First Results from the Oil Sands Passive Air Monitoring Network forPolycyclic Aromatic CompoundsJasmin K. Schuster, Tom Harner,* Ky Su, Cristian Mihele, and Anita Eng

Air Quality Processes Research Section, Environment Canada, Toronto, Ontario M3H 5T4, Canada

*S Supporting Information

ABSTRACT: Results are reported from an ongoing passive airmonitoring study for polycyclic aromatic compounds (PACs) inthe Athabasca oil sands region in Alberta, Canada. Polyurethanefoam (PUF) disk passive air samplers were deployed forconsecutive 2-month periods from November 2010 to June 2012at 17 sites. Samples were analyzed for polycyclic aromatichydrocarbons (PAHs), alkylated PAHs, dibenzothiophene and itsalkylated derivatives (DBTs). Relative to parent PAHs, alkylatedPAHs and DBTs are enriched in bitumen and therefore consideredto be petrogenic markers. Concentrations in air were in the range0.03−210 ng/m3, 0.15−230 ng/m3 and 0.01−61 ng/m3 for∑PAHs, ∑alkylated PAHs and ΣDBTs, respectively. Anexponential decline of the PAC concentrations in air with distancefrom mining areas and related petrogenic sources was observed. The most significant exponential declines were for the alkylatedPAHs and DBTs and attributed to their association with mining-related emissions and near-source deposition, due to their lowervolatility and greater association with depositing particles. Seasonal trends in concentrations in air for PACs were not observedfor any of the compound classes. However, a forest fire episode during April to July 2011 resulted in greatly elevated PAH levelsat all passive sampling locations. Alkylated PAHs and DBTs were not elevated during the forest fire period, supporting theirassociation with petrogenic sources. Based on the results of this study, an “Athabasca PAC profile” is proposed as a potentialsource marker for the oil sands region. The profile is characterized by ∑PAHs/∑Alkylated PAHs = ∼0.2 and ∑PAHs/∑DBTs= ∼5.

■ INTRODUCTION

The Athabasca oil sands Region (AOSR) in northern Alberta,Canada is the third largest bitumen deposit in the world,covering a mineable area about 4800 km2. The oil industry inthe area has been growing since mining activities started in1967. In 2012, the production was quoted as 1.9 million barrelsof crude oil per day. The recovery of the oil is done throughsurface mining of the bitumen, from which crude oil is extractedin upgrader facilities, and by steam-assisted gravity drainage.Important elements of the mining activities include opensurface mines, bitumen upgrader facilities, and waste storagefacilities such as isolated tailing ponds for containingcontaminated water used for bitumen extraction.1

Following the publications by Kelly et al. on the effects of theAOSR mining activities on the Athabasca River basin, theFederal Minister of the Environment convened the Federal oilsands Advisory Panel in 2010 to address pollution concernsfrom oil sands activities in Alberta.2,3 As a result of the panelfindings, it was decided to develop an environmentalmonitoring plan for the lower Athabasca River and tributaries.In 2011, Environment Canada released the Integrated oil sandsEnvironment Monitoring Plan, which focused on air quality,biodiversity and water quality in the Athabasca oil sands region.This was followed in 2012 by the release of the Joint Canada/

Alberta Implementation Plan on oil sands Monitoring (JOSM)by Environment Canada and Alberta Environment andSustainable Resource Development, which outlined a collabo-ration to phase-in monitoring activities.One of the early initiatives under the Integrated Monitoring

Plan was the establishment of a 17-site passive air samplingmonitoring network to measure polycyclic aromatic compound(PAC) concentrations in air. This network, which is now partof JOSM, uses passive samplers to address the logisticalchallenges associated with monitoring in this largelyundeveloped region. Passive air sampling is a convenient andcost-effective method to monitor air concentrations on a largespatial scale and in remote areas. PUF disk passive samplershave been previously used to monitor polycyclic aromatichydrocarbons (PAHs) in ambient air.4−10 During the initialstages of the oil sands passive sampling network, the PUF disksamplers were calibrated for a broader range of polycyclicaromatic compounds (PACs) against high volume samplers at a

