UBC Faculty Research and Publications

Measurement of acidic aerosol species in Eastern Europe : implications for air pollution epidemiology Brauer, Michael; Dumyahn, Thomas S.; Spengler, John D.; Gutschmidt, Kersten; Heinrich, Joachim; Wichmann, H.-Erich May 31, 1995

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
52383-Brauer_M_et_al_Measurement_acidic_aerosol_species.pdf [ 1.97MB ]
Metadata
JSON: 52383-1.0074695.json
JSON-LD: 52383-1.0074695-ld.json
RDF/XML (Pretty): 52383-1.0074695-rdf.xml
RDF/JSON: 52383-1.0074695-rdf.json
Turtle: 52383-1.0074695-turtle.txt
N-Triples: 52383-1.0074695-rdf-ntriples.txt
Original Record: 52383-1.0074695-source.json
Full Text
52383-1.0074695-fulltext.txt
Citation
52383-1.0074695.ris

Full Text

~~l --- B -Measurement of Acidic Aerosol Species in EasternEurope: Implications for Air PollutionEpidemiologyMichael Brauer,' Thomas S. Dumyahn, John D. Spengler, KerstenGutschmidt,3Joachim Heinrich,3 and H.-Erich Wichmann31Department of Respiratory Medicine, Occupational Hygiene Program, The University ofBritish Columbia, Vancouver, BC V6T 1Z3 Canada; 2Department of Environmental Health,Harvard School of Public Health, Boston, MA 02115 USA; 3GSF-lnstitut furEpidemiologie, Neuherberg, GermanyA large number-of studies have indicatedassociations betw partiulate air pltion and .dv..se health outWintertme arplution inprilar hasbeen associtid with increased :ortality.Identification of causal constituents ofinhal-able particuilate matter has been elisive,although one c ite has been the adityof the: aer.W...............et.sof aidic _eo s made or prx-matly15yes iErfurt, G n adSokolov, C pc. In b lthe burning ofh-sfur coal s thepprma-ry source of amint air polution TwenityEfur-hour a measureme ereWmadef1or Pm1o$04partculaa mtter w.ith a eoit MlomsX;<. ............... ....... .....dynamic dia_enet(i.. ). ..m... as... llflnpartide(d>t25 pm) HAndSO rtheetre stuy Adtoally,separt dayand nIightmOf fin.e ic H,S4, N03 andH-aH and the SO2HNO3, HONO a NH we c edwith an nnlrdenuderffr pacc ssteover a 7.mot lt wintr r pr...W ...s:... :we....co..wtWfh addtional mesuem ntdrngplle-t on.pis.tr fl n w . At bothsites,24-hr SO2 (meanconcentration,- rf 52pg/m3, with peak levels of >585 " ) andPM10 (meanw c n ion 60 pg m=) con-* . .: ...:: e.......c.entration. were quit hitgh. However,...^e..~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. 1S;,.: ... ......trationofappim te 10p we notas gra as3xec8 gie thhigh SO con-*centratons,and aciditywa.very......l.o(concentrationof ci pg/in3, with peak levelsof only 7 pg ow).L acdity is:likey to bethe result of NH neutralization dconversion o S to. SO 7. T a..i .. :.. .. ;... .. :... . 4.. .. .. .. ::.along with evdence.thataer l...i....t.........y..dq... ..exposureare uiiriiady loDwer thn tusent levels and the reported ssociatonbetween fine particulate air pollution andhealth outcomes in regions where littleaerosol acidity a been me d suggtthat prti.ct di one Mi pi-.mary copq n...e6.nt.ig fin .atclate..a.ir pol.luti.o.n.'.t. oxiciy :e ad:aiaerosols, air pollution, Ea.stern ur epe,ei-demiology, particulates. Environ HealthPepcte 103:482488 (1995)* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~........ ... : . ::..:*..: ......~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. .:.: ... .... ...... . .:Beginnning more than 50 years ago, winterepisodes of high levels of air pollution wereassociated with excess mortality in a num-ber of locations, such as London; Donora,Pennsylvania; and the Meuse Valley inBelgium. Although comprehensive air qual-ity data were often not available for theseepisodes, analysis suggested that althoughall fine particle concentrations were elevat-ed, acidic aerosols in particular, in additionto sulfur dioxide, were the constituentsassociated with effects (1,2). The potentialeffect of acidic aerosol exposure has beeninvestigated in North America, where inthe summer acidic species are produced viaphotochemical oxidation mechanisms (3).One motivating factor for focusing on sum-mer acid aerosol episodes in North Americawas the suggestion that the historical winterfog episodes produced high levels of acidicaerosols (1,4).As a result of severe air pollutionepisodes, control strategies were imple-mented to reduce the burning of coal forresidential heating in London, high-sulfurcoal was replaced with low-sulfur varieties,and emission control strategies were imple-mented, such as the addition of tall stackswhich emit above inversion layers. Thesestrategies have greatly reduced the severityof localized wintertime episodes in westernEurope and North America. In contrast,the use of tall stacks and the increaseddemand for summertime power (for airconditioning, for example) has led to long-range transport of sulfur oxides aboveinversion layers. As this is a summertimephenomenon, photochemical oxidationmechanisms are responsible for productionof acidic aerosol species (3). Therefore,although the production mechanisms aredifferent, the same agent that was suspect-ed in earlier winter episodes has also beeninvestigated for North American summersituations, even though typical summer-time levels of aerosol acidity in NorthAmerica are significantly lower than in thehistorical winter fog episodes.Recently, several studies have attemptedto examine the relative importance ofaerosol acidity for the health effects of airpollution. Pope and colleagues have shownthat wintertime air pollution, especially fineparticulate matter <10 pm in diameter(PM1O, da c 10 mm), is associated withexcess mortality, as well as increased schoolabsences and hospital admissions in an areaof Utah (5-8). Although these studiesshowed elevated levels of wintertime airpollution, levels of acidic aerosols wereextremely low (7). Dockery et al. examinedthe association among PM1O, aerosol acidi-ty, and gaseous pollutants with daily mor-tality in eastern Tennessee and St. Louis,Missouri (9). The authors found associa-tions of similar magnitude for PM inboth locations and weaker associations withaerosol acidity (5S. The consistency of thePM1O associations with daily mortality isstriking given that mean aerosol acidity lev-els in eastern Tennessee were more thanthree times higher than the mean levels inSt. Louis, although PM1O and aerosol sul-fate concentrations were