REVIEW

Health effects of air in : Expert panel findings for The Canadian Advisory Program

DAVID M STIEB*t MD MSc CCFP FRCPC, L DAVID PENGELLYt+ PhD, N INA ARRON* BScPHN MHA, S MARTIN T AYLORt§ PhD, MARK E RAIZENNE* BSc *A ir Quality Health Effects Research Section, Health Canada, Ottawa, tJnstitute of Environment and Health. McMaster University and University of Toronto, +Departments of Medicine and Engineering Physics, McMaster University, Hamilton, §Department of Geography, McMaster University, Hamilton.

OM STIEU, LO PE GE LLY, N ARRON , SM TAYLOR, ME its among indi viduals with heart or lung disease. rcducL'ci R AIZF.N E. Health effects of in Canada: exercise capaL·ity, increased hospital admissions and possi­ Expert panel findings for The Canadian Smog Advisory ble increased mortality. Similar effects were felt to occur in Program. Can Respir J 1995;2(3): 155-1 60. association with airborne particlL·s. with the l'xccption of inflammatory changes, and with the addition or increaseJ O n.J ECTIVE: To revit:w the evidrnce on health effects of air school absenteeism. Poor data 011 individual exposure were pollution for the Canadian Smog Advisory Program. identified as a limitation of studi..:s on hospital admi.,.,ions METHODS : Evide nce w;1s reviewed by two expert pane ls. and mortality. who were asked to define the health effects expected at RECOMMENDATIONS: The panels identified the need to levels o f exposure given by the National Ambient Air Qual­ reflect the evidence accurately without unduly r;1i .,i11g pub­ ity Objectives. to examine a variety or issue., re lated to lic concern and r..:commended that advisory health mes­ communicating with the public about environmental health sages identify expected health elkcts. while health care risks. and to draft health messages for the advisory program. providers could more appropriately recommend protective R ESU LTS : The panels concluded that health effects or actions to individuals. Supple mentary educational strat..:­ ground-level 01011..: at k'vcls that occur in Canada include gies and evaluation of the advi.,ory program were also pulmonary inflammation. pu lmon;iry fu11c1 ion decrements. recommended. (Po11r I<' rc;_1-u,11 c. rnir 11ag<' [56) airway hypcrreactivity. rc.,piratory .,y mptoms, pos.,iblc in­ neas..:d medication u.,c and physician/cmngency room vi.,- Key Words: i\cfrisorics. ;\ir 1>01!111io11. ( !:one. S111og

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Can Resp1r J Vol 2 No 3 Fall 1995 155 STIEB ET AL

Effets sur la sante de la pollution atmospheri­ de !'utilisati on des medic ament s ct des consultations ti l'urgence nu chcz le medecin parmi !cs individus soufl'rant d'une affection que au Canada : Resultats rapportes par un pulmonairc ou cardiaquc. unc tolerance rcduitc a r·cxcrcicc. unc groupe d'experts pour le Programme ca­ augrnenlation des hospitalisations ct augmentation possible de la mortalitc. On pense quc des clTcts sirn ilaircs sc produisent en nadien d'avertissement de smog association avec !cs particulcs aerogcncs. f1 l'exl'cption des changemcnts inllammatoircs, ct en y ajoutanl une augmcntation de 0BJECTIF : Passer en revue !es prcu ves des eflets sur la sante de l'abscnrcismc scolaire. Des donnccs in suflisantcs sur !'exposition la pollution atmospheriqm· puur le Programme canadien d\1verti,;­ individue ll e ant etc iclcnti fiecs comme unc limita tion des etudcs sement de smog. sur lcs hospitalisations et la mortalitc. METHODES : Les preuvcs ont etc examinees par dcux groupcs RF.COMMANOATIONS : Les experts ont idcntilil' le bcsoin de d'experts a qui !'on a demandc de dctennincr Ies cffcts attendus rclleter correctcmcnt lcs preuvcs sans trop sou lever d'inquietudes sur la santc [1 des nive;iux d'exposition fournis par !es objectifs dans la population et ont recommandc quc !cs mcssagcs-sante nationaux afferents f1 la qualite de ['air ambianr, d'cxamincr unc icl entifient lcs e !Tcts attcndus sur la santc. pendant quc !cs varietc de questions ayant trait al 'ini"ormation de la population sur pourvoycurs des soins de santc pourraicnt plus adcqualcmcnt !cs risques environncmentaux pour la sante, et d'cbaucher des recommancler des comportemcnts protcctcurs aux indiviclus. messages sanitai res pour le Programme cl 'averti ssement. Des strategies cducatives supplcmcntaircs ct unc evaluation du RESULTATS : Les groupes d 'experts ant conclu que lcs effets Programme d'avcrtisscmcnt ont aussi cte rccommandccs. sur la sante de !' au ras du sol 11 des niveaux detcctes au Canada comprennent notammcnt l'int1ammation pulmonaire, la deterioration de la fonction pulmonairc, l'hyperreactivite bron­ Po11r nhtcnir la rcr.1·ion.fi·an(·aise i1111igra!e cl<' <"<'I article. nm111111- chiqlll·. de,, .,yrnptflmes respiratoircs. une augmentation possible 11i<111 ec m •ec f" all/Cur {/ f" adreSSC i11tfi

