Risk assessment and spatial chemical variability of PM collected at selected bus stations Ricardo H. M. Godoi & Ana F. L. Godoi & Lis C. de Quadros & Gabriela Polezer & Thiago O. B. Silva & Carlos I. Yamamoto & Rene van Grieken & Sanja Potgieter-Vermaak Received: 26 July 2013 /Accepted: 2 October 2013 /Published online: 1 November 2013 # Springer Science+Business Media Dordrecht 2013 Abstract The chemical characterization of particulate matter inside and outside of confined bus shelters has been discerned for the first time. Transit patrons are at risk due to the close vicinity of densely trafficked areas resulting in elevated pol- lution footprints. Incomplete combustion processes, as well as exhaust and wear and tear emissions from public and personal transportation vehicles, are key contributors to degraded urban air quality and are often implicated as causal to various dis- eases in humans. Urban planning, therefore, includes efficient public transport systems to mitigate the effect. The bus rapid transit system was inaugurated in Curitiba to ensure dedicated traffic lanes, major bus interchanges and semi-confined bus stops called “tube stations”. To assess the chemical risk that the passengers are exposed to, an investigation of the aerosol inside and outside five of these tube stations was launched. Electron probe X-ray micro-analysis and X-ray fluorescence were used to determine the elemental composition of individual and of bulk particle samples. An aethalometer quantified the black carbon. Elemental concentrations inside the shelters were in general higher than outside, especially for traffic-related elements. The lead concentration exceeded the NAAS standard at times, although the average was below the guideline. The biogenic, organic and soot clusters showed the highest abundance for the city centre sites. The overall carci- nogenic risk could be classed as moderate, and the risk was significant at two sites during one of the sampling campaigns. The non-carcinogenic risk is well below the significant value. Keywords Particulate matter . TSP . Black carbon . Semi-confined bus stop Introduction Continued urbanization and its impact on human health re- mains a current topic. One aspect concerns itself with the ever- increasing exposure of commuters to pollution. Health experts and transport planners warned the society a long time ago that commuters should be protected against increasing vehicular emissions, and as a result, urban planning usually contains public transport as an integral part. Various methods have been adopted by megacities to reduce emissions and traffic congestion, one of which is a bus transport system that will ensure high-capacity vehicle travel. Bus transport (mostly diesel powered) has been recognized as one of the major sources of pollutants and its emission volume is growing every day in urban areas due to the increasing demand. Essentially, incomplete combustion results in emissions such as NO x , CO, CO 2 , benzene, toluene, ethyl benzene and xy- lene, black carbon and particulate matter (PM) (WHO 2006; Sandradewi et al. 2008). Many epidemiological studies have evidenced the effects of long-term exposure of PM mass concentration and particle R. H. M. Godoi (*) : A. F. L. Godoi : L. C. de Quadros : G. Polezer : T. O. B. Silva Department of Environmental Engineering, Federal University of Parana—UFPR, Curitiba, Parana, Brazil e-mail: [email protected]C. I. Yamamoto Department of Chemical Engineering, Federal University of Parana, Curitiba, Parana, Brazil R. van Grieken Department of Chemistry, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium S. Potgieter-Vermaak Division of Chemistry and Environmental Science, School of Science and the Environment, Manchester Metropolitan University, Manchester, UK S. Potgieter-Vermaak School of Chemistry, University of the Witwatersrand, Johannesburg, South Africa Air Qual Atmos Health (2013) 6:725–735 DOI 10.1007/s11869-013-0210-2
Transcript
Risk assessment and spatial chemical variability of PMcollected at selected bus stations
Ricardo H. M. Godoi & Ana F. L. Godoi & Lis C. de Quadros & Gabriela Polezer &
Thiago O. B. Silva & Carlos I. Yamamoto & Rene van Grieken & Sanja Potgieter-Vermaak
Received: 26 July 2013 /Accepted: 2 October 2013 /Published online: 1 November 2013# Springer Science+Business Media Dordrecht 2013
