Detailed Characterization andProfiles of Crankcase and DieselParticulate Matter ExhaustEmissions Using Speciated OrganicsB A R B A R A Z I E L I N S K A , * , †

D A V I D C A M P B E L L , †

D O U G L A S R . L A W S O N , ‡

R O B E R T G . I R E S O N , §

C H R I S T O P H E R S . W E A V E R , |

T H O M A S W . H E S T E R B E R G , ⊥

T I M O T H Y L A R S O N , # M A R K D A V E Y , ∇ A N DL . - J . S A L L Y L I U ∇ , O

Desert Research Institute, 2215 Raggio Parkway,Reno, Nevada 89512-1095, National Renewable EnergyLaboratory, Golden, Colorado 80401-3393, Air QualityManagement Consulting, Greenbrae, California 94904, EngineFuel & Emissions Engineering, Inc., Rancho Cordova,California 95742, International Truck and EngineCorporation, Warrenville, Illinois 60555, Department of Civiland Environmental Engineering, and Department ofEnvironmental and Occupational Health Sciences, Universityof Washington, Seattle, Washington 98105, and Institute ofSocial and Preventive Medicine, University of Basel,CH-4051 Basel, Switzerland

Received December 7, 2007. Revised manuscript receivedMarch 5, 2008. Accepted May 15, 2008.

A monitoring campaign was conducted in August-September2005 to compare different experimental approaches quantifyingschool bus self-pollution. As part of this monitoring campaign,a detailed characterization of PM2.5 diesel engine emissionsfrom the tailpipe and crankcase emissions from the road drafttubes was performed. To distinguish between tailpipe andcrankcaseventemissions,adeuteratedalkane,n-hexatriacontane-d74 (n-C36D74) was added to the engine oil to serve as anintentional quantitative tracer for lubricating oil PM emissions.This paper focuses on the detailed chemical speciation ofcrankcase and tailpipe PM emissions from two school busesused in this study. We found that organic carbon emission rateswere generally higher from the crankcase than from thetailpipe for these two school buses, while elemental carboncontributedsignificantlyonly in thetailpipeemissions.Then-C36D74that was added to the engine oil was emitted at higher ratesfromthecrankcasethanthetailpipe.Tracersofengineoil (hopanesand steranes) were present in much higher proportion incrankcase emissions. Particle-associated PAH emission rates

were generally very low (<1 µg/km), but more PAH specieswere present in crankcase than in tailpipe emissions. Thespeciation of samples collected in the bus cabins was consistentwith most of the bus self-pollution originating from crankcaseemissions.

IntroductionThe U.S. Environmental Protection Agency’s recent regula-tions required all new on-road diesel vehicles to change tolow-emission engines and ultralow-sulfur fuels by 2007 (1).The rule includes two components: (1) emission standards;and (2) diesel fuel regulation. The first component of theregulation introduces new, very stringent emission standardsfor diesel particulate matter (PM, 0.01 g/bhp-hr), oxides ofnitrogen (NOx, 0.20 g/bhp-hr), and nonmethane hydrocar-bons (NMHC, 0.14 g/bhp-hr). The diesel fuel regulation limitsthe sulfur content in on-highway diesel fuel to 15 ppm, downfrom 500 ppm. In spring 2003, the U.S. EPA announced anationwide voluntary school bus retrofit initiative (see http://www.epa.gov/cleanschoolbus) that established a cost-sharedgrant program to assist school districts in retrofitting andupgrading their bus fleets. In July 2003, the state ofWashington legislature enacted a statewide “Diesel Solutions”program (see http://www.pscleanair.org/programs/dieselso-lutions) that provides 25 million dollars by 2008 to retrofitdiesel school buses with cleaner-burning fuels and engines,making it one of the largest and most active voluntary schoolbus retrofit programs in the country. This program maysubstantially reduce potential in-cabin exposures to bus self-pollution, especially to students and drivers who ride schoolbuses daily. Although recent work (2) suggests the possibilitythat PM emissions from the crankcase vent, in addition totailpipe emissions, may contribute to in-cabin PM, no studieshave examined detailed organic compositions of PM in theseemission sources of the school bus.

We conducted a monitoring campaign in summer 2005to compare different experimental approaches quantifyingschool bus self-pollution (3). As part of this monitoringcampaign, a detailed characterization of PM2.5 diesel engineemissions from the tailpipe and from the crankcase via theroad draft tube was performed. To distinguish betweentailpipe and crankcase vent emissions, a deuterated alkane,n-hexatriacontane-d74 (n-C36D74) was added to the engineoil, and organometallic iridium (Ir) complex was added tothe diesel fuel. These served as intentional quantitative tracersfor lubricating oil and fuel combustion PM emissions,respectively. The results from this novel dual tracer methodfor bus self-pollution estimates are described in separatepapers (3, 4). This paper focuses on the detailed chemicalspeciation of crankcase and tailpipe PM emissions from twoschool buses used in this study. These data served asimportant inputs for our other papers (3–5) and demonstratedthat crankcase and tailpipe emissions could be differentiatedusing specific organic tracers.

Experimental SectionStudy Design. Two Seattle school buses equipped with dieseloxidation catalysts were monitored: Bus 1 was a newer 2002model with 49,012 miles and Bus 2 was an older 1999 modelwith 79,482 miles. Source sampling used an on-board dilutiontunnel (RAVEM) (6) to collect PM2.5 samples from the tailpipeor the crankcase of each bus. Buses were driven along regularroutes, including stops, and three 30-min isokinetic sampleswere collected for each bus from the tailpipe, followed bythree 15- to 20-min crankcase sampling runs in which all

* Corresponding author phone: 775-674-7066; fax: 775-674-7060;e-mail: Barbara.Zielinska@dri.edu.

† Desert Research Institute.‡ National Renewable Energy Laboratory.§ Air Quality Management Consulting.| Engine Fuel & Emissions Engineering, Inc.⊥ International Truck and Engine Corporation.# Department of Civil and Environmental Engineering, University

of Washington.∇ Department of Environmental and Occupational Health Sci-

ences, University of Washington.O University of Basel.

Environ. Sci. Technol. 2008, 42, 5661–5666

10.1021/es703065h CCC: $40.75 2008 American Chemical Society VOL. 42, NO. 15, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 5661

Published on Web 06/28/2008

exhaust air from the road draft tube was directed into thedilution tunnel. The details of the on-board dilution tunnelsampling are provided in the Supporting Information.Samplers equipped with 2.5 µm cutpoint impactor inlets and47 mm Teflon (Gelman, RPJ047) filters for mass and elementsor quartz fiber (Pallflex, 2500 QAT-UP) filters for organic andelemental carbon and detailed organic speciation were used.An additional sampler was operated upstream of the exhaustinlet to the dilution system as the sampling tunnel blank,alternating between a Teflon and quartz filter for each run.Prior to sampling, 100 g of n-C36D74 (Cambridge IsotopeLaboratories, Inc.) was added to approximately 20 quarts ofnew lubricating oil, which was added to the first bus followingan oil change, with additional oil added to bring the engineoil up to normal operating levels. This oil was drained fromthe first bus and used to refill the second bus prior to thetesting of the second bus. An organo-metallic coordinationcomplex of iridium was dissolved in a small amount of tolueneand added to the fuel of each bus to yield an approximateconcentration of 10 mg of Ir per gallon of fuel, as describedby Ireson et al. (4).

To quantify the levels and major sources of a bus’s self-pollution, we performed in-cabin sampling when buses weredriven along their regular routes. In addition, we monitoredon-road background levels using a lead vehicle that wasdriven approximately 5 min ahead of the bus with its windowswide open. The details of these sampling methods aredescribed in another paper (3).

Sample Analysis. Teflon filters were analyzed for PM massby gravimetry. Quartz filters were analyzed for “organic” and“elemental” carbon (OC/EC) and for potential organic markercompounds, which are key inputs into receptor models. A0.56 cm2 punch from the prefired, quartz-fiber filters wasanalyzed by the Thermal-Optical Reflectance (TOR) methodfor OC/EC, using the IMPROVE (Interagency Monitoring ofProtected Visual Environments) temperature/oxygen cycle(7, 8). The minimum detection limit (MDL) for this methodis 0.8 and 6.2 µg of EC and OC, respectively, per 47 mm filter.

After taking a punch for TOR analysis, quartz filters werespiked with the following deuterated internal standards:chrysene-d12, pyrene-d12, benz[a]anthracene-d12, benzo[a]py-rene-d12, benzo[e]pyrene-d12, benzo[k]fluoranthene-d12, ben-zo[g,h,i]perylene-d12, coronene-d12, cholestane-d50, 1-nitro-pyrene-d9, n-hexadecane-d34, n-eicosane-d42, n-tetracosane-d50, n-octacosane-d58, and n-triacontane-d62. The sampleswere extracted with dichloromethane followed by n-hexaneutilizing a pressurized fluid extraction method with acceler-ated solvent extractor (Dionex Corporation, Sunnyvale, CA).The extracts were then concentrated by rotary evaporationat 20 °C under gentle vacuum to ∼1 mL and filtered through0.45 mm Acrodiscs (Gelman Scientific), rinsing the sampleflask twice with 1 mL of dichloromethane (CH2Cl2) each time.Approximately 100 µL of toluene was added to the sampleand CH2Cl2 /hexane was evaporated under a gentle streamof nitrogen.

The extracts were analyzed for polycyclic aromatichydrocarbons (PAH) and alkanes with a Varian Star 3400CXgas chromatograph equipped with an 8200CX automaticsampler interfaced to a Varian Saturn 4000 ion trap gaschromatograph/mass spectrometer (GC/MS), operated inan electron impact (EI) ionization mode and selective ionstorage (SIS) analysis mode. Splitless injections (1 µL) weremade onto a phenylmethylsilicone fused-silica capillarycolumn (30 m, 0.25 mm i.d., 0.25 µm film thickness; DB-5ms, J&W Scientific). The GC operating conditions were asfollows: for PAH, 75 °C for 2 min; 14 °C/min to 300 °C; 10°C/min to 325 °C; hold at 325 °C for 8 min; and for alkanes,70 to 300 °C hold for 4.5 min; 40 °C/min to 325 °C; hold at325 °C for 12 min.

Hopanes and steranes were analyzed using the Varian1200 triple quadrupole gas chromatograph/mass spectrom-eter (GC/MS/MS) system with CP-8400 autosampler, oper-ating in EI and multiple ion detection (MID) mode. Splitlessinjections (1 µL) were made onto a phenylmethylsiliconefused-silica capillary column (30 m, 0.25 mm i.d., 0.25 µmfilm thickness; Chrompack Factor four VF-5 ms). The GCoperating conditions were as follows: 85 °C for 2 min; 12°C/min to 200 °C; 8 °C/min to 320 °C; hold at 320 °C for 8min.

