# Health 

# Effects ofAcid Aerosols on 

# NorthAmerican 

# Children: Respiratory 

# Symptoms Douglas W 

### Dockery,12 Joan Cunningham,1 

### AndrewL. 

### Damokosh,1 Lucas M. 

### Neas,12'3 

### John D. 

### Spengler,1 Petros 

### Koutrakis,1 James H. 

### Ware,4 Mark

### Raizenne,15 

### andFrankE. 

### Speizer 1,2 

### 'Department of Environmental Health, Harvard School of Public Health, 2Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, 3Department of Epidemiology, Harvard School of Public Health, and 4Department of Biostatistics, Harvard School of Public Health, Boston, MA 02115 USA; 5Environmental Health Directorate, Health Canada, Ottawa, K1AOL2 Canada

We min e 

### respiratoryea effe of esur to 

### aidic 

### air

### pi among 1369 whitechildee St12 ye 

### Iars

ldfmm"C 24cmmn tie n h United.

### State.: ndCnada'Lbetween, 

### 1988 and 

### 1991. Each 

### child's parent or udi 

### completed a 

### questnnie. Air qual and 

### meteorologyweremeasd

### in-each

### communityfora

### 1-year

### period. We

### usda

### two-stagelogistic regression

### model to

### analyze the

### dat, 

### adjusting for e ef of his

### tory of 

### aergies parental 

### ama, panta eduction, nd current 

### snomking in the home. Chil4renIiX,in in the commnt withth highes Is ofpatcetog acdt wee snft 

## one-isdI of

### bnhit a e p t 

### year oaedtwo children lI i l l
co ny Fine 

### aice tewas aso a ia wthh er repor ofbron ti (OR

- 

### 1.65;95% CI 

### 1.12-2.42). Noother

### respiratorlysymptoms were Sinfatl higherinasoi
-onwihanyofthe Iir

poluret No eni bgruIps were id ified Rpotedl brnhts bulnithe asthma i;hes cuh norjbem were asoitdwith levl ofprt}! cle atrnizj8a;xdsty.forthese child... living Sinanostuif. 