HE TERM "SMOG" IIAS BEEN US ED IN NORT H AMERICA served ground-level ozone concentrations in a number or T to describe a characteris tic form or air pollution that regions, its impacr is particularly apparent in Atlantic Can­ generally occurs from late spring to early fall. Smog was ada. where peak concentrations may occur at night. In most recogni zed as a Canadian pollution issue in the federal other areas, peaks occur during the late afternoon and early 'Green Plan' in 1990, and in 1993 Environment Canada evening in the summer months. In Canada, the current Na­ introduced the Canadian Smog Advisory Program. This re­ tional Ambient Air Quality Objective for ground-level ozone port presents background infonnation on air pollution in (I h maximum of 82 parts per bil lion ippbl - maximum Canada and summarizes the findings of an expert panel acceptable concentration) is exceeded most often in southern process undertaken in support of the Canadian Smog Advi­ Ontario. southern Quebec, Vancouver and southern New sory Program. It is a condensed and modified version of the Brunswick (5) (Figure I). original report on the panel process (I). Its purpose is to Airborne particles are very smal l pieces of solid or liquid provide clinicians and public health workers with the infor­ matter, which vary in si ze, chemical composition and sou1n·. mation needed to respond appropriately to questions or con­ Smaller particles. which have the greatest health signifi­ cerns of patients and members of the public that may he cance, tend to arise from man-made sources, particularly fuel triggered by snro.!! advisories. combustion, and include acid aerosols such as sulphates and nitrates, as well as metal oxides (6). Larger particles consist BACKGROUND mainly of naturally occurri ng substances. particularly soil Although air 4uality in Canada has generally improved (6). Particles less than IO ~1111 in diameter (PM 10) are consid­ over the past 15 years, smog episodes still Ol'cur. These ered 'inhalable' (7). The current National Ambient Air Qual­ episodes. which are primarily a summer phenomenon. con­ ity Objective for total suspended particles (TSP - airborne sist principally of elevated concentrations of ground-level particles of all sizes) is 120 µg/111 3 for 24 h concentration. ozone. although al'icl aerosols (a type of airborne particle) which is still exceeded at least I 0% of the time in some cities may also be present (2). A different form or smog, 'winter across Canada (5). The current US standard fo r PM 10 is 150 smog ' , may also lll'l'ur, whose principal constituents are µg/rn 3 for 24 h concentration. Recent data reveal 24 h con­ sulphur dioxide and airborne particles (inl'luding acid aero­ centrations that exceed I 00 µg/m3 in a number of Canadian sols) (2). G round-lewl owne and airbornL· particles were the cities (8). Health Canada is currently developing a Canadian focus of the panel process. PM 10 objective. Ground-lcwl ('tropospheric') ozone. which should be dis­ The Smog Advisory Program was introduced in the sum­ tinguished from stratosphcriL· o;:one ('the ozone layer'). is a mer of l 993 under Canada's Green Plan as a means of gas that is formed when its precursors, oxides of nitrogen and info1ming the public about both environmental and health hydrocarbons. interact in the aunosphere in the presence of aspects of smog episodes. The program was fi rst imple­ high temperatures and sunlight (3 ). Smog and its precursors mented in Saint John, New Brunswick, in southern Ontario may be transported long distances through the atmosphere and in the Greater Vancouver Regional District, and began in (3) with the result that high concentrations of ground-level Montreal in 1994. As described earlier, these areas are situ­ owne may be found in both rural and urban areas (4). Al­ ated in the geographic regions in which the hi ghest ground­ though long range transport contributes significantly to ob- level ozone concentrations have been observed. Under the