similar. It is alsoimportant to note that in easternTennessee and St. Louis, PM1O concentra-tions peak during the summer months,whereas in the Utah Valley, elevated PM1Ois a winter phenomenon.Dockery and colleagues also reportedon the relationship between mortality andair pollution in six U.S. cities (10). In thisanalysis, mortality was more strongly asso-ciated with levels of fine and inhalable par-ticulates, as well as sulfate particles, than itwas with aerosol acidity (10). Somewhatdifferent results were presented byThurston et al. for analysis of Toronto,Ontario, data: aerosol acidity showed astronger relationship to summer hospitaladmissions than did other particle measuressuch as aerosol SO4 -, PM10 or PM25(11). Such results are perplexing, especiallywhen one considers that even when aerosolacidity is measurable in the ambient air,exposure is likely to be low due to neutral-ization in indoor environments (12,13).Another opportunity to investigate theimpact of aerosol acidity and the epidemi-ological association between winter smogand health came with the end ofCommunist rule in Eastern Europe. Amajor air pollution epidemiology studywas undertaken in former East Germanyand in the Czech Republic. An initialanalysis of data from the period1980-1989, just before the reunificationof Germany, has associated excess mortali-ty in Erfurt, Germany, with levels of SO2and suspended particulates (14). Althoughair pollution data were available for thesepollutants, there were no measurementsavailable of fine particulates nor of theAddress correspondence to M. Brauer, Depart-ment of Respiratory Medicine, OccupationalHygiene Program, The University of BritishColumbia, 2206 East Mall, 366A,Vancouver, BCV6T 1Z3 Canada.Received 19 August 1994; accepted 15 February1995.Environmental Health Perspectives4821-- 7A- -iir. M9 9 ,Ew 9 9' -chemical composition (such as acidity) ofthe particulates. With the reunification ofGermany in 1989 and the end ofCommunist rule in the neighboring CzechRepublic, the opportunity arose not onlyto conduct a more detailed epidemiologicalstudy, but also to collect measurements ofaerosol acidity and fine particulate matter(15). During 1990-1992, the effect ofambient S02 and total suspended particu-lates (TSP) on peak flow, medicationintake, and daily respiratory symptoms in apopulation of 160 asthmatic children and110 adults with asthma or chronic bron-chitis was analyzed. A small but consistentdecrease in evening peak flow and anincrease in daily symptoms was associatedwith elevated levels of SO2 and TSP,whereas the effects of aerosol acidity andso042 were generally weaker (15).In the Czech Republic, several studieshave indicated effects of ambient air pollu-tion on health. Bobak and Leon report anecological study in which associations wereobserved between PM1O, and to a lesserextent SO2 and NOX, and post-neonatal res-piratory mortality in Czech infants (16).Lower pulmonary function and a higherprevalence of respiratory symptoms in 2nd-,5th-, and 8th-grade children living in thehighly polluted region of northern Bohemiawere observed when compared to the lungfunction and respiratory symptoms of chil-dren living in the less polluted area of south-ern Bohemia (17). In northern Bohemia,high levels of PM1O and SO2 (12-hr averagesof 800 and 1100 pg/mi3) were measured in a1993 winter episode. During this periodso42- levels were also quite high (200pg/m3) and the fine aerosol was acidic,although only a few percent of the SO42-was in the form of sulfuric acid (Stevens RK,personal communication).Ambient air measurements of PM10,acidic aerosols, acidic gases, and NH3 wereconducted for approximately 1.5 years inErfurt, Germany, and Sokolov, CzechRepublic. This study provided a uniqueopportunity to examine levels of acidicaerosol species in environments directlyimpacted by both local and regionalsources of high sulfur (up to 5%) lignite"brown coal." Monitoring was specificallyfocused on winter inversions during whichpollutant concentrations were expected tobe highest. Here we report on these mea-surements and compare them to our sub-stantial database of acid aerosol measure-ments in North America and the availabledata for Europe. We also compare charac-teristics of the chemical composition ofthese Eastern European winter atmos-pheres to other coal-burning regions andwith summer episodes in North America.Our purpose was to determine if aerosolacidity can be measured in wintertime airpollution episodes in locations where theburning of high-sulfur coal is a major airpollution source. Our primary hypothesiswas that the health effects associated withwintertime air pollution in similar settingsare associated with acidic aerosols.Extensive measurements of acidic aerosolspecies were collected to support an indi-rect test of this hypothesis.MethodsTwo cities were selected for air monitoring,Erfurt, in the former East Germany, andSokolov, in the Czech Republic. BothErfurt and Sokolov were reported to besubject to winter inversions, which resultedin poor ambient air quality (high TSP andSO2 concentrations) and reduced visibility.Erfurt (population approximately 220,000)is northwest of Frankfurt, approximately100 km east of the former east-west bor-der, and is a regional center of commerce.The city has an older, central area wherethe primary heating source is individualcoal furnaces. The outer areas of the citycontain large apartment complexes withsteam heat supplied by a large coal-burningpower plant located several kilometers eastof the city center. Erfurt is situated on a flatplain bordered by a 100-m high ridge on allsides but north. The sampling site was 1km from the town center, 15 m from thenearest structure, and 30 m from the near-est major road. Sampler inlets were locatedapproximately 2 m above ground level.Sokolov (population approximately60,000) is an industrial town in a coal-mining region of the Czech Republic, 100km east of the German-Czech border, atthe southern edge of the northern Bohemiaregion where some of the largest SO2sources in Europe are located. In theimmediate vicinity of Sokolov are severalpower plants and large industrial complex-es in the region, in addition to a coal gasifi-cation plant. Sokolov is in the broad Ohreriver valley, which is bordered by 400-mhigh valley walls. The sampling