s contiguou s set s o f hom e districts

. ste p 2 : Defin e cohorts
. T o appl yHAPE M t o a particula r source , th e analys t mus t specif ya method o f dividin g th e population-at-ris k int o cohorts
. Eac h cohor t i s assume d t o contai n person s wit h identica l exposure s durin g th e specifie d exposur e period

. I n typica l applications , th e analys t identifie s eac h cohor t a s a distinc t combinatio n o f 1 ) hom e district , 2 ) demographi c group , an d 3 ) wor k distric t (i f applicable)

. Specifyin g th e hom e an d wor k district s o f a cohor t provide s a mean s o f linkin g cohor t exposur e t o ambien t pollutan t concentrations

. Th e demographi c grou p specificatio n provide s a mean s o f linkin g cohor t exposur e t o activit ypattern s tha t var ywit h ag e an

d wor k status
. Tabl e I list s nin e demographi c group s define d fo r a recen t HAPE M analysis , i n thi s application , th e analys t define d 3 5 hom e district s an

d 2 0 wor k districts

. Eac h o f th e 6 nonworkin g demographi c group s wa s associate d wit h 3 5 cohorts , on e fo r eac h possibl e hom e district

. Eac h o f th e thre e workin g demographi c group s wa s associate d wit h 70 0 cohorts , on e fo r eac h possibl e combinatio n o f hom e distric t an d wor k district

. Th e tota l numbe r o f cohort s wa s ( 6 x 35 ) + ( 3 x 700 ) o r 2310
. Ste p 3 : Estimat e Fractio n o f Tim e Spen t b yEac h Cohor t i n Eac h combinatio n o f Geographi c Locatio n an d Microenvironment

. Th e HAPE M provide s a n algorith mfo r estimatin g th e fractio n o f tim e eac h cohor t spend s a t hom e an d a t wor k i n user-specifie d microenvironments

. Th e algorith massemble s a n exposur e even t sequenc e fo r eac h cohor t spanning th e exposur e perio d ( a calenda r year)
. Eac h sequenc e consist s o f 36 5 person-day s sample d fro man activit ydiar ydat a base
. i n pas t analyses , th e Cincinnat i Activit yDiarystudy 2 ha s serve d a s th e sourc e o f thi s dat a base
. Durin g thi s stud yove r 90 0 subject s complete d 3-da yactivit ydiarie s an d detaile d back

ground questionnaires

. Eac h person-dayo f Cincinnat i diarydat a wa s classifie d accordin g t o th e fou r indices : demographi c grou p (Tabl e I) , seaso n (summe r o r winter) , da ytyp e (weekda yo r week

end) , an

d temperatur e rang e (hig h o r low)
. Th e demographi c grou p inde x wa s determine d b yth e demographi c grou p t o whic h th e subjec t fillin g ou t th e diar ybelonged
. Th e seaso n an d da ytyp e indice s wer e base d o n th e calenda r dat e o f th e diarydata
. Th e temperatur e rang e inde x wa s base d o n th e dail ymaximu m temperatur e i n Cincinnat i o n tha t date
. Furthe r informatio nP. 6

91-172. 6 TABL E I
. Numbe r o f cohort s define d fo r a HAPE M analysi s using 9 demographi c groups , 3 5 hom e districts , an d 2 0 wor k districts

.
Demographi c group Include s commutin g cohort s Numbe r o f cohort s

associate d wit h grou p
1
. Childre n 0 t o 5 2
. Childre n 6 t o 1 3 3
. Childre n 1 4 t o 1 8 year s 4
. Worker s wit h lowprobabilit y o f outdoo r wor k 5
. Worker s wit h moderat e probabilit yo f outdoo r wor k 6
. Worker s wit h high probabilit y o f outdoo r wor k 7
. Nonworkin g adult s unde r 3 5 year s 8
. Nonworkin g adult s 3 5 t o 5 4 year s 9
. Nonworkin g adult s 55 + year s N o N o N o ye s Ve s Ye s No N o No 3 5

3 5 3 5 70 0 70 0 70 0 3 5 3 5

231 0 oncernin g th e classificatio n procedur e i s provide d b yJohnso n e t l. 1 co n a T o ru

n th e algorithm , th e analys t provide s a sequenc e o f dail ymaximu

mtemperature s fo r th e stud yare a fo r th e calenda r yea r unde r analysi s (e.g. , 1989)
. Thes e dat a ar e use d t o assign eac h calenda r dayt o on e o f th e temperatur e range s use d i n classifyin g th e Cincinnat i diarydata
. T o construc t th e exposur e even t sequenc e fo r a particula r cohort , th e algorith mselect s a person-dayo f Cincinnat i diarydat a fo r eac h calenda r da yi n 198 9 accordin g t o th e demographi c grou p o f th e cohor t an d th e season , da ytype , an

d temperatur e rang e associate d wit h th e calenda r day
. Eac h exposur e even t sequenc e consist s o f a serie s o f event s wit h duration s varyin g fro m1 t o 6 0 minutes