156 Can Respir J Vol 2 No 3 Fall 1995 Health effects of air pollution in Canada

DAYS

30

25

20 15

I o EDMONTON I I o CALGARY 2.3

WINDSOR 30.0 \J

Figure I) Numhcr of days per year H'ith o:011e /cre/.1 in excess of the f hair quality ohicctirc of 82 pun.1 f>N /Jil/i,m. ,11 ·cmgc of 1/1/"l'c /1ig/ws1 rears !':)83- / 990 (Source: Cm'iro 11111 e11t Canada. 1994) program, ground-level ozone forecasts arc produced coop­ measurement, and health care delivery. The chair and several erativ ely by Environment Canada, the provincial ministries panel members had independently conducted literature re­ of environment and municipal air quality offices. based on views before their participation in the panels and key refer­ meteorological and air monitoring data. Advisories are issued ences were provided to panel members in preparation for when l h maximum levels are forecastcd to exceed a speci­ one-clay meetings of each group. Each panel was asked to fie d level, depending on the jurisdiction, but generally define the health effects expected at levels of exposure given 82 ppb. They consist of an environmental message that de­ hy the National Ambient Air Quality Objectives; to examine scribes the pollution sources that contribute to smog (chiefly a variety of issues related to communicating with the puhlic automobile transport) and the need for the public to reduce its about environmental healt h ri sks: and to draft health me:s ­ dependency on cars, as well as a health message that advises sages for the advisory program. Although un der the Smog the public of possible health risks associated with smog Advisory Program. advisories are issued only for ground­ exposure. The exact content of the messages is determined by level ozone, effects of airborne particles were also L'Onsidered provincial environmental and health authorities. ln I 993. the by the panels. While the same indiv idual chaircd bnth panels. tirst summer of the program's existence, four advisories were great care was taken to allmv each group scope to produce issued - two in Saint John and one each in southern Ontario differing conclusions and recommendations. Nonetheless. a and the Greater Vancouver Regional Di strict. A si milar num­ strong concurrence was noted between the findi ngs of the two be r of adv isories was issued in 1994. As seen in Figure I. a panels . Once the panels were completed, mi nutes of each signifi cantly greater number of episodes of elevated ground­ panel as well as a synthesis were circulated to the panel level ozone concentrations has occurred in these areas in members for comment and revision. previous years. PANEL FINDINGS METHODS The panels considered a variety of evidence on the rela­ Health aspects of the advisory program were addressed for ti onship between air pollution and health. This included laho­ Health Canada and Environment Canada hy two expert pan­ ratory studies, which have examined the pathophysiologic:al els convened by the Institute of Environment and Health of mechanisms through which pollutants exert their effects: McMaster University and the University of Toronto. The chamber stud ies. which have been used to measure various panels comprised individuals with experience in air pollution human health effects at contro lled exposure· levels: panel health research. public hcalth, air pollution meteorology and studies, in which (for example) children attending summer

Can Respir J Vol 2 No 3 Fall 1995 157 STIEB ET AL

the effects or individual pollutants. particularly ground-kvel '\ o;onc and acid aerosols. The panels conceptualized the potential health effects or air pollution as occurring in a logical \:ascade' or ·pyramid'. ranging from severe. uncommon events (cg. death) to mild. Mortality common effects (eg. eye. nose and throat irritation) and Hospital asymrtomatic changes of unclear clinical significance (cg. admissions

\ small pulmonary function decrements and pulmonary in­ Emergency room visits \ 6 sc,e,;i, flammation) (9.10). Thus. while according lo this 11H1dcl Physician off ice visits ~ of effect SL:vcre health events prec ipitated by air pollution would Ill' Reduced physical performance rare. there is a potentially large overall impact on he,lllh and well-being (Figure 2). Medication use With respect lo ground-level 01,one. the panels kit that Symptoms current palhophysiological evidence suggested that ozone is Impaired pulmonary function associated with an inflammatory response manifested by increased airway membrane permeability and bronchial Subclinical ettects I hype1Teactivity ( 11.12). Some or the nxenl epidemiulogic:11 I Iilerature reviewed by the panels indicated that pulmonary runction measures in children attend ing summer camp in southern Ontario were reduced on average by 3.5 to 7<1< wlll'Il