### envsronniestt*R.. u.rm.i. ac.d aerosols, 

### air 

### polla.tSio bronchitis, children 

### respiao^ symptom. 

### 'srnsem iO4:550050l

### 9X6)



### Although there 

### has been much 

### public and 

### scientific debate about acid rain 

### and its precursors, 

### the 

### focus in 

### the past was 

### largely on 

### ecological effects and

### secondaryhealtheffects related to 

### mobilization 

### of toxic 

### metals. Concern 

### about the 

### possible adverse human 

### healtheffects 

### resulting from exposure to 

### acid aerosols hasbeenmore recent 

### (1,2). Experimental studies 

### of sulfur dioxide and total 

### suspended particulates have shown 

### adversehealth

### effects in

### bothanimals 

### (3) and 

### human subjects (4). In 

### epidemiologic studies, 

### particulate 

### pollution has been associated with

### decrements in 

### lung function 

### (5), 

### higher prevalence of respiratory symptoms 

### and illness 

### (6-8), and 

### higher rates 

### ofhospitalizations 

### (9,10) and 

### mortality (11), even at 

### the 

### levels 

### currentlyfound inmany

### urbanareas. Fine 

### particles, which penetrate 

### deeply into 

### the 

### lungs, are

### producedbydirect emissions 

### from combustion sources or atmos

### pheric reactions 

### of gaseous 

### pollutants. These 

### fine 

### particles are 

### often very 

### acidic. The observed health 

### effects associated with 

### particulate 

### pollution may 

### be attributable at 

### least in part to 

### the 

### acidity ofthe 

### fine parti

### cles 

### (12,13). Previous 

### population-based studies lacked direct measures 

### of 

### ambient aerosol 

### acidity, but recent 

### improvements in 

### atmospheric monitoring 

### techniques have made it

### possible to 

### directlymeasure

### particle strong

### acidity 

### (14). In 

### children from the Six Cities 

### Study, reportedbronchitis and chronic 

### coughwere 

### associated

### withtotal 

### suspendedparticles (7) and with 

### particulate matter 

### less than 15 

### pm in 

### aerodynamic diameter (8). In 

### a

### later 

### analysis ofchildren from the same six communities 

### plus Kanawha County, West Virginia 

### (15), the 

### city-specific summertime mean 

### of

### particle strong 

### acidity was 

### associated with 

### significantly higher risk 

### of 

### bronchitis andchronic

### cough. This 

### studywas 

### specifically designed to examine 

### the 

### relationship between longterm, 

### intermittent exposure to 

### particle strong 

### acidityand the respiratory

### health of 

### children (16). In 

### this 

### article, we 

### describe the associations 

### between 

### particle strong 

### acidityandrespiratorysymptoms. 

### Methods Air

### monitoring. We 

### selected 24 communities on 

### the basis of previously 

### measured 

### sulfate and ozone concentrations 

### and 

### demographic characteristics (17). The 

### study included 18 sites in 

### the United States 

### and 6 sites in 

### Canada to 

### provide a 

### wide range 

### of

### expectedparticle strong

### acidity 

### and ozone 

### levels. Communities were 

### predominantly suburban or 

### rural with 

### homogeneous, relatively stable 

### populations andno major 

### local sources 

### ofair

### pollution. Air 

### pollution measurement 

### methods and calibration 

### procedures are 

### described in an 

### accompanyingpaper 

### (17). Air

### pollution 

### monitoring 

### began at 

### each site 

### before the summer 

### high acid-ozone exposure 

### period and continued 

### for at 

### least 11 months. 

### Particulate 

### pollutants were sam

### pled for 24 

### hr every 

### other day. Inhalable particulate matter 

### with an 

### aerodynamic diameter >10 

### pm 

## (PM1O) was 

### sampled using a 

### Harvard Impactor 

### (18). Fine par

### ticulate matter 

### with an 

### aerodynamic diameter >2.1 pm 

## (PM2.1) was 

### sampled using a 

### glass 

### impactor/filter pack system. Fine par

### ticle strong 

### acidity, fine 

### particle sulfate, and gaseous 

### acids (nitrous 

### and nitric 

### acids)
were 

### sampled using 

### the Harvard EPA 

### Annular Denuder System (HEADS) in 21 communities 

### (19-21). In 

### three communities 

### with 

### expected low levels of 

### gas-phase 

### acidity, the Harvard Impactors 

### with ammonia 

### denuders were 

### used. Strong 

### acidity was 

### measured 

### by pH 

### analysis (20) 

### and 

### sulfate was 

### measured 

### by ion 

### chromatography 

### of the extracted 

### particles. Ozone was 

### monitoredcontinuously. We 

### grouped the 24 communities 

### by the
sources 

### of

### particulate mass 

### and acidity (17). 

### The Sulfate Belt was 

### defined as 

### the 11 sites 

### with 

### high sulfate and 

### acidity concentrations 

### lying

### generallyalong theAppalachian Plateau 

### and the 

### Allegheny Mountains. 

### The Trans

### port

### Region 

### indudedcommunities 

### northand east 

### of the 

### Sulfate 

### Belt, which are 

### generally downwind 

### of the 

### principal sulfur emissions in 

### the

### UnitedStates. 

### The remaining commuAddress correspondence to D.W. Dockery, Environmental Epidemiology Program, Department of Environmental Health, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115 USA. We thank C. Franklin, D. Villeneuve, and R. Burnett for theiradvice and support. This studywas possible because of the hard work of M. Fay, A. Jemas, E. Donahue, C. Fischer, S. Hanig, L. Kern, J. L. McClelland, C. Panek, B. Phelps, E. Solomon, J. Mortimer, K. Wilby, and J. Moore, E. Graham, E. Haynes, M. Ramsey, the air monitoring staff at the Harvard School ofPublic Health, and the field staff at the various locations. We thank the school administrators, teachers, and especially the parents and children in the participating communities. This paperwas presented in part at an international conference sponsoredbytheAmericanThoracic Society in San Francisco, California, 18 May 1993. This studywas supported inpartbyNational Institute of Environmental Health Science grants ES-04595 and ES-0002, U.S. Environmental Protection Agency cooperative agreement CR 816071, and Health Canada. L. M. N. andJ. C. were supported in part by a National Institute of Health National Research ServiceAward (HL-07427). Received 21 August 1995; accepted 22 January 1996.