Received: November 20, 2014Revised: January 13, 2015Accepted: January 20, 2015

Article

pubs.acs.org/est

Published XXXX by the American ChemicalSociety A DOI: 10.1021/es505684e

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subset of three sites. The results validated the samplingapproach for both gas-phase and particle-phase PACs.11

The PAHs are the most ubiquitous PACs and the mostwidely monitored. They are released into the environment fromcombustion processes (e.g., forest fire, heating, wasteincineration, traffic) and fossil fuels. PAHs are listed underthe United Nations Economic Commission for Europe(UNECE) Convention on Long Range Transboundary AirPollution (CLRTAP) and on the Priority Substances List underthe Canadian Environmental Protection Act as toxic pollutants.Certain PAH species are known for their toxicity and potentialto cause cancer and mutations.12 The alkylated PAHs arethought to be even more toxic than their parent com-pounds.3,133,13 Alkylated PAHs and dibenzothiophenes (in-cluding their alkylated derivatives, DBTs) are enriched inbitumen relative to the parent PAHs and therefore act asmarkers for emissions from petrogenic sources.14

Only a handful of published studies has investigated theenvironmental occurrence and fate of PACs in the AOSR. For

instance, Kelly et al. showed in a study on particulate PACs insnowpack and dissolved PAC concentrations in Athabasca rivertributaries, that there is a detectable impact from the miningindustry on the Athabasca river ecosystem.3 A study onsediment cores from lakes in the Athabasca oil sands by Kureket al. showed a significant increase of PACs, and especiallyalkylated PAH levels with increasing mining activities from the1960s to the present.15 Parajulee and Wania applied amultimedia model to assess available emissions data for PAHsassociated with mining activities and found that these emissionsdid not account for all sources of PAHs and resulted in modelunder-predictions to observed concentrations. They furtheridentified secondary emissions (e.g., emissions to air fromtailings ponds) as a key fate pathways for the PAHs.16

Evaporative emissions of PAHs from tailings were recentlyestimated by Galarneau et al.17

The aim of this study is to assess the spatial and eventuallythe temporal patterns for PACs in air in the AOSR and todefine a “baseline” concentration against which future levels can

Figure 1. Athabasca oil sands region is shown with the location of the passive air samplers and details on the local oil industry. Map details wereadded from information reported by Alberta Energy, Alberta Environment and MODIS.1,32,44

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be compared. Ultimately these data will contribute todeposition estimates for PACs in the AOSR. The results willalso be used to assess cumulative environmental effects and belinked with other process studies and modeling efforts underJOSM.

■ EXPERIMENTAL SECTIONMethod. Details for sampling media preparation, deploy-

ment and analysis are described elsewhere.11 In short, PUFdisks were cleaned with accelerated solvent extraction (ASE)using acetone, petroleum ether (PE) and acetonitrile prior todeployment and dried under nitrogen. PUF disks weredeployed in double-domed sampling chambers, identical tothose used in the GAPS (Global Atmospheric PassiveSampling) network.18 Samplers were exposed for consecutivetwo month periods at 17 sites (Figure 1, SupportingInformation (SI) Table 1). The monitoring sites that wereused in this study were based on an existing network of airsampling sites operated by the Wood Buffalo EnvironmentalAssociation (WBEA).19 Two field blanks were deployed duringeach period and duplicate samples were deployed at sites L05and L06.Prior to the extraction with ASE, the PUF disks were spiked

for recovery monitoring with a labeled standard mixture (d10-acenaphthene, d10-anthracene, d12-benz[a]anthracene, d12-chrysene, d12-benzo[b]fluoranthrene, d12-benzo[e]pyrene, d12-indeno[123-cd]pyrene, d14-dibenzo[ah]anthracene, d13-5-meth-ylchrysene, d10-benzo[b]naphtho[2,1-d]-thiophene, d13-5-methylchrysene, d10-benzo(b)naphtho(2,1-d)-thiophene, d12-2,6-dimethylnaphthalene, d12-triphenylene). Samples wereextracted using PE/acetone (75/25, v/v; 2 cycles). Sampleswere fractionated on a column (i.d. 0.9 cm, 4 g activated silica,2.5 g activated alumina and 2 g sodium sulfate) with 20 mL PE(Fraction 1: nonpolar, aliphatic compounds), with 25 mL PE/acetone (50/50, v/v) (Fraction 2: aromatic PACs) and with 20mL methanol (Fraction 3: oxygenated and nitrated PACs).Fractions were reduced to 1 mL using nitrogen blow down andspiked with 13C-phenanthrene prior to analysisSample extracts were analyzed using an Agilent 6890 series