Abstract The chemical characterization of particulate matterinside and outside of confined bus shelters has been discernedfor the first time. Transit patrons are at risk due to the closevicinity of densely trafficked areas resulting in elevated pol-lution footprints. Incomplete combustion processes, as well asexhaust and wear and tear emissions from public and personaltransportation vehicles, are key contributors to degraded urbanair quality and are often implicated as causal to various dis-eases in humans. Urban planning, therefore, includes efficientpublic transport systems to mitigate the effect. The bus rapidtransit system was inaugurated in Curitiba to ensure dedicatedtraffic lanes, major bus interchanges and semi-confined busstops called “tube stations”. To assess the chemical risk thatthe passengers are exposed to, an investigation of the aerosolinside and outside five of these tube stations was launched.Electron probe X-ray micro-analysis and X-ray fluorescencewere used to determine the elemental composition of
individual and of bulk particle samples. An aethalometerquantified the black carbon. Elemental concentrations insidethe shelters were in general higher than outside, especially fortraffic-related elements. The lead concentration exceeded theNAAS standard at times, although the average was below theguideline. The biogenic, organic and soot clusters showed thehighest abundance for the city centre sites. The overall carci-nogenic risk could be classed as moderate, and the risk wassignificant at two sites during one of the sampling campaigns.The non-carcinogenic risk is well below the significant value.
Keywords Particulate matter . TSP . Black carbon .
Semi-confined bus stop
Introduction
Continued urbanization and its impact on human health re-mains a current topic. One aspect concerns itself with the ever-increasing exposure of commuters to pollution. Health expertsand transport planners warned the society a long time ago thatcommuters should be protected against increasing vehicularemissions, and as a result, urban planning usually containspublic transport as an integral part. Various methods havebeen adopted by megacities to reduce emissions and trafficcongestion, one of which is a bus transport system that willensure high-capacity vehicle travel. Bus transport (mostlydiesel powered) has been recognized as one of the majorsources of pollutants and its emission volume is growingevery day in urban areas due to the increasing demand.Essentially, incomplete combustion results in emissions suchas NOx, CO, CO2, benzene, toluene, ethyl benzene and xy-lene, black carbon and particulate matter (PM) (WHO 2006;Sandradewi et al. 2008).
Many epidemiological studies have evidenced the effectsof long-term exposure of PM mass concentration and particle
R. H. M. Godoi (*) :A. F. L. Godoi : L. C. de Quadros :G. Polezer : T. O. B. SilvaDepartment of Environmental Engineering,Federal University of Parana—UFPR, Curitiba, Parana, Brazile-mail: [email protected]
C. I. YamamotoDepartment of Chemical Engineering, Federal University of Parana,Curitiba, Parana, Brazil
R. van GriekenDepartment of Chemistry, University of Antwerp, Universiteitsplein1, 2610 Antwerp, Belgium
S. Potgieter-VermaakDivision of Chemistry and Environmental Science, School ofScience and the Environment, Manchester Metropolitan University,Manchester, UK
S. Potgieter-VermaakSchool of Chemistry, University of the Witwatersrand,Johannesburg, South Africa
Air Qual Atmos Health (2013) 6:725–735DOI 10.1007/s11869-013-0210-2
numbers to human health. Mostly, associations betweenrespiratory-related mortality and morbidity were reported(Dockery et al. 1993; Pope and Dockery 2006; Pope et al.1995). Short- and long-term exposure to PM is also linked toincreased hospital admissions due to cardiovascular illnesses,strokes, cancer, and other diseases (Yim and Barrett 2012;Vinzents et al. 2005). Recent studies demonstrated that com-bustion generated particles, including traffic-related aerosols,directly affects human health; they range from irritation of theeye, nose and throat, allergies, nausea and airway inflamma-tion to cancer (Salvi et al. 1999; Mills et al. 2005; Mills et al.2007; Barath et al. 2010; Tortajada et al. 2003; Halonen et al.2009; Kooter et al. 2011). Although exposure and healtheffects of traffic-related particles have been widely studied,the authors are not aware of publications forecasting the riskassociated with exposure based on the chemical character ofthe particles, rather than the PM mass concentration. The areaof interest was semi-confined bus stations/stops, frequentedby diesel-powered buses in the metropolis of Curitiba, Brazil.