site waslocated on the terrace of a two-story build-ing approximately 2 km from the centraldistrict. Sampler inlets were located 2 mabove the terrace surface.Particulate acidity (measured in thePM2 5 particulate size fraction) and PM10samples were collected with the HarvardImpactor (with the addition of a citricacid-coated honeycomb denuder for acidi-ty sampling) (18,19). The Harvard-EPAAnnular Denuder System (HEADS) wasused to measure gaseous and particlespecies during some portions of the study.Sampling and analysis procedures arereported in detail elsewhere (20,21). Dailyor every second day 24-hr samples of fineparticulate (da <2.5 pm) mass, H+, andso42- were collected from December1990-June 1992, and 24-hr PM1O sampleswere collected February 1991-June 1992.Annular denuder measurements were madetwice daily (0800 hr-1600 hr, 1600hr-0800 hr) from February 1991 toSeptember 1991 and during episode peri-ods from October 1991 to April 1992.Detection limits for 12-hr denuder mea-3 3surements were 16.2 pg/m , 1.2 pg/mI0.8 pg/mi (as H2SO4), 2.3 pg/m3, 0.6pg/m3 and 0.3 pg/m3, for SO2, NH3, H+,s042, NH4+, and N03, respectively. Thedetection limit for PM10 was 9 pg/m3, andthe Harvard Impactor 24-hr detection lim-its were 0.4 (as H2SO4) and 1.4 pg/mi3 forH+ and SO4 -, respectively.One of the features of the annulardenuder system is a multistage filter packwhich includes a Teflon filter to collect thefine particles as well as backup Na2CO3and citric acid-coated filters to collectgaseous HNO3 and NH3, respectively,that have evolved from the collected parti-cles as the result of artifact reactions (22).Backup filters are used to determinewhether any aerosol acidity has been "lost"due to particle-particle interactions. Forexample, acidic sulfate aerosols that reactwith NH4NO3 aerosols will be neutralized,and gaseous HNO3 will be liberated (Eq.1). An additional source of volatilizedHNO3 is from the dissociation of particu-late NH4NO3 into gaseous HNO3 andNH3 (Eq. 2).H2S04 (p), NH4HS04 (p), (NH4)3H(SO4)2 (P)+ (NH4)N03 (p) -*(NH4)2S04 (p) + HN03 (g) (1)NH4NO3 (p) -* NH3 (g) + HN03 (g) (2)By quantifying the amount of HNO3 (asNO3-) and NH3 (as NH4') on the backupfilters, the measured acidity can be correct-ed for any acidity that is lost due to parti-cle-particle neutralization reactions.Results and DiscussionTables 1-3 present summary statistics andcompare the winter and summer concen-trations measured in Erfurt and Sokolov tothose measured in 23 North Americancommunities as part of a major epidemio-logical study (23). These sites were usedfor comparison because the studies usedthe same or equivalent measurement andanalytical techniques for aerosol acidity asthe Eastern European sites, measurementswere collected over an entire year, and allmeasurements were of 24-hr duration.Additional measurements of aerosol acidityin North America have been reported pre-viously (3) and demonstrate that the 23North American communities used forcomparison represent a reasonable descrip-tion of the range of aerosol acidity andVolume 103, Number 5, May 1995 483Table 1. Summer (May-September) and winter (November-March) concentrations of particulate matter .10 pm (PM10; pg/in3 measured in Sokolov, Erfurt, and23 communities in the United States and CanadaaSummer WinterSite N Mean S0 Min Max Site N Mean SD Min MaxPenn Hills, PA 73 46.3 24.6 6.4 119.3 Erfurt 76 63.5 42.9 12.2 208.9Erfurt 53 44.3 19.6 16.5 89.3 Sokolov 72 54.2 34.7 3.2 171.2Sokolov 36 40.9 19.7 9.2 84.1 Monterey, CA 72 32.6 11.2 13.7 61.1Simi Valley, CA 71 39.8 11.7 15.2 73.5 Livermore, CA 74 30.6 17.2 3.1 83.8Morehead, KY 71 39.5 17.9 8.6 77.1 Parson, WV 73 29.6 17.7 5.2 93.6Zanesville, OH 65 39.2 17.1 10.9 84.9 Simi Valley, CA 74 28.9 14.4 6.8 64.6Springdale, AZ 65 37.3 13 0 67.9 Hendersonville, TN 68 27.9 12.7 8.9 60.2Hendersonville,TN 75 37.1 15.7 10.6 77.3 Uniontown, PA 72 27.8 11.5 10.9 70.5Uniontown, PA 76 36.5 19.3 14.5 116.5 Penn Hill, PA 61 26.4 11.9 4.9 76.7Athens, OH 76 34.8 16.4 10.7 99.5 Springdale, AZ 71 26 15 0 89.3Blacksburg, VA 73 30.9 11.4 5 60.5 Morehead, KY 68 24.9 9.2 8.5 49.5Parson, VWV 76 30.5 14.5 8.1 73.3 Leamington, ON 70 23.4 11.5 7 78.5Dunville, ON 68 30.3 18.8 0 83.3 Newtown, CT 59 23.3 11.9 0 58.5Oak Ridge, TN 64 29.6 11.3 13.3 64.4 Athens, OH 75 23 9.4 5.2 49.6Leamington, ON 77 28.6 13.1 9.5 78.8 Blacksburg, VA 70 22.7 8.7 5.5 41.9Charlottesville, VA 74 27.2 12.6 7 61.3 Oak Ridge, TN 65 21.8 10 3.6 53.7Newton, CT 73 27.1 17.7 0 79.4 Zanesville, OH 66 21 10.3 1.7 58.1State College, PA 73 26.8 13.1 0 67.3 Penticton, BC 72 19.9 9.9 6.5 47.6Livermore, CA 70 26.3 10.9 4.8 53.2 Charlottesville, VA 62 19.8 8.2 7.5 60.1Aberdeen, SD 78 25 11.4 5.3 74.2 Dunville, ON 58 17.1 9.5 0 47.7Egbert, ON 77 23.2 13.5 0 70.8 Egbert, ON 68 16.7 9.4 4.6 51.3Yorktown, SK 73 22.8 9.7 5.1 48.6 State College, PA 72 16.6 6.8 0 38.6Pembroke, ON 75 21.2 14.2 0 64 Aberdeen, SD 67 16.5 8.4 3.4 41.2Monterey, CA 71 20.3 9.8 0 45.5 Pembroke, ON 47 16.1 11.4 0 51.1Penticton, BC 73 18.9 9.1 4 47 Yorktown, SK 60 14.1 6.1 1.7 34aFor each season, the sampling sites are listed in order of highest mean concentration.Table 2. Summer (May-September) and winter (November-March) concentrations of aerosol strong acidity (pg/in3 as H2504) measured in Sokolov, Erfurt, and 23communities in the United States and Canada8aSummer WinterSite N Mean SD Min Max Site N Mean SD Min MaxUniontown, PA 69.0 4.3 5.3 0.1 39.1 Oak Ridge, TN 65.0 1.3 1.5 0.0 8.8Parson,WV 71.0 4.0 4.7 0.0 19.2 Uniontown, PA 71.0 1.2 1.1 0.2 6.5Morehead, KY 72.0 3.8 3.3 0.1 14.8 Parson, WV 68.0 1.1 1.0 0.1 4.5Athens, OH 75.0 3.8 4.0 0.1 24.6 Hendersonville,TN 71.0 1.1 1.2 0.0 7.2Penn Hills, PA 66.0 3.4 4.2 0.0 19.4 Morehead, KY 69.0 1.1 1.0 0.2 5.3Oak Ridge, TN 70.0 3.3 2.9 0.0 14.3 State College, PA 71.0 1.0 0.9 0.0 4.1State College, PA 66.0 3.3 3.2 0.4 16.5 Charlottesville, WV 68.0 0.9 0.9 0.0 4.5Zanesville, OH 59.0 3.2 3.7 0.0 17.8 Zanesville, OH 70.0 0.8 1.0 0.0 6.7Hendersonville, TN 70.0 3.2 2.5 0.2 10.9 Athens, OH 75.0 0.7 0.7 0.0 4.2Charlottesville, VA 66.0 3.1 2.7 0.0 15.5 Pembroke, ON 43.0 0.6 0.5 0.0 1.7Blacksburg,VA 72.0 2.9 2.2 0.3 10.9 Blacksburg,VA 71.0 0.6 0.6 0.0 2.8Dunville, ON 57.0 2.6 3.4 0.0 13.9 Simi Vally, CA 70.0 0.6 0.9 0.0 5.6Newtown, CT 70.0 2.0 2.2 0.0 9.1 Newton, CT 63.0 0.6 0.5 0.0 