. Eac h exposur e even t assign s th e cohor t t o a particula r combinatio n o f geographi c locatio n an

d microenvironment

. Th e geographi c locatio n i s eithe r th e hom e distric t o r th e wor k locatio n associate d wit h th e cohort
. Th e home/wor k decisio n i s base d o n th e activit ydiary dat a associate d wit h th e exposur e event
. Th e microenvironmen t assignmen t i s typicall yeithe r indoor s o r outdoors
. Micro

environmen t code s appearing i n th e Cincinnat i activit ydiarydat a bas e ar e use d t o determin e thes e assignments

.P. 7

91-172. 6 Th e exposur e even t sequence s ar e analyze d t o determin e th e fractio n o f tim e spen t b yeac h cohor t i n eac h combinatio n o f geographi c locatio n an d microenvironment

. Tabl e I I list s thes e fraction s fo r 9 cohorts
. Eac h cohor t represent s 1 o f th e 9 demographi c group s i n Tabl e I
. Fraction s ar e specifi c t o a locatio n i n Nort h Carolin a during 1989
. Ste p 4 : Estimat e th e Annua l Averag e Exposur e o f Eac h Cohort
. Th e annua l averag e exposur e o f eac h cohor t i s estimate d b y th e expressio n C(d,h,w ) = s F(d,h,w,i,j ) x M(i ) x A(j ) (l ) wher e C(d,h,w ) i s th e annua l averag e pollutan t concentratio n t o whic h th e cohor t i s exposed , d i s th e demographi c grou p identifier , h i s th e hom e locatio n identifier , wi s th e wor k locatio n identifie r (i f applicable) , F(d,h,w,i,j ) i s th e fractio n o f tim e spen t b

yth e cohor t i n microenvironmen t i a t locatio n j , M(i ) i s th e microenvironmen t facto r associate d wit h micro

environmen t i , an

d A(j ) i s th e annua l averag e ambien t pollutan t concentratio n fo r locatio n j

. Th e summatio n i s carrie d ou t fo r al l value s o f i an

d j

. Th e value s fo r F(d,h,w,i,j ) ar e develope d i n Ste p 3
. value s o f M(i ) fo r th e outdoo r microenvironmen t [M(outdoors) ] an d fo r th e indoo r microenvironmen t [M(indoors) ] ar e specifie d b yth e analyst
. Th e valu e o f M(outdoors ) i s typicall yassume d t o b e 1.0
. Th e valu e o f M(indoors ) i s selecte d t o represen t a reason abl e indoor/outdoo r rati o fo r th e pollutan t i n th e absenc e o f indoo r sources . Th e valu e wil l b e les s tha n 1. 0 i f a pollutan t ha s reactiv e propertie s o r i s adsorbe d ont o indoo r surfaces
. Th e locatio n inde x (j ) indicate s eithe r th e cohort' s home distric t o r th e cohort' s wor k district

. Th e valu e o f A(j ) fo r eac h hom e o r wor k distric t i s assume d t o b e constan t ove r th e entir e distric t an

d t o b e equa l t o th e averag e o f th e pollutan t concentration s estimate d fo r al l receptor s whic h fal l withi n th e district

. Pollutan t concentration s a t th e receptor s ar e estimate d b y th e industria l sourc e comple x lon g ter m(ISCLT ) dispersio n model
. Inpu t dat a fo r th e ISCL T mode l includ e loca l meteorologica l dat a an d an estimat e o f th e pollutan t emission s fro mth e source . I n a typica l HAPE M application , th e ISCL T dispersio n mode l i s use d t o estimat e th e annua l averag e pollutan t concentratio n a t th e centroi d o f eac h o f th e censu s unit s use d t o defin e th e home an d wor k districts , 3 6 fencelin e location s space d a t 10 ' increments , an d 39 6 receptor s i n 1 1 ring s o f 3 6 receptor s eac h a t variou s distance s betwee n 50 0 m an d 10,00 0 m . Th e 10,00 0 ra rin g define s th e oute r boundaryo f th e residentia l zone .P. 8

91-172. 6 TABL E II
. Fractio n o f tim e spen t b ya cohor t representin g eac h demographi c grou p i n eac h combinatio n o f geographi c locatio n an d microenvironment

.