gas chromatography (GC) system with a 5975 mass selective(MS) detector on a DB-XLB column (30 m, i.d. of 250 μm,0.25 μm film thickness). Samples were injected at pulsedsplitless mode and injector, source, and quadrupole were set to290 °C, 230 °C, and 150 °C respectively. The oventemperature program started at 60 °C, where it was held for1 min and then increased to 320 °C at 5 °C/min where it washeld for 10 min. PAHs, alkylated PAHs and DBTs weredetected by electron impact (EI) in selected ion monitoring(SIM) mode. The target compounds were the parent PAHsacenaphthylene (AL), acenaphthene (AE), fluorene (FL),phenanthrene (PHE), anthracene (AN), fluoranthene (FLT),pyrene (PY), benzo(a)anthracene (BaAN), chrysene (CHR),benzo(b)fluoranthene (BbFLT), benzo(k)Fluoranthene(BbFLT), benzo(a)pyrene (BaPY), perylene (PER), indeno-(1,2,3-c,d)pyrene (IP), dibenzo(a,h)anthracene (DahAN),benzo(g,h,i)perylene (BghiPER), the alkylated PAH retene(RET), the C1-, C2-, C3-, and C4-alkylated PAH groups fornaphthalene (NAP), FL, PHE/AN, FLT/PYR, BaAN/CHR/triphenylenes and DBTs.Quality Assurance/Quality Control. (a.). Data Analysis.

All data were recovery and blank corrected. Average surrogaterecoveries estimated from the labeled compounds spiked priorto extraction were (90 ± 40) %. The method detection limit

(MDL) was estimated as the average of the field blanks plusthree times the standard deviation (SD). Instrumentaldetection limits (IDL) and MDLs are reported in the SITable 2. It was found that 11% of the data was <IDL and 23%was <MDL. The values for parent PAHs, alkylated PAHs andDBTs found above the limit of detection were 69%, 59% and82% respectively. For the purpose of data analysis, values belowMDL were replaced by (2/3 × MDL).Effective air volumes and air concentrations were estimated

and adjusted for temperature following the process describedby Shoeib and Harner, while using a sampling rate of 5 m3/dayas determined in the initial calibration period of this study byHarner et al.11,20

(b.). Data Validation. i. Interlaboratory Calibration:Comparison between PAC data derived by Low-Resolution(LR) and High-Resolution (HR) GC/MS. The analysis ofalkylated PAHs and DBTs is considered challenging due tothe large number of isomers encompassed in each homologuegroup. Based on a study on diesel fuel and crude oil samplesZeigler and Robbat discouraged the use of low resolution (LR)GC/MS for the quantitative analysis of these compoundsbecause of possible overestimation due to matrix interference.21

To validate the analytical precision and accuracy of the PACanalysis performed by the Hazardous Air Pollutants (HAPs)laboratory, an intercalibration study was performed withMaxxam - Analytical Testing Laboratory. This allowed thecomparison between results gained from LR-GC/MS (HAPslab) and high resolution (HR) GC-MS (Maxxam). Theinterlaboratory study was performed on a PAC standard withdefined concentration and four unknown air samples. Results ofthe analyses (see SI Table 3) using the two methods were notsignificantly different in the paired t test (p > 0.05) for mostcompounds. We expect that the matrix effects in air samples areless pronounced than in petroleum samples such as diesel fuelsand crude oil, which were originally analyzed by Zeigler andRobbat.21 This may explain the relatively good performance of(LR) GC/MS for analysis of PACs in air sample extracts.

ii. Interlaboratory Calibration: Comparison between PACdata derived at HAPs laboratory and National Air PollutionSurveillance (NAPS) Network laboratory. A second inter-laboratory study was performed to assess comparability ofresults analyzed by the two Environment Canada laboratoriesinvolved in analysis of air samples. This included the NAPSlaboratory which analyzes high volume active air samples fromthree enhanced deposition sites and the HAPs laboratory thatanalyzes passive air samples.11 The interlaboratory study wasperformed for a NIST dust standard, two PAC standards withknown concentrations, and two air sample extracts. Satisfactoryagreement was found between laboratories and the results wereused to improve comparability of data generated by these twolaboratories. Further details are provided in SI Tables 4 and 5.