2.2Leamington, ON 73.0 1.5 2.1 0.0 13.5 Livermore, CA 72.0 0.6 0.4 0.0 1.6Pembroke, ON 64.0 1.4 2.2 0.0 13.3 Leamington, ON 73.0 0.5 0.6 0.0 3.0Springdale, AR 71.0 1.0 0.6 0.0 2.6 Monterey, CA 72.0 0.5 0.3 0.1 1.5Simi Valley, CA 68.0 0.9 0.6 0.0 3.0 Penn Hills, PA 63.0 0.5 0.5 0.0 2.4Sokolov 74.0 0.5 0.3 0.0 1.5 Penticton, BC 70.0 0.4 0.3 0.0 1.4Livermore, CA 73.0 0.5 0.4 0.0b 1.9 Dunville, ON 54.0 0.4 0.4 0.0 2.3Egbert, ON 48.0 0.5 1.2 -0.4 6.0 Sokolov 72.0 0.3 0.6 0.0 4.8Monterey, CA 72.0 0.4 0.3 0.0 1.5 Springdale, AZ 67.0 0.3 0.3 0.0 1.0Penticton, BC 69.0 0.4 0.2 0.0 1.1 Erfurt 74.0 0.2 0.3 0.0 1.7Erfurt 75.0 0.4 0.3 0.0 1.4 Aberdeen, SD 66.0 0.0 0.1 -0.3 0.4Aberdeen, SD 74.0 0.2 0.2 -0.2 0.9 Yorktown, SK 30.0 0.0 0.1 -0.3 0.2Yortown, SK 75.0 0.0 0.2 -1.2 0.5 Egbert, ON 16.0 -0.1 0.1 -0.4 0.1aFor each season, the sampling sites are listed in order of highest mean concentration.bNegative values indicate alkaline samples.aerosol S042- concentrations found in here, Hoek et al. found low levels of pg/mr3 in a coastal area of southeastNorth America. aerosol acidity (0-8.8 pg/m3 as H2SO4) England (25). In a limited series of mea-2-European measurements are extremely and aerosol SO4 - (1-24 pg/mr) in an surements, Puxbaum, et al. (26) measuredlimited and more difficult to compare extensive monitoring study conducted in 6- to 12-hr averages of wintertime aerosolbecause of different sampling and analyti- The Netherlands (24), and Kitto and acidity and So42- concentrations incal techniques and small sample sizes. Harrison measured aerosol acidity levels of Ljublijana (formerly Yugoslavia), in a ruralUsing similar techniques to those described 0-8.7 and So42- concentrations of 1-48 site in Italy (Po Valley), and at a suburbanEnvironmental Health Perspectives--1----484A Al.- ~ 9 *Table 3. Summer (May-September) and winter (November-March) concentrations of aerosol sulfate (pg/in3) measured in Sokolov, Erfurt, and 23 communities inthe United States and Canada"Summer WinterSite N Mean SD Min Max Site N Mean SD Min MaxPenn Hills, PA 62.0 12.1 9.2 0.0 42.6 Erfurt 74.0 8.4 6.5 0.9 30.5Uniontown, PA 70.0 10.4 8.1 0.0 51.5 Sokolov 72.0 7.7 5.4 1.4 23.8Morehead, KY 72.0 10.1 5.4 1.7 27.4 Athens, OH 74.0 4.6 2.4 0.4 12.0Athens, OH 74.0 10.0 7.7 0.0 43.1 Uniontown, PA 71.0 4.4 2.2 1.2 11.9Zanesville, OH 60.0 9.9 7.7 0.0 37.5 Oak Ridge, TN 66.0 4.2 2.4 0.9 12.9Hendersonville, TN 69.0 9.6 5.1 2.4 22.5 Penn Hills, PA 63.0 4.1 2.1 0.0 10.7Blacksburg, VA 72.0 9.4 5.3 1.2 23.8 State College, PA 71.0 4.0 2.4 0.5 10.0Dunville, ON 59.0 9.1 7.9 0.0 30.6 Morehead, KY 69.0 3.8 2.2 1.1 9.7State College, PA 67.0 9.1 7.0 0.6 29.5 Zanesville, OH 70.0 3.8 2.2 0.7 11.3Parson, WV 71.0 8.6 7.7 0.0 33.8 Parson, WV 67.0 3.8 1.8 1.0 10.3Oak Ridge, TN 70.0 8.6 5.7 0.0 29.4 Blacksburg, VA 70.0 3.6 1.7 0.6 9.9Sokolov 67.0 8.6 5.0 1.4 21.2 Hendersonville, TN 73.0 3.5 2.4 0.0 13.2Charlottesville, VA 67.0 8.2 5.4 0.0 26.4 Charlottesville, VA 68.0 3.5 1.9 0.7 9.2Erfurt 69.0 8.0 4.7 1.5 21.5 Leamington, ON 73.0 3.4 1.9 0.0 8.7Newtown, CT 69.0 6.3 6.0 0.0 26.0 Newtown, CT 61.0 3.3 2.0 0.0 9.7Leamington, ON 74.0 6.3 5.9 0.0 33.1 Dunville, ON 53.0 3.3 1.7 0.0 8.2Springdale, AR 72.0 4.8 2.9 0.0 12.8 Egbert, ON 16.0 2.4 1.5 0.6 6.8Egbert, ON 48.0 4.7 7.2 0.0 30.7 Springdale, AR 66.0 2.4 1.6 0.0 8.2Pembroke, ON 67.0 4.4 5.6 0.0 27.8 Simi Valley, CA 70.0 2.2 3.3 0.0 14.8Simi Valley, CA 63.0 4.0 2.5 0.0 10.0 Pembroke, ON 41.0 2.2 1.3 0.0 6.1Aberdeen, SD 74.0 2.4 3.2 0.3 20.4 Aberdeen, SD 66.0 1.4 1.2 0.0 5.5Livermore, CA 73.0 1.6 1.1 0.0 5.7 Monterey, CA 71.0 1.1 0.9 0.0 5.3Monterey, CA 66.0 1.4 0.7 0.0 3.1 Livermore, CA 72.0 1.0 0.8 0.0 3.7Yorktown, SK 76.0 0.8 0.7 0.0 4.3 Yorktown, SK 30.0 0.8 0.8 0.0 3.5Penticton, BC 68.0 0.7 0.5 0.0 2.3 Penticton, BC 69.0 0.7 0.6 0.0 3.2aFor each season, the sampling sites are listed in order of highest mean concentration.site in Vienna. Concentrations of so42-and acid aerosols in Ljublijana were com-parable to those measured in this study,after accounting for the different samplingdurations. Due to the limited number ofEuropean measurements available, wechose to compare our measurements pri-marily to the more extensive NorthAmerican database, as well as other mea-surements collected in coal-burning areas(10,27,28) (Table 4).Erfurt and Sokolov report aerosol acid-ity concentrations that are at the low endof the observations in North America andmuch lower than those measured inLondon during the 1963-1972 period(Tables 2 and 4). Winter PMIO and SO2concentrations at both eastern Europeansites were also much lower than those mea-sured in London (28), but well above con-centrations observed in the NorthAmerican communities used for compari-son (Tables 1, 3, and 4).Mean concentrations of PMIO in Erfurtand Sokolov were significantly higher inthe winter than in summer (Table 1),which is consistent with the occurrence ofwinter inversions and increased coal burn-ing (particularly in Erfurt) for residentialheating. Although the record of S02 sam-pling was not complete, concentrationsalso appeared to be higher in winter thanin summer. During 1991, two consecutive12-hr samples were collected daily in bothErfurt and Sokolov with the HEADS sam-pler. In Erfurt during February-April, themean 24-hr SO2 concentration was 125Pg/m3 (SD = 122, range: 27-656, N= 35),while in May-September, the mean was 22fig/mi (SD = 21, range: 3-93, N= 55). InSokolov the February-April 24-hr meanSO2 concentration was 76 pg/mi (SD =45, range: below detection-205, N= 31),while in May-September, the mean was 31pg/m3 (SD = 22, range: 3-97, N = 46).Aerosol acidity was slightly higher in thesummer than in winter at both sites (Table2). This contrasts with observations fromNorth America in which summer aciditylevels are much greater than those mea-sured in the winter (3) (Table 2).Although acid aerosol levels were verylow, comparisons to the North Americandatabase of SO42 measurements (Table 2)indicates that the eastern European sitespresented somewhat higher SO4 concen-trations, particularly during the winterperiod. As SO42 concentrations can beviewed as "potential acidity," it is evidentthat little of the aerosol so42- was acidic,suggesting substantial neutralization.H+/SO4 2- ratios were below 0.4 for allsamples except for one 24-hr winter sam-ple collected in