Demograph

y group *

l 2 3 4 5 6 7 8 9

a Se e Tabl e 

### L c

I Hom e

Indoor s

0.92 6 0.88 8 0.92 1 0.73 7 0.75 2 0.74 7 0.93 8 0.94 3 0.95 1 Fractio n Distric t

outdoor s

0.07 4 0.11 1 0.07 9 0.04 4 0.05 3 0.03 8 0.06 2 0.05 6 0.04 9 o f tim e

Wor k Distric t

Indoor s

0 0 0 0.21 5 0.16 4 0.13 8 0 0 0 Outdoor s

0 0 0 0.00 5 0.03 1 0.07 8 0 0 0

Ste p 5 : Extrapolat e Cohor t Exposure s t o Population-at-Ris k an d Estimat e Associate d Risk

. Th e cohort-specifi c exposur e estimate s develope d i n Ste p 4 ar e extrapolate d t o th e population-at-ris k b yestimatin g th e siz e o f eac h cohort
. Aspecia l compute r progra mestimate s cohor t 3iz e directl yfro

mcensu s an

d commutin g dat a specifi c t o eac h hom e district

. Thes e dat a ar e obtaine d fro mth e BOC
. Atwo-ste p proces s i s use d t o determin e cohor t population

. I n Ste p 1 , th e populatio n o f eac h demographi c grou p residin g i n a particula r hom e distric t i s calculate d usin g detaile d BO C data
. Thi s ste p provide s th e population s o f al l nonworkin g cohorts
. Th e population s o f th e workin g cohort s ar e determine d b yfurthe r subdividin g th e population s o f th e working demographi c group s associate d wit h eac h hom e district

. Th e formul a use d fo r thi s ste p is : Com(d,h,w ) = Pop(d,h ) x F(h,w ) (2 ) wher e Cora(d,h,w ) i s th e numbe r o f person s i n th e commutin g cohor t associate d wit h demographi c grou p d , hom e distric t h , an d wor k distric t w ; P(d,h ) i s th e numbe r o f person s i n demographi c grou p d i n hom e distric t h ; an d F(h,w ) i s th e fractio n o f al l worker s residin g i n hom e distric t h wh o commut e t o wor k distric t w . Value s o f F(h,w ) ar e obtaine d fro m a n origin-destinatio nP. 9

91-172.f i (0-D ) tabl e produce d b ya specia l commutin g model
. Thi s mode l i s describe d i n detai l i n th e nex t sectio n o f thi s paper . Th e populatio n exposur e estimat e fo r a particula r cohor t i s converte d t o a n expecte d annua l cance r incidenc e [I(d,h,w) ] usin g th e expressio n

I(d,h,w ) = C(d,h,w ) x P(d,h,w ) x URE/7 0 (3 ) wher e C(d,h,w ) i s th e annua l averag e pollutan t concentratio n associate d wit h th e cohort , P(d,h,w ) i s th e estimate d populatio n o f th e cohort , an

d UR E i s th e lifetime (70-year ) uni t ris k estimat e fo r th e pollutant
. A n exposur e an

d ris k valu e ar e estimate d fo r eac h cohort , an d th e result s ar e summe d ove r al l cohorts
. Th e HAPE M provide s histogram s o f annua l averag e exposur e concentration s fo r the population-at-risk

. I t als o provide s annua l an d lifetime cance r incidenc e estimate s fo r eac h
' home distric t an

d fo r th e population-at-risk

. Th e lifetime ^incidenc e value s ar e calculate d b yassumin g th e annua l incidenc e estimate d fo r eac h hom e distric t i s repeate d fo r 7 0 years . TH E HAPE M COMMUTING MODE L Th e HAPE M an

d NE M ar e simila r i n tha t eac h mode l account s fo r th e mobilit yo f workin g cohorts
. Eac h use s Equatio n 2 t o estimat e th e population s o f thes e cohorts , an d thu s theyrequir e a tabl e listin g value s fo r F(h,w)
. Eac h calculate s F(h,w ) b yth e expression : F(h,w ) = Com(h,w)/Work(h ) (4 ) wher e Com(h,w ) i s th e numbe r o f worker s i n al l demographi c group s tha t commut e fro

mhom e distric t h t o wor k distric t wan d Work(h ) i s th e tota l numbe r o f worker s i n hom e distric t h
. Th e basi c requiremen t fo r thes e calculation s i s a n origin-destinatio n (O-D ) tabl e listin g Com(h,w ) value s fo r al l combination s o f h an d w . I n curren t NE M applications , Com(h,w ) value s ar e obtaine d fro ma specia l commutin g dat a base
. Thi s dat a base , th e Sixt y Citie s Dat a Fil e (SCDF) , contain s o- D table s b ycensu s trac t fo r 6 0 citie s base d o n survey s conducte d b yth e BO C fro