Proportion of population affected I h av erage coneentrations of ground-level 01011L'. reached 140 ppb ( 13) . that approximately 5% of Ontario hospital Figure 2) Schrnulfic rc11J'('sc111a1io11 o{//1e /)/}f<'nlial heal!!, cffcc/s of admissions ror respiratory disease may be attributable lo air pol/11 1in11. 1\da1>tccl ll'ith 1>cm,issio11Ji·n1111!1c 1\111crica11 Thoracic elevated conccnlralion.s of ground-level O/\lllC (4.14) (up to S11cic1r (()J \ 5';{ in those umicr two years of age I in combination with sulphate particles 1141). and that in Los Angeles the combina­ tion of ground-level ozone. nitrogen dioxide and lemperalltre camp have been followed with respect lo pulmonary function accounted for 4% of the day lo day variability in mortality and ymptoms in relation to ambient pollutant levels: and (excluding accidents and suicides) ( 15). Whether the effects studies based on administrative data on emergency room observed in epidemiological studies can be directly allributccl visits. hospital admissions and mortality and their relation­ to inflammatory responses seen in laboratory studies is un­ ship to changing pollutant level s. ll was noted that the latter clear. The evidence for chronic effects is also unclear. The ·ecologic' studies haw been criticized because they lack panels concluded that there was some evidence that certain important data on individual exposure. and that in studies or groups arc more susceptible 10 the acute clTccts or ground­ exposure lo ambient pollution. il has been di ffic ult to sep:iratL' level ornne. either on the basis of increased sensitivity (lhe

TABLE 1 Expert panel summary of health effects of ground-level ozone Ground-level ozone concentration (parts per billion - 1 h maximum)* 50-80 80-1 50 >1 50 Air quality descriptor Population Good Fair Poor Ve po_o_r __ General population No known Resp iratory symptoms with Inflammation of respiratory tract Higher probability of (adults and children) harmful effects heavy outdoor exercise in Decrements in pulmonary function effects described in sensitive people Airway hyperreactivity 'poor' category Larger proportion of population Respiratory illness in experiences symptoms with heavy children with less outdoor exercise intense exercise Reduced capacity for exercise/physical work Probability and severity of expected health effects increases with increasing exposure (time and level) Individuals with No known Above plus possible Above plus higher probability of Higher probability of heart harmful effects increased: medication use; effects described in 'fair' category effects described in or lung disease physician/e mergency room Possible mortality ·poor' category (including ) visits; and hospital admissions

"50 ppb = Maximum desirable concentration: 80 (82) ppb = Maximum acceptable concentration: 150 ppb = Maximum tolerable concentration. Source reference 1