1-Nitropyrene (1-NP) was quantified using the Varian 1200GC/MS/MS system operating in negative chemical ionization(NICI) mode. Injections (1 µL) were made in the cool-on-column mode (90 °C injection temperature, 50 °C/min to320 °C) onto a 30 m long × 0.25 mm i.d., 0.25 µm film thickness50% phenylmethylsilicone fused-silica capillary column (DB-17 ms, J&W Scientific). The GC oven operating conditionswere as follows: 90 °C for 2 min; 12 °C/min to 210 °C; 10°C/min to 250 °C; hold at 250 °C for 2 min, 20 °C/min to 320°C; hold at 320 °C for 16 min. Methane was used as a CIreagent gas. The MS/MS method was used to detect 1-NP.The molecular ions of 1-NP and deuterated internal standard1-NP-d9 (m/z 247 and 256, respectively) were isolated by thefirst quadrupole (Q1) and fragmented by collision with argonat 15 V in the collision cell. The second quad (Q2) was setto monitor [M - NO]+ fragment ion at m/z 217 and 226,respectively. Use of the NICI GC/MS/MS technique allowsfor quantification of 1-NP without the necessity of rigoroussample precleaning.

Samples were quantified by comparing the response ofthe deuterated internal standards to the analyte of interest.Analyte response was referenced to five-point calibrationcurves created from standard solutions made with certifiedPAH mixtures purchased from Sigma-Aldrich, Inc., ACCUStandards, Ultra SCI and CDN, Inc. The National Instituteof Standards and Technology Standard Reference Materials(SRM 1941 and 2260a) served as reference standards for QA/QC purposes. Alkane calibration solutions were made fromcertified alkane mixtures obtained from Chiron (Norway),ACCU Standard, and Ultra SCI. NIST SRM 2266, containingfive hopanes and five steranes, was used for preparingcalibration solutions for hopanes/steranes. The remaininghopanes and steranes were identified based on comparisonof their mass spectra and retention time with data availablein the literature (9–11). Compounds for which authenticstandards were not available were quantified based on theresponse factor of standards most closely matched instructure and retention characteristics. For 1-nitropyrene,calibration solutions were made from NIST SRM 2265. TheMDL is approximately 20 pg/µL for PAH, alkanes, andhopanes/steranes, and 0.5 pg/µL for nitro-PAH.

Lubrication oil and fuel samples were obtained from thevehicles immediately after emissions sampling and wereanalyzed for PAH, alkanes, and hopanes/steranes. The oilswere cleaned and fractionated prior to analysis using themethod described by Wang et al. (9). Cleanup was conductedon a 12 mL Supelco solid phase extraction (SPE) cartridgepacked with 2 g of SiOH. Cartridges were placed on a vacuummanifold and conditioned prior to cleanup with 14 mL ofhexane. Prior to cleanup, oils and fuels were diluted in hexane(100 and 300 µL/mL, respectively). Three hundred microlitersof the diluted oil or fuel were spiked onto a SPE cartridgealong with 100 µL of deuterated internal standard mixturedescribed above. Samples were eluted with 8 mL of hexanefollowed by 10 mL of benzene/hexane (1:1). Both fractionswere combined, evaporated to 1 mL, and analyzed for PAH,alkanes, hopanes, and steranes by GC/MS, as describedabove.

Emission Rates Calculations. The measured sourceconcentration from each filter sample was corrected for

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background air contaminants contained in the dilution airby subtracting the measured concentration of the corre-sponding dilution air filter samples. The dilution air con-centrations were adjusted before subtraction to compensatefor the fraction of air in the source samples that was producedby the engine, using the following equation:

CadjS )Cm

S -CmB (1- 1

DF) (1)

where CadjS ≡ concentration in diluted source air adjusted for

background; CmS ≡ concentration as measured in diluted

source air; CmB ≡ concentration as measured in background

(dilution) air [For crankcase emissions source testing, whentwo dilution air samples were collected each day, the dailyaverage concentration was subtracted from each sourcesample.]; and DF ≡ dilution factor (ratio of diluted air volumeto source volume).

The resulting background-adjusted concentrations werethen converted to total emissions for each test (mg per cycle)by multiplying by the total volume of air that passed throughthe dilution chamber (Vmix):

ET )CadjS ·Vmix (2)

From this total emissions value (ET), emission rates in mg/km or mg/sec were calculated by dividing by the total distancedriven or the total sampling time, respectively.

Results and DiscussionThe crankcase and tailpipe emission rates of species mea-sured during this study for Bus 1 and Bus 2 are presented inTable S1 in the Supporting Information. The detailedspeciations of in-cabin bus and lead vehicle samples arepresented in Supporting Information Tables S2 and S3,respectively.

PM2.5 Mass and Organic/Elemental Carbon EmissionRates. Figure 1 shows the average crankcase (CK) and tailpipe(TP) fine PM, organic, and elemental carbon emission ratesfor Bus 1 (B1) and Bus 2 (B2). The data in this figure areaveraged over three separate runs for each bus and thestandard deviations between the runs are also shown. Asdescribed in the Experimental Section, the buses were drivenalong their regular routes, including stops, and the crankcaseand tailpipe emission samples were collected using an on-board dilution tunnel (6). Thus, the variations in PM, OC,and EC emission rates are expected, since they are highlydependent on driving modes, which were not standardizedbut varied according to actual traffic conditions. Two OC/EC measurements from Bus 1 tailpipe emissions sample wereinvalidated, due to a suspected leak during sampling, and

one PM value was lower than expected (4). Figure 1 illustratesthat the OC/EC ratio is very different for crankcase andtailpipe emissions; while OC dominates crankcase emissions,both OC and EC are important for tailpipe emissions withEC a larger contributor to PM than OC.

Figure 2 shows the OC and EC fractions for these samples.Carbon fractions in the IMPROVE method correspond totemperature steps of 120 °C (OC1), 250 °C (OC2), 450 °C(OC3), and 550 °C (OC4) in a nonoxidizing helium atmo-sphere, and at 550 °C (EC1), 700 °C (EC2), and 850 °C (EC3)in an oxidizing atmosphere. The IMPROVE TOR method usesvariable hold times of 150-580 s at each heating stage sothat carbon responses return to baseline values (7). As Figure2 shows, the crankcase emissions are composed mostly ofOC1 and OC2 fractions, whereas tailpipe emissions containall four OC fractions and EC1 and EC2 fractions.

All samples collected in the Bus 1 and 2 cabins containa higher proportion of OC than EC (see Table S2, SupportingInformation, average OC/EC ratio 7 and 4 for Bus 1 and 2,respectively), which is consistent with the observation (2–5)that the majority of the self-pollution in the bus cabins is notdue to tailpipe emissions.

Organic Tracer Emissions. Several classes of particle-associated organic compounds were analyzed for this study,including alkanes, n-alkylcyclohexanes, PAH, hopanes/steranes, and nitro-PAH (1-nitropyrene) as potential tracersfor crankcase and tailpipe emissions. The emission rates forindividual species and their in-cabin and lead-vehicleconcentrations are shown in the Supporting Information(Tables S1-S3).

Hopanes and Steranes. Hopanes and steranes are com-pounds present in crude oil as a result of the decompositionof sterols and other biomass and they are not byproducts ofcombustion (10). They have been used as molecular markersfor vehicle emissions and are higher in vehicles that emit oil(10–14). Figure 3 shows total hopane and sterane emissionsas a percentage of total carbon (TC ) OC + EC) measuredby the IMPROVE protocol. Only one valid sample wasavailable for TPB1, thus no standard deviations are shown.As expected, crankcase emissions contain a much higherproportion of hopanes/steranes than tailpipe emissions.

The in-cabin concentrations of hopanes and steranes(Table S2) support the conclusion that the majority of theself-pollution in the buses originated from crankcase emis-sions (3–5). These concentrations are much higher (by a factorof 4-9) when the buses are driven with closed windows thanwith open windows. In addition, as Figure S1 (SupportingInformation) shows, the total concentrations of hopanes andsteranes in background air (as measured by a lead vehicle,Table S3) are much lower than in-cabin concentrations withthe windows closed.

The lube oil and fuel samples from the two buses wereanalyzed for the same organic species (with exception of

FIGURE 1. Average crankcase (CK) and tailpipe (TP) fine PM,and organic (OC) and elemental (EC) carbon emission rates forBus 1 (B1) and Bus 2 (B2). Error bars are standard deviationsbetween the runs (only one valid OC/EC measurement forTPB1).

FIGURE 2. OC and EC fraction emission rates for crankcase(CK) and tailpipe (TP) samples. See text for definitions of ECand OC fractions.

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1-nitropyrene) as emission samples. Figure 4a and b showthe comparison of individual hopanes and steranes species,respectively, in the lube oil (in µg/g) and crankcase emissions(in µg/km) for Bus 1 and 2. The composition of hopanes andsteranes in crankcase emissions follow closely the lube oilcomposition. Although the concentrations of these species

are much lower in tailpipe emissions, their profiles areessentially the same (see Table S1).

Alkanes. n-Alkanes and n-alkylcyclohexanes constituteup to 1% of total carbon (TC)OC+EC) emissions, as shownin Figure 5. Deuterated n-hexatriacontane that was added tothe lube oil as an intentional tracer is much more abundantin crankcase than tailpipe emissions. Since no solid adsorbentwas used following the filter to account for the gas-phaseportion of semivolatile organic compounds (SVOC), onlyn-alkanes greater than C20 are shown, as those are pre-dominantly distributed to the particle phase. However, theconcentrations of alkanes from C14 up to C40 (includingbranched alkanes norfarnesane, farnesane, norpristane,pristane, and phytane) were measured in emissions and dieselfuel/lube oil, as shown in Table S1 (Supporting Information).

The concentrations of n-alkanes and n-alkylcyclohexaneswere also higher in the cabins of the buses driven withwindows closed than open, by a factor of 2-3 (Table S2).Also, the concentrations of n-hexatriacontane-d74 were muchhigher in the cabins of buses driven with windows closedthan measured by the lead vehicle (Table S3). The contribu-tion of the crankcase and tailpipe emissions to the bus self-pollution is discussed in our other papers (3–5).

Figure 6a and b compare the distribution of n-alkanesand n-alkylcyclohexanes, respectively, in the fuel and lubeoil obtained from both school buses after the sampling(the mean concentrations in fuel and lube oil are used). Theconcentrations of n-alkanes >C24 are not reported in thelube oil, since their identification is highly uncertain due tothe presence of the large hump, known as the unresolvedcomplex mixture (UCM) in the chromatograms, whichinterferes with the chromatographic separations of n-alkanesin the range of C25-C36. The UCM is due to the presenceof many higher molecular weight (mw) branched alkanesand alkylated cycloalkanes that have very similar massspectra. This complex mixture causes coelutions and theretention time shift of n-alkanes that is difficult to predict.It has been recently reported (15) that molecular sievetreatment of lube oil removes the superimposed UCM humpthus allowing the correct identification and quantificationsof n-alkanes in the range of C25-C36, that were otherwisegreatly overestimated.