Volume 

### 104, Number5, May 

### 1996

- EnvironmentalHealth

### Perspectives 

### 500Articles * Acid aerosols and respiratory symptoms in children

nities were 

### grouped as West Coast 

### (three sites) 

### andBackground 

### (foursites). Respiratory 

### health questionnaire. 

### The 

### studyprotocol andmethods were 

### approved by the 

### Institutional Review 

### Board at 

### the Harvard 

### School of Public Health and also 

### by the local 

### health 

### department and 

### school board(s) in 

### each community. We 

### contacted principals 

### of selected schools directly 

### and invited them to 

### participate. In communities 

### with 

### fewer than 750 

### children in 

### the fourth and fifth 

### grades, all schools with at 

### least 10 

### students in 

### each grade were 

### approached. In 

### larger communities, 

### selection

### ofschoolswas 

### basedeither on

### proxim

### ity to 

### the air

### monitoring station or on ran

### dom 

### selection, 

### depending on 

### the geography 

### of the school district(s). We 

### distrib

### uted standard respiratory 

### health questionnaires to 

### the 

### children at 

### participating 

### schools in 

### September and October 

### of 1988 

### (eight communities), 1989 

### (nine communities), 

### and 1990 

### (seven communities). 

### Children were 

### instructed to 

### have 

### the questionnaire 

### completed by a 

### parent or 

### guardian and to return it to 

### school the 

### followingday. Classroom (but not 

### individual) incentives were 

### used to encourage 

### participation, 

### and questionnaires were 

### distributed multiple times over 

### several weeks. The overall response rate 

### (returned questionnaires 

### plus written 

### refusals) was 91%, 

### with

a range 

### of 85-99% 

### for the 

### individual communities 

### (Table 1). Later in 

### the schoolyear, 

### eachschoolwas 

### visitedagain

### and the

### pulmonaryfunction

### of children who had their 

### parents' permission to 

### participate was 

### measured. The results 

### of the 

### analysis of 

### pulmonary function are 

### reported inan

### accompanying

### article 

### (23). 

### Definition ofrespiratory symptoms. 

### Children's respiratory symptoms in 

### the previous year were 

### determined from questionnaire 

### responses 

### defined as 

### follows: 

### 1) asthma: ever

### diagnosedwith 

### asthma 

### bya

### physician

### plus asthmatic symptoms present in 

### the pastyear; 

### 2) 

### attacks of

### wheezing: 

### episodes of shortness ofbreath with 

### wheezing and/or 

### episodes of

### wheezing after 

### playing hard or exercising; 

### 3) persistent 

### wheeze: wheeze apart 

### from colds and/or wheeze 

### for 3 or more 

### days out 

### of the week 

### for a 

### month or 

### longer; 4) chronic 

### cough: 

### cough first 

### thing in 

### the morning 

### for as 

### longas 

### 3 

### months in a row 

### and/or 

### cough at 

### other times 

### during the 

### day or 

### night for as 

### long as 3 

### months in a row; 

### 5) chronic 

### phlegm: congestion in 

### the chest or

### bringingup

### phlegmotherthan

### with colds for as 

### long as 

### 3 

### months in a 

### row; 

### 6) bronchitis: a

### chest illness 

### diagnosed as 

### bron

### chitis; 7) asthmatic symptoms: 

### asthma, attacks of 

### wheezing, and/or persistent 

### wheeze; and 

### 8) bronchitic symptoms: 

### chronic 

### cough, chronic 

### phlegm, and/or 

### bronchitis. Onlyreports 

### ofsymptoms in 

### the past 12 

### monthswere

### considered. 

### Statisticalmethods. Previously reported 

### analyses of 

### city-specific health outcomes 

### have 

### demonstrated a 

### larger 

### between-city variation 

### than would be 

### predicted by 

### interindividual variation (7,8). In the present 

### study, we 

### used a two-step 

### analysis to correct 

### for anyexcess 

### between-city

### variability. In 

### the first step, 

### city-specific-adjusted logits 

### ofsymptom

### prevalencewere 

### calculat

### ed 

### from a 

### logistic regression 

### model for the respiratory symptom 

### ofinterest controlling 

### for sex, 

### child's history ofdiagnosed allergies, 

### parental history 

### of diagnosed asthma 

### (foreither

### biological parent), 

### parental post

### high 

### school education 

### (for either parent), 

### and current 

### smoking in 

### the home. In 

### the second step, 

### these 

### city-specific-adjusted logits were 

### regressed against 

### the city-specific 

### annual mean 

### air 

### pollution concentrations using 

### weights inversely proportional to 

### the sum 

### ofthe 

### between-cityandwithincity variances 

### of the adjusted logits. Analyses were 

### done using 

### the SAS 

### software (SAS Institute, Inc., Cary, 

### North 

### Carolina). We 

### scaled the regression 

### coefficients 

### from 

### the second step to 

### the range 

### of the 

### city-specific means 

### for the air

### pollutant of interest 

### (highest to 

### lowest; 

### Table 1) 

### and 

### expressed them as 

### odds ratios 

### (OR) 

### and 95% 

### confidence intervals (95% 

### CI). To assess 

### the consistency 

### of the evi

### dence and to 

### search for sensitive 

### subgroups, the 

### analyses were 

### repeated stratifying for sex; 

### history of a severe 

### chest illness 

### before the age 

### of 2; use 

### of a 

### humidifier in 

### the 

### home; lung 

### function in 

### the 

### lowest 

### quartile of 

### forced vital capacity 

### (FVC); current 

### exposure to 

### environmental tobacco smoke at 

### home; exposure to 

### maternal smoking during pregnancy; year 

### of study; country; andeasternversuswestern

### cities. 

### Results The city-specific ranges in the 

### annual pol

### lutant means 

### (Table 1) were 51.9 

### nmol/m3 for particle strong 

### acidity, 6.8 

### pg/m3 for 

### sulfate particles, 14.9 

### pg/m3 for respirable 

### particulate matter 

### (PM21), and 17.3

## pg/m3 for inhalable 

### particulate matter 

## (PM1O). The gaseous 

### acids 

### (HNO2 and 

### HNO3)
were 

### measured in 

### all but three communities 

### and 

### together had a 

### range 

### of 111 

### nmol/m3. City-specific mean 

### particle strong 

### acidity was 

### moderately correlated with 

## PM1O [Pearson's 

### correlation coefficient 

### (r) = 

### 0.47], strongly correlated with 

### sulfate (r= 0.90) 

### and

### PM2.1 (r= 0.82), 

### and 

### essentially uncorrelated with gaseous 

### acids (r = 

### 0.07). Three exposure parameters were 

### considered 

### for the 

### annual mean ozone concentration: 

### the average maximum 

### 1-hr
mean 

### (range 

### 46 ppb), the average 

### daytime 8-hr (1000-1800 hr 

### local time) mean (range 39 

### ppb), 

### and the average 

### daily24-hr
mean (range 19 

### ppb). All 

### three ozone 

### parameters were 

### highly correlated across 

### the 24 communities 

### with Pearson 

### correlation coefficients ranging 

### from 

### 0.74 to 0.98. By 

### design, 

### city-specific mean 

### particle strong 

### aciditywas 

### only

### weaklycorrelatedwith the 

### three ozone

### parameters; 

### the strongest corre

### lation was 

### with the average 

### 1-hr maximum
ozone concentration 

### (r= 

### 0.37). A

### total of 17,008 

### children were 

### eligible to 

### participate in 

### the 

### study, of whom 15,523 

### children (91%) 

### returned a 

### questionnaire. 

### Children who were 

### reported to 

### have cystic 

### fibrosis, a 

### history 

### of a 

### chest

Table 1. Summary of city-specific annual mean air pollution concentrations: 24 communities, United States andCanada, 1988-1991
Pollutant Grand mean SD Minimum Maximum Range Particulate matter Inhalable 

### (pg/m3) 23.8 5.0 15.4 32.7 17.3 Respirable 

### (pg/m3) 14.5 4.2 5.8 20.7 14.9 Sulfateparticles (pg/m3)a 4.7 2.2 0.7 7.4 6.8 Particle strong acidity (nmol/m3) 27.5 16.2 0.0 51.9 51.9

Gaseous pollutants Ozone, 1-hrmax. 