m197 5 t o 1977
. Th e BO C aske d eac h membe r o f a random sampl e o f commuter s i n eac h cit yt o provid e th e addresse s o f hi s residenc e an d workplace
. Thes e addresse s wer e converte d t o censu s tract s t o produc e a n O- D table
. I t shoul d b e note d tha t onl yO- D combination s specifie d b yth e sample d commuter s appea r i n thes e tables
. A s th e sample d commuter s represen t onl ya smal l fractio n o f th e possibl e O- D combination s fo r a give n city , th e SCD F i s bes t use d fo r estimatin g genera l intercit ycommutin g pattern s rathe r tha n th e numbe r o f commuter s associate d wit h a particula r pai r o f hom e an

d wor k censu s tracts
.

8P.1 0

91-172. 6 Althoug hthe SCD

F i s currentl y

th e preferredsourc e o f O- D dat a fo r NEM , i t ha s thre e significant deficiencies . First , th e dat a are no

w 1 5 year s ol dan

dma y no t accuratel y

represen t current urba

ncommutin

g patterns . Second , th e dat a exclude man

y smalle r urbanizedarea s an dal l rura l areas . Third , th e dat a are "grainy " at th

e censu s trac t level . As discussedabove , thi s grainines s reflect s th e smal l number of commuter s wh o wer e surveye di neacho f th

e 6 0 citie s b

y th e BOC . For HAPE

M applications , PA

B ha s investigated a nindirec t metho dfor constructin

g o- D table s tha t use s tri pduratio ndata . Tri pduratio

ndat a ar e collecte ddurin g eachcensu s fo

r al l area s of th e U.S . The dat a ar e reporte da s the numbe r o f person s i n eac hcensu s uni t withone-wa y commut e time s tha t fal l int o eac h of th e followin

g 8 commut e duratio nranges : 1 . Les s tha

n5 minutes . 2 . 5 t o 9 minutes . 3 . 1 0 t o 1 4 minutes . 4 . 1 5 t o 1 9 minutes . 5 . 2 0 t o 2 9 minutes . 6 . 3 0 t o 4 4 minutes . 7 . 4 5 t o 5 9 minutes . 8 . 60 + minutes . Th e metho d assume s tha t eac hcommut e duratio

nrange ca

nb e convertedint o a correspondin g range o f geodesi c distances . Geodesi c distanc e i s define dher e a s th

e shortes t distanc e betwee ntw o point s o

nth e globe , i.e. , th

e distanc e "a s th

e cro w flies. " Conside r a commute r i na larg

e urbanizedarea wh o report s tha t hi s commut e take s betwee n2 0 an d2 9 minutes . I f th e average geodesi c commut e spee di nth e are a i s 0. 3 kilometer s per minut e (km/min) , th

e commut e duratio

nrange of 2 0 t o 2 9 minute s i s equivalen t t o a geodesi c distanc e range (GDR ) o f 6 t o 8. 7 km . I na simila r manner , eac ho f th e eigh t commut e distanc e range s i s convertedt o a GD Rindexe

da s i = 1 , 2 , ... , 8 . Th e locatio nof eachexposur e distric t i s representedb y it s geographi c centroid . I f th e distric t i s a

norigi nlocatio

nfo r commuter s (i.e. , a "home " district) , one ca ndelineat e eight concentri c ring s centeredo nth e centroid , on

e fo r eac hGDR . Th

e i-t hGD Rcenteredo

nhom e distric t hi s identifie da s GDR(h,i) . Othe r usefu l term

s are define

dbelow . com(h) : th

e number of commuter s residin g i nhom e distric t h Com(h,i) : th

e number o f commuter s residin g i nhom e distric t hwh

o commut e t o a wor k distric t i

n GDR(h,i )P.1 1

91-172. 6 Com(h,i,w) : th e numbe r o f commuter s residin g i n hom e

distric t h wh o commut e t o wor k distric t w wher e wor k distric t wi s i n GDR(h,i ) N(h,i) : th e numbe r o f wor k district s i n GDR(h,i ) Tot(h,i,w) : th e tota l numbe r o f commuter s wh o wor k i n

wor k distric t wi n GDR(h,i ) Tot(h,i) : th e tota l numbe r o f commuter s tha t wor k i n