Erfurt (ratio = 1.25) andtwo winter samples collected in Sokolov(ratios = 0.60 and 0.65).As suggested by the observations of lowaerosol acidity and high so42- concentra-tions, levels of NH3 were elevated (Table4) in Sokolov and Erfurt. Ambient NH3measurements are indicative of the extentto which acid aerosols may be neutralizedinto nonacidic species, since NH3 neutral-izes acidic sulfate aerosols to produce neu-tral salt species. Although the record ofNH3 concentrations is less complete thanTable 4. Summary statistics of ambient concen-trations (pg/M3) measured in Sokolov and Erfurtand comparisons to measurements in Wuhan,China (27), Steubenville, Ohio (10) and historicalmeasurements in London (28)Site Mean SD PeakAerosol acidity (as H2SO4)Sokolov 0.5 0.6 7.6Erfurt 0.4 0.4 8.1Wuhan 0.7 NA 2.4Steubenville 1.2 NA NALondon 6.5 6.7 134so 204Sokolov 9.6 6.0 36.4Erfurt 11.0 9.0 74.1Wuhan 50.4 NA 94.1Steubenville 12.8 NA NANH3Sokolov 2.6 3.2 23.6Erfurt 1.7 1.1 13.9SO2Sokolov 52 63.7 592Erfurt 60 94.5 715Wuhan 42 NA 73Steubenville 63 NA NALondon 317 163 1298Pariculate matter <10 pm (PM10)Sokolov 59 35 171Erfurt 66 45 269Wuhan NA NA 350Steubenville 47 NA NALondona 92 71 709NA, data not available from references.aLondon PM10 measurements are estimated fromBritish smoke measurements where Britishsmoke is assumed to be equal to PM1O as a lowerbound (43). Mean measurements of acidity ands04 - from Erfurt and Sokolov are from Harvardimpactor (24-hr) measurements; peak measure-ments for all species except PM10 are fromHEADS (12-hr) measurements.Volume 103, Number 5, May 1995 485the aerosol acidity and sulfate measure-ments, mean concentrations during thesampling periods were consistently high(>1.4 pg/mi3) throughout the year. Annualaverages in North American communitiesare typically below 1 pg/mi3, with onlyrural sites reporting annual means above1.4 pg/m .The observation of higher sO42- levelsin Wuhan, China (27) than in Erfurt orSokolov is indicative of low conversion ofS52 to So42-, given the higher SO2 levelsmeasured in Erfurt and Sokolov (Table 4).SO2 levels in Erfurt and Sokolov were wellbelow those measured in London, but sig-nificantly higher than those measured inChina. In contrast, the Wuhan environ-ment may have presented more completeconversion, but acidity appeared to be con-trolled by neutralization. In both theWuhan study and this study, levels ofaerosol acidity were surprisingly low, giventhe high measured concentrations of SO2and PM10. PMIO concentrations in Erfurtand Sokolov were similar to concentrationsmeasured in Wuhan. Although these com-parisons are limited, they suggest that theconditions encountered in Erfurt andSokolov may be typical of regions in whichhigh-sulfur coal is burned during the win-ter. In such situations, although SO2 levelsmay be greater than concentrationsobserved in North America, aerosol aciditylevels are very low.Sampling and Analytical IssuesOne explanation for our inability toobserve aerosol acidity lies with the mea-surement itself. Were the measurementsused in this study unable to measure aciditythat was present in the atmosphere, or werethe studies in London in the 1950s andafterwards measuring acidity produced viaartifact reactions? Although few data arepresented, the analytical method used inLondon was apparently insensitive to arti-fact formation of acid from SO2, eventhough only a small amount of S02 wouldneed to react on the filter to produce a rela-tively large artifact of sulfate (29). At thelevels of S02 measured in London (Table4), this artifact could easily account for allof the measured aerosol acidity. In futurestudies in similar environments it would beadvisable to attempt to directly replicate themeasurement method ofCommins (29P).Although there was no measured acidi-ty, we examined the possibility that thehigh particle concentrations led to parti-cle-particle interactions on the filter whichresulted in an apparent loss of measurableacidity. For this analysis we used the data(approximately 230 samples) from themultistage filter pack of the HEADS(Table 5). The acid correction is minimal,although there is a tendency for a negativecorrection due to higher NH4+ on the back-up filter. These results are consistent withthose reported by Koutrakis et al., whofound little correction for samples collectedin six locations in North America (22).Although NH4+ concentrations were quitehigh, most of the NH4+ and N03- wasfound on the Teflon filter and not on thebackup, suggesting only minimal volatiliza-tion of NH4NO3. Ion balances ([H+] +[NH4]/2 ([SO42 ] + [NO3]) on the Teflonfilter were only slightly less than 1, sug-gesting that all anions associated withacidity were accounted for (Table 5).Alternatively, although the methodused in the measurements reported here issuitable for generated atmospheres ofacidic sulfate species (30) and for acidicaerosols produced during summer photo-chemical processes (18), it may not ade-quately measure aerosol acidity that is like-ly produced via heterogeneous mechanismsand associated with carbon particles. Thisquestion remains unanswered because allapplications of this method in winter pol-lution situations (7,27), including ourstudy, have measured little or no acidity,while the method has only been evaluatedfor aerosols likely to resemble those pro-duced in summer conditions.We also investigated the possibility thatin the humid environments with high con-centrations of particles characteristic ofwinter episodes, acidity was present in larg-er size fractions than collected by our sam-pler. Measurements of so42- in the PMfraction were made on a subset of the sam-ples collected in Erfurt (N = 35) andSokolov (N = 45). so42- in the PM1 and4 10~~~2PM2 5 fraction were highly correlated (r =0.94), and there was little indication ofadditional So42- in the PM fraction.This limited analysis suggests that no addi-tional aerosol acidity would be associatedwith particles of aerodynamic diameter>2.5 pm.Acid Production and NeutralizationAnother explanation for our observation oflow aerosol strong acidity is the effect oflow so42- production or neutralization ofacidic sulfate species by ambient NH3. Themeteorological conditions of local winterinversions suggests that SO2 and conse-quently s042- ("potential acidity") concen-trations and NH3 will