■ RESULTS AND DISCUSSIONPAC Concentrations in Air. The data set discussed in this

publication represents 172 samples collected at 17 sites over theperiod November 2010 to June 2012. Information on samplingperiods and dates are available in the SI. The sites aredistinguished as remote (R) and local (L) sites. Local sites areaccessible by road and tend to be closer to mining areas,whereas remote sites are mainly accessible only by helicopter.The concentrations in air for all PACs ranged from 0.08−370

ng/m3 across all sampling sites and sampling periods. For theseparate PAC groups the concentrations were in the following

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ranges: 0.03−210 ng/m3, 0.15−230 ng/m3 and 0.01−61 ng/m3

for PAHs, alkylated PAHs and DBTs respectively (Table 1, SITable 6−8). The average values for the PAHs, alkylated PAHsand DBTs observed at the individual sites are plotted in Figure2, whereas SI Figure 1 shows the statistical distribution for allreported sampling periods. Levels of ∑PAHs in the oil sandsregion are generally in the range of values reported for selectedEuropean and North American sites including urban/industrialsites such as Moscow, Russia (70 ng/m3), Chicago, IL, U.S. (85ng/m3) and Middlesbrough, UK (40 ng/m3).6,22,23 The NAPSnetwork reported somewhat lower average values for Calgaryand Edmonton of 12 ng/m3 and 9.2 ng/m3, respectively, for theyear 2010. The lower range of PAH levels monitored at themore remote sites in this study are comparable to and higherthan values reported at background sites such as SturgeonPoint, MI, U.S. (a “background” site in the Great Lakes area butimpacted by city of Buffalo, 8.3 ng/m3), Mace Head, Ireland(1.3 ng/m3) and Iceland (0.3 ng/m3). WBEA reported averagePAH concentrations in air at four sites in the AOSR (AMS 1 =L01, AMS 5 = L05, AMS 6 = L06, AMS 14 = L14) for 2011,which are in the same order of magnitude as the PAHconcentrations reported in this study.24

In contrast to PAHs that are emitted from a wide variety ofsources, most alkylated PAHs and DBTs are associated withpetrochemical pollution. They are also much less frequentlymonitored and reported in air compared to parent PAHs.Fraser et al. measured concentrations of selected alkylatedPAHs in Los Angeles, CA, U.S. in 1993 and reported values foralkylated naphthalenes (∼300/400/300/150 ng/m3 for C1/C2/C3/C4-NAP, respectively) that were more than an order ofmagnitude higher than the average concentrations monitored inthis study (13.6/10.3/6./5.2 ng/m3 for C1/C2/C3/C4-NAPrespectively).25 However, levels of the alkylated fluorenes(15.1/14.1 ng/m3 for C1/C2-FL respectively) in the LosAngeles study were similar to those reported in the oil sandsregion (5.1/4.8 for C1/C2-FL, respectively). The same is truefor the alkylated phenanthrene and anthracene groups (in LosAngeles 18.4/10.3/3.3/0.5 ng/m3 and in the oil sands 3.6/4.0/3.0/1.5 ng/m3 for C1/C2/C3/C4-PHE+ANT, respectively).For the higher molecular weight alkylated PAHs, higher

concentrations were found in the oil sands (1.3/1.6 ng/m3

for C1/C2-FLT+PYR and 1.8/2.4 ng/m3 for C1/C2-BTC,respectively) compared to Los Angeles (2.0/0.03 ng/m3 forC1/C2-FLT+PYR and 0.5/0.09 ng/m3 for C1/C2-BTCrespectively).Parent dibenzothiophene was monitored in the U.S. at an

urban site in Los Angeles and a remote site San Nicolas Islandwith reported levels of 6.3 ng/m3 and 0.3 ng/m3, respectively.25