Several studies on PM levels in bus cabins and tramsperformed in various countries have been conducted overthe past few years. Most of these focused on mass concentra-tion profiles over long- and short-distance journeys, and stopand go bus routes in urban and suburban areas (Tsang et al.2008; Asmi et al. 2009; Yim and Barrett 2012).
Since the majority of public transport passengers spend aconsiderable amount of time waiting for buses (either at open-air, semi-confined or totally confined bus stops), normallyclose to high traffic volumes, air quality inventories are need-ed. In Curitiba, the average waiting time is about 30 min, butcould reach up to 1 h depending on the itinerary. In this way,passenger exposure to possible elevated levels of vehicularpollution can be estimated and therefore adverse health effectspredicted. One of the promising approaches to mitigate airpollution discharges produced by buses in metropolitan areasis to provide an efficient urban public transport. Therefore,many public transportation facilities are now located in semi-confined or completely confined terminals, often inside mas-sive commercial buildings (Cheng et al. 2012).
Curitiba’s public transportation system inaugurated the busrapid transit system as a new concept for public transportation,which was replicated in many cities worldwide due to itssuccessful implementation. The main innovations establishedare the dedicated lanes, major bus interchange and the semi-confined bus stops called “tube stations” because of its tubulardesign, Fig. 1. These tube stations do not, however, precludeentrance or concentration of particles. It has recently beenshown that the air quality of the microenvironment in andaround bus shelters in terms of particle counts and PM massconcentrations are dependent on a number of factors as fol-lows: shelter design, bus idling time, and meteorologicalvariables (Moore et al. 2012; Moore and Figliozzi 2013). Asfar as we could establish, no previous reports could be found
in open literature on the chemical characterization of PM insemi-confined bus stops.
Chemical state of the particles, and thus particle origin, canalso have an impact on the health response. As previousstudies focused on mass concentrations, it was decided toapply a single-particle analytical technique, low-Z particleelectron probe X-ray microanalysis (EPXMA) and bulk ele-mental analysis by energy-dispersive X-ray fluorescence tocharacterise aerosols collected inside and outside the tube. Inthis way, the chemical character of the inhalable particles andconsequently its potential risk to human health could bediscerned.
Materials and methods
Background of the study area
Curitiba (25°25′ S; 49°16′W) is the capital and the largest cityin the Parana State in Brazil. The Curitiba Metropolitan area,comprising of 26 municipalities, has a total population of 3.2million people. Curitiba is in many aspects on the forefront interms of sustainable development, and its urban planning isreckoned as one of the best worldwide. Due to their successfulimplementation of a large public transport network, consistingof bus transport only (1,100 buses make 12,500 trips daily,serving more than 1.3 million passengers), 80 % of travellersnow use the service and thereby 27 million passenger vehicletrips are saved annually. In addition, the buses in Curitiba usea low sulphur diesel fuel (S-50/50 mg/kg) and emissions areregulated by the Automotive Vehicle Air-Pollution ControlProgram (PROCONVE), created by the national environmentcouncil—CONAMA.
Sampling of airborne PM
Sampling of air PM was carried out at five of the tube stationsdescribed in the introduction in the centre of town, and itsgeographical positions are illustrated in Fig. 2, and the statis-tics are displayed in Table 1. Prior to choosing the tube station
Fig. 1 Curitiba passenger tube station system constructed in metal frameand curved glass
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locations for sampling, the sites were evaluated based on setcriteria. These included (1) representativeness of the samplingsite with regards to the rest of the city, (2) adequate powerrequirements and (3) security of the site.
Sampling was performed during two sampling campaigns:August 20–September 23, 2010 and August 2–September 15,2011. It is noteworthy that both sampling campaigns wereconducted in winter. The samplers were installed simulta-neously inside and outside of stations and nominated as ME,JA, CM, PT and VN (Fig. 2).