peak at the sametimes, limiting the opportunity for acidicparticles to avoid neutralization. This con-trasts with North American summerepisodes, for which it is believed that con-vective mixing replaces stagnant surface-level air (high ammonia content) withacid-laden air that has been transportedabove inversion layers where it is protectedfrom neutralization (3,31). The situationin eastern Europe also differs in terms ofthe proximity of the sources, with localsources emitting SO2 below inversion layerheights and therefore in close proximity toNH3 sources, providing ample opportuni-ty for neutralization.Further, the SO2 conversion reactionsare expected to differ between the (easternEuropean) winter and the North Americansummer, where photochemical reactionspredominate. In North America, emissionsare typically above the height of inversionlayers under conditions of low particle con-centrations, facilitating transport ofgaseous species at heights where slow con-version may occur while the air mass isprotected from neutralization by surfacelevel sources of NH3. The predominantconversion mechanism in North Americais photochemical, based on the reaction ofhydroxyl radical with SO2 in the presenceof water (32). In eastern Europe, wherewinter inversions reduce the impact ofphotochemistry and where high particulateconcentrations provide sufficient surfacearea, heterogeneous reactions are expectedto predominate.Aqueous-phase oxidation mechanismsmay explain our observations of lower thanexpected sulfate levels at a given SO2 con-centration, as well as the high levels ofNH4' ion observed (mean concentrations>4 pg/m3). In the winter inversion setting,concentrations of oxidizing species may bequite low and conversion of SO2 limited.Homogeneous gas-phase conversions, asso-ciated with North American summertimeacidity, occur at rates of 0.3-2%/hr, whileaqueous phase (nonmetal catalyzed) oxida-tion is slower (0.2%/hr) (33).The extent of SO2 conversion may beestimated by the [SO42-/SO42- + SO2] ratio.Much like the North American situation,the ratios in Erfurt and Sokolov were lowerin the winter than in the summer. RatiosTable 5. Summary statistics for denuder/filter pack measurements of particulate speciesaH+ H+ H+ Ion so42- N03- NH4+ NO3 NH4+Site uncorrected correction total balance (teflon) (teflon) (teflon) (backup) (background)Sokolov 13.6 -8.4 15.9 0.95 99.3 51.9 225.0 8.1 14.6Erfurt 8.9 -19.3 12.9 0.89 109.7 48.8 245.6 14.6 37.8aAll concentrations in nmol/m3. All values are mean values for the (approximately) 230 denuder samplescollected (i.e., the H+ total is the mean of the 230 H+ total measurements, not the sum of the mean H+uncorrected + mean H+ correction). H+ correction refers to F2 N03- - F4 NH4+. H+ total = H+ uncorrected +H+ corrected.Environmental Health Perspectives486El, :M M AX i z i -iwere typically below 0.25 in the winter, andreached peaks of 0.6 or higher in the sum-mer. While these ratios suggest considerableconversion in the summer, SO2 concentra-tions were low during this period. In thewinter, when SO2 concentrations are elevat-ed, [SO42-/SO42- + SO2] ratios were belowmean ratios of 0.4-0.6 seen in summeracidic atmospheres in North America(21,31), suggesting the impact of slowerso42- production processes.ImplicationsAnalysis of aerosol acidity as a causal factordistinct from fine particulate matter is par-ticularly important for North Americabecause levels of fine particulates may beelevated throughout the year and inregions without high acid aerosol levels. Incontrast, aerosol acidity is elevated duringthe summer, and high concentrations areusually only found in the eastern portionof the continent (3). The comparisons pre-sented in this article suggest that whileaerosol acidity may be present in elevatedconcentrations during summertimeepisodes in eastern North America, thereare few other settings with similar levels ofaerosol acidity. In particular, areas wherehigh-sulfur coal was burned showed lowlevels of acid aerosols. Additionally, short-term acidity concentrations typically mea-sured in North America are well below lev-els shown to elicit effects in controlledchamber experiments (3). These findingswhen viewed along with the observationthat in summer episodes in North Americaacid particles are inherently correlated withfine particulate levels, makes it difficult todistinguish the acidic fraction as a causalagent. Therefore, analysis of the healthimpact of inhalable particulates in settingswith elevated particle concentrations(5-8,14,34,35) where acidity is low sug-gests that aerosol acidity may not be theprimary particulate parameter associatedwith increased morbidity and mortality.Further evidence for the absence ofaerosol acidity as a causal factor in air pol-lution health studies comes from its lowindoor:outdoor ratio (12,13). Althoughfine particles penetrate efficiently indoorsso that indoor:outdoor ratios are approxi-mately 0.8 (36,37), acid levels are quitelow indoors as a result of indoor ammonia,which neutralizes aerosol acidity.Indoor:outdoor ratios of sulfate are alsonear 0.8 (12,38). Accordingly, outdoorconcentrations of fine particles and sulfatesare likely to be better indicators of totalexposure than are acid aerosols becausetheir indoor:outdoor ratios are high andsince the majority of an individual's time isspent indoors.Much of the epidemiological evidencealso does not support aerosol acidity as theprimary causal factor in the health effectsof particulate air pollution. In addition tothe comparative analysis of St. Louis andKingston-Harriman Tennessee (9),Dockery and colleagues analyzed theHarvard Six-Cities Study and reported thatmortality was more strongly associatedwith levels of fine and inhalable particu-lates, as well as sulfate particles, than it waswith aerosol acidity (10). One of the citiesincluded in this analysis, Steubenville,Ohio, had air quality levels which werequite similar to those measured in thisstudy (Table 4). These data, along with theUtah Valley (5-8) and Seattle (35) studies,and results presented here indicate eitherstronger associations between health effectsand PMIO mass than aerosol acidity orrelationships between particle pollutionand health in areas where aerosol aciditylevels are low.In an investigation of hospital admis-sions in