Lim et al. reported urban air concentrations of dibenzothio-phene in Birmingham, UK in 1996 with an average of 0.3 ng/m3.26 This is in the range of the average concentration of 0.5ng/m3 observed in the current study. However, the general lackof published concentrations of alkylated PAHs and DBTs in airmakes it difficult to put the values observed in the AOSR into abroader global context.Figure 2 shows levels of the different PAC classes with

increasing distance from site L11 which is designated torepresent the main mining-related source region, following theapproach by Kelly et al.2 Site L11 is identical to the WBEA airmonitoring site Lower Camp (AMS 11). This site is close tothe Athabasca River and upwind from an upgrader facility andan open pit mining site. There are several tailings ponds within∼6 km of site L11, which may represent substantial emissionsources of PACs.16,17 PAHs (Figure 2a) exhibit fairly consistentconcentrations in air across the region and only a modest drop-off in concentrations for the more distant sites. This reflects thewidespread nature of PAH sources across the region coupledwith the ability of PAHs to be transported effectively in air.Furthermore, most of the PAH burden resides in the gas-phaseand is therefore prone to long-range transport, versus theparticle-phase that is more subject to deposition from air. Incontrast to the PAHs, the alkylated PAHs and DBTs showstronger declines with distance from site L11. These PACclasses are less volatile and have a greater association with theparticle-phase and so will be less efficiently transported in air.25

They are also mainly associated with petrogenic/miningsources and therefore exhibit elevated concentrations in aircloser to mining sites and related sources.The exponential decline of oil sands related pollutants with

the distance from a major source in the oil sands was noted

Table 1. Average and Range of Concentrations in Air for PAHs, Alkylated PAHs and DBTs Covering the Period November2010 to June 2012

∑PAHs [ng/m3] ∑alkylated PAHs [ng/m3] ∑DBTs [ng/m3]

site ID average ± SD range average ± SD range average ± SD range

L01 15.1 ± 13.9 3.8−49.0 86.2 ± 41.2 20.9−138 8.9 ± 5.1 2.5−20.0L04 18.4 ± 28.7 1.8−88.7 76.4 ± 52.6 9.4−167 4.2 ± 3.5 0.1−11.0L05 14.9 ± 11.0 1.4−43.2 95.3 ± 43.8 0.9−164 11.9 ± 5.6 0.3−25.6L06 16.9 ± 15.5 1.6−64.3 70.0 ± 37.7 5.8−150 5.8 ± 4.0 0.1−14.5L09 22.6 ± 26.6 2.3−90.1 93.5 ± 50.7 15.9−181 8.2 ± 5.6 0.6−17.7L11 18.9 ± 10.3 1.6−34.6 131 ± 68.6 4.9−248 20.1 ± 14.6 0.0−41.5L13 8.7 ± 8.4 3.2−29.6 59.5 ± 37.3 21.0−139 5.0 ± 2.6 0.9−9.7L14 25.0 ± 26.6 2.5−73.7 45.6 ± 29.4 17.8−116 1.7 ± 1.2 0.1−3.6R01 6.8 ± 7.7 0.4−23.2 36.0 ± 33.7 3.6−93.6 5.4 ± 9.1 0.2−25.8R02 11.8 ± 18.3 3.2−60.0 42.3 ± 29.0 16.2−116 6.0 ± 3.9 0.8−12.6R03 6.5 ± 5.3 0.6−17.7 49.8 ± 62.4 3.3−220 4.0 ± 3.4 0.1−10.5R04 11.3 ± 11.9 1.0−42.2 71.4 ± 58.5 7.8−192 12.8 ± 15.2 0.5−38.4R05 10.0 ± 9.5 1.2−34.5 73.4 ± 62.7 5.2−225 11.8 ± 10.7 0.4−35.1R06 8.0 ± 4.5 4.1−13.9 68.9 ± 30.9 35.6−110 3.6 ± 1.5 2.2−5.0R07 4.5 ± 2.1 2.4−6.7 37.4 ± 20.5 14.7−54.7 4.9 ± 4.6 1.2−10.1R08 9.8 ± 11.4 1.2−36.8 43.3 ± 27.7 14.3−105 3.7 ± 2.5 1.1−8.0R09 7.0 ± 4.6 1.6−14.4 57.6 ± 48.0 11.1−152 4.5 ± 4.4 0.2−11.0