GDR(h,i ) (include s commuter s fror a al l home districts ) Th e indirec t metho d fo r developin g an o- D tabl e ca n b e state d a s follows : 1
. com(h,i ) an

d N(h,i ) ar e known
. Mak e a n initia l estimat e o f com(h,i,w ) usin g th e expressio n Cora(h,i,w ) = [Com(h,i)]/[N(h,i)]

. (5 ) 2
. Calculat e Tot(h,i,w ) b ysumming Com(h,i,w ) value s associate d wit h specifie d wvalue
. 3
. Calculat e Tot(h,i ) b ysumming Tot(h,i,w ) value s fo r al l wor k district s i n GDR(h,i)

. 4
. Mak e a ne westimat e o f com(h,i,w ) usin g th e expressio n com(h,i,w ) - [Com(h,i)][Tot(h,i,w)]/[Tot(h,i)]

. (6 ) 5
. G o t o Ste p 2
. I n Ste p l , commuter s associate d wit h a particula r combinatio n o f hom e distric t an

d GDR ar e evenl ydistribute d acros s th e wor k district s i n th e GDR
. Thi s ste p i s Iteratio n 0
. Step s 2 through 4 ar e repeate d n time s wher e n i s determine d b yth e user . I n eac h iteratio n o f Step s 2 through 4 , th e commuter s ar e redistribute d acros s th e wor k district s i n th e GDR i n proportio n t o th e numbe r o f worker s assigne d t o eac h wor k distric t during th e las t iteration

. Tes t Usin g AHypothetica l Dat a Se t A s an initia l tes t o f th e indirec t method , analyst s create d a hypothetica l stud yare a containin g 1 6 exposur e districts

. Base d o n th e distance s betwee n th e centroid s o f thes e districts , a hypothetica l o- D tabl e wa s develope d i n whic h shor t commute s wer e mor e numerou s tha n long commutes
. Th e tabl e provide d 25 6 "actual " Com(h,i,w ) values , on e fo r eac h possibl e combinatio n o f hom e an d wor k district

. Th e tabl e als o provide d a valu e fo r th e distanc e separatin g eac h pai r o f 1 0P.1 2

91-172. 6 hom e an d wor k districts

. Thes e distance s wer e converte d t o commut e times

. Base d o n thes e commut e times , eac h wor k distric t wa s assignedt o a GDR wit h respec t t o eac h hom e district

. Thes e assignment s provide d a mean s o f constructin g a tri p duratio n tabl e simila r i n forma t t o tha t whic h woul d b e provide d b yth e BOC
. I f 5 0 commuter s i n hom e distric t h travele d t o wor k district s withi n th e GD R denote d a s 5 t o 9 minutes , i t wa s assume d tha t BO C record s woul d indicat e tha t 5 0 resident s o f hom e distric t h commute d 5 t o 9 minutes

. Applyin g thi s procedur e t o al l hom e district s an d al l GDR's , analyst s wer e abl e t o creat e a tri p duratio n tabl e tha t wa s completel yconsisten t wit h th e "source " O- D table
. Th e indirec t procedur e describe d abov e wa s applie d t o thi s tri p duratio n tabl e wit h th e goa l o f recreatin g th e sourc e 0- D table
. Th e resul t wa s a pai r o f value s fo r eac h combinatio n o f hom e an d wor k district : th e "actual " Com(h,i,w ) valu e an d th e mode l estimate

. I f th e procedur e performe d perfectly , the n th e actua l an

d estimate d value s woul d b e identica l fo r eac h combi

nation

. Alinea r regressio n analysi s o f actua l versu s estimat e woul d yiel d a slop e valu e o f 1.00 , a n intercep t o f 0 , an d a n R

square d valu e o f l.oo . Regressio n result s clos e t o thes e value s indicat e tha t th e mode l perform s well
. I n performin g th e test , analyst s foun d tha t mode l per formanc e improve d wit h eac h iteratio n o f th e procedure
. Tabl e II I list s th e slope , intercept , an d R-square d valu e fo r selecte d value s o f n , wher e n i s th e numbe r o f iterations

. Not e tha t n - 0 indicate s eve n distributio n o f commuter s among wor k district s (i.e. , implementatio n o f Ste p l only)
. Th e R-square d value s i n Tabl e II I increas e a s n increases

. Mode l performanc e a t n • 1 0 i s quit e good : slop e = 1.0511 , intercep t = -2.000 5 commuters , an d R-square d valu e = 0.9319
. A t n = 100 , performanc e i s excellent : slop e = 0.9973 , intercep t = 0.093 1 commuter , an d R

square d valu e - 0.9705
. Thes e result s probabl yrepresen t th e uppe r boun d o f mode l performanc e tha t ca n b e expecte d whe n rea l tri p duratio n dat a ar e use d fo r mode l input