Stacked filter units (SFU) collected PM as total suspendedparticles (TSP) on Nuclepore membranes with a pore-size of0.4 μm, for bulk elemental analysis. Bulk elemental analysiswere performed with an Epsilon-5 high-energy polarizedbeam EDXRF spectrometer, as described in Avigo et al.(2008). In addition, SFUs equipped with Pallflex filters wereused to collect TSP for black carbon (BC) analysis, for whicha Magee Scientific aethalometer (model OT-21) was used forquantification. In this study, we considered the attenuation fora light source of 880 nm and the classical Magee sigma of16.6 m2g−1 in order to relate the obtained attenuation and BC
concentration (Hansen et al. 1984). Both stacked filter unitswere simultaneously operated for 24 h at a flow rate of35 L min−1.
A two-stage May cascade impactor (aerodynamic diameterranges from 0.5 to 2.0 μm (stages 6–4) and from 2.0 to 8.0 μm(stages 4–2)), operated at a flow rate of 20 L min−1, was usedto collect PM for single-particle analysis on silver foil sub-strates. Low-Z EPXMA was performed on a JEOL 733equipped with an Oxford detector with an atmospheric ultra-thin window. Details concerning measurement, quantificationand clusterisation may be found elsewhere (Godoi et al.2004).
Carbonaceous particles were divided into three differentclass groups, i.e. soot, biogenic and organic particles. Particlesare identified to be biogenic when the concentrations of C andO in the particles are similar and when they also contain N, P,Cl and/or S (>10 % wt), which are characteristic elements forbiogenic species. When the C content is about three timeshigher than the O content (or even more), the particles areidentified as C-rich/soot. Particles are considered to be organicwhen they do not match the criteria above for biogenic or sootparticles.
Results and discussion
Bulk elemental analysis
The bulk elemental profiles of the TSP as determined byEDXRF are displayed in Table 2. It is observed that elements(Al, Si, K, Fe, Ti and Ca), typically originating from theearth’s crust, are present in micrograms per cubic meter quan-tities and as such could be classified as majors and minors. Of
Fig. 2 Sampling locations in thecity of Curitiba
Table 1 Characteristics and statistics of the sites investigated
Stations Number of passengers Number of buses
Month Working day Working day
ME Commercial area 73,371 3,383 338
JA Residential area 62,271 2,289 335
CM City centre 43,024 2,043 203
VN 17,489 743 190
PT 61,926 2,489 156
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the elements that are related to industrial and vehicular emis-sions (S, Cl, Zn, Cu and Mn), only S and Cl are grouped withthe majors and minors and the rest are classified as present intrace level quantities. From the average values illustrated inTable 2, it can be seen that elemental concentration follow ingeneral Si > Fe ∼ Ca > Al > K > S > Cl ∼ Ti for the majors andminors, and Zn > Cu > Mn > Pb > Cr > V > Ni ∼ Sr.Furthermore, it is noticeable that the bus stations in the citycentre have the lowest average concentrations. The concen-trations at the stations in the residential and commercial areasare on average 1.5 and 3 times those in the city centre follow-ing a similar ratio to the number of passengers/month. The Pbconcentration exceeded the National Air Quality Standards asset by the US Environmental Protection Agency (US EPA
1990) only in one place (outdoor 2010 at ME), and theaverage concentration of 0.04 μg m−3 is well below the0.15 μg m−3 primary criterium guideline value.