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previously in several studies including, inter alia: biomonitoringof PAHs using lichen samples, by Studabaker et al., PAHs insnowpack samples by Cho et al., heavy metals in snowpacksamples by Kelly et al. and snow deposition samples by Bari etal. (2014).2,27−29 These observations were attributed topreferential deposition of particle-bound species closer tosources. Studabaker et al. (2012) reported a more pronouncedexponential decline for PAHs in lichen samples than observedin the passive air samples in this study. This can be explained bythe known bias of lichens for sampling the particle phase,

whereas the passive air samplers accumulate particle and gasphase PACs at similar rates.11,30

It is possible that seasonality may impact the strength of thisexponential decline with distance from source as PACs shouldbe further dispersed from the source during the warmersummer months when partitioning shifts toward the gas-phase;though this effect could be counterbalanced by higher PACdegradation rates during the longer daylight hours in summerthat would limit the transport of gas-phase PACs.31

Variations in PAC Concentrations. In order to assess theimpact of the oil sands mining industry on the atmosphericPAC levels, other possible PAC sources have to be evaluated.Figure 3 shows the average PAH levels at all sites for theindividual sampling periods. The PAH concentrations in air areconsistent throughout the sampling periods, with the exceptionof substantially higher levels for the sampling periods P04 andP05 (from April−July 2011).32 During this period a forest fireevent was observed north of the major mining area (Figure 1).The most southern edge of the affected area was withinapproximately 1.5 km of Fort MacKay and the passive samplinglocations L01 and L09. The area impacted by the forest firesextended 140 km north of Fort MacKay with a total affectedarea of approximately 8000 km2 over a 4 month period. Themost northern sampling site R07 was destroyed by the forestfire. A number of smaller forest fires during this time periodimpacted regions to the east and south of the mining area.Contributions from forest fire emissions are evaluated bymonitoring retene (RET), which is often used as a marker forwood burning. The air concentrations for RET for the wholesampling period are plotted for all sites in SI Figure 2. The RETlevels for most sites were highly elevated during April−July2011. The total levels of alkylated PAHs and DBTs were notelevated during the forest fire event (SI Figure 3). AlkylatedPAHs are not stable at higher temperatures and are depleted incombustion processes, so forest fires are not expected tocontribute to elevated alkylated PAHs concentrations in air.33

Previous studies exploring seasonal trends of PAHs haveobserved higher concentrations during the colder wintermonths that is attributed to higher PAH emissions due toheating.34 Furthermore, shorter daylight hours in the winterreduce the photolytic degradation rate of PAHs. The currentstudy does not show substantially different concentrationsbetween PAC concentrations in winter and summer months(estimates for summer exclude the forest fire period). Thisindicates that inputs from domestic sources in the region arerelatively minor; or that seasonally varying sources balance eachother throughout the year (e.g., higher combustion in winterversus higher evaporation in summer).

Source Apportionment Using Compound Ratios. PAHratios are commonly used for source apportionment of PAHs,especially for the compounds fluoranthene (FLT), pyrene(PYR), benzo[a]anthracene (BaA), chrysene (CHR),indeno-[1,2,3-cd]pyrene (IP), and benzo[ghi]perylene (BghiP). Thisapproach has to be assessed critically as numerous factors maycomplicate source apportionment and generate misleadingresults. Sources of ambiguity include: uncertainties associatedwith low concentration data near the detection limits, variabilityin the atmospheric degradation rates among PAHs, anddifferences in gas-particle partitioning and deposition ratesthat can alter the PAH composition in air.35 However, despitethese caveats, there may be value in exploring PAH ratios acrossthe sampling network to assess relative differences and howthese ratios compare spatially across the sampling network.

Figure 2. Concentrations in air for all sampling periods for PAHs (a),alkylated PAHs (b), and DBTs (c) at the passive air sampling siteswith increasing distance from site L11. Site L11 is located in the areaof most intense mining activity. The drop-off in concentrations ofPACs with distance from site L11 is regressed using an exponential fit,following the approach of Kelly et al.2 The exponential fit wassignificant for all three chemical groups with p-values of 0.032, 0.005,and 0.017 for PAHs, alkylated PAHs and DBTs, respectively. (Site L14showed extreme PAH values during the summer months and isexcluded in the decline fit for PAHs.).