As shown in Figure 6, the concentrations of alkanes andn-alkylcyclohexanes peak at nC14-nC16 and C7-C8-cyclo-hexanes, respectively, for diesel fuel, whereas for the lube oilthese concentrations peak at nC20-nC23 and C17-C18cyclohexanes, respectively. The n-alkane and n-alkylcyclo-hexane profiles for crankcase emissions resemble moreclosely the lube oil profile than tailpipe emission profile(Figure S2, Supporting Information). The carbon preferenceindex (CPI), defined as the ratio of the sum of the odd carbonnumber n-alkanes homologue to the sum of even carbonnumber homologue should be close to 1 for materials ofanthropogenic origin, such as fuel and oil. Consequently, forthe n-alkanes in the C14-C40 range, the CPIs are 0.81, 0.86,1.00, and 1.2 for fuel, oil, crankcase, and tailpipe emissions,respectively. The CPIs for in-cabin n-alkanes are 1.4 and 2.2for the buses driven with closed and open windows,respectively. For lead vehicle measurements, the mean CPIis close to 2. This indicates the contribution of outsideambient air to in-cabin concentrations when the bus windowsare open.

The concentrations of n-hexatriacontane-d74 in the lubeoil were 2.2 and 1.4 mg/g for Buses 1 and 2, respectively. Asmentioned in the Experimental Section, the oil from the firstbus was drained and reused for the second bus. Since someoil was left in the first bus and more lube oil was added tothe second bus, the concentration of n-hexatriacontane-d74

is lower for the second bus.

FIGURE 3. Total hopane and sterane emissions as a percentageof total carbon (TC) for crankcase (CK) and tailpipe (TP)samples. Error bars are standard deviations between the runs.

FIGURE 4. Comparison of individual hopanes (a) and steranesspecies (b) in the lube oil (in µg/g) and crankcase emissions(in µg/km) for Buses 1 and 2. The abbreviations are as follows:hop13 ) 18r(H)-22,29,30-trisnorneohopane; hop15 ) 17r(H)-22,29,30-trisnorhopane; hop17 ) 17r(H),21�(H)-29-norhopane;hop19 ) 17r(H),21�(H)-hopane; hop21 ) 22S-17r(H),21�(H)-30-homohopane; hop22 ) 22R-17r(H),21�(H)-30-homohopane; hop23)17�(H),21�(H)-hopane;hop24)22S-17r(H),21�(H)-30,31-bishomo-hopane; hop25 ) 22R-17r(H),21�(H)-30,31-bishomohopane; hop26) 22S-17r(H),21�(H)-30,31,32-trishomohopane; hop27 ) 22R-17r-(H),21�(H)-30,31,32-trishomohopane; ster42 ) 20S-5r(H),14r(H),-17r(H)-cholestane; ster43 ) 20R-5r(H),14�(H),17�(H)-cholestane;ster44 ) 20S-5r(H),14�(H),17�(H)-cholestane; ster45_40 ) 20R-5r(H),14r(H),17r(H)-cholestane and 20S-13�(H),17r(H)-diasti-gmastane; ster46 ) 20S-5r(H),14r(H),17r(H)-ergostane; ster47 )20R-5r(H),14�(H),17�(H)-ergostane; ster48_41 ) 20S-5r(H),14�-(H),17�(H)-ergostane and 20R-13r(H),17�(H)-diastigmastane;ster49 ) 20R-5r(H),14r(H),17r(H)-ergostane; ster50 ) 20S-5r-(H),14r(H),17r(H)-stigmastane; ster51 ) 20R-5r(H),14�(H),17�(H)-stigmastane; ster52 ) 20S-5r(H),14�(H),17�(H)-stigmastane;ster53 ) 20R-5r(H),14r(H),17r(H)-stigmastane.

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Polycyclic Aromatic Hydrocarbons. Since no solid ad-sorbent was used with the quartz filter, only 19 particle-associated PAHs and oxy-PAHs were quantified (see TableS1 for PAH emission rates). Figure 7 shows the crankcaseand tailpipe emissions of selected PAHs and oxy-PAHsexpressed as the percentage of total carbon and comparesthem with the average lube oil PAH concentrations. As canbe seen from this figure and Table S1, the abundance ofparticle-associated PAH is very low in both diesel crankcaseand tailpipe emissions. This is consistent with the previousreports (13, 14). However, more PAH species are present incrankcase than tailpipe emissions; only benzo(e)pyrene (BeP)and benzo(b), (j), and (k)-fluoranthanes (due to the coelutionproblem these three isomers are quantified together) areconsistently present in tailpipe emissions. In addition,benzo(c)phenanthrene (BcPh), benzanthrone, and ben-z(a)anthracene-7,12-dione (BaA-7,12-dione) are detected insome tailpipe emission samples. In contrast, all PAH speciesare consistently present (although in very low concentrations)in crankcase emissions.

The same PAH species were detected in the lubricatingoil samples from both buses, and their concentrations werehigher in the oil from Bus 2, as expected (since this oil was

already used once in the Bus 1). However, as Figure 8 shows,the PAH patterns in the crankcase emissions and lube oilsamples are not similar. The concentrations of the 19 PAHspecies in diesel fuel are negligible (see Table S1). Similarly,the in-cabin bus and lead vehicle PAH concentrations arevery low (Tables S2 and S3), although for Bus 2 theseconcentrations are significantly higher (by a factor of 3) whenthe bus windows are closed.

1-Nitropyrene. Because 1-nitropyrene is considered tobe a tracer for diesel emissions, it was quantified in crankcaseand tailpipe emission samples. It was not detected inquantifiable amounts in crankcase emissions, but it waspresent in tailpipe emissions. 1-Nitropyrene emission rateswere 0.34 and 1.0 µg/km for Bus 1 and 2, respectively. Similaremissions rates were reported for current technology dieselvehicles in the previous study (13). Since the sampling timewas short (30 min) it is likely that 1-nitropyrene is thecombustion product and not the artifact produced duringsampling on the filter (16). The lube oil and fuel sampleswere not analyzed for this compound; however it would berather unlikely to find it there. Although 1-nitropyrene wasdetected in several in-cabin bus and lead vehicle samples(Table S2 and S3), its concentrations were extremely low (inthe range of 1-2 pg/m3), and no consistent pattern wasobserved.

FIGURE 5. n-Alkanes and n-alkylcyclohexanes emissions as a percentage of total carbon (TC) for crankcase (CK) and tailpipe (TP)samples.

FIGURE 6. Distribution of n-alkanes (a) and n-alkylcyclo-hexanes (b), in the fuel and lube oil obtained from both schoolbuses. nCx ) n-alkane with x carbon numbers (i.e., nC14 )n-tetradecane); Cx-Cyhx ) Cx: n-alkyl with x carbon numbers,where Cyhx ) cyclohexane (i.e., C7-Cyhx ) n-heptylcyclo-hexane).

FIGURE 7. Comparison of crankcase (CK) and tailpipe (TP)emissions of selected PAHs and oxy-PAH from Buses 1 and 2(B1 and B2) expressed as the percentage of total carbon withthe average lube oil PAH concentrations. The abbreviations areas follows: BcPh ) benzo(c)phenanthrene; BaA ) benz(a)-anthracene; Chr/Tphe ) chrysene/triphenylene; 7-MeBaA ) 7-methylbenz(a)anthracene; BaA-7,12-dione ) benz(a)anthracene-7,12-dione; B(b+j+k)F ) benzo(b+j+k)fluoranthene; BeP ) ben-zo(e)pyrene; BaP ) benzo(a)pyrene; Per ) perylene; 7-MeBaP) 7-methylbenzo(a)pyrene; B(ghi)Per ) benzo(ghi)perylene;In[123-cd]P ) indeno[123-cd]pyrene; DB(ah+ac)A ) dibenzo-(ah+ac)anthracene; coronene.

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AcknowledgmentsFinancial support for this work was provided by the DOEOffice of Vehicle Technologies through the National Renew-able Energy Laboratory (Dr. James Eberhardt, Chief Scientist)and by the National Institute of Environmental HealthSciences (#1R01ES12657-01A1). We thank Mr. Mark McDanieland Mrs. Anna Cunningham of Organic Analytical Laboratoryof DRI for help in sample collection and analyses.

Supporting Information AvailableTables S1-S3 list the crankcase and tailpipe emission ratesof species measured during this study, and the detailedspeciations of in-cabin bus and lead vehicle samples. FigureS1 illustrates hopanes and steranes concentrations in buscabins and in ambient air. This information is available freeof charge via the Internet at http://pubs.acs.org

Literature Cited(1) U.S. EPA. Federal Register, 40 CFR, Parts 69, 80 and 86, January

18, 2001.(2) Hill, L. B.; Zimmerman, N. J.; Gooch, J. A. A Multi-city

Investigation of the Effectiveness of Retrofit Emissions Controlsin Reducing Exposures to Pariculate Matter in School Buses;Clean Air Task Force: Boston, MA, 2005 (available at http://www.catf.us/publications/view/82).

(3) Liu, L.-J. S., Webber W. L., Davey, M., Lawson, D. R., Ireson,R. G., Zielinska, B., Ondov, J. M., Weaver, C. S., Lapin, C. A.,Easter, M., Hesterberg, T. W., Larson, T. Estimating Self-Pollutionfrom Diesel School Buses Using Three Methods. submitted toEnviron. Sci. Technol.

(4) Ireson, R.; Ondov, J.; Zielinska, B.; Weaver, C.; Easter, M.; Lawson,D.; Hesterberg, T.; Davey, M.; and Liu, L-J.S. Development andDemonstration of a Dual Intentional Tracer Method forQuantifying In-Cabin Concentrations of Tailpipe and CrankcasePM2.5 in School Buses. Environ. Sci. Technol (in preparation).

(5) Larson, T., Webber, W., Zielinska, B., Ireson, R., Liu, L-J.S. Sourceapportionment of PM2.5 inside a diesel school bus: a comparisonof weighted partial least squares regression and chemical massbalance with a synthetic tracer-based method. Environ. Sci.Technol (in preparation).

(6) Weaver, C. S.; Petty, L. E. Reproducibility and accuracy of on-board emissions measurements using the RAVEM system;SAEPaper 2004-01-0965; SAE International: Warrendale, PA, 2004.

(7) Chow, J. C.; Watson, J. G.; Pritchett, L. C.; Pierson, W. R.; Frazier,C. A.; Purcell, R. G. The DRI Thermal/Optical Reflectance carbonanalysis system: Description, evaluation and applications inU.S. air quality studies. Atmos. Environ. 1993, 27A, 1185–1201.

(8) Chow, J. C.; Watson, J. G.; Crow, D.; Lowenthal, D. H.; Merrifield,T. Comparison of IMPROVE and NIOSH carbon measurements.Aerosol Sci. Technol. 2001, 34, 23–34.

(9) Wang, Z.; Fingas, M.; Li, K. Fractionation of a light crude oil andidentification and quantification of aliphatic, aromatic, andbiomarker compounds by GC-FID and GC-MS. Part II. J. Chro-matogr. Sci. 1994, 32, 367–382.

(10) Simoneit, B. R. T. Application of molecular marker analysis tovehicular exhaust for source reconciliation. Int. J. Environ. Anal.Chem. 1985, 22, 203–233.