. Th e tes t use d hypothetica l tri p duratio n dat a tha t wer e complet e an d internall yconsistent

. Th e mode l outpu t (i.e. , th e estimate d O- D table ) wa s compare d t o a n "actual " o- D tabl e tha t wa s perfectl yconsisten t wit h th e inpu t tri p duratio n data
. Test s usin g rea l dat a wil l b e affecte d b y error s an

d missin g value s i n bot h th e inpu t tri p duratio n dat a obtaine d from

th e BO C an

d th e O- D tabl e use d t o validat e th e mode l output
. Th e nex t sectio n o f thi s pape r present s th e result s o f test s using rea l data
.



### 1 1P.1 3

91-172. 6 TABL E III . Result s for hypothetica l stud y area of linear regressionanalyse s o f actua l versu s estimate d number of commuter s Result s of linear regressio nanalysi s o

f actua l versu s estimatedvalue s (n-256 )


### Iteratio n

o ar-l 2 5 1 0 1 5 2 0 3 0 5 0 10 0 Slop e

0.998 8 1.118 3 1.099 2 1.066 2 1.051 1 1.037 8 1.025 3 1.009 2 0.999 1 0.997 3 Intercep t

0.078 4 4.606 7 3.882 7 2.610 5 2.000 5 1.491 2 0.982 0 0.367 6 0.011 5 0.093 1 0.483 1

0.702 6 0.781 0 0.875 3 0.931 9 0.953 9 0.962 9 0.968 5 0.970 3 0.970 5
dEve ndistributionof commuter s withi neachgeodesi c distanc e range .
Tes t Usin

g Atlant a Dat a Atlanta , Georgi a wa s selecte dfo r testin

g purpose s becaus e validatio

ndat a wer e availabl e for Atlant a fro m th e SCDF . Tes t dat a wer e prepareda s follows . Tri p duratio ndat a fo

r 198 0 wer e obtainedfor the cit y at th e censu s trac t leve l fro m th e BOC . Th e SCD F providedo- D dat a fo r Atlant a fo

r 1975 , als o at th

e censu s trac t level . As th e tw o dat a set s di dno t us e a consisten t se t o f censu s trac t boundaries , a specia l progra m wa s developedt o aggregat e th e censu s tract s use di neac hdat a se t int o a se t of exposur e district s withboundarie s consisten t with bothdat a sets . Tw o impac t area s were defined . Th e residentia l zon

e (Zon e R ) include

d the 10 3 exposur e district s withi n1 0 k m o f a nimagi nar y emissio

nsourc e positione

dnea r th

e city center . Th

e com mutin g zon e (Zon e C ) wa s define

da s includin

g th e 23 2 exposur e district s withi n5 0 k m of th e emissio

nsource . Zon

e Rwa s assume dt o include al l hom e an dwork location s withsignifican t ambient pollutan t concentration s associatedwithth e source . W

e assume dtha t impac t Zon

e c , whichcontain s al l of Zon e R , in clude dal l possibl e wor k location s associatedwit hresident s o f Zon e R .


### 1 2P.1 4

91-172. 6 The mode l wa s appliedt o tri pduratio ndat a for th

e resident s o f Zone Rusin g a serie s of assumedgeodesi c speed s between0.2 6 km/mi nan d0.5 2 km/min . Teniteration s wer e specifie

dfo r eachmode l run . Eac hru nproduceda

n0- D tabl e listin g a nestimat e o f th

e number o f commuter s associated wit h eac hof 23,89 6 o- D combination s (i.e. , 10 3 hom e district s x23 2 work districts) . A simila r O- D tabl e wa s develope dfro m the SCDF . Becaus e th e SCDF dat a ar e basedo na relativel y

smal l sampl e o f Atlant a commuters , onl y

230 7 o f th

e 23,89 6 modeled0- D combination s appearedinthe SCD F O- D table . T o provide a mean s o f comparin g th e detailedmode l estimate s withth e "grainy " SCDF data , analyst s aggregatedth e 23 2 district s withi nZon e C int o 2 0 "super districts. " Th e supe r district s wer e definedb y radia l line s fro

m the emissionsourc e at th e four compas s point s an db y fiv e circle s wit hcenter s at th e sourc e an