### (ppb) 46.5 8.5 26.9 72.5 45.6 Ozone, 8-hrdaytime avg. (ppb) 38.4 7.5 21.0 60.4 39.4 Ozone, 24-hravg. 

### (ppb) 27.8 5.1 16.3 34.8 18.5 Sulfurdioxide 

### (ppb)b 4.8 3.5 0.2 12.9 12.7 Ammonia 

### (ppb)b 1.3 1.4 0.1 5.8 5.7 Nitrous acid 

### (ppb)bc 0.6 0.4 0.1 1.4 1.3 Nitric acid 

### (ppb)bc 0.9 0.4 0.3 2.1 2.7 

### Acidityb Particle strong acidity

### (nmol/m3) 31.1 14.0 8.5 51.9 43.4 Gaseous acids 

### (nmol/m3)d 59.4 28.4 22.7 134.0 111.3 Total 

### (nmol/m3) 90.6 33.9 38.0 150.5 112.5
al 

### pg/m3

= 

### 10.4nmol/m3. 

### bExcluding Egbert, Ontario; Yorkton, Saskatchewan; andAberdeen, South Dakota. 

### Cl ppb = 40.9

### nmol/m3. dGaseous acids = nitrous + nitric acid.

Environmental Health 

### Perspectives

. Volume 

### 104, Number

### 5, 

### May 1996 501Articles * Dockery et al.

Table 2. Distribution of covariates used inthe respiratory symptoms model bycommunity: 13,369 children, 24 comunities, United States and Canada, 1988-1991
Parental Current Site Participation No. ofchildren Females Allergy Parental post-highschool smoking in code (%) Excluded Included (%) history (%) asthma (%) education (%) thehome (%) Sulfate Belt Hendersonville, TN HEN 85 59 504 56 40 13 68 55 OakRidge,TN OAK 96 119 540 46 41 15 83 42 Morehead, KY MOR 93 48 393 50 30 14 52 61 Blacksburg, VA BLB 94 124 666 48 37 16 74 37 Charlottesville, VA CHV 91 171 522 46 24 12 45 53 Zanesville, OH ZAN 90 122 647 51 26 16 50 61 Athens, OH ATH 88 82 609 53 29 13 69 52 Parsons, WV PAR 91 50 580 51 28 13 43 56 Uniontown, PA UNT 94 63 584 48 24 10 46 62 PennHill, PA PEN 90 119 566 49 32 11 80 44 State College, PA STC 91 97 601 51 31 16 89 30 TransportRegion Leamington, ON LEM 93 111 586 51 30 10 54 55 Newtown, CT NEW 92 50 458 52 37 16 89 38 Egbert, ON EGB 90 76 618 49 37 13 63 62 Pembroke, ON PMB 96 55 530 49 33 9 53 64 Dunnville, ON DUN 89 37 442 50 29 15 51 58 SouthBrunswick, NJ SBK 88 131 329 48 42 11 79 46
WestCoast SimiValley, CA SIM 88 129 539 49 31 17 78 40 Livermore, CA LIV 84 102 582 52 46 18 87 36 Monterey, CA MTY 90 92 642 52 32 17 91 29 Background Springdale, AK SPG 91 58 506 53 38 13 50 61 Aberdeen, SD ABD 96 71 676 51 26 11 77 49 Yorkton, SK YOR 95 82 628 47 39 10 58 58 Penticton, BC PCT 95 106 621 47 33 13 65 52 All 24communities 91 2154 13369 50 33 13 67 50

Table 3. Adjusted prevalence ofrespiratory symptoms bycommunityand symptom: 13,369 children, 24 communities, United States and Canada, 1988-1991a
Asthmatic symptoms (%) Bronchitic symptoms (%) Attacks of Persistent Anyasthmatic Chronic Chronic Anybronchitic Asthma wheeze wheeze symptoms Bronchitis 

### cough phlegm symptoms Sulfate Belt Hendersonville, TN 3 5 4 7 6 5 2 10 OakRidge, TN 5 7 7 10 10 3 2 13 Morehead, KY 5 7 7 9 5 4 3 9 Blacksburg, VA 5 9 9 12 10 5 3 13 Charlottesville, VA 5 8 6 9 9 5 3 12 Zanesville, OH 6 9 7 12 7 6 5 13 Athens, OH 6 8 8 11 7 5 4 12 Parsons, WV 7 7 7 11 7 5 1 11 Uniontown, PA 5 6 7 10 7 5 2 12 PennHill, PA 8 10 10 12 9 5 4 14 StateCollege, PA 11 11 12 16 7 9 4 15 TransportBelt Leamington, ON 5 7 6 10 4 7 3 12 Newton, CT 6 8 8 11 5 6 3 10 Egbert, ON 9 11 10 14 4 8 5 12 Pembroke, ON 5 8 8 11 4 7 3 11 Dunnville, ON 9 10 10 14 5 8 3 10 SouthBrunswick, NJ 7 7 7 10 7 7 4 13
WestCoast SimiValley, CA 10 10 9 14 7 6 3 12 Livermore, CA 7 8 8 11 3 5 3 9 Monterey, CA 7 8 9 11 8 5 3 14 Background Springdale, AR 4 6 6 8 5 5 2 9 Aberdeen, SD 7 9 10 12 8 5 3 14 Yorkton, SK 10 9 9 15 4 4 2 8 Penticton,BC 5 7 6 9 5 4 1 9 