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This may yield insight regarding potential markers for oil sands-related emissions of PACs.The PAH ratios PHE/(PHE+AN), FLT/(FLT+PYR),

BaAN/(BaAN+CHR), and IP/(IP+BghiP) are commonlyused for source apportionment (i.e., to distinguish petroleumvs combustion sources).36 The ratios PHE/(PHE+AN), FLT/(FLT+PYR), BaAN/(BaAN+CHR), and IP/(IP+BghiP) weredetermined for all samples and were found to have an averageof 0.96 ± 0.08 (0.52−0.99), 0.54 ± 0.11 (0.24−0.90), 0.36 ±0.10 (0.07−0.81), and 0.39 ± 0.13 (0.002−0.91), respectively.Higher variability was observed for remote sites. This variabilitycould be associated with lower concentrations at these sites(i.e., greater analytical uncertainty) or a combination of longeratmospheric residence time and variable atmospheric process-ing of the PAHs. The PAH marker ratio values remainedrelatively constant at the individual sampling sites for all thesampling periods, that is, no variation was observed seasonallyor during the periods spanning the forest fires. However, theforest fire episode was expressed by a higher RET/(RET+CHR) ratio, which is considered a specific wood burningmarker.37 The average values of this ratio during periods P04and P05 were 0.96 and 0.97, respectively, which is very close topredicted wood combustion value of ∼1; whereas the averageratio for the nonforest fire periods was 0.84 ± 0.05 (0.79−0.90)(SI Figure 4).SI Figure 5 shows the variations for the PHE/(PHE+AN),

FLT/(FLT+PYR), BaAN/(BaAN+CHR), and IP/(IP+BghiP)ratios over the period of November 2010 − June 2012 for theindividual sites. While the observed average ratios for PHE/(PHE+AN) and BaAN/(BaAN+CHR) were relatively con-sistent for all sites, the ratios for FLT/(FLT+PYR) and IP/(IP+BghiP) increase with increasing distance from the source(designated by site L11) (R2 = 0.33, p = 0.02 and R2 = 0.38, p =0.01 respectively).We explore the use of PAH ratios further by considering the

volatility of a typical Athabasca crude oil. The PAH“fingerprint” of crude oil can shift depending on the area of

its origin. Yang et al. reported data for the PAH composition ofthe crude oil extracted from the Athabasca oil sands.38 Wetranslate this composition to an air profile (at equilibrium)using estimated vapor pressures (PL values) for fluoranthene(FLT), pyrene (PYR), benzo[a]anthracene (BaA), chrysene,indeno[1,2,3-cd]pyrene (IP) and benzo[ghi]perylene (BghiP)(SI Text 1).20,39 The following predicted “evaporative ratios”for crude oil are discussed:BaAN/(BaAN+CHR) = 0.02; SI Figure 5.b. shows the ratio

of BaAN/(BaAN+CHR) in the passive samplers arranged byincreasing distance from the main source region. The ratioobserved in the passive samples (0.29−0.45) does not varysubstantially with distance from the source region and is muchhigher than the predicted evaporative ratio for crude oil of 0.02.This finding suggests that this ratio has little value as an oilsands marker. The reason for the relatively high ratio observedin the passive samples is unclear; however, based on analysis ofpublished literature, Yunker et al. also reported a high BaAN/(BaAN+CHR) ratio of 0.2 that was attributed to petrogenicsources.36

FLT/(FLT+PYR) = 0.35; SI Figure 5.c. shows the ratio ofFLT/(FLT+PYR) in the passive samplers. There is a generaltendency for the ratio to increase with distance from the sourceregion, from a value of about 0.34 to about 0.6−0.7. Theaverage ratio for FLT/(FLT+PYR) observed at site L11 (0.34± 0.06) is in the range of values for petrogenic sources (<0.4)as suggested by Yunker et al.36 The increase in this ratio withdistance from the major source region may be partly due todifferent atmospheric lifetimes of FLT and PYR as discussed byTobiszewski and Namiesnik.40

IP/(IP+BghiP) = 0.43; finally, SI Figure 5.d. shows that theratio of IP/(IP+BghiP) in passive samplers is consistent withthis predicted evaporative ratio for Athabasca crude oil. Theobserved ratios in the passive samplers increase gradually fromabout 0.3 at near-source sites to about 0.45 at more distant,remote sites. We note that Yunker et al. suggested a ratio of<0.2 as indicative of petrogenic sources which is substantially

Figure 3.Mean concentrations of PAHs in air for all sites over different sampling periods. Higher levels during spring 2011 (in orange) are attributedto a period of forest fires in the region.