158 Can Respir J Vol 2 No 3 Fall 1995 Health effects of air pollution in Canada

very young, the elderly. those with chronic cardiac or respi­ ratory di sease) or increased exposure during outdoor activity "Ground-level ozone, the major component of smog. is of (school children. joggers, cyclists and other athle tes, and out­ primary co ncern because it is a powerful irritant and can door workers such as fann and construction workers). How­ have potentially harmful effects on the respiratory system. Symptoms are most li kely to occur in individuals who are ever. this was recogni zed as a controversial area. The panels physically active outdoors. People with heart or lung differed in their interpretation of the evidence on the occur­ disease. especially asthma, may experience a worsening rence of hannful effects in th e general population at levels of their condition ." below 80 ppb. /\ synthesis of the effects identified by the panels at con­ ·· commonly reported symptoms include irritation of the nose centrations given by th e Nat ional Ambient Air Quality Ob­ and throat, cough , and chest tightness. Minimize your exposure by avoiding outdoor exercise particularly in the jectives is presented in Table I. This table summarizes the afternoon and early evening when ground-level ozone current scientific ev idence. weighing what the panels saw as concentrations tend to be at their highest." the relative strength of the evidence for various effects al various levels. The contents of the table do not translate the "Children tend to be more sensitive tt1 an adults because evidence into appropriate messages fo r communicating with they breathe faster and in the summer spend more time the general public. outdoors being physically active. Reduce your child's exposure by encouraging outdoor activities early in the day Although the panels were not specifically asked to address when pollutant levels are lower." the issue or whether there was a threshold concentration for ground-level ozone below which effects wo ul d not be ex­ pected, they were required to frame their findi ngs according Figure 3) Sa111r1le of public infomwri,111 111 essagcs //la de arnilahlc to the National Ambient Air Quality Objectives. which inevi­ hy Health Cllnlldu to s11p1,le111 e111 Slllog i\drisory Prograill /1/Cs­ tably rai sed the threshold issue. There was little support sllgcs. S011ffc refere11cc 22 among panel members for the concept of a threshold concen­ tration fo r effects of ground-level ozone, which is re fl ected by their conclusion that the probability and severity of ex­ PANEL RECOMMENDATIONS pected health effects increases with increasing exposure (Ta­ While the panels made a number of wide-ranging recom­ ble I). However. it was recognized that this was a separate mendations, only those relating to the content of health mes­ issue from choosing an admin istrative threshold concentra­ sages and their implementation are summarized here. tion ( 16) for the purposes of issuing adv isori es. The latter W ith respect to the content of health messages, pa,1icular issue was fe lt to be more appropriately addressed by authori­ issues identified by the panels included the followi ng: appro ­ ti es in the individual regions where advisories are issued (as priate emphasis fo r ' diagnostic' versus ' prescriptive' mes­ described earlier). sages (those that ident ify expected health effects versus those With respect to airborne particles. the panels felt that the that recommend protective actions): identification of target pat hophysiological mechanism through which they exert groups: ensuring that messages accurately reflect the scien­ their effects on respiratory health was not well understood. ti fi c evidence and do not unduly raise public concern: and Some of the recent epidemiological li terature reviewed by the selection of an appropriate threshold for the ground-level panels (much of which ori gi nates in the United States) indi­ ozone advisory. In consultation with provincial public health cated that elevations of PM to concentrations of approxi­ authorities. it was strongly recommended that the health mately I 00 to 150 ~tg/mJ are associated with reductions in messages be diagnostic only, wi th the recommendation that peak expiratory !low of up to 6% ( 17.18). approximately more specific prescriptiw advice be obtai ned from local si xfold increases in medication use :nnong asthmatics ( 18 ). public health authorities and/or personal health care provid­ 1. 5- to twofold increases in respiratory symptom reporting ers fam iliar with the individual's clinical history. ( 17.18), 40% increa ·es in school absenteeism (19). statisti­ W ith respect to implen11:·ntation aspects of the advisory cally significant increases in respiratory hospital admissions program. the panels recommended supplementary education (20) and up to 16% increases in mortality (excluding acci­ strategies di rected towards individuals at risk as well as dents and suicide) (21 ). The panels concluded that groups parents , teachers. athletes, coaches, health professionals and with greatest susceptibility appear to be those with chronic public health officials, and identified the need for evaluation cardiac and respiratory disease, although this was recognized of the impact of the advisory program. as a controversial area. As was the case for ground-level In response to these recommendations Health Canada has ozone, although the panels were not specificall y asked to developed a series of supplementary public informat ion mes­ address the 4uestion of the e xi stence or level of a threshold sages, which have been made available to the public in both concentration fo r the effects of airborne p;.irtic les. the ques­ official languages through the media. physicians' offices, ti on again arose because the panel was re4uired to fra me its hospitals and parenting magazines (sec Figure 3 for sample fin dings according to various levels of exposure as was done messages). In addition, Health Canada is collaborating with for ground-level ozone. There was little support among panel Environment Canada in conducting public surveys to evalu­ members for the concept of a threshold for the effects or ate variou · aspects of the advisory program. including aware­ airborne particle~ . ness of advisories and advisory-related changes in behaviour.