dradi i o f 2 km , 5 km , 1 0 km , 2 0 km , an

d 5 0 km . Thi s schem e produced1 2 supe r district s withi nzon

e Ran d8 outside Zon

e R . Tw

o o f th e supe r district s near th e sourc e i

nZon e Rwer e subsequentl y foun dt o contai nn

o exposur e district s an dwer e omitte

dfro m the comparison . Thus , th e compariso

nincludedio super district s i nZon e Ran d 8 supe r district s outsid e Zon e R . Th e comparisonwa s conducte da s follows . A

supe r distric t o- D tabl e wa s developed fro m th e mode l estimate s for a particula r geodesi c speed . A correspondin

g super distric t O- D tabl e wa s develope

dfro m the SCDF . Th

e tw o table s wer e combinedt o produc e a tabl e whichliste d a mode l estimat e an da SCD F estimat e fo

r eac hcombinatio

nof hom

e super distric t an dwork supe r district . Th e tabl e provided dat a fo r 18 0 0- D combinations : 1 0 hom e super district s i

nZon e Rx1 8 wor

k super district s i nZon e C . A s discusse

dabove , onl y

commutin

g trip s originatin g i nzon e Rwer e considere

d inthe analysis . Severa l statistically-derivedindicator s wer e use dt o asses s th e level-of-agreemen t betwee nth e modele

dan dSCD F values . Thre e of thes e indicator s wer e obtaine dthroug

hlinea r regressio n analyse s wher e the SCD F value wa s th

e dependen t value an dth e modele dvalu e wa s th

e independent value . Eac hanalysi s yielde

d a nintercep t value , a slop e value , an

da nR-squaredvalue . A perfec t match-u

p woul dproduc e a

nintercep t o f zero , a slop e o f 0.79 , an

da nR-squaredvalue of 1.0 . Th e specifiedslope value (0.79 ) i s no t unity becaus e th

e populatio

nrepresentedb

y th e SCD F dat a (140,106 ) i s les s tha nth e populatio

nrepresentedb

y th e mode l estimate s (177,730) . Th e rati o o f thes e population s i s 0.79 . I f th

e tw o population s wer e equal , the slop e value associate

dwit ha perfec t match-u pwoul db

e 1.0 .



### 1 3P.1 5

91-172. 6 W e als o use

dth e Spearma

nran k coefficien t a s a nindicator o f th e level-of-agreemen t betwee nmodele

dan dSCD F values . As a

n indicator o f correlation , thi s statisti c ma y be preferabl e t o th e R-squared value , a s th e Spearma

ncoefficien t i s no t basedo nan y assumption s concernin g th e distributio

no f the value s bein g compared . Tabl e I V provide s modelin

g result s fo

r 5 assumedgeodesi c speeds . For eachgeodesi c speed , th e linear regressio

ncoef ficient s an

d the Spearmancoefficien t ar e providedfo r eac ho f tw o work locatio

ncategories : l ) insid e Zon e Ronl y

an d2 ) al l work location s withi nZon e C . Base

do nthe Spearmanran k coef ficient , th

e geodesi c spee

dproducin

g th e bes t possibl e match-u p o f mode l an

d SCDF value s appear s t o fal l somewher e between0.3 0 km/mi nan

d0.3 5 km/min . Th e Spearma

nran k coefficien t exceed s 0.7 2 withi nthi s rang e fo r bot hwork locatio ncategories . Tabl e I V als o provide s model-derivedestimate s fo r th e fractio nof commuter s residin g i nZon e Rtha t work outside Zon e R . Estimate s rang e fro m 0.09 7 t o 0.540 , suggestin g tha t thi s fractio

ni s highl y

sensitiv

e t o th e choic e o f geodesi c speed . Base

do nth e 0- D tabl e derive

dfro m th e SCDF , w

e woul d estimat e th

e "true " fractio

nt o b e 0.244 . The closes t modeled value (0.218 ) correspond s t o a geodesi c spee d of 0.3 5 km/min . Thes e analyse s sugges t tha t 0.3 5 i s clos e t o th e optimu

m geodesi c spee

dfor the modeledarea . Simila r analyse s ca nbe conductedfo

r othe r area s t o determine whethe r a "rule-of-thumb " geodesi c spee

dexist s whichi s applicabl e t o mos t areas . SUMMAR YAN D DISCUSSIO

N Th e HAPE M methodolog

y attempt s to accoun t fo r variou s factor s tha t ar e expectedt o affec t exposur e t o hazardou s ai r pollutant s i

npopulation s residin g near emissio

nsources . Thes e factor s include age , work status , residentia l location , an dwork location . Consideredtogether , the y provide a mean s fo r definin

g a collectio

no f cohorts , eac

hwit ha distinc t patterno f exposure . A n0- D tabl e listin g th e number of commuter s associatedwith eachcombinatio