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lower than either the predicted evaporative ratio or the ratiosobserved in this study.36

In summary, although the interpretation of PAH ratios forsource apportionment should be treated with caution due tothe sources of uncertainty by this approach, we see some valuein exploring source attribution by this approach across ournetwork of sampling sites. Our findings have been able tocharacterize consistent changes in the PAH ratios (FLT/(FLT+PYR), IP/(IP+BghiP)) with increasing distance from site L11that is close to the center of petrogenic emissions associatedwith mining activities.In addition to exploring PAH ratios, the broader data set of

alkylated PAHs and DBTs in this study provides anopportunity to explore how the different classes of PACs varyspatially, and if ratios can be used to identify the oil sandssource. Some source apportionment and forensic studies havebeen carried out on sediment and soil contamination andusually target individual congeners.33,38,41 However, no studieshave measured all three classes of PACs in air across a regionalscale as in this current study, which provides an opportunity toexplore class-based ratios.Alkylated PAHs and DBTs are enriched in bitumen and

therefore markers for fossil fuel activities. The average ratios forPAHs/Alkylated PAHs and PAHs/DBTs for all sampling sitesduring the period from November 2010 to June 2012 were 0.22± 0.10 (0.10−0.42) and 5.09 ± 2.96 (1.60−11.1,) respectively.The ratios were consistent over the sampling period and at theindividual sites, with the exception of elevated ratios during theforest fire episode and at site L14. MODIS maps show fireactivity during the sampling period in close proximity to theupgrader located close to L14. The samples during theseperiods show higher levels for lower molecular weight PAHs,but there are no elevated RET levels, which suggest that theelevated PAH levels were not due to forest fires. This will befurther explored as more data becomes available. Based onthese results, we suggest that the ratios PAHs/Alkylated ∼ 0.2and PAHs/DBTs ∼ 5 are generally representative of theAthabasca oil sands mining region.We compare this “Athabasca profile” to a profile for another

industrial region associated with PAC emissions, in HamiltonHarbour, Ontario. The PUF disk passive air samplers weredeployed at several locations during the summer 2013 andanalyzed for the PACs in the HAPs lab using the same analysismethods as for the oil sands samples. The average ratios forPAHs/Alkylated PAHs and PAHs/DBTs in Hamilton Harbourwere 0.62 ± 0.10 and 17 ± 5.6, respectively (SI Figure 6).42,43

The ratios for Hamilton were relatively consistent among sitesbut clearly different from the average profile observed in theAthabasca oil sands. This finding suggests that the “AthabascaPAC profile” may be unique to the oil sands and useful as amarker of emissions from this large and important bitumensource region. Future work should compare the PAC signaturesfor a broader range of source types in other parts of Canada, asthese data become available, in order to further assess thepotential of the applicability of the “Athabasca PAC profile” as atool for source apportionment.

■ ASSOCIATED CONTENT*S Supporting InformationIndividual PAC data observed in this study, information on thesampling sites, statistical data and additional figures. Thismaterial is available free of charge via the Internet at http://pubs.acs.org/.

■ AUTHOR INFORMATIONCorresponding Author*Phone: +1 416 739 4837; e-mail: Tom.Harner@ec.gc.ca.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe thank WBEA support staff for logistical support. We alsothank EC staff, Pamela Martin and Glenn Barrett (WSTD,Hamilton Harbour samples), Jean-Pierre Charland and May Siu(ASTD) for their support.

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■ NOTE ADDED AFTER ASAP PUBLICATIONThere were errors in the average ratios presented in the lastparagraph of the article, and in Figure S6 of the SupportingInformation in the version of this paper published February 5,2016. The correct version published February 9, 2015.

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