(11) Rogge, W. F.; Hildemann, L. M.; Mazurek, M. A.; Cass, G. R.;Simoneit, B. R. T. Sources of Fine Organic Aerosol 2. Noncatalystand Catalyst-Equipped Automobiles and Heavy-Duty DieselTrucks. Environ. Sci. Technol. 1993, 27, 636–651.

(12) Fraser, M. P.; Cass, G. R.; Simoneit, B. R. T. Particle-Phase OrganicCompounds Emitted from Motor Vehicle Exhaust and in UrbanAtmosphere. Atmos. Environ. 1999, 33, 2715–2724.

(13) Zielinska, B.; Sagebiel, J.; McDonald, J. D.; Whitney, K.; Lawson,D. R. Emission Rates and Comparative Chemical Compositionfrom Selected In-Use Diesel and Gasoline-Fueled Vehicles. J.Air Waste Manage. Assoc. 2004, 54, 1138–1150.

(14) Fujita, E. M.; Zielinska, B.; Campbell, D. E.; Arnott, W. P.; Sagebiel,J. C.; Reinhart, L.; Chow, J. C.; Gabele, P. A.; Crews, W.; Snow,R.; Clark, N. N.; Wayne, W. S.; Lawson, D. R. Variations inspeciated emissions from spark-ignition and compression-ignition motor vehicles in California’s South Coast Air Basin.J. Air Waste Manage. Assoc. 2007, 57, 705–720.

(15) Caravaggio, G. A.; Charland, J.-P.; Macdonald, P.; Graham, L.n-Alkane profiles of engine lubricating oil and particulate matterby molecular sieve extraction. Environ. Sci. Technol. 2007, 41(10), 3697–3701.

(16) Schuetzle, D.; Perez, J. M. Factors influencing the emissions ofnitrated-polynuclear aromatic hydrocarbons (nitro-PAH) fromdiesel engines. J. Air Pollut. Control Assoc. 1983, 33, 751–755.

ES703065H

5666 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 15, 2008

1

Detailed Characterization and Profiles of Crankcase and Diesel Particular Matter Exhaust Emissions Using Speciated Organics.

Barbara Zielinska1*, David Campbell1, Douglas R. Lawson2, Robert G. Ireson3 , Christopher S. Weaver4 , Thomas W. Hesterberg5, Timothy Larson6, Mark Davey7 and L.-J. Sally Liu7,8

1Desert Research Institute, 2215 Raggio Pkwy, Reno, NV 89512-1095, 2National Renewable Energy Laboratory, Golden, CO 80401-3393, 3Air Quality Management Consulting, Greenbrae, CA 94904, 4Engine Fuel & Emissions Engineering, Inc., Rancho Cordova, CA 95742, 5International Truck and Engine Corporation, Warrenville, IL 60555, 6Department of Civil and Environmental Engineering, 7Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA 98105, 8Institute of Social and Preventive Medicine, University of Basel, CH-4051 Basel, Switzerland.

Supplemental Material

2

Details of Dilution Tunnel Sampling

Tailpipe and crankcase vent emissions testing was conducted using the Ride Along-Vehicle Emissions Measurement System (RAVEM) (1). RAVEM is a portable dilution tunnel based on proportional partial-flow constant volume sampling (CVS) from the vehicle exhaust pipe. Isokinetic sampling in the tailpipe and subsequent dilution produces a diluted exhaust stream comparable to that of full-flow CVS systems used in chassis and engine dynamometer testing, but allows measurements to be made on-board a moving vehicle (see http://www.efee.com/ravem.html for more information regarding RAVEM).For the tailpipe sampling, the RAVEM was mounted inside the bus, and the isokinetic partial-flow sampling was used (i.e. the normal RAVEM operating mode). To collect crankcase vent emission samples, the RAVEM dilution tunnel module was mounted on the front bumper of each bus, and the full flow from the road draft tube was ducted directly into the tunnel. A "road draft tube" is a tube (typically about 3/4 inch ID, made of rubber or steel) that carries gases from the rocker arm cover (near the top of the engine) vertically downward to near the bottom of the vehicle, where the end is exposed to the air. Its purpose is to ventilate the crankcase that is full of the hot lubricating oil that is being agitated by the motion of the pistons and crankshaft. Blowby gases that leak past the piston rings pass into the crankcase, where they mix with oil vapor and oil aerosol.From there, they pass via the road draft tube to the air under the vehicle. The venturi effect of air passing by the end of the tube creates a slight suction ("draft") that aids in the ventilation by drawing fresh air into the crankcase. For front-engine buses, the road draft tube discharge is typically about three feet forward (and thus directly upwind) of the firewall between the passenger compartment and the engine. This firewall has a number of penetrations, including those for the pedals and steering, that could allow air mixed with crankcase vapors to enter the passenger compartment.For crankcase sampling, we connected the end of the road draft tube to a liquid trap (a short section of 2 inch PVC pipe), then to a 1/2 inch ID rubber hose that was approximately 36 inches long. Purpose of the liquid trap was to collect any liquid that dripped from the road draft tube and prevent it from being drawn into the dilution tunnel.The other end of the rubber hose was connected to raw gas inlet of the RAVEM dilution tunnel. The throttle at the entrance to the dilution tunnel was adjusted to bring the pressure inside the tunnel slightly below atmospheric, thus simulating the slight suction due to the venturi effect on the end of the road draft tube. In operation, crankcase gases passed through the road draft tube and our sampling tube into the dilution tunnel, where they were mixed with filtered air. The tunnel control system was programmed to maintain a constant molar flow rate of 800 standard liters per minute out of the dilution tunnel. Pre-weighed 47 mm particulate filters were exposed to (1) the mixture of crankcase gas and filtered air and (2) the filtered air alone by drawing them through the filters at a controlled flow rate of 16.6 liters per minute. The filters were then reweighed to determine the PM mass collected on the filter, and from this, the PM mass contained in the crankcase emissions.

3

Table S1: Crankcase and tailpipe emission rates of measured species for Bus 1 and Bus 2 and these species concentrations in lube oil and diesel fuel used in these buses

CKB1 CKB2 TPB1 TPB2 Lube Oil FuelSpecies MnemonicAverage

St. Dev.a

Average

St. Dev.a

Average

St. Dev.a

Average

St. Dev.a

Oil B1 Oil B2 Aver age

PM2.5 (mg/km) 35.82 11.41 98.67 32.88 152.02 49.70 141.15 18.69OC (mg/km) 22.06 2.46 46.15 20.91 20.99 b 33.10 6.32EC (mg/km) 0.76 0.40 1.01 0.89 145.09 b 94.08 8.11Alkanes (microgram/km) Alkanes (microgram/g)Norfarnesane 2,6,10-C14 0.00 0.00 0.19 0.20 7.61 b 1.22 2.11 20.99 21.67 1209.4Heptylcyclohexane C7-Cyhx 0.00 0.00 0.37 0.36 0.00 b 5.46 6.55 0.79 0.23 513.43Farnesane 2,6,10-C15 0.42 0.41 1.18 0.82 6.20 b 2.58 4.47 1.70 0.34 1572.7Tetradecane nC14 1.07 0.69 8.38 5.07 0.00 b 36.83 35.48 29.15 16.35 4488.8Octylcyclohexane C8-Cyhx 0.00 0.00 0.48 0.67 0.00 b 3.18 5.51 1.85 0.72 330.89Pentadecane nC15 0.72 0.87 14.99 9.33 32.98 b 74.93 27.86 35.30 24.16 3557.0Nonylcyclohexane C9-Cyhx 0.21 0.36 0.82 0.64 0.00 b 0.27 0.46 4.38 1.28 383.70Hexadecane nC16 4.74 2.63 21.15 11.80 35.71 b 105.24 36.61 69.32 61.47 5355.5Norpristane 2,6,10-C18 1.42 2.00 9.38 5.27 4.94 b 36.52 33.03 25.22 21.71 2371.8Heptadecane nC17 5.63 8.08 42.31 24.72 84.67 b 316.47 134.2 126.78 105.68 4872.3Decylcyclohexane C10-Cyhx 0.16 0.15 2.06 1.34 0.00 b 10.05 4.34 4.95 2.08 311.73Pristane 2,6,10,14-C19 0.00 0.00 0.38 0.43 0.00 b 9.56 16.55 34.06 34.47 418.94Undecylcyclohexane C11-Cyhx 1.62 1.31 2.46 1.27 0.00 b 0.00 0.00 12.91 10.27 340.58Octadecane nC18 13.39 4.97 31.82 16.81 266.75 b 345.94 64.13 172.47 155.82 4587.9Phytane 2,6,10,14-C20 11.25 2.61 18.09 9.34 21.76 b 79.20 17.90 107.38 97.52 431.17Dodecylcyclohexane C12-Cyhx 2.53 0.70 3.80 2.07 3.28 b 16.26 7.93 21.44 20.05 356.97Nonadecane nC19 22.52 3.20 33.31 16.45 516.48 b 554.83 95.82 221.21 208.29 3911.8Tridecylcyclohexane C13-Cyhx 1.79 1.72 5.13 2.55 27.84 b 26.75 8.45 33.60 32.73 115.30Eicosane nC20 19.80 3.26 37.36 21.14 460.38 b 407.69 88.21 318.31 311.59 2983.9Tetradecylcyclohexane C14-Cyhx 2.52 2.81 8.87 3.12 11.49 b 11.56 1.18 103.86 104.36 156.15Heneicosane nC21 15.68 4.05 41.13 21.39 263.78 b 368.73 336.4 415.49 391.14 3737.7Pentadecylcyclohexane C15-Cyhx 10.84 2.31 19.83 7.94 0.00 b 33.72 18.01 262.02 248.69 77.45Docosane nC22 12.63 2.07 38.04 19.48 29.66 b 79.85 31.44 448.23 434.86 1600.6Hexadecylcyclohexane C16-Cyhx 5.04 3.53 15.75 15.59 2.70 b 7.56 3.49 251.64 251.22 31.87