### aAdjusted for

### sex, historyofallergies, parental asthma, parental education, and 

### currentsmoking in the

### home. See textfor

### definition of

### symptoms.

Volume 104, Number5, 

### May 1996 * EnvironmentalHealth

### Perspectives 

### 502Articles

-Acid aerosols and 

### respiratory

### symptoms in children



### operation, serious chest injury, or

### heartdisease, or

### who were 

### reported to 

### have received oxygen 

### formore 

### than 2 

### weeks as 

### newborns
were 

### excluded (n = 790). 

### Other 

### exclusions

were

### based onage 

### (not 8-12 

### years; n = 14),
race 

### (not 

### white; n = 1013), 

### and missing 

### information on 

### covariates 

### of interest 

### (n = 337). A total 

### of 13,369 

### children in 24 

### communities were 

### included in

### this analysis. 

### Overall, half (50%) 

### ofthe 

### subjects were 

### girls, 33% 

### had a

### historyof

### diagnosed allergies, 13% 

### had at 

### least one 

### parent with a 

### history 

### of asthma, 67% 

### had at 

### least one parent 

### with some 

### post-high school 

### education, 

### and 50% were 

### currently exposed to 

### environmental tobacco 

### smoke at 

### home. The 

### prevalence 

### of these factors varied by community 

### (Table 2). 

### After 

### adjusting for these 

### factors, the community-specific 

### prevalence 

### of asthma was 

### 3-11%; attacks 

### of 

### wheeze, 5-1 1

### %; 

### persistent 

### wheeze, 

### 4-12%; any 

### asthmatic symptoms, 

### 7-16%; 

### bronchitis, 3-10%; 

### chronic 

### cough, 3-9%; 

### chronic 

### phlegm, 1-5%; 

### and any

### bronchitic symptoms, 8-15% 

### (Table 3). Particle strong 

### acidity was 

### associated with 

### significantlyhigher reporting ofbron

### chitis in 

### the past 

### year 

### (Fig. 1 

### and Table 

### 4; OR = 

### 1.66, 95% 

### CI, 1.11-2.48 

### for the range 

### of 52 

### nmol/m3), as was 

### annual mean 

### sulfate (OR = 

### 1.65, 95% CI, 1.12-2.42 

### for the range 

### of7 

### pg/m3). None 

### of the 

### particulate 

### pollutants was 

### associated with 

### significantly higher reporting 

### ofasthma, attacks ofwheeze, persistent 

### wheeze, chronic 

### cough, or 

### chronic 

### phlegm 

### (Table 4). There was a 

### significant inverse association 

### between chronic 

### cough and PM

### O. Gaseous 

### acids were 

### associatedwith a 

### significantly higher risk 

### of asthma 

### (OR = 

### 2.00; 

### 95% CI, 

### 1.14-3.53) and showed a 

### positive association

### with

### higher reporting

### of attacks 

### of

### wheezing, persistent 

### wheeze, and any 

### asthmatic symptoms 

### (Table 4). Ozone
was not 

### associated

### with a

### significantlyhigher 

### risk 

### of any 

### of the respiratory symptoms 

### of interest, 

### regardless of the averaging time 

### used 

### (Table 4). There was a 

### suggestion 

### ofa 

### higherrisk

### ofchronic 

### coughassociatedwith 24-hr average ozone 

### (OR = 1.29; 95% 

### CI, 0.87-1.91). Ozone 

### for all three averaging times 

### showed some association 

### with 

### higher reporting

### ofbronchitis. The association 

### between 

### particle strong 

### acidityand

### bronchitis was 

### similarwhen the 

### sample was 

### stratified 

### by sex 

### (Fig. 2). The 

### association was 

### sensitive to 

### the 

### inclusion of the Canadian sites, 

### which tended to 

### have lowbronchitis 

### prevalence and low to 

### moderate 

### particle strong 

### acidity. 

### Thus, much weaker associations were 

### found when the 

### sample was 

### restricted to U.S. cities or cities 

### studied in 

### the secondyear, 

### whichwerepre

### dominantly U.S. cities 

### (Fig. 2). No 

### sub12

10



### WI1

C3

.0

0 C)
160

10 0.

10 St

=- 8

6

4

0 0 10 20 30 40 50 60

Particle strongacidity (annual mean innmol/m3)
Figure 1. Association of bronchitis with particle strong acidity adjusted for sex, child's history of atopy, parental education, parental asthma, and current smoking in the home: 24 cities, United States and Canada, 1988-1991. One-half 95% Cls for each city-specific bronchitis prevalence are shown. Site codes

are provided inTable 2.