Toronto, Thurston and colleagues(11) found a stronger relationship withaerosol acidity than with either fine parti-cles or inhalable particles; however, thisresult is not in direct conflict with studiesthat show weaker relationships with aerosolacidity than with other particle metrics. AsThurston et al. have discussed (11), aerosolcomposition may differ dramatically evenin locales where significant associationswere observed between inhalable particu-lates and health effects. In the Torontoarea, during summer episodes the submi-crometer aerosol is dominated by acidicsulfate aerosols. It is plausible that in thissetting aerosol acidity merely acts as a sur-rogate for the submicrometer aerosolwhich most fully penetrates into indoorenvironments. In regions such as Erfurtand Sokolov where submicrometer aerosolsare not acidic, other particle metrics maybe associated with health effects. Futureepidemiological studies should collectmore detailed information on size-fraction-ated particle composition, with specialemphasis placed on the PM2 5 fractionwhich penetrates indoors.As Dockery and Pope have suggested(39), the available epidemiological dataindicate that the associations observedbetween particulate air pollution and healtheffects are due to the mass concentration ofthe particle mix common to urban areasrather than to specific chemical specieswithin the mix. Even in locales where parti-cle composition, as it is traditionally mea-sured, is quite different, and where majorparticle sources are different (auto exhaust,woodsmoke, steel mill emissions, transport-ed power plant emissions), relationshipsbetween particle concentrations and mea-sured health outcomes appear to be remark-ably consistent. One common feature ofthe particulates in these studies is that theyare produced in combustion processes.Studies of naturally produced particlesshow a much smaller impact on health out-comes for a given particle concentration(40). These data support the hypothesisthat any particulate air pollution producedby combustion will be associated withadverse health outcomes. The implicationof this hypothesis is that particulates areassociated with adverse health effects in allsettings with combustion air pollution, oressentially all urban areas.Although the identification of specificinhalable particle components associatedwith adverse health outcomes is importantfor understanding air pollution epidemiol-ogy and for implementing control strate-gies, perhaps the most compelling reasonto investigate the relationship between par-ticle composition and health outcomes isto understand the biological mechanism bywhich airborne particulates may causeeffects. The epidemiological evidencewhich suggests that aerosol acidity is notthe primary particle parameter associatedwith health effects implies that the biologi-cal mechanism associated with particulateair pollution may be different from thatexperienced in animal and controlledchamber studies with sulfuric acid aerosolexposures. That adverse health effects maybe found in settings where aerosol acidityis not observed indicates that other particleparameters in addition to aerosol acidityshould be investigated in both epidemio-logical and mechanistic studies. For exam-ple, recent evidence from in vitro studiessuggests that iron present on the surface ofparticles may promote lung injury (41,42).For epidemiologists it is important to iden-tify settings with different particle compo-sitions and to investigate whether thehealth effects are still observed. In particu-lar, thorough analysis of particle composi-tion for PMIO samples collected duringroutine monitoring is recommended, espe-cially for locations where partide-associatedhealth effects have already been observed.ConclusionsA large number of studies have indicatedassociations between particulate air pollu-tion and adverse health outcomes.Wintertime air pollution in particular hasbeen associated with increased mortality.Identification of causal constituents ofinhalable particulate matter has been elu-sive, although one candidate has been theacidity of the aerosol. Here we report onlow levels of aerosol acidity in relativelypolluted environments which were directlyimpacted by the burning of high-sulfurcoal. These measurements, along withreported associations between fine particu-late air pollution and health outcomes inother regions where little aerosol acidityVolume 103, Number 5, May 1995 487_1 ehas been measured, suggest that particulateacidity alone is not the primary componentdefining the toxicity of fine particulate airpollution.REFERENCES1. Lippmann M. Background on health effects ofacid aerosols. Environ Health Perspect 79:3-6(1989).2. Ito K, Thurston GD, Hayes C, Lippmann, M.Associations of London, England, daily mortal-ity with particulate matter sulfur dioxide andacidic aerosol pollution. Arch Environ Health48:213-220 (1993).3. Spengler JD, Brauer M, Koutrakis P. Acid Airand Health. Environ Sci Technol 24:946-955(1990).4. U.S. EPA. An acid aerosols issue paper: aero-metrics and health effects. EPA/600/8-88/005F. Washington, DC:Office of Healthand Environmental Assessment, EnvironmentalProtection Agency, 1989.5. Pope CA III. Respiratory hospital admissionsassociated with PM-10 pollution in Utah, SaltLake and Cache Valleys. Arch Environ Health46:90-97 (1991).6. Pope CA III, Schwartz J, Ransom MR. Dailymortality and PM-10 pollution in Utah Valley.Arch Environ Health 47:211-217 (1992).7. Pope CA. III, Dockery DW, Spengler JD,Raizenne ME. Respiratory health and PM-10pollution: a daily time series analysis. Am RevRespir Dis 144:668-674 (1991).8. Ranson MR, Pope CA III. Elementary schoolabsences and PM-10 pollution in Utah Valley.Environ Res 58:204-219 (1992).9. Dockery DW, Schwartz J, Spengler JD. Airpollution and daily mortality: Associationswith particulates and acid aerosols. EnvironRes 59:362-373 (1992).10. Dockery DW, Pope CA III, Xu X, SpenglerJD, Ware JH, Fay ME, Ferris BG, Speizer FE.An association between air pollution and mor-tality in six U.S. cities. N Engl J Med329:1753-1759 (1993).11. Thurston GD, Ito K, Hayes CG, Bates DV,Lippmann M. Respiratory hospital admissionsand summertime haze air pollution inToronto, Ontario: consideration of the role ofacid aerosols. Environ Res 65:271-290 (1994).12. Brauer M, Koutrakis P, Keeler