4

CKB1 CKB2 TPB1 TPB2 Lube Oil FuelSpecies MnemonicAverage

St. Dev.a

Average

St. Dev.a

Average

St. Dev.a

Average

St. Dev.a

Oil B1 Oil B2 Aver age

Tricosane nC23 5.21 7.45 21.84 9.30 5.41 b 14.00 12.12 335.04 339.95 923.06Heptadecylcyclohexane C17-Cyhx 15.63 5.25 18.79 9.03 0.00 b 68.66 59.62 303.17 276.25 16.95Octadecylcyclohexane C18-Cyhx 2.18 0.65 7.38 7.20 0.00 b 0.23 0.41 318.09 251.03 5.82Tetracosane nC24 8.07 1.51 20.13 8.26 0.02 b 25.67 7.26 257.38 296.42 493.14Pentacosane nC25 8.90 2.64 17.70 20.25 10.52 b 10.47 14.51 UCM UCM 254.71Nonadecylcyclohexane C19-Cyhx 5.21 5.01 5.71 3.04 0.00 b 11.48 16.36 141.28 157.82 18.94Hexacosane nC26 4.61 1.01 23.75 23.09 0.00 b 1.64 2.85 UCM UCM 97.38Eicosylcyclohexane C20-Cyhx 0.78 0.45 2.08 1.53 0.00 b 1.20 2.08 128.03 137.39 0.19Heptacosane nC27 11.15 3.85 8.02 6.75 0.00 b 10.15 14.08 UCM UCM 41.96Heneicosylcyclohexane C21-Cyhx 2.95 1.81 2.72 3.30 0.00 b 0.49 0.84 UCM UCM 0.92Octacosane nC28 2.81 3.28 14.53 3.34 0.00 b 16.96 25.40 UCM UCM 20.44Nonacosane nC29 4.46 2.66 24.80 25.95 0.00 b 9.11 6.03 UCM UCM 12.55Triacontane nC30 12.64 1.31 15.57 16.93 0.00 b 1.92 1.83 UCM UCM 12.62Hentriacontane nC31 0.76 0.92 14.27 8.72 8.40 b 0.00 0.00 UCM UCM 7.60Dotriacontane nC32 1.11 0.29 4.52 3.44 0.00 b 0.00 0.00 UCM UCM 7.45Tritriacontane nC33 1.14 1.06 4.17 3.25 15.55 b 1.22 2.11 UCM UCM 4.05Tetratriacontane nC34 2.49 1.81 1.04 1.08 0.00 b 4.91 2.07 UCM UCM 4.83Pentatriacontane nC35 0.55 0.87 2.09 1.96 3.67 b 2.06 2.45 UCM UCM 1.17Hexatriacontane-d74 nC36d74 124.34 26.40 165.78 88.09 71.00 b 37.31 10.34 2198.2 1375.2 1.09Hexatriacontane nC36 0.16 0.04 0.00 0.00 2.03 b 0.00 0.00 UCM UCM 2.34Heptatriacontane nC37 0.13 0.13 0.13 0.09 0.29 b 0.26 0.46 UCM UCM 1.05Octatriacontane nC38 0.27 0.30 0.11 0.07 0.00 b 0.24 0.42 UCM UCM 2.39Nonatriacontane nC39 0.14 0.08 0.05 0.09 0.00 b 0.01 0.02 UCM UCM 0.59Tetracontane nC40 0.18 0.21 0.14 0.11 0.00 b 1.52 1.32 UCM UCM 1.19Hopanes (microgram/km) Hopanes (microgram/g)18α(H)-22,29,30-Trisnorneohopane

hop13 5.37 1.23 10.51 3.78 1.35 b 2.32 2.39 100.66 138.28 0.52

17α(H)-22,29,30-Trisnorhopane hop15 2.39 0.44 4.68 1.70 0.68 b 1.75 0.55 143.61 195.53 0.6517α(H),21ß(H)-29-Norhopane hop17 24.08 6.07 47.82 17.89 4.73 b 13.39 7.68 571.52 731.81 1.1917a(H),21ß(H)-Hopane hop19 12.77 2.51 24.67 9.22 4.06 b 7.85 4.90 300.02 386.12 0.9117ß(H),21α(H)-hopane hop20 1.39 0.42 2.60 1.07 0.00 b 0.76 0.80 18.84 24.56 0.1322S-17α(H),21ß(H)-30- hop21 8.91 2.04 17.12 6.29 2.03 b 4.83 3.39 200.93 248.68 0.52

5

CKB1 CKB2 TPB1 TPB2 Lube Oil FuelSpecies MnemonicAverage

St. Dev.a

Average

St. Dev.a

Average

St. Dev.a

Average

St. Dev.a

Oil B1 Oil B2 Aver age

Homohopane22R-17α(H),21ß(H)-30-Homohopane

hop22 7.00 1.86 14.33 5.40 0.00 b 3.82 2.89 162.65 188.05 0.35

17ß(H),21ß(H)-Hopane hop23 1.78 0.31 3.29 1.20 1.35 b 0.34 0.49 20.20 31.81 0.1422S-17α(H),21ß(H)-30,31-Bishomohopane

hop24 4.89 0.85 8.67 3.44 0.00 b 5.46 2.84 111.04 117.76 0.31

22R-17α(H),21ß(H)-30,31-Bishomohopane

hop25 3.59 0.67 6.30 2.79 0.00 b 0.79 1.38 72.02 77.57 0.23

22S-17α(H),21ß(H)-30,31,32-Trisomohopane

hop26 2.85 0.47 5.21 2.01 0.68 b 1.80 1.88 53.61 61.45 0.23

22R-17α(H),21ß(H)-30,31,32-Trishomohopane

hop27 2.16 0.35 3.68 1.45 0.00 b 2.57 2.62 41.77 41.52 0.15

Steranes (microgram/km) Steranes (microgram/g)20S-5α(H),14α(H),17α(H)-cholestane

ster42 0.42 0.15 0.83 0.30 0.00 b 1.01 0.50 35.06 38.03 0.59

20R-5α(H),14ß(H),17ß(H)-cholestane

ster43 2.80 1.05 5.66 2.77 0.71 b 1.85 1.29 96.19 138.39 0.66

20S-5α(H),14ß(H),17ß(H)-cholestane

ster44 3.42 0.91 7.24 2.93 1.35 b 2.28 1.47 75.71 96.98 0.35

20R-5α(H),14α(H),17α(H)-cholestane & 20S-13ß(H),17α(H)-diastigmastane

ster45_40 4.68 0.99 6.89 1.87 2.03 b 2.76 1.05 123.88 166.46 0.65

20S-5α(H),14α(H),17α(H)-ergostane

ster46 1.32 0.30 1.75 0.21 0.00 b 0.00 0.00 25.76 19.89 0.22

20R-5α(H),14ß(H),17ß(H)-ergostane

ster47 3.36 0.98 4.77 1.65 1.41 b 2.37 2.09 56.94 98.71 0.09

20S-5α(H),14ß(H),17ß(H)-ergostane & 20R-13α(H),17ß(H)-diastigmastane

ster48 2.59 0.70 6.02 2.24 0.68 b 1.04 1.22 103.85 155.44 1.41

20R-5α(H),14α(H),17α(H)-ergostane

ster49 2.44 0.36 4.40 1.53 0.71 b 1.24 0.45 41.25 51.09 0.14

20S-5α(H),14α(H),17α(H)-stigmastane

ster50 3.13 0.95 5.55 2.30 0.68 b 1.49 0.09 36.35 47.21 0.09

20R-5α(H),14ß(H),17ß(H)- ster51 5.01 1.20 9.48 3.77 1.38 b 2.99 0.91 129.12 150.57 0.35

6

CKB1 CKB2 TPB1 TPB2 Lube Oil FuelSpecies MnemonicAverage

St. Dev.a

Average

St. Dev.a

Average

St. Dev.a

Average

St. Dev.a

Oil B1 Oil B2 Aver age

stigmastane20S-5α(H),14ß(H),17ß(H)-stigmastane

ster52 3.26 0.76 6.13 2.36 0.68 b 1.25 0.48 94.51 114.24 0.22

20R-5α(H),14α(H),17α(H)-stigmastane

ster53 2.46 0.48 4.64 1.89 0.68 b 0.76 0.80 61.93 74.49 0.15

PAH (microgram/km) PAH (microgram/g)Retene Retene 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.11 0.08 0.22Benzonaphthothiophene BNapTph 0.04 0.00 0.09 0.04 0.00 0.00 0.00 0.00 0.98 0.57 0.22Benzo(c)phenanthrene BcPh 0.04 0.03 0.05 0.02 0.34 0.48 0.00 0.00 0.00 0.60 0.10Benz(a)anthracene BaA 0.12 0.14 0.05 0.05 0.00 0.00 0.00 0.00 0.19 0.11 0.12Chrysene-Triphenylene Chr/Tphe 0.04 0.07 0.10 0.04 0.00 0.00 0.00 0.00 0.60 1.36 1.53Benzanthrone Bzanthrone 0.09 0.05 0.24 0.21 0.34 0.48 0.00 0.00 0.64 2.27 0.217-methylbenz(a)anthracene 7-MeBaA 0.02 0.02 0.05 0.02 0.00 0.00 0.00 0.00 0.64 0.34 0.03Benz(a)anthracene-7,12-dione BaA-7,12-

dione0.31 0.23 0.30 0.10 0.35 0.49 0.06 0.05 1.21 1.28 0.28

5+6-methylchrysene 5,6-MeChr 0.04 0.00 0.09 0.10 0.00 0.00 0.00 0.00 0.00 0.91 0.05Benzo(b+j+k)fluoranthene B(b+j+k)F 0.19 0.10 0.06 0.04 0.69 0.01 1.01 0.50 0.42 0.34 0.05BeP BeP 0.09 0.10 0.05 0.04 0.34 0.48 0.74 0.05 0.00 0.26 0.08BaP BaP 0.06 0.04 0.03 0.01 0.00 0.00 0.00 0.00 0.19 0.57 0.02Perylene Per 0.13 0.12 0.12 0.09 0.00 0.00 0.00 0.00 0.30 0.19 0.029,10-dihydrobenzo(a)pyrene-7(8H)-one

9,10-DiHBz(a)P7on

0.22 0.16 0.06 0.00 0.00 0.00 0.23 0.41 0.30 0.83 0.01

7-methylbenzo(a)pyrene 7-MeBaP 0.05 0.02 0.04 0.02 0.00 0.00 0.00 0.00 0.00 0.08 0.01Benzo(ghi)perylene B(ghi)Per 0.18 0.02 0.06 0.03 0.00 0.00 0.00 0.00 0.00 0.26 0.01Indeno[123-cd]pyrene In[123-cd]P 0.10 0.12 0.02 0.02 0.00 0.00 0.00 0.00 0.19 0.45 0.01Dibenzo(ah+ac)anthracene DB(ah+ac)A 0.05 0.02 0.04 0.05 0.00 0.00 0.00 0.00 0.38 0.64 0.00Coronene Coronene 0.03 0.01 0.05 0.05 0.00 0.00 0.00 0.00 0.08 0.15 0.001-Nitropyrene (microgram/km) Npy 0.00 0.00 0.00 0.00 0.34 b 1.00 0.24 c c c

Notes:CK: cranckase emissions, TP: tailpipe emissions; B1: bus 1; B2: bus2; a: standard deviation between individual bus runs; b: only one valid measurement; c: not measured; UCM: unresolved complex mixture

7

Table S2. The in-cabin concentrations (in ng/m3, unless indicated otherwise) of species measured from bus 1 and bus 2 emissions

B1C_AMa

n=3bB1C_PMn=3

B1O_AMn=3

B1O_PMn=2

B2C_AMn=3

B2C_PMn=3

B2O_AMn=3

B2O_PMn=3

Species Mne-monic

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev

Average

StDev

Average

St.Dev.