### These results are consistent 

### with earlier reports 

### from the Six Cities 

### Study (7,8,15), 

### which noted

### higher rates 

### of

### reported bron

### chitis, but not 

### asthma or

### wheeze, in association 

### with total 

### suspended particles (7), 

### with

### particulate matter < 

### 15 pm in 

### aerodynamic 

### diameter (8), or

### with levels 

### ofparti

### cle strong

### acidity (15). In 

### these 

### earlier 

### studies, 

### reporting 

### ofchronic 

### cough was 

### higher, but not 

### significantly so, in association 

### with these

### pollutants. Prior 

### controlled exposure 

### studies 

### of animals and humans 

### provide support 

### for a 

### relationship between 

### acid aerosols and bronchitis. Short-term exposures to 

### acid aerosols have been shown to 

### result in 

### alterations 

### of 

### mucociliary clearance in 

### rabbits, mice, 

### donkeys, and humans 

### (24). Thus it is 

### reasonable to 

### suspect 

### that chronic exposure to 

### moderate levels of 

### acidic air 

### pollution may 

### affect children's 

### nonspecific defense mechanisms 

### adversely, increasing their riskofrespiratory

### illness. groups 

### appeared to 

### be 

### markedly more sensitive to 

### particle strong 

### acidity than 

### the overall 

### sample of children 

### with respect to 

### their risk 

### ofbronchitis (Fig. 

### 3). The risk

### of bronchitis among 

### childrenwho were in 

### the lowest 

### quartile of FVC was not 

### associated with

### level of

### particle strong

### acidity. 

### Discussion This 

### study was 

### designed to 

### determine whether 

### long-term exposure to 

### acidic 

### aerosols, estimated 

### by annual mean con

### centrations, was 

### associated with 

### differences in 

### reported respiratory symptoms in 

### chil

### dren. The data from this 

### study indicate that 

### adjusted prevalence of bronchitis in 

### children 

### aged 8-12 years was 

### significantly associated with 

### particle strong 

### acidity concentrations. 

### Asthma, persistent 

### wheeze, chronic 

### cough, and chronic 

### phlegm were not 

### significantly associatedwith

### higher lev

### els ofacid aerosols. No sensitive 

### subgroups

were 

### identified.

EnvironmentalHealth

### Perspectives * Volume 

### 104, Number5, 

### May 1996 

### 503Articles * Dockery et al.

Table4. Association ofairpollutantswith respiratorysymptoms bysymptomand pollutant: 13,369 children, 24 communities, United States and Canada, 1988-1991a

Particle strong acidity (52nmoVm3) Sulfateparticles (6.8pg/iM3) Respirable particulatematter (14.9pg/m3) Inhalable particulatematter (17.3

### pg/M3)
Gaseous acids 

### (2.7

### ppb) Total acid (114nmol/m3)
Max. ozone, 1-hravg. (45.6

### ppb) Sulfurdioxide (12.7ppb) OR

95% Cl
OR 95% Cl
OR 95% Cl
OR 95% Cl
OR 95% Cl
OR 95% Cl
OR 95%Cl
OR 95% Cl Asthma

0.71 0.43-1.16 0.80 0.50-1.29 0.72 0.40-1.28 0.77 0.44-1.35 2.00 1.14-3.53 1.64 0.98-2.73 1.02 0.44-2.33 1.05 0.57-1.93 Attacks of

wheeze 0.79 0.59-1.06 0.93 0.70-1.24 0.82 0.58-1.15 0.79 0.57-1.08 1.40 0.99-1.99 1.26 0.92-1.73 0.99 0.61-1.60 1.07 0.75-1.55 Persistent

wheeze 0.83 0.60-1.15 0.96 0.70-1.31 0.80 0.55-1.16 0.75 0.53-1.07 1.34 0.87-2.05 1.24 0.86-1.79 0.90 0.52-1.54 1.19 0.80-1.79 Anyasthmatic

symptoms 0.81 0.60-1.10 0.91 0.67-1.24 0.79 0.55-1.12 0.75 0.54-1.05 1.34 0.91-1.96 1.24 0.89-1.72 0.89 0.53-1.50 1.16 0.80-1.68 Bronchitis

1.66 1.11-2.48 1.65 1.12-2.42 1.50 0.91-2.47 1.50 0.93-2.43 1.18 0.67-2.08 1.43 0.89-2.28 1.49 0.72-3.12 1.56 0.95-2.56 Chronic

cough 0.92 0.64-1.31 1.04 0.74-1.47 0.82 0.54-1.23 0.69 0.48-0.99 1.02 0.64-1.61 0.98 0.66-1.45 1.13 0.62-2.04 1.02 0.66-1.58 Chronic

phlegm 0.95 0.60-1.49 1.29 0.84-1.96 1.02 0.61-1.73 1.05 0.64-1.72 1.48 0.90-2.43 1.40 0.91-2.15 1.12 0.53-2.39 1.55 1.01-2.37 Anybronchitic

symptoms 1.19 0.92-1.53 1.27 1.01-1.61 1.08 0.80-1.46 1.07 0.80-1.43
1.11 0.80-1.53 1.18 0.90-1.55 1.17 0.76-1.81 1.29 0.98-1.71 aSymptoms adjusted for sex, historyofallergies, parental asthma, parental education, and current smoking in home. Odds ratio (OR) represents relative risk over the range ofcity-specific airpollution; Cl, confidence interval.