Various publications relating elemental presence and con-centrations in the particle phase to traffic-related emissionscan be found (Yli-Tuomi et al. 2005 contains a summary ofsome). Traffic-related elements most commonly reported foroutdoor air PM (TSP, PM10 and PM2.5) are Cu, Zn, Pb, Ba,Cd, Sn and Fe. Relatively high concentrations of Ca, Fe and Tiare considered to represent road dust (Aarnio et al. 2005).Sulphur is correlated with fossil fuel combustion, whereas Clis typically associated with the combustion of gasoline, bio-mass, plastics and metals that form volatile chlorides, if notfrom marine origin (John et al. 2007). From the data in
Table 2 Elemental concentrations of TSP as determined by EDXRFS during two campaigns
Station Year Environment Major and minor elements (μg m−3) Trace elements (ng m−3)
Tables 1 and 2, one can deduce a causal relationship betweenthe number of buses and the concentrations of Cu, Zn, Pb, Crand Mn, which could be interpreted that they are of vehicularemission origin. This relationship is not so pertinent in thecase of V, Sr and Ni and may therefore point to another source.Pearson correlation coefficients ranging between 0.96 and0.99 for crustal-related elements (viz. Al, Si, Ca, Ti, K andFe) are indicative of their crustal origin.
Indoor/outdoor ratios (I/O ratio) for the elemental compo-sition based on average elemental concentrations indicatedthat in 70 % of the cases, the concentrations inside the tubestations were higher than outside the tube stations. Suchevidence suggests that the tube stations are somehow accu-mulating the pollution coming from outside. The average I/Oratio for MEwas 0.8, JAwas 1.6, CMwas 3.0, PTwas 1.0 andVNwas 0.6. It is apparent that the average I/O elemental ratiosshowed no clear correlation with traffic density, consideringthat all the stations are built in the same way, with the samematerials and are, moreover, semi-opened. It is, however,noteworthy to add that the traffic related elements’ I/O ratioswere considerably higher than the crustal elements andreached values of up to 1.7.
In order to assess the contribution of anthropogenic versuscrustal sources, enrichment factors (EF) were calculated usingAl as a reference.When EF approaches unity, the predominantsource is crustal; on the other hand, EFs much higher than 10are considered to originate mainly from anthropogenicsources (Liu et al. 2003). For the average concentrations ofelements in the earth’s crust, the data reported by Mason(1966) were applied. Figures 3, 4, 5, and 6 show the averagevalues of EF both inside and outside the stations for years2010 and 2011. The conclusion drawn from the Pearsoncorrelation coefficients of the elemental concentrations ofcrustal origin is reinforced by their EFs always below 10 andoften unity. The elements Cu, Zn, Pb, S and Cl were highlyenriched (with average EFs Cu=123.5, Zn=112.7, Pb=339.3,S=172, Cl=240.7), therefore having a major contribution ofanthropogenic sources, especially vehicular emissions as ex-plained earlier. It is further noteworthy that enrichment dif-fered between the inside and outside environments, especially
for Cu, Pb andMn, each reporting 2.6, 3.1 and 1.6 higher EFs,respectively. Carter et al. (1997) demonstrated that metals maybe responsible for the production and release of inflammatorymediators by the respiratory tract epithelium and suggestedthat these mediators contribute to the toxic effects of particu-late air pollutants reported in epidemiological studies (Singhet al. 2002).
Single particle analysis
Figure 7 plots the abundance of the ten clusters identified bymeans of individual particle analysis for the sample collectedon August 20, 2010, and is representative of the samplescollected during both sampling campaigns. The reader isreferred to Godoi et al. (2004) and Potgieter-Vermaak et al.(2012) for a detailed explanation. In short, the relative X-rayintensities of individual particles as determined by EPXMAare used to infer elemental associations, thereby clusteringparticles with similar composition together. This informationis useful to evaluate particle-specific passenger exposure.
Soil dust concentrations were estimated by summing theoxides of aluminium and silicon, plus a small percentage(>10 % wt) of Fe, Ca, K, Ti, Mn, S and P. Aluminosilicateparticles showed the highest abundance for both the fine andcourse fractions. Furthermore, there was no significant differ-ence between indoor and outdoor concentrations. The highestoverall abundancewas found at the commercial site, where up to80 % of the outside particles could be classed as aluminosili-cates, probably coming from road dust. Abrahams (2002) notedthat inhaled soil dust is retained in the lungs where they cancause irritation and damage, eventually resulting in bronchitis,fibrosis (pneumoconiosis) and cancer. The equal proportion ofaluminosilicates in the fine fraction (<2.5 μm) in comparisonwith the coarse fraction (>2.5 μm) is certainly a concern.