OC (ug/m3) 14.6 0.98 20.7 2.28 14.4 4.28 6.48 0.54 23.1 2.61 16.4 0.77 6.47 0.48 9.39 0.76EC (ug/m3) 2.08 0.17 2.74 0.05 1.62 0.11 1.30 0.05 5.20 0.78 4.29 0.28 1.76 0.25 2.68 0.61Alkanes (ng/m3)Norfarnesane 2,6,10-

C141.80 0.57 4.28 1.46 2.12 0.66 3.15 2.23 0.00 0.00 8.20 4.30 0.19 0.11 8.75 2.76

Heptylcyclohexane C7-Cyhx

0.16 0.09 0.68 0.17 0.45 0.07 0.82 0.13 0.69 0.18 0.21 0.12 0.74 0.22 2.07 0.49

Farnesane 2,6,10-C15

0.29 0.17 3.94 2.28 0.00 0.00 0.45 0.32 0.61 0.26 6.62 3.82 8.98 4.36 11.1 6.43

Tetradecane nC14 1.20 0.63 0.31 0.18 0.00 0.00 1.60 1.13 0.00 0.00 6.79 1.96 0.81 0.46 0.00 0.00Octylcyclohexane C8-

Cyhx0.00 0.00 0.11 0.07 0.00 0.00 1.32 0.26 0.28 0.16 1.86 0.28 0.28 0.08 0.00 0.00

Pentadecane nC15 1.25 0.72 0.62 0.36 0.00 0.00 9.52 2.43 3.42 1.97 25.3 5.67 2.23 0.81 6.03 3.48Nonylcyclohexane C9-

Cyhx0.86 0.32 0.17 0.10 0.28 0.16 0.00 0.00 1.11 0.41 3.52 0.16 2.17 0.85 0.92 0.53

Hexadecane nC16 2.27 0.48 0.68 0.32 0.00 0.00 2.73 1.30 0.11 0.06 7.55 1.97 0.84 0.48 1.14 0.66Norpristane 2,6,10-

C180.16 0.09 0.03 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Heptadecane nC17 0.00 0.00 3.86 2.23 0.00 0.00 9.01 4.59 0.00 0.00 28.1 8.36 3.19 0.94 27.0 7.81Decylcyclohexane C10-

Cyhx0.68 0.20 0.26 0.10 0.88 0.29 2.03 0.12 1.06 0.02 0.59 0.19 0.93 0.16 2.06 0.14

Pristane 2,6,10,14-C19

0.73 0.38 19.2 9.93 21.4 12.1 2.94 0.81 79.5 4.61 47.3 24.9 1.73 0.50 41.7 22.6

Undecylcyclohexane C11-Cyhx

0.16 0.07 0.34 0.15 0.96 0.29 1.37 0.18 2.61 0.06 3.27 0.16 6.01 3.12 1.03 0.30

Octadecane nC18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.58 0.52Phytane 2,6,10,1

4-C200.52 0.26 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.12 0.07 3.04 0.33

Dodecylcyclohexane C12-Cyhx

0.05 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Nonadecane nC19 2.25 0.48 4.28 0.64 0.00 0.00 3.30 0.63 4.69 1.41 11.5 1.85 5.73 0.36 10.6 0.03

8

B1C_AMa

n=3bB1C_PMn=3

B1O_AMn=3

B1O_PMn=2

B2C_AMn=3

B2C_PMn=3

B2O_AMn=3

B2O_PMn=3

Species Mne-monic

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev

Average

StDev

Average

St.Dev.

Tridecylcyclohexane C13-Cyhx

2.82 0.34 2.27 0.68 1.69 0.50 0.29 0.05 1.69 0.40 0.69 0.07 0.87 0.22 1.09 0.22

Eicosane nC20 4.21 0.54 2.32 1.34 1.86 0.44 0.80 0.56 6.05 0.88 9.55 1.08 7.22 0.76 10.1 1.50Tetradecylcyclohexane C14-

Cyhx0.18 0.11 0.57 0.33 0.45 0.24 1.04 0.73 0.50 0.17 0.03 0.02 0.46 0.11 0.00 0.00

Heneicosane nC21 9.41 0.92 21.0 3.84 23.3 9.08 14.6 2.95 19.1 2.00 29.8 6.03 21.3 5.48 10.9 1.00Pentadecylcyclohexane C15-

Cyhx4.99 2.06 3.06 0.94 1.98 0.39 0.18 0.13 6.61 1.00 19.1 2.24 2.17 0.74 0.00 0.00

Docosane nC22 7.61 0.51 9.84 0.46 6.92 0.69 5.75 0.13 16.6 1.16 17.8 1.05 11.7 1.44 8.53 1.53Hexadecylcyclohexane C16-

Cyhx0.13 0.04 0.54 0.17 0.31 0.18 0.34 0.09 2.25 0.30 1.17 0.19 1.30 0.08 1.41 0.22

Tricosane nC23 20.2 0.54 26.9 3.26 6.72 0.38 7.43 1.20 27.4 2.06 35.1 2.24 10.2 1.49 5.54 1.64Heptadecylcyclohexane C17-

Cyhx2.64 0.80 12.8 2.06 11.3 3.28 7.07 0.06 15.3 3.50 39.9 2.81 15.9 0.64 9.24 5.24

Octadecylcyclohexane C18-Cyhx

0.60 0.17 1.02 0.43 0.42 0.24 0.69 0.00 6.03 2.04 3.65 1.43 0.25 0.07 0.65 0.25

Tetracosane nC24 23.2 0.70 32.4 2.13 4.38 0.67 6.42 0.34 29.9 4.58 37.9 3.50 6.84 0.57 2.28 1.27Pentacosane nC25 32.2 2.73 39.5 5.04 5.39 0.43 5.01 0.61 29.5 5.33 31.6 0.47 3.84 1.08 1.90 1.01Nonadecylcyclohexane C19-

Cyhx5.33 0.41 7.12 0.84 0.93 0.29 1.90 0.25 9.33 0.78 10.9 1.28 2.42 0.27 3.59 1.04

Hexacosane nC26 22.5 2.54 20.2 2.68 0.93 0.28 4.56 0.49 25.3 4.18 25.7 3.59 2.29 0.95 2.23 0.70Eicosylcyclohexane C20-

Cyhx0.00 0.00 0.34 0.20 0.00 0.00 0.77 0.17 1.47 0.45 0.31 0.06 0.37 0.11 0.11 0.06

Heptacosane nC27 18.2 2.78 28.3 5.94 2.88 0.42 5.67 0.04 20.1 3.87 21.2 2.33 2.38 0.47 2.23 0.23Heneicosylcyclohexane C21-

Cyhx1.62 0.27 0.71 0.28 0.00 0.00 1.08 0.28 2.08 0.51 0.21 0.12 0.03 0.02 0.60 0.19

Octacosane nC28 13.8 2.74 13.6 2.28 3.02 0.29 0.61 0.02 13.8 2.79 14.2 1.70 0.81 0.13 1.30 0.43Nonacosane nC29 7.50 1.05 13.0 2.88 2.20 0.15 9.48 0.13 11.6 2.22 10.8 1.03 1.80 0.22 1.25 0.36Triacontane nC30 7.37 1.75 8.68 1.52 0.90 0.26 3.18 2.25 9.58 0.93 7.82 0.65 0.53 0.28 0.49 0.24Hentriacontane nC31 4.00 1.43 8.99 1.76 2.26 0.55 3.22 0.55 8.75 2.56 8.14 0.91 1.46 0.28 3.15 0.63Dotriacontane nC32 2.17 0.84 1.81 0.74 0.11 0.07 1.34 0.95 3.58 1.07 1.17 0.46 0.16 0.06 0.05 0.03Tritriacontane nC33 1.07 0.08 1.25 0.30 0.73 0.14 0.39 0.24 1.36 0.74 0.55 0.12 0.68 0.29 0.49 0.16Tetratriacontane nC34 0.68 0.22 0.54 0.11 0.25 0.12 0.03 0.02 0.44 0.19 0.17 0.07 0.00 0.00 0.00 0.00

9

B1C_AMa

n=3bB1C_PMn=3

B1O_AMn=3

B1O_PMn=2

B2C_AMn=3

B2C_PMn=3

B2O_AMn=3

B2O_PMn=3

Species Mne-monic

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev

Average

StDev

Average

St.Dev.

Pentatriacontane nC35 1.39 0.43 0.71 0.04 0.40 0.12 0.29 0.20 0.42 0.15 0.00 0.00 0.00 0.00 0.00 0.00Hexatriacontane-d74 C36d74 33.5 5.95 39.3 7.80 1.78 0.25 1.21 0.26 56.2 9.11 22.9 3.41 6.29 1.25 6.63 0.84Hexatriacontane nC36 1.73 0.81 0.71 0.09 2.37 0.60 1.51 0.29 0.00 0.00 1.28 0.21 0.71 0.21 0.38 0.22Heptatriacontane nC37 0.00 0.00 0.17 0.06 0.00 0.00 0.03 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Octatriacontane nC38 0.13 0.08 0.23 0.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Nonatriacontane nC39 0.13 0.05 0.06 0.03 0.03 0.02 0.00 0.00 0.00 0.00 0.10 0.03 0.00 0.00 0.00 0.00Tetracontane nC40 0.08 0.03 0.28 0.08 0.08 0.03 0.00 0.00 0.03 0.02 0.00 0.00 0.00 0.00 0.00 0.00Hopanes (ng/m3)18α(H)-22,29,30-Trisnorneohopane

hop13 1.31 0.12 1.93 0.03 0.17 0.50 0.21 0.00 3.53 0.32 1.72 0.00 0.56 0.16 0.49 0.05

17α(H)-22,29,30-Trisnorhopane

hop15 0.50 0.09 0.71 0.02 0.03 0.27 0.05 0.00 1.72 0.09 0.90 0.00 0.22 0.04 0.22 0.03

17α(H),21ß(H)-29-Norhopane

hop17 6.19 1.03 8.22 0.08 0.51 2.44 0.63 0.04 17.2 1.57 7.69 0.05 1.83 0.75 2.34 0.32

17a(H),21ß(H)-Hopane hop19 3.92 0.73 4.74 0.02 0.28 1.28 0.34 0.02 9.30 0.98 4.65 0.02 1.02 0.43 1.41 0.2117ß(H),21α(H)-hopane hop20 0.39 0.09 0.54 0.00 0.00 0.20 0.03 0.02 1.06 0.12 0.41 0.02 0.06 0.07 0.05 0.0322S-17α(H),21ß(H)-30-Homohopane

hop21 2.25 0.46 3.09 0.05 0.17 0.86 0.24 0.06 6.36 0.64 3.14 0.07 0.65 0.28 1.03 0.08

22R-17α(H),21ß(H)-30-Homohopane

hop22 1.73 0.30 2.52 0.03 0.17 0.71 0.18 0.02 5.14 0.51 2.31 0.02 0.43 0.27 0.81 0.09

17ß(H),21ß(H)-Hopane hop23 0.55 0.09 0.65 0.03 0.06 0.18 0.05 0.00 1.30 0.13 0.45 0.00 0.15 0.14 0.27 0.0322S-17α(H),21ß(H)-30,31-Bishomohopane

hop24 1.99 0.27 1.62 0.08 0.37 0.43 0.21 0.04 3.36 0.40 2.00 0.05 0.37 0.11 0.71 0.03