### The higher reporting 

### of bronchitis, in contrast to 

### asthma, persistent 

### wheeze, or 

### chronic 

### cough, is consistent 

### with an 

### increased 

### susceptibility to 

### illness in association 

### with 

### particle strong 

### acidity. Alternatively, there may 

### be more 

### misclassification 

### of 

### relatively subjective symptoms like 

### cough and wheeze in contrast to 

### diagnosed bronchitis. 

### Such 

### misclassification may have limited our 

### ability to observe associations 

### ofsymptomswithair

### pollution. Although these data indicate anassociation 

### between 

### particulate air 

### pollution, 

### specifically particle strong 

### acidity, and bronchitic symptoms, 

### there is no 

### evidence 

### for

### higherreporting 

### ofasthmatic symptoms 

### associated with these 

### pollutants. Similar 

### results in 

### which 

### particulate air 

### pollution
was 

### associated with bronchitic symptoms 

### but not 

### with any 

### indicator ofasthma have been 

### reported in 

### the Six Cities 

### Study (7, 8) for the 

### United States 

### and in German 

### studies 

### (25). 

### Children in 

### Leipzigwith

### high sul

### fur dioxide and 

### particle exposures were 

### compared to 

### children in 

### Munich with 

### much lower 

### exposures to these 

### pollutants. Bronchitic symptoms were 

### elevated in 

### the high sulfur 

### dioxide/particle exposures, 

### but 

### asthmatic symptoms were 

### decreased in 

### Leipzig, the community with 

### higher parti

### cle and 

### sulfur dioxide 

### pollution. The 

### authors 

### suggested that asthmatic symptoms
were 

### associated with 

### higher ozone concentrations in 

### Munich. However, in 

### the current 

### data the association 

### between asthmatic symptoms and measures 

### of chronic ozone 

### exposure were 

### very 

### slight. No association

was 

### found between ozone 

### and respiratory symptoms in 

### the SixCities 

### Study (7,8). The 

### observed association 

### ofasthma and Geography l
All cities

U.S. cities

Eastern cities

Yearof study

Year

Year 2

Year3

Gender

Males
Females

1 2 3 Adjusted odds ratios Figure 2. Odds of bronchitis and 95%confidence intervals for a 52 nmol/m3 increment in particle strong acidityfor stratified samples of children or cities adjusted for sex, child's history of atopy, parental education, parental asthma, and current smoking in the home: 24 cities, United States and Canada, 1988-1991. Dashed line indicates overall estimated effect.



### asthmatic 

### symptoms with 

### gaseous acids must 

### be 

### interpreted with caution 

### because this association 

### appears to be 

### driven by 

### onlyone 

### community. The annual mean 

### for gaseous 

### acid in Simi 

### Valley was 

### one-third 

### higher than the mean 

### for the next 

### highest community 

### (17), and Simi

### Valleyalso 

### had the second

### highest rate 

### of

### reported asthma. 

### If Simi 

### Valley is 

### excluded from consideration, the association 

### between gaseous acid 

### levels andasthma is no 

### longersignificant. All children r
Any chest illness 1_. before age 2
Persistentwheeze, attacks of shortness of breath withwheeze, orasthma

Lowestquartile offorced vital capacity (RVC) (n =22)

Parental asthma

Maternal smoking during pregnancy

ETS inthe home

Any use ofhumidifiers

1 2 3

Adjusted odds ratios Figure 3. Odds of bronchitis and 95% confidence intervals for a 52 nmol/m3 increment in particle strong acidity for potentially sensitive subgoups of children or cities adjusted for sex, child's history of atopy, parental education, parental asthma, and current smoking in the home: 24 cities, United States and Canada, 1988-1991. Dashed line indicates overall estimated effect.