The most abundant cluster was soot (32 %), followed bythe biogenic (13%), organic (11%), iron oxide (4%), chlorine(0.6 %) and aluminium (0.6 %) containing calcium carbonate(0.5 %) and other iron-rich (0.2 %) clusters. It is noted that forthe biogenic, organic and soot clusters, the highest abundanceis reported for the city centre sites, with up to three times
0
1
10
100
1000
10000
Si K Ca Ti V Fe Sr Cr Ni Mn Cu Zn Pb S Cl
ME
JA
CM
PT
VN
Fig. 3 Average crustalenrichment factors for differentelements at tube stations 2010
Air Qual Atmos Health (2013) 6:725–735 729
higher abundance than at the other sites, probably due to theeffects of street geometry and roadside structure on the localdispersion of traffic emissions.
Moreover, the inside abundance of the aluminosilicate,soot, biogenic and organic clusters are sometimes elevated(up to five times at some sites, suggesting again that thestations could be accumulating the outside pollutants). In thelight of the fact that bioaerosols can impact adversely thehuman respiratory system, spanning from infectious diseasesto acute toxic effects, allergies and asthma (Després et al.2012), the elevated biogenic inside abundance at four of thefive sites are a concern. There is, however, no obvious rela-tionship between bus traffic density and the four main clustersidentified. The iron oxide clusters were only identified at theresidential site, and were present both indoors and outdoorsand in both size fractions. Furthermore, the inside abundancefor this cluster was between three and six times lower than theoutside. Similarly, the calcium carbonate cluster was onlyidentified in the finer fraction, inside the residential tubestation.
Soot is associated with motor vehicles exhaust and wearemissions, in particular those using diesel, and has beenimplicated as causal to allergies and irritation of mucousmembranes and decrease in resistance to infection (Campos2003). The percentage of soot found in this work is, some-times, comparable to the percentage found near sugarcaneplantations in the city of Araraquara, Brazil (Godoi et al.
2004). The highest soot abundance (77 % of particlesanalysed) was reported outside the CM station (one of the citycentre sites). This may be attributed to the fact that it is locatedin an area with several bus stations in the immediate surround-ings. None of the city centre sites showed a higher indoorabundance. In contrast, the soot abundances indoors werenotably higher at the commercial and residential sites (2 and1.7 times, respectively).
Black carbon
Table 3 shows the average concentrations of BC for each tubestation studied. BC levels varied markedly and irregularlyduring the sampling period, particularly inside of the tubestations. The BC concentration profiles between 2010 and2011 differed significantly. During 2010, the normal tendencywas that the concentration on the outside was on average twicethat of indoors, except in the case of the residential site wherethe exact opposite was observed. The BC concentrationsinside and outside where, within experimental error, the sameduring the 2011 campaign. It is notable that the highest con-centrations, as well as the largest discrepancies between in-door and outdoor environments, occurred during 2010, rang-ing from 3.1 to 16.0 μm m−3, whereas in 2011, the BCconcentrations had slight variations, ranging from 3.7 to6.0 μg m−3. There is once again no obvious relationshipbetween the absolute concentrations and the number of buses
0
1
10
100
1000
10000
Si K Ca Ti V Fe Sr Cr Ni Mn Cu Zn Pb S Cl
ME
JA
CM
PT
VN
Fig. 4 Average crustalenrichment factors for differentelements at Urban Environment2010
0
1
10
100
1000
10000
Si K Ca Ti V Fe Sr Cr Ni Mn Cu Zn Pb S Cl
ME
JA
PT
VN
Fig. 5 Average crustalenrichment factors for differentelements at tube stations 2011
730 Air Qual Atmos Health (2013) 6:725–735
stopping at the station, and are most probably due to meteo-rological factors.