22R-17α(H),21ß(H)-30,31-Bishomohopane

hop25 0.73 0.13 0.99 0.02 0.03 0.29 0.05 0.04 2.25 0.23 1.10 0.05 0.12 0.07 0.38 0.03

22S-17α(H),21ß(H)-30,31,32-Trisomohopane

hop26 0.68 0.16 0.99 0.02 0.11 0.32 0.05 0.00 1.97 0.28 0.96 0.00 0.19 0.12 0.38 0.06

22R-17α(H),21ß(H)-30,31,32-Trishomohopane

hop27 0.73 0.08 0.57 0.04 0.11 0.18 0.03 0.02 1.47 0.14 0.76 0.02 0.12 0.17 0.27 0.06

Steranes (microgram/km)20S-5α(H),14α(H),17α(H)-cholestane

ster42 0.08 0.05 0.26 0.02 0.03 0.07 0.18 0.02 0.31 0.12 0.28 0.02 0.06 0.04 0.11 0.03

20R-5α(H),14ß(H),17ß(H)- ster43 1.05 0.23 0.74 0.04 0.11 0.20 0.16 0.08 1.61 0.11 1.07 0.10 0.34 0.20 0.38 0.03

10

B1C_AMa

n=3bB1C_PMn=3

B1O_AMn=3

B1O_PMn=2

B2C_AMn=3

B2C_PMn=3

B2O_AMn=3

B2O_PMn=3

Species Mne-monic

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev

Average

StDev

Average

St.Dev.

cholestane20S-5α(H),14ß(H),17ß(H)-cholestane

ster44 1.07 0.14 1.22 0.02 0.14 0.39 0.18 0.02 2.42 0.17 1.28 0.02 0.37 0.11 0.38 0.03

20R-5α(H),14α(H),17α(H)-cholestane & 20S- 13ß(H)17α(H)-diastigmastane

ster45_40

1.28 0.23 1.62 0.03 0.20 0.44 0.29 0.02 3.14 0.28 1.86 0.02 0.46 0.17 0.43 0.06

20S-5α(H),14α(H),17α(H)-ergostane

ster46 0.31 0.07 0.43 0.00 0.00 0.07 0.00 0.00 0.92 0.13 0.45 0.00 0.03 0.07 0.11 0.03

20R-5α(H),14ß(H),17ß(H)-ergostane

ster47 1.96 0.21 1.84 0.04 0.37 0.30 0.66 0.05 1.89 0.28 0.72 0.07 0.09 0.09 0.11 0.06

20S-5α(H),14ß(H),17ß(H)-ergostane & 20R-13α(H),17ß(H)-diastigmastane

ster48 0.92 0.31 0.88 0.02 0.11 0.11 0.48 0.00 2.61 0.26 1.34 0.00 0.31 0.24 0.27 0.06

20R-5α(H),14α(H),17α(H)-ergostane

ster49 0.89 0.13 0.91 0.03 0.08 0.27 0.26 0.04 1.72 0.13 1.00 0.05 0.19 0.04 0.22 0.03

20S-5α(H),14α(H),17α(H)-stigmastane

ster50 0.84 0.19 1.05 0.02 0.06 0.28 0.18 0.02 1.94 0.17 0.93 0.02 0.25 0.09 0.27 0.06

20R-5α(H),14ß(H),17ß(H)-stigmastane

ster51 1.83 0.26 1.67 0.03 0.17 0.49 0.21 0.04 3.47 0.32 1.72 0.05 0.43 0.16 0.60 0.08

20S-5α(H),14ß(H),17ß(H)-stigmastane

ster52 1.05 0.14 1.11 0.02 0.06 0.31 0.11 0.00 2.19 0.22 1.10 0.00 0.25 0.09 0.33 0.05

20R-5α(H),14α(H),17α(H)-stigmastane

ster53 0.71 0.18 0.88 0.00 0.00 0.26 0.05 0.04 1.78 0.19 0.93 0.05 0.19 0.07 0.22 0.03

PAH (ng/m3)Retene Retene 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Benzonaphthothiophene BNapT 0.00 0.00 0.03 0.02 0.00 0.00 0.00 0.00 0.17 0.00 0.17 0.02 0.03 0.02 0.05 0.03Benzo(c)phenanthrene BcPh 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.06 0.03 0.00 0.00 0.00 0.00 0.00 0.00Benz(a)anthracene BaA 0.00 0.00 0.03 0.02 0.03 0.02 0.00 0.00 0.14 0.02 0.14 0.05 0.03 0.02 0.11 0.03Chrysene-Triphenylene Chr/Tp 0.03 0.02 0.06 0.02 0.00 0.00 0.08 0.06 0.72 0.11 0.45 0.05 0.03 0.02 0.16 0.09Benzanthrone Bzanthr 0.03 0.02 0.03 0.02 0.00 0.00 0.03 0.02 0.08 0.00 0.14 0.02 0.03 0.02 0.00 0.007-methylbenz(a)anthracene 7-

MeBaA0.00 0.00 0.03 0.02 0.00 0.00 0.00 0.00 0.03 0.02 0.03 0.02 0.00 0.00 0.00 0.00

Benz(a)anthracene-7,12- BaA- 0.13 0.02 0.34 0.12 0.00 0.00 0.07 0.00 0.14 0.03 0.21 0.06 0.00 0.00 0.00 0.00

11

B1C_AMa

n=3bB1C_PMn=3

B1O_AMn=3

B1O_PMn=2

B2C_AMn=3

B2C_PMn=3

B2O_AMn=3

B2O_PMn=3

Species Mne-monic

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev.

Average

St.Dev

Average

StDev

Average

St.Dev.

dione 7,12-dione

5+6-methylchrysene 5,6-MeChr

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.06 0.02 0.03 0.02 0.00 0.00 0.00 0.00

Benzo(b+j+k)fluoranthene B(b+j+k) F

0.39 0.03 0.48 0.09 0.23 0.02 0.21 0.04 0.81 0.11 0.66 0.07 0.40 0.07 0.38 0.08

BeP BeP 0.10 0.03 0.14 0.02 0.11 0.02 0.11 0.00 0.28 0.04 0.28 0.04 0.12 0.04 0.11 0.03BaP BaP 0.05 0.02 0.00 0.00 0.03 0.02 0.05 0.00 0.08 0.03 0.10 0.03 0.03 0.02 0.11 0.06Perylene Per 0.10 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.08 0.05 0.03 0.02 0.00 0.00 0.00 0.009,10-dihydrobenzo(a)pyrene-7(8H)-one

9,10-DiHBz(a)P-7-on

0.16 0.05 0.00 0.00 0.03 0.02 0.00 0.00 0.06 0.02 0.24 0.02 0.00 0.00 0.05 0.03

7-methylbenzo(a)pyrene 7-MeBaP

0.03 0.02 0.03 0.02 0.00 0.00 0.00 0.00 0.06 0.02 0.07 0.02 0.00 0.00 0.00 0.00

Benzo(ghi)perylene B(ghi)Per

0.10 0.02 0.14 0.04 0.11 0.02 0.11 0.00 0.33 0.05 0.07 0.02 0.25 0.05 0.27 0.11

Indeno[123-cd]pyrene In[123-cd]P

0.00 0.00 0.08 0.05 0.03 0.02 0.03 0.02 0.14 0.04 0.21 0.06 0.03 0.02 0.00 0.00

Dibenzo(ah+ac)anthracene DB(ah+ac)A

0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.02 0.06 0.02 0.03 0.02 0.03 0.02 0.00 0.00

Coronene Coronene

0.00 0.00 0.03 0.02 0.00 0.00 0.00 0.00 0.03 0.02 0.03 0.02 0.00 0.00 0.05 0.03

1-Nitropyrene (ng/m3) Npy 0.000 0.000 0.000 0.002 0.002 0.001 0.000 0.001 0.000 0.002 0.002 0.001 0.000 0.001 0.000 0.000

Notes: a: B1: bus 1; B2: bus2; C: window closed; O: window open; AM: morning sampling; PM: afternoon sampling; b: n=number of bus runsc: the average is weighted according to sampling volumes of each run

12

Table S3. Ambient concentrations of the bus emissions species, as measured by the lead vehicle

Species Mnemonic LVB1C_AM

LVB1C_PM

LVB1O_AM

LVB1O_PM

LVB2C_AM

LVB2C_PM

LVB2O_AM

LVB2O_PM

OC (ug/m3) 6.25 10.27 8.02 7.89 5.03 5.74 4.84 6.39EC (ug/m3) 1.03 1.40 1.11 0.69 0.85 1.04 1.08 1.26Alkanes (ng/m3)Norfarnesane 2,6,10-C14 0.00 9.90 1.52 0.00 3.54 0.00 23.58 0.54Heptylcyclohexane C7-Cyhx 0.00 1.16 0.17 0.68 0.11 0.72 23.01 0.22Farnesane 2,6,10-C15 0.00 0.13 0.06 6.75 0.70 21.53 0.21 2.48Tetradecane nC14 0.31 0.00 0.00 1.59 0.00 0.00 0.00 0.00Octylcyclohexane C8-Cyhx 0.00 0.00 0.28 3.80 0.00 0.00 1.06 0.00Pentadecane nC15 0.36 0.00 1.30 31.31 0.00 0.00 10.56 0.00Nonylcyclohexane C9-Cyhx 0.00 0.00 0.00 0.00 0.21 1.01 0.21 0.00Hexadecane nC16 0.00 0.00 0.00 8.23 0.00 0.00 4.22 0.00Norpristane 2,6,10-C18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Heptadecane nC17 0.00 0.00 0.00 43.79 0.00 0.00 4.79 10.88Decylcyclohexane C10-Cyhx 0.31 0.00 1.18 1.93 0.32 0.00 0.21 0.00Pristane 2,6,10,14-C19 0.00 2.44 1.69 6.86 0.00 0.00 3.66 0.00Undecylcyclohexane C11-Cyhx 0.83 0.13 0.00 1.70 1.13 1.08 2.75 1.83Octadecane nC18 0.00 0.00 0.00 0.00 0.00 0.00 0.63 0.00Phytane 2,6,10,14-C20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Dodecylcyclohexane C12-Cyhx 1.29 0.00 0.00 0.34 0.00 0.00 0.00 0.00Nonadecane nC19 0.88 0.00 0.56 9.36 0.00 1.87 14.00 1.40Tridecylcyclohexane C13-Cyhx 1.45 0.00 2.03 1.36 0.75 1.87 1.55 1.72Eicosane nC20 2.22 1.93 0.45 2.16 0.00 2.09 5.56 4.31Tetradecylcyclohexane C14-Cyhx 0.00 0.13 0.00 0.40 0.21 0.58 0.42 0.00Heneicosane nC21 5.11 8.61 4.06 43.28 25.28 38.23 14.78 3.23Pentadecylcyclohexane C15-Cyhx 0.05 4.76 2.42 0.68 0.48 0.86 0.77 0.00Docosane nC22 3.20 9.00 7.32 12.59 4.29 8.35 8.30 5.50Hexadecylcyclohexane C16-Cyhx 0.00 0.64 0.45 0.34 1.02 0.00 0.70 0.32Tricosane nC23 8.21 12.08 14.87 27.79 6.70 12.96 11.26 6.79Heptadecylcyclohexane C17-Cyhx 8.11 2.31 0.23 18.95 9.70 16.13 9.22 0.00Octadecylcyclohexane C18-Cyhx 0.00 0.64 0.51 0.96 0.00 2.66 0.00 0.00