Can Respir J Vol 2 No 3 Fall 1995 159 STIEB ET AL

CONCLUSIONS '>. Ameri can Thoracic Society. G uidel ines as to what constitull's The expert panel process se rved as a rapid means of an adverse respi ra tory health cflecl. with special re ference to epidemiologic stud ies o r air pollution. Am Rev Rcspir Di s identi fying and interpreting the e vidence on health effects or 1985: 13 1:66 6-8. ground-le ve l ozone and airborne partic les. Mounting evi­ I 0. Bates DY. Health indices o f the adverse e ffects or air pollution. dence was identified linking e le vated concentrat ions of these The question or coherence. Environ Res 1992:59:336-49. pollutants with a spectrum of harmful effects on health, and I I. C rapo J. Miller FJ. Mossman B, Prior WA, Kiley JP. recomme ndations were made regarding e ffective communi­ Relationship between acute inllammatory responses to air pollu1a11t s and chronic lung disease. Am Rev Rcspi1· Dis cation with the public about these risks. 1992; 145: 1506- 12. Note: The original report of the panels (refe rence I). includ­ 12. Devlin RB . McDonnell W F. Mann R. ct al. F. xposurc or ing a detailed reference list, as we ll as public information humans to ambient levels o f 01,o nc for 6.6 hours causes ce llula1 materia ls on various air pollutants, arc available t'rom the and biochem ical changes in the lung. Am J Rc·spir Cell Mo! correspond ing author. Biol 199 1:4 : 72-8 1. IJ. Rai 1,e nnc M E. Burnett RT, Stern B. Franklin CA, Speng ler JD. Acute lung fun cti on response:; to ambient acid aeroso l REFERENCES exposures in childn:n. Env iron H(·alth Perspect I. Pengelly LO, Taylor SM. Stieb D. CanaJian Smog Advisory 1989;79: 179-85. Health Matrices for Ozone and Suspended Particles, Final I+. Ball's DY. S izto R. Air pollution and hospital admissions in Report . I lamilton anJ Toronto: Institute of Environment and Southern O ntario: the ac id summer haze c!Tecl. Environ Res Health. prepared for Hc:dth and Welfare Canada I 987:43 :3 17-3 1. Environmental Health Directorate, 1993. 15. Kinney PL. 0 1,kaynak H. Associati ons o f daily mortality and 1 Wor!J Health Organization, Reg ional Office for Europe : acute· air poll ution in Los Angele:; ounty. Environ Res effects on health of smog episodes. Report on a W HO meeting: 199 1; 54:99- 120. I 990 Oct JO-Nov 2, 's Hertogenbosch, Neth c rla11 ds. I (1. Pengelly LD. Silverman FS. Taylor S M. A Hierarc hy o r Copenhagen: WHO Regional Publicati ons. European Seri es. Potential Health Effec ts From Air Pollution Exposure. Final No 43. 1992. Report. Hamilton and Trnonto: Institute of Environment and .l. Li ppman M. Health e ffects or 01one - a critical rev iew. J Air Health. 1994 . Poll Control Assoc 1989:19:672-95. I 7. l'upe CA, Dockery D\V. Arntc health eflel'ls or PM 10 pollution +. Burnett RT . Dales R. Raizcnnc ME. ct al. Effects of low on symptomatic and asymptomatic ch ildren. Am Rev Rcspir ambient level, of ozone and sulfates on the frequency or Di s 1992: 145: 11 23-8. respiratory admissions to Ontario ho:; pital:;. Env iron Rc·s I~. Pope C A. Dockery OW, Speng ler JD. Rai,.cnnc ME. 1994:65: 172-94. Respiratory health and PM 10 pollution. A Jaily time se ri es ~ Hilborn J, Still M. Canadian Perspectives on Air Pollution. analysis. Am Rev Rcspir Di s 199 I:! 44:668-74. Ottawa: Minister o r Supply and Services Canada. 1990. I'>. Ransom MR. Pope CA. Elementary school abse nces and Prvl Iii 6. Spengler JD. Outd oor and indoor air pollution. In: Tarchcr A B. pollution in Utah Valley. Envi ron Res 1992:58: 204- 19. ed . Principles and Practi ce of Environmental Med ic ine. New 20. Pope CA. Respi ra tory hospital admi~s ions associat ed with York: Plenum Medical Book Company, 1992:2 1-4 1. PM 1n pollution in Utah , Salt Lake. and Cache Valleys. Arch 7. Review or the national air quality standards for partirnlatc'. matte r: Environ Health 1991;46:C0 ,7. assessment o r scientific and technical information. Rcp,11·1 No 21. Pope C A. Schwartz J. Ransom MR. Dai ly mortality and PM Iii EPA-450/5-82--00 I. Re:;earch Triangle Park: Strateg ics and Air pollution in Utah Valley. Arc h Env iron Health 1992;47:2 11 -7. StandarJs Division. ()!lice or Air Quality Planning and 11 Environment Canada, Health and Welfare Canada. Ene rgy. Standards, US Env ironmental Protection Agency. 1982. Mines and Resources Canada, \ madian Counc il of Ministers X. Dann T. PM 10 and PM 2_ 5 Concentrations at Canadian Urban of the Environment NOx/VOC Office. . Air Care: A parents Sites: 1984- 1993. Ottawa: Environment Canada. 1994. Guide to Air Quality and Health. Today 's Parent G ro up, 1993.

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