The BC concentrations found in the present study arecomparable with heavily polluted metropolitan area ofSao Paulo city, but ME and VN average concentrationswere higher than the ones found during rush hour inSao Paulo city during winter time (Castanho and Artaxo2001).
Risk assessment
To predict the potential health risk of transit patrons, a simpli-fied risk calculator, risk assessment information system(RAIS), was used in this study (RAIS-A 2013). Bulk
elemental concentrations together with biometric data specificfor the area were inputted (Brazilian lifetime, 74.1 years,exposure durations of 40 years, exposure time of 1 h andexposure frequency of 250 days per year).
The reader is referred to the RAIS website for more infor-mation (RAIS-B 2013). Briefly, the risk calculator modelspotential risks (carcinogenic (CR) and non-carcinogenic (haz-ardous quotient (HQ)) risks) arise through ingestion, inhala-tion and dermal contact with the pollutant. CR and HQ are theprobabilities of an individual to develop cancer and non-carcinogenic diseases, respectively, over a lifetime. The USEnvironmental Protection Agency (US EPA 1989; US EPA2013) developed guidance for estimation of such risks, whichis briefly summarized in the form of equations.
0
1
10
100
1000
10000
Si K Ca Ti V Fe Sr Cr Ni Mn Cu Zn Pb S Cl
ME
JA
PT
VN
Fig. 6 Average crustalenrichment factors for differentelements at Urban Environment2011
Fig. 7 Abundance (%) of the fine and coarse fractions of the ten clusters identified with EPXMA collected on August 20, 2010
& ED: exposure duration (years)& EF: exposure frequency (day/year)& ET: exposure time (hour/day)& LT: lifetime (years)& C: concentration of each element found in the air (micro-
grams per cubic meter)& RfCi: inhalation reference concentrations (in milligrams
per kilogram per day)& IUR: inhalation unit risk (1/(μg/m3))
The values for RfCi, IUR, RfDo and SFo can be found inthe US EPAwebsite. CR values lower than 10−6 is classed asinsignificant, acceptable if it is lower than 10−4, and indeedneeding remediation when it is higher than 10−4. Avalue closeto or higher than 1 for the non-carcinogenic risks is classed as asignificant risk (US EPA 1989; US EPA 2013; Hu et al. 2011).
Special mention of the use of the Cr concentrations in thiscalculator should be made. Cr is present in more than oneoxidation state in environmental particles, and it has beenreported by Swietlik et al. (2011) that Cr(VI) is between 30and 40 % of total Cr measured in urban aerosols. Because ourcalculations have shown that the Cr(VI) species would have tobe less than 10 % of the total Cr, not to pose a risk, we usedCr(VI) in our risk calculator.
Tables 4 and 5 present the CR and HQ data. As far as thecarcinogenic risk is concerned, it is observed that only in the
Table 3 Average black carbonconcentration (μg m−3) Black Carbon Concentration (μg m-3)
Station 2010 2011
Indoor Outdoor Indoor Outdoor
Mean S.D. Mean S.D. Mean S.D. Mean S.D.
ME 7.3 1.5 15.2 2.8 6.0 1.8 5.5 1.4
JA 10.6 15.9 4.9 6.8 3.9 0.7 3.7 0.8
CM 5.3 0.8 7.7 2.5
PT 3.1 1.9 7.0 2.1 4.2 1.7 4.1 0.6
VN 9.5 4.2 15.9 4.4 5.4 0.6 5.7 0.3
Table 4 Non-carcinogenic risks obtained for each station
Chemical Aluminium Chromium(VI) Manganese (non-diet) Nickel refinery dust Total risk
JA 2010 Indoor 0.0352 0.0234 0.0799 0.0139 0.152
Outdoor 0.0213 0.0106 0.0502 0.00897 0.091
JA 2011 Indoor 0.00686 0.0016 0.0154 0.0192 0.043
Outdoor 0.00334 0.0016 0.00685 0.0917 0.104
CM 2010 Indoor 0.0039 0.00457 0.0303 0.00734 0.0461
case of Cr(VI) values close or larger than the significantthreshold (1 in 10,000) are reported. This value was exceededat the residential and commercial sites and was larger than 1×10−5 in seven other instances. In general, the CR values for thecity centre sites could be classified as insignificant, except forone site (PT) where values higher than 1×10−5 were deter-mined during the 2010 campaign. Pearson correlations indi-cated that the two campaigns correlated well at some of thelocations (MEin=0.99, PTout=0.81, VNin=0.80 andVNout=0.98) and weakly to not at all at others (JAin=0.19,JAout=−0.43, MEout=−0.27 and PTin=0.43). This is indic-ative of the fact that exposure to carcinogenic risk varies andthat continuous and long-termmonitoring should be a priority.The total risk for the average of both indoor and outdoorconcentrations over the five sites was 2.4×10−5 and couldtherefore be classed as a moderate concern.