13

Species Mnemonic LVB1C_AM

LVB1C_PM

LVB1O_AM

LVB1O_PM

LVB2C_AM

LVB2C_PM

LVB2O_AM

LVB2O_PM

Tetracosane nC24 7.39 9.13 10.03 18.32 5.52 7.99 9.08 1.40Pentacosane nC25 8.83 11.18 10.20 11.63 4.77 5.11 6.69 1.62Nonadecylcyclohexane C19-Cyhx 1.45 2.96 1.75 6.07 1.29 4.82 0.99 1.83Hexacosane nC26 3.87 3.86 3.32 12.71 1.98 7.63 2.53 0.32Eicosylcyclohexane C20-Cyhx 0.00 0.51 0.00 1.76 0.00 1.15 0.77 0.00Heptacosane nC27 5.94 5.27 4.68 7.83 2.09 3.46 2.53 0.65Heneicosylcyclohexane C21-Cyhx 0.00 0.26 0.00 1.36 0.00 0.14 0.00 0.00Octacosane nC28 4.60 7.20 6.59 6.47 4.93 5.40 2.25 3.77Nonacosane nC29 2.22 1.03 1.75 1.59 1.82 0.22 0.14 3.02Triacontane nC30 1.91 0.00 0.39 1.65 0.00 0.43 0.00 1.94Hentriacontane nC31 4.44 1.03 1.69 3.01 0.54 1.22 0.70 3.66Dotriacontane nC32 2.69 0.00 0.96 1.36 0.00 0.00 0.00 1.51Tritriacontane nC33 2.89 1.67 0.06 0.00 0.27 0.72 0.00 3.77Tetratriacontane nC34 1.19 0.26 0.00 0.00 0.00 0.00 0.00 0.00Pentatriacontane nC35 1.50 0.64 0.39 0.00 0.00 0.00 0.00 0.00Hexatriacontane-d74 nC36d74 0.00 0.00 0.00 0.00 0.05 0.00 0.00 0.00Hexatriacontane nC36 2.63 0.64 0.45 5.45 0.54 0.00 0.92 0.32Heptatriacontane nC37 0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00Octatriacontane nC38 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Nonatriacontane nC39 0.00 0.13 0.06 0.45 0.00 0.00 0.00 0.00Tetracontane nC40 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.00Hopanes (ng/m3)18α(H)-22,29,30-Trisnorneohopane hop13 0.16 0.00 0.11 0.17 0.05 0.14 0.00 0.0017α(H)-22,29,30-Trisnorhopane hop15 0.00 0.00 0.06 0.06 0.00 0.07 0.00 0.0017α(H),21ß(H)-29-Norhopane hop17 0.31 0.00 0.17 0.28 0.43 0.07 0.00 0.3217a(H),21ß(H)-Hopane hop19 0.16 0.00 0.00 0.17 0.32 0.07 0.00 0.1117ß(H),21α(H)-hopane hop20 0.00 0.00 0.00 0.06 0.00 0.00 0.00 0.0022S-17α(H),21ß(H)-30-Homohopane hop21 0.10 0.00 0.00 0.06 0.05 0.00 0.00 0.2222R-17α(H),21ß(H)-30-Homohopane hop22 0.00 0.00 0.00 0.11 0.00 0.07 0.00 0.2217ß(H),21ß(H)-Hopane hop23 0.00 0.00 0.00 0.06 0.05 0.07 0.00 0.1122S-17α(H),21ß(H)-30,31-Bishomohopane

hop24 0.10 0.00 0.06 0.23 0.11 0.07 0.00 0.54

22R-17α(H),21ß(H)-30,31- hop25 0.00 0.00 0.00 0.00 0.05 0.00 0.00 0.11

14

Species Mnemonic LVB1C_AM

LVB1C_PM

LVB1O_AM

LVB1O_PM

LVB2C_AM

LVB2C_PM

LVB2O_AM

LVB2O_PM

Bishomohopane22S-17α(H),21ß(H)-30,31,32-Trisomohopane

hop26 0.05 0.13 0.00 0.06 0.05 0.00 0.00 0.11

22R-17α(H),21ß(H)-30,31,32-Trishomohopane

hop27 0.00 0.13 0.06 0.06 0.05 0.00 0.00 0.11

Steranes (microgram/km)20S-5α(H),14α(H),17α(H)-cholestane ster42 0.05 0.00 0.06 0.45 0.05 0.14 0.07 0.0020R-5α(H),14ß(H),17ß(H)-cholestane ster43 0.16 0.00 0.06 0.45 0.11 0.07 0.07 0.0020S-5α(H),14ß(H),17ß(H)-cholestane ster44 0.00 0.00 0.06 0.11 0.11 0.14 0.07 0.0020R-5α(H),14α(H),17α(H)-cholestane & 20S-13ß(H),17α(H)-diastigmastane

ster45_40 0.16 0.13 0.11 0.34 0.16 0.14 0.07 0.11

20S-5α(H),14α(H),17α(H)-ergostane ster46 0.05 0.00 0.00 0.06 0.00 0.00 0.00 0.0020R-5α(H),14ß(H),17ß(H)-ergostane ster47 0.57 0.13 0.34 0.51 0.16 0.07 0.00 0.2220S-5α(H),14ß(H),17ß(H)-ergostane & 20R-13α(H),17ß(H)-diastigmastane

ster48 0.00 0.00 0.00 0.06 0.00 0.00 0.00 0.00

20R-5α(H),14α(H),17α(H)-ergostane ster49 0.05 0.13 0.06 0.11 0.05 0.00 0.00 0.0020S-5α(H),14α(H),17α(H)-stigmastane ster50 0.05 0.13 0.00 0.17 0.05 0.07 0.00 0.0020R-5α(H),14ß(H),17ß(H)-stigmastane ster51 0.10 0.13 0.11 0.11 0.16 0.07 0.07 0.1120S-5α(H),14ß(H),17ß(H)-stigmastane ster52 0.05 0.00 0.00 0.00 0.05 0.00 0.00 0.0020R-5α(H),14α(H),17α(H)-stigmastane ster53 0.00 0.00 0.00 0.06 0.00 0.00 0.00 0.00PAH (ng/m3)Retene Retene 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Benzonaphthothiophene BNapTph 0.00 0.00 0.00 0.00 0.05 0.00 0.00 0.00Benzo(c)phenanthrene BcPh 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Benz(a)anthracene BaA 0.00 0.00 0.00 0.06 0.00 0.14 0.00 0.00Chrysene-Triphenylene Chr/Tphe 0.00 0.00 0.00 0.00 0.05 0.07 0.00 0.11Benzanthrone Bzanthrone 0.00 0.00 0.00 0.00 0.05 0.07 0.00 0.007-methylbenz(a)anthracene 7-MeBaA 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Benz(a)anthracene-7,12-dione BaA-7,12-dione 0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.005+6-methylchrysene 5,6-MeChr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Benzo(b+j+k)fluoranthene B(b+j+k)F 0.21 0.39 0.28 0.40 0.27 0.50 0.21 0.22BeP BeP 0.10 0.13 0.11 0.11 0.05 0.22 0.07 0.00BaP BaP 0.05 0.13 0.06 0.06 0.05 0.00 0.00 0.00

15

Species Mnemonic LVB1C_AM

LVB1C_PM

LVB1O_AM

LVB1O_PM

LVB2C_AM

LVB2C_PM

LVB2O_AM

LVB2O_PM

Perylene Per 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.009,10-dihydrobenzo(a)pyrene-7(8H)-one 9,10-DiHBz(a)P-

7-one0.00 0.00 0.00 0.00 0.05 0.00 0.00 0.22

7-methylbenzo(a)pyrene 7-MeBaP 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Benzo(ghi)perylene B(ghi)Per 0.10 0.64 0.06 0.11 0.11 0.14 0.21 0.22Indeno[123-cd]pyrene In[123-cd]P 0.00 0.00 0.06 0.06 0.21 0.07 0.00 0.00Dibenzo(ah+ac)anthracene DB(ah+ac)A 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Coronene Coronene 0.00 0.00 0.00 0.06 0.05 0.07 0.00 0.001-Nitropyrene (ng/m3) Npy 0.01 0.00 0.00 0.00 0.01 0.01 0.00 0.01

Notes: a: LV: lead vehicle; B1: bus 1; B2: bus2; C: window closed; O: window open; AM: morning sampling; PM: afternoon sampling

16

0

10

20

30

40

50

60

B1C_AM

B1C_PM

B1O_AM

B1O_PM

B2C_AM

B2C_PM

B2O_AM

B2O_PM

LVB1C_A

MLVB1C

_PM

LVB1O_AM

LVB1O_PM

LVB2C_A

MLVB2C

_PM

LVB2O_AM

LVB2O_PM

ng

/m3

Total Hop Total Ster

Figure S1. Concentrations of hopanes and steranes in bus cabins and in ambient air as measured by the lead vehicle. B1: bus 1; B2: bus 2; C: window closed; O: window open; AM: morning sample; PM: afternoon sample; LV: lead vehicle

17

0

100

200

300

400

500

600

C14nC15

nC16nC17

nC18nC19

nC20nC21

nC22nC23

nC24nC25

nC26nC27

nC28nC29

nC30nC31

nC32nC33

nC34nC35

nC36nC37

nC38nC39

nC40

Oil

(ug

/g)

or

TP

B E

mis

sio

n r

ate

(ug

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)

0

5

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15

20

25

30

35

CK

B E

mis

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ate

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)

Oil TPB CKB

0

50

100

150

200

250

300

350

C7-Cyh

x

C8-Cyh

x

C9-Cyh

x

C10-C

yhx

C11-C

yhx

C12-C

yhx

C13-C

yhx

C14-C

yhx

C15-C

yhx

C16-C

yhx

C17-C

yhx

C18-C

yhx

C19-C

yhx

C20-C

yhx

Oil

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TP

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mis

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n R

ate

(ug

/km

)

02468101214161820

CK

B E

mis

sio

n r

ate

(ug

/km

)

Oil TPB CKB

Figure S2. Comparison of n-alkanes (upper panel) and n-alkylcyclohexanes (lower panel) in average crankcase (CKB) and tailpipe (TPB) emissions profiles from both school buses with lube oil (Oil) composition

18

References:

1. Weaver C.S. and Petty L.E. Reproducibility and accuracy of on-board emissions measurements using the RAVEM system. SAE International, 2004, SAE Paper No.2004-01-0965