no f hom

e locatio

nan dwork locatio

ni s necessar

y fo r estimatin

g th e siz e of eac

hworkin

g cohort . A

commutin

g mode l tha t estimate s value s i nth e O- D tabl e basedo nBO C tri p duratio ndat a ha s beendevelope dan dapplie

dt o Atlanta , GA . Th e correlatio

nbetweenO- D tabl e value s estimate db y th e mode l an

d correspondin

g value s obtaine

dfro m th e SCD F exceeded0.7 2 fo r assume dgeodesi c speed s between0.3 0 km/mi nan d0.3 5 km/min . Additiona l testin

g o f the commutin

g mode l i s planned .


### 14TABL E IV . CasparISO B o f coamntin g mode l estiaate s Mit b'lit a obtaine dfrc

m tb e sixt y

citie s dat a file .

Geodesi c Speed , to/Min

0.2 6

0.3 0

0.3 5

0.4 2

0.5 2 Itar tLocation "

Zon e C Zon e R

2o«i e C Zon e R

Zon e C Zon e B

Zon e C Zon e E

Zon e C Zon e R n

ie o 10 0

18 0 10 0

18 0 100

18 0 10 0

18 0 10 0 LinearRegressio n Gesults
Intercep t

23 0 200

10 9 34

36 7 1

1 7 22 4

26 5 39 2 Slop e

0.55 4 0.53 5

0.67 6 0.67 2

0.74 8 0.70 8

0.767 0.71 6

0.51 6 0.81 0 R 2

0.39 2 0.37 0

0.44 2 0.42 5

0.44 3 0.38 8

0.377 0.30 5

0.18 4 0.20 8 Spearaa

n Ran k Coefficien t

0.68 3 0.75 4

0.72 0 0.76 6

0.76 7 0.72 7

0.73 3 0.64 8

0.60 3 0.55 7 Estinate d Fractio n

Countin g Outsid e Zon e R

0.09 7

0.14 1

0.21 3

0.34 7

0.54 0

* Zon e C : al l mit

district s withi n5 0 i no f sourc e Zon e P. : al l war t district s to thi a 1 0 k m o f sourc e

I

"^ 1 Cs i

T

J O )P.1 7

91-172. 6 Th e HAPE M

i s a nevolvin g mode l tha t th e PA B intend s t o up dat e an

drefin e a s new

dat a become available . Fo r example , PAB i s currentl y

reviewin g new

researc hwhic hprovide s estimate s o f M(indoors) , th e rati o o f indoo r to outdoo r concentration , fo r a numbe r o f hazardou s pollutants . Th e PAB also intend s t o adda n are a sourc e modelin g capabilit y t o HAPE M

andt o provid e algorithm s fo r estimatin g exposur e b y nonai r route s suc ha s ingestion . ACKNOWLEDGMENT S Th e author s woul d lik e t o than k Ro y Pau l fo r obtainin g th e BO C dat a use dfo r testin g th e commutin g model . Ji m Cape l processe dthes e dat a fo r inpu t int o th e commutin g model * Te dJohnso ndevelope d th e commutin g mode l andperforme dth e test s describe d i nthi s report . Thi s study

wa s funde db

y EP A unde r Contrac t No . 68-DO-0062 . Mr . To m Lahr e serve d a s EPA Wor k Assignmen t Manage r fo r th e project . Ms . Diann e Byrn e i s th e chie f o f th e Progra m Analysi s an dTechnolog y

Sectio no f th e Pollutan t Assessmen t Branch . Ms . Byrne' s sectio ni s responsibl e fo r developin g andmaintainin g exposur e model s use dt o asses s ris k fro m hazardou s ai r pollutants . REFERENCE S 1 . T . Johnson , R . Paul , J . Capel , an dT . McCurdy, "Estimationo f Ozon e Exposur e i nHousto nUsin g a Probabilisti c Versio no f NEM, " Pape r No . 90-150.1 , Presente d a t 83r dAnnua l Meetin g o f th e Ai r an dwast e Managemen t Association , Pittsburgh , Jun e 1990 . 2 . T . Johnson , A Stud y o f Huma nActivit y Pattern s inCincinnati . Ohio , Electri c Powe r Researc hInstitute , Pal o Alto , Novembe r 1987 . 3 . 197 7 Nationwid e Persona l Transportatio nStud y Home-tn-Wor k TrJP s andTravel . U.S . Departmen t o f Transportation , Federa l Highwa y

Administration , FHWA/PL/81/002 , Decembe r 1980 .



### 16

TOTA L P.1 7