There 

### appears to be no 

### evidence that the 

### prevalence ofasthma or asthmatic 

### symptoms in 

### children is associated with chronic 

### exposure to 

### particulate, sulfur 

### oxide, or ozone air 

### pollution. This does not 

### implythat acute air 

### pollution episodes do not 

### trigger or exacerbate 

### asthmatic 

### attacks, as has been shown in 

### multiple studies. 

### However, air

### pollutiondoes not 

### appear to contribute to 

### the increased 

### prevalence ofnewcases of

### asthma, as is 

### often claimed inthe

### popularpress.

Volume 104, Number5, 

### May 1996 * EnvironmentalHealth 

### Perspectives 504Articles * Acid aerosols and 

### respiratory symptoms in children

In this 

### study, at 

### least 11 months 

### ofair 

### monitoring 

### data were 

### used to 

### calculate 

### annual means 

### of

### pollutants as a surrogate 

### for lifetime exposure. 

### The

### validityofsuch a monitoring 

### scheme 

### depends on 

### the repre

### sentativeness 

### ofthe 

### selectedyear's aerometrics. Brook and 

### Spengler (26) have examined 

### historical aerometric data and con

### cluded that community air 

### pollution levels have been relatively 

### stable over these chil

### dren's lifetimes and that the relative 

### rankings 

### of the communities 

### with respect to 

### particle strong 

### acidity, ozone, 

### and 

## PM1O
were not 

### likely to 

### have 

### changed. Although it is 

### possible 

### that the children 

### differed in 

### their 

### personal activity 

### and exposure patterns 

### between communities, 

### these 

### differences were not 

### likely to 

### be related to annual means 

### ofacidair

### pollution. Particle strong 

### acidity, 

### sulfate, and fine 

### particulate matter are 

### all 

### formed in sec

### ondaryreactions 

### ofthe emissions 

### from fossil 

### fuel combustion. 

### They have similar 

### regional and 

### temporal 

### distributions. The strong 

### correlations of several 

### pollutants in 

### this 

### study, especiallyparticle strong 

### acidity with sulfate (r = 

### 0.90) 

### and PM2.1 (r = 

### 0.82), 

### make it 

### difficult to 

### distinguish the agent 

### of interest. 

### This 

### study was 

### designed to 

### have a 

### low correlation 

### ofparticle strong 

### acidity with ozone, 

### and although 

### high

ozonewas 

### positivelyassociatedwith report

### ing 

### of bronchitis, the association 

### was not 

### statistically

### significant. The 

### sampled children in

### each community were 

### selected to 

### have a narrow range 

### of age 

### and race. Communities 

### also were 

### select

### ed to 

### have similar 

### demographic characteristics. We

### adjustedfor

### differences amongcommunities in 

### the 

### distributions 

### of sex, 

### child's allergy

### history, parental 

### education, parental asthma, andcurrent 

### smoking in 

### thehome in 

### the 

### first stage 

### of the two-stage 

### model. No 

### evidence ofeffect 

### modification was 

### observed among 

### these 

### children. The association 

### of bronchitis with 

### particle strong 

### acidity was 

### similar 

### regardless ofsex, year 

### of

### study, country, 

### home 

### characteristics, or 

### child's health 

### history. The 

### onlyexception was 

### for 

### children in 

### the lowest 

### quartile of FVC, 

### who had no association 

### between a

### higherriskofbronchitis

### and

### particlestrong

### acidity. These data indicate that chronic exposure to acid 

### aerosol pollution may 

### have observable negative consequences 

### for the health ofchildren. Although the long-term consequences 

### ofbronchitis in 

### these children remain 

### unclear, respiratory illnesses in 

### childhood may 

### be a 

### risk factor 

### for chronic obstructive disease. These childrenalso may be at a

### higher risk 

### from other environmental 

### andoccupational exposures later in

### life.

REFERENCES

1. American Thoracic Society. Health effects of atmospheric acids and theirprecursors. Am Rev Respir Dis 144:464-467 (1991). 2. U.S. EPA. An acid aerosols position paper: health effects and aerometrics. ECAO-R-0140. Research Triangle Park, NC:Environmental ProtectionAgency, 1987. 3. Graham JA. Review, discussion, and summary: toxicology. Environ Health Perspect 79: 191-194 (1989). 4. Gong H. Health effects of air pollution. A review of clinical studies. Clinics Chest Med 13:201-214 (1992). 5. Dassen W, Brunekreef B, Hoek G, Hofschreuder P, Staatsen B, deGroot H, Schouten E, Biersteker K. Decline in children's pulmonary function during an air pollution episode. J Air Pollut Control Assoc 36:1223-1227 (1986). 6. Graham NMH. The epidemiology ofacute respiratory infections in children and adults: a global perspective. Epidemiol Rev 12:149-178 (1990). 7. WareJH, Ferris BGJr., Dockery DW, Spengler JD, Stram DO, Speizer FE. Effects of ambient sulfur oxides and suspended particulates on respiratory health ofpreadolescent children. Am RevRespir Dis 133:834-842 (1986). 8. Dockery DW, Speizer FE, Stram DO, Ware JH, Spengler JD, Ferris BGJr. Effects ofinhalable particles on respiratory health of children. AmRevRespir Dis 139:587-594 (1989). 9. Bates DV, Baker-Anderson M, Sizto R. Asthma attack periodicity: A study of hospital emergency visits in Vancouver. Environ Res 51:51-70 (1990). 10. Pope CA III. Respiratory hospital admissions associated with 

### PMIO pollution in Utah, Salt Lake, and Cache Valleys. Arch Environ Health 46:90-97 (1991). 11. Ostro B. The association of air pollution and mortality: Examining the case for inference. Arch Environ Health48:336-342 (1993). 12. Lippmann M. Background on health effects of acid aerosols. Environ Health Perspect 79:3-6 (1989). 13. Spengler JD, Brauer M, Koutrakis P. Acid air and health. Environ Sci Technol 24:946-956 (1990). 14. SpenglerJD, Keeler GJ, Koutrakis P, Ryan PB, Raizenne M, Franklin CA. Exposures to acid aerosols. Environ Health Perspect 79:43-51 (1989). 15. Damokosh Al, Spengler JD, Dockery DW, Ware JH, Speizer FE. Effects ofacidic particles

on respiratory symptoms in 7 US communities. AmRevRespirDis 147:A632 (1993). 16. Speizer FE. Studies ofacid aerosols in six cities and in a new multi-city investigation: design issues. Environ Health Perspect 79:61-67 (1989). 17. Spengler JD, Koutrakis P, Dockery DW, Raizenne M, Speizer FE. Health effects ofacid aerosols in North American children: air pollution exposures. Environ Health Perspect 104:492-499 (1996). 18. Marple VA, Rubow KL, Turner W, Spengler JD. Low flow rate sharp cut impactors for indoor air sampling: design and calibration. J AirPollut ControlAssoc 37:1303-1307 (1987). 19. Koutrakis P, Wolfson JM, SlaterJL, Brauer M, Spengler JD, Stevens RK. Evaluation of an annular denuder/filter pack system to collect acidic aerosols and gases. Environ Sci Technol 22:1463-1468 (1988). 20. Koutrakis P, Wolfson JM, Spengler JD. An improved method for measuring aerosol strong acidity: results from a nine-month study in St. Louis, Missouri and Kingston, Tennessee. Atmos Environ 22:157-162 (1988). 21. Keeler GJ, Spengler JD, Castillo RA. Acid aerosol measurements at a suburban Connecticut site. Atmos Environ 25A:681-690 (1991). 22. Keeler GJ, SpenglerJD, Koutrakis P, Allen GA, Raizenne M, Stern B. Transported acid aerosols measured in southern Ontario. Atmos Environ 24A:2935-2950 (1990). 23. Raizenne M, Neas LM, DamokoshAI, Dockery DW, Spengler JD, Koutrakis P, Ware JH, Speizer FE. Health effects of acid aerosols on North American children: Pulmonary function. Environ Health Perspect 104:506-514 (1996). 24. Schlesinger RB. The interaction ofinhaled toxicants with respiratory tract clearance mechanisms. CritRevToxicol 20:257-286 (1990). 25. VonMutius E, Fritzsch C. Prevalence ofasthma andallergic disorders among children inUnited Germany; a descriptive comparison. Br Med J 6866:1395-1399 (1992). 26. BrookJR, Spengler JD. Exposure to fine particle acidity and sulfate in 24 North American communities: the relationship between single year observations and long-term exposures. Air WasteManageAssoc 45:709-721 (1995).

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