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Atmospheric Environment 107 (2015) 262e272

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Atmospheric Environment

journal homepage: www.elsevier .com/locate/atmosenv

Quantification of PAHs and oxy-PAHs on airborne particulate matter inChiang Mai, Thailand, using gas chromatography high resolution massspectrometry

Christophe Walgraeve a, *, Somporn Chantara b, Khajornsak Sopajaree c,Patrick De Wispelaere a, Kristof Demeestere a, Herman Van Langenhove a

a Research Group EnVOC (Environmental Organic Chemistry and Technology), Department of Sustainable Organic Chemistry and Technology,Faculty of Bioscience Engineering, Ghent University, Belgiumb Environmental Chemistry Research Laboratory, Chemistry Department, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailandc Department of Environmental Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai, 50200, Thailand

h i g h l i g h t s

� A PTV GC high resolution mass spectrometry method was developed for oxy-PAHs and PAHs.� Accelerated solvent extraction was evaluated as an extraction technique.� Recoveries and matrix effects were evaluated for both oxy-PAHs and PAHs.� First concentration data for oxy-PAHs on PM10 in Chiang Mai, Thailand.� The level of

Poxy-PAHs (1.1 ng/m3) is significant when compared to

PPAHs (3.4 ng/m3).

a r t i c l e i n f o

Article history:Received 11 September 2014Received in revised form30 January 2015Accepted 19 February 2015Available online 21 February 2015

Keywords:Oxy-PAHsOPAHsPAHsPM10Chiang MaiGas chromatographyHigh resolution mass spectrometryPLEPressurized liquid extraction

* Corresponding author. Research Group EnVOC (EFaculty of Bioscience Engineering, Ghent University, C

E-mail addresses: Christophe.Walgraeve@GMail.co

http://dx.doi.org/10.1016/j.atmosenv.2015.02.0511352-2310/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

An analytical method using gas chromatography high resolution mass spectrometry was developed forthe determination of 16 polycyclic aromatic hydrocarbons (PAHs) and 12 oxygenated PAHs (of which 4diketones, 3 ketones, 4 aldehydes and one anhydride) on atmospheric particulate matter with anaerodynamic diameter less than 10 mm (PM10). The magnetic sector mass spectrometer was run inmultiple ion detection mode (MID) with a mass resolution above 10 000 (10% valley definition) andallows for a selective accurate mass detection of the characteristic ions of the target analytes. Instru-mental detection limits between 0.04 pg and 1.34 pg were obtained for the PAHs, whereas for the oxy-PAHs they ranged between 0.08 pg and 2.13 pg. Pressurized liquid extraction using dichloromethane wasevaluated and excellent recoveries ranging between 87% and 98% for the PAHs and between 74% and110% for 10 oxy-PAHs were obtained, when the optimum extraction temperature of 150 �C was applied.The developed method was finally used to determine PAHs and oxy-PAHs concentration levels fromparticulate matter samples collected in the wet season at 4 different locations in Chiang Mai, Thailand(n¼ 72). This study brings forward the first concentration levels of oxy-PAHs in Thailand. The median ofthe sum of the PAHs and oxy-PAHs concentrations was 3.4 ng/m3 and 1.1 ng/m3 respectively, whichshows the importance of the group of the oxy-PAHs as PM10 constituents. High molecular weight PAHscontributed the most to the

PPAHs. For example, benzo[ghi]perylene was responsible for 30e44% of the

PPAHs. The highest contribution to

Poxy-PAHs came from 1,8-napthalic anhydride (26e78%), followed

by anthracene-9,10-dione (4e27%) and 7H-benzo[de]anthracene-7-one (6e26%). Indications of thedegradation of PAHs and/or formation of oxy-PAHs were observed.

© 2015 Elsevier Ltd. All rights reserved.

nvironmental Organic Chemistry and Technology), Department of Sustainable Organic Chemistry and Technology,oupure Links 653, B-9000 Ghent, Belgium.m, Christophe.Walgraeve@UGent.be (C. Walgraeve).

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272 263

1. Introduction

There is an increasing awareness among scientists and policymakers of public health problems caused by exposure to airpollution. The World Health Organization (WHO) has defined airquality guidelines for key pollutants such as particulate matter(PM), ozone, nitrogen dioxide and sulfur dioxide (WHO, 2005). Forexample, the concentration of PM10, i.e. particulate matter with anaerodynamic diameter less than 10 mm, should be lower than 10 mg/m3 to be in accordancewith the annual meanWHO guideline value.However, attention should not only be focused on a reduction ofmass concentrations of particulate matter. For example, in Mexico,control strategies implemented by the government resulted indecreasing PM10 concentrations, but were not adequate for con-trolling mutagenic and carcinogenic compounds such as benzo[a]pyrene (Amador-Munoz et al., 2013). Therefore, it is of paramountimportance to amplify the knowledge on the chemical compositionof the particles, as the latter plays an important role in the observedtoxicity (Shiraiwa et al., 2012). This is a challenging task sinceairborne particulate matter can be considered as a complex matrixconsisting of both inorganic compounds like salts, metals,elementary carbon, and a diverse group of organic substances (e.g.alkanes, alcohols, fatty acids, polycyclic aromatic hydrocarbons(PAHs) and derivatives) (Mirante et al., 2013). Among the class oforganic compounds, PAHs have received the most attention so far(Ravindra et al., 2008a; Ball and Truskewycz, 2013). This is alsoexemplified by the incorporation of the limit value for benzo[a]pyrene (max 1 ng/m3) in the European legislation (Legislation,2004). Recently, however, there is a focus on the study of themore polar fraction of particulate matter, to which the group of theoxygenated PAHs (oxy-PAHs) belongs (Lintelmann et al., 2005,2006; Wingfors et al., 2011; Cochran et al., 2012; Delgado-Saboritet al., 2013; Manzano et al., 2013; Bandowe et al., 2014). It isproven that oxy-PAHs quinones participate in redox cycling,resulting in the formation of reactive oxygen species in the humanlung epithelial A549 (Shang et al., 2014). The latter authors stressthe importance of the quantitative determination of quinones onPM for evaluating the health effects.