As far as the non-carcinogenic risk (HQ) is concerned, it isobserved that the highest value is reported at the commercialsite (0.227), and that values in general are well below the toxiclevel. There seems to be no clear pattern in terms of indoor andoutdoor risks between the sites. On average though, as wehave seen from previous data on elemental concentrations andcluster abundances, it is interesting that the average risk for thecity centre cites are between three and four times lower than atthe residential and commercial sites. The same observationcan be made for the CRs where the difference is even morepronounced and was up to eight times lower in the city centre.This poses the question as to why the risk in the residentialarea is so much higher and often comparable with that of the
commercial site. It is also of concern in that one can make theassumption that this station will be frequented by the morevulnerable cohorts (the elderly and children), and thereforefurther monitoring is recommended. In addition, factors suchas mass concentration, particle counts and meteorologicalconditions should be included in future investigations.
Conclusion
This study performed an investigation of the aerosol pollutioninside and outside of semi-confined bus shelters in Curitiba,Brazil. Measurement results indicated that the chemical com-position of the TSP differed between the various areas inves-tigated and that in general, the concentrations at the commer-cial and residential sites were 1.5 to 3 times higher. It was alsonoted that 70 % of the elements detected had I/O ratios higherthan 1, pointing to higher risk, with reference to the mediumand high atomic weight elements, inside the shelters in com-parison with outside the shelter. The single particle analysis,however, indicated that cluster composition at the city centresites were high in biogenic, organic and soot particles, andoften elevated inside the shelters. RAIS results pointed to-wards a moderate carcinogenic risk and an insignificant toxicor non-carcinogenic risk, overall. It is, however, important tonote that these risks are highly variable and taking into ac-count that the lead concentration was exceed in at least one ofthe sites, it seems imperative that continuous monitoringshould be performed at these stations.
Table 5 Carcinogenic risks ob-tained for each station Chemical Chromium(VI) Lead and Compounds Nickel Refinery Dust Total Risk
10-5 10-9 10-9 10-5
JA 2010 Indoor 10.60 10.50 25.10 10.60
Outdoor 4.79 6.47 16.30 4.79
JA 2011 Indoor 0.73 0.00 34.80 0.73
Outdoor 0.73 0.00 166.00 0.74
CM 2010 Indoor 2.07 14.20 13.30 2.07
Outdoor 0.75 4.07 4.44 0.75
ME 2010 Indoor 5.18 16.30 23.70 5.18
Outdoor 11.00 29.20 44.40 11.00
ME 2011 Indoor 1.81 1.85 31.10 1.81
Outdoor 1.68 1.52 322.00 1.71
PT 2010 Indoor 1.22 4.25 11.10 1.22
Outdoor 1.29 5.18 9.98 1.30
PT 2011 Indoor 0.61 0.00 26.60 0.61
Outdoor 0.54 0.00 24.00 0.55
VN 2010 Indoor 0.38 4.99 4.81 0.38
Outdoor 0.69 1.85 8.87 0.69
VN 2011 Indoor 0.57 0.00 19.60 0.57
Outdoor 0.69 0.43 17.40 0.69
Air Qual Atmos Health (2013) 6:725–735 733
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