GJ, SpenglerJD. Indoor and outdoor concentrations ofinorganic acidic aerosols and gases. J Air WasteManage Assoc 41:171-181 (1991).13. Suh HH, Spengler JD, Koutrakis P. Personalexposures to acid aerosols and ammonia.Environ Sci Technol 26:2507-2517 (1992).14. Spix C, Heinrich J, Dockery D, Schwartz J,Volksch G, Schwinkowski K, Collen C,Wichmann HE. Air pollution and daily mor-tality in Erfurt, East Germany, 1980-1989.Environ Health Perspect 101:518-526 (1993).15. Heinrich J, Spix C, Franke K, Wolke G,Luttman H, Gutschmidt K, Spengler JD,Volksch G., Vyhlidal F, Wichmann HE.Epidemiologic studies on respiratory effects ofacid particles in central and eastern Europe. In:Proceedings of the first international sympo-sium on comparative risk analysis and prioritysetting pollution issues. Keystone, Colorado.7-11 June 1993. Pittsburgh, PA:Air and WasteManagement Association, in press.16. Bobak M, Leon DA. Air pollution and infantmortality in the Czech Republic, 1986-1988.Lancet 340:1010-1014 (1992).17. Horstman D, Kotesovec F, Vitnerova N.Respiratory health status of elementary schoolchildren residing in Teplice Czech Republic.Am J Resp Crit Care Med 149:A663 (1994).18. Koutrakis P, Wolfson JM, Spengler JD. Animproved method for measuring aerosol strongacidity: results from a nine-month study in St.Louis, Missouri and Kingston, Tennessee.Atmos Environ 22:157-162 (1988).19. Marple V, Rubow KL, Turner W, SpenglerJD. Low flow rate sharp cut impactors forindoor air sampling: design and calibration. JAir Pollut Control Assoc 37:1303-1307(1987).20. Koutrakis P, Wolfson JM, Slater JL, Brauer M,Spengler JD, Stevens RK, Stone CL.Evaluation of an annular denuder/filter packsystem to collect acidic aerosols and gases.Environ Sci Technol 22:1463-1468 (1988).21. Keeler GJ, Spengler JD, Castillo RA. Acidaerosol measurements at a suburban Connecticutsite. Atmos Environ 25A.681-690 (1991).22. Koutrakis P, Thomson KM, Wolfson JM,Spengler JD, Keeler GJ, Slater JL.Determination of aerosol strong acidity lossesdue to interactions of collected particles: resultsfrom laboratory and field studies. AtmosEnviron 26A(6):987-995 (1992).23. Speizer FE. Studies of acid aerosols in six citiesand in a new multi-city investigation: designissues. Environ Health Perspect 79:61-67(1989).24. Hoek G. Acute effects of ambient air pollutionepisodes on respiratory health of children (PhDthesis). Wageningen, The Netherlands:Wageningen Agricultural University, 1992.25. Kitto A-MN, Harrison RM. Processes affectingconcentrations of aerosol strong acidity at sitesin eastern England. Atmos Environ 26A:2389-2399 (1992).26. Puxbaum H, Weber M, Pech G. Occurrence ofinorganic and organic acids components atfour source-dominated sites in Europe (Vienna,Linz, Ljublijana, Bologna) (extended abstract).In: Proceedings of the symposium on heteroge-neous processes in source-dominated atmos-pheres, New York, October 1985.27. Waldman JM, Lioy PJ, Zelenka M, Jing L, LinYN, He QC, Qian ZM, Chapman R, WilsonWE. Wintertime measurements of aerosolacidity and trace elements in Wuhan, acidity incentral China. Atmos Environ 25B:1 13-120(1991).28. Ito K, Thurston GD. Characterization andreconstruction of historical London, Englandacidic aerosol concentrations. Environ HealthPerspect 79:35-42 (1989).29. Commins BT. Determination of particulateacid in town air. Analyst 88:364-367 (1963).30. Purdue LJ, Pahl DA, Wilson WE. Overview ofthe AREAL acid aerosol research program. In:Proceedings of the 1992 U.S. EPA/AWMAinternational symposium on the measurementof toxic and related air pollutants. Pittsburgh,PA:Air and Waste Management Association,1992;259-263.31. Keeler GJ, Spengler JD, Koutrakis P, AllenGA, Raizenne M, Stern B. Transported acidaerosols measured in southern Ontario. AtmosEnviron 24A:2935-2950 (1990).32. Koutrakis P, Mueller PK. Atmospheric acidity:chemical and physical factors paper 89-71.4.In: Proceedings of the 82nd annual meeting ofthe Air and Waste Management Association,Anaheim, California, 25-30 June, 1989.Pittsburgh, PA:Air and Waste ManagementAssociation, 1989.33. Lioy PJ, Waldman JM. Acidic sulfate aerosols:Characterization and exposure. Environ HealthPerspect 79:15-34 (1989).34. He QC, Lioy PJ, Wilson WE, Chapman RS.Effects of air pollution on children's pul-monary function in urban and suburban areasof Wuhan, People's Republic of China. ArchEnviron Health 48:382-391 (1993).35. Schwartz J, Slater D, Larson TV, Pierson WE,Koenig JQ. Particulate air pollution and hospi-tal emergency room visits for asthma in Seattle.Am Rev Respir Dis 147:826-8831 (1993).36. Colome SD, Kado NY, Jaques P, Kleinman M.Indoor-outdoor air pollution relations: particu-late matter less than 10 pm in aerodynamicdiameter (PM10) in homes of asthmatics.Atmos Environ 26A:2173-2178 (1992).37. Wallace LW, Pellizari E, Sheldon L. TheTEAM study of inhalable particles (PM-10):study design, sampler performance and prelimi-nary results. Paper 91-171.3. In: Proceedings ofthe 84th annual meeting of the air and WasteManagement Association, Vancouver, BritishColumbia, 16-21 June, 1991. Pittsburgh,PA:Air and Waste Management, 1991.38. Dockery DW, Spengler JD. Indoor-outdoorrelationships of respirable sulfates and particles.Atmos Environ 15:335-344 (1981).39. Dockery DW, Pope CA III. Acute respiratoryeffects of particulate air pollution. Annu RevPublic Health 15:107-132 (1994).40. Hefflin BJ, Jalaludin B, McClure E, Cobb N,Johnson CA, Jecha L, Etzel RA. Surveillancefor dust storms and respiratory diseases inWashington State, 1991. Arch Environ Health49:170-174 (1994).41. Pritchard RJ, Ghio AJ. Humic acid-like sub-stances are present in air pollution particles.Am J Resp Crit Care Med 149:A840 (1994).42. Tepper JS, Lehmann JR, Winsett DW, CostaDL, Ghio AJ. The role of surface-complexediron in the development of acute lung inflam-mation and airway hyperresponsiveness. Am JResp Crit Care Med 149:A839 (1994).43. U.S. EPA. Review of the national ambient airquality standards for particulate matter: assess-ment of scientific and technical information.EPA-450/5-82-001. Washington, DC:Officeof Air Quality Planning and Standards,Environmental Protection Agency, 1982.488 Environmental Health Perspectives

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.52383.1-0074695/manifest

Comment

Related Items