In contrast to the PAHs, oxy-PAHs are not solely produced dur-ing incomplete combustion processes, but are also formed duringtransformation processes in which PAHs undergo photochemicalreactions or reactions with hydroxyl radicals, nitrate radicals andozone (Keyte et al., 2013). The pathways through which oxy-PAHsare formed in the atmosphere are not completely understood,and it is difficult to distinguish between the contribution of primaryand secondary sources (Eiguren-Fernandez et al., 2008).

It should be noted that the current knowledge of the oxy-PAHs isnot mature when compared to the PAHs, as illustrated by ourprevious review (Walgraeve et al., 2010). This can partially beexplained by the limited availability of analytical methods toanalyze oxy-PAH in complex matrices such as PM. The objectives ofthis study are twofold. The first goal is to develop a new andadvanced analytical method for the simultaneous analysis of boththe 16 US-EPA priority PAHs and 12 oxy-PAHs on atmosphericparticulate matter. Gas chromatography hyphenatedwithmagneticsector high resolution mass spectrometry (mass resolution above10 000 (10% valley definition)) was evaluated as a technique toquantify trace levels (lower pg/m3) of oxy-PAHs and PAHs incomplex PM solvent extracts. Programmed temperature vapor-ization injection (PTV) was chosen to avoid discrimination betweenlow and higher molecular weight compounds and the high reso-lution mass spectrometer was operated in multiple ion detectionmode (MID), to allow for a maximum selectivity and sensitivitytowards the target compounds. The different steps in the analyticalsequence are optimized and pressurized liquid extraction (PLE) is

evaluated as a quick and modern extraction technique. The secondgoal is to apply the developed method to PM10 samples collected inthe summer of 2011 in Chiang Mai, Thailand. Because the PAHs andoxy-PAHs could be determined in the same sample, relative ratioscould be calculated with high confidence and might be importantto improve our understanding in the atmospheric transformationof PAHs in the atmosphere. During summer, the high temperaturesand solar irradiation in Chiang Mai may create optimal conditionsfor the formation of oxy-PAHs.

2. Materials and methods

2.1. Chemicals

Information about the standards can be found in Supplementaryinformation.

2.2. Sample collection

Particulate matter samples were taken at 4 locations in the cityof Chiang Mai, Thailand, during the summer of 2011 (July): (i)Faculty of Pharmacy Chiang Mai University (PH), (ii) Kowit Tham-rong school (KW), (iii) Nakorn Ping Hospital (NP), and (iv) Mae FaekMunicipal (MF, background location). Sample details and amap canbe found as supporting information (Fig. S1). PM10 was sampled onnew quartz microfiber filters (8� 10 inch; baked at 550 �C for 2 hand held in a desiccator before use), using a High Volume PM10 AirSampler (Wedding and Associates Inc., USA) operating at a flow rateof 1130 l/min (24 h). The loaded filters were stored in individualaluminum bags at �20 �C until analysis.

2.3. Sample preparation

2.3.1. PLE extractionExtraction was carried out using an ASE350 apparatus (Dionex,

Amsterdam, The Netherlands). All extractions were performed in22 ml stainless steel extraction cells (equipped with PEEK seal ringsand Teflon O-rings). Prior to extraction, the extraction cells weredisassembled, sonicated in acetone (15 min), and put overnight inan oven (105 �C) in order to remove impurities. On the bottom ofthe cell, a glass fiber filter (27 mm, Dionex, Amsterdam, TheNetherlands) was inserted to remove particles and quartz filterdebris from the extract. One fourth of the PM10-loaded quartz filterwas reduced into parts (±25 mm2) and was mixed with 3.50 g ofdiatomaceous earth (ASE prep DE, Dionex, Amsterdam, TheNetherlands), after which the mixture was poured into theextraction cell.

Dichloromethane was used as the extraction solvent. Theextraction temperature (50 �C; 100 �C and 150 �C) was optimizedand finally a temperature of 150 �Cwas selected. The ASE extraction(between 10.3 and 11.7 MPa) was performed using three static cy-cles of 5 min, and with a rinse volume of 100% (total volume ofsolvent added after all static cycles, expressed as % of emptyextraction cell). After the extraction, the remaining solvent waspurged out of the extraction cell by a flow of nitrogen gas (90 s).

2.3.2. Extract reduction: evaporationThe PLE-extract was reduced in volume by means of a Syncore

Analyst (Büchi Labortechnik GmbH, Hendrik-Ido-Ambacht, TheNetherlands) evaporation system. The pressure program started at800 mbar and decreased in 2 mine650 mbar, and was further keptconstant. The vacuum pump (V-700, Büchi) was controlled by a V-855 vacuum controller (Büchi). The platform temperature was setat 50 �C and the orbital movement of the platform was set at300 rpm (eccentricity 4 mm). In order to reduce the sorption of

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272264

target analytes on the glass wall of the sample vessel, a FlushbackR12 module (Büchi) was mounted on the sample rack whichpartially condenses the vapor at the top of the sample vessel andcauses a continuous film of solvent on the glassware. The locallycooled appendix of the sample vessel (10 �C) enabled the evapo-ration to stop at a final volume of 1 ml. Finally, 1 mL of a mix of 7perdeuterated PAHs was added to the extract.

2.4. Separation and detection

The analysis of the reduced extract was performed on a Trace GCsystem (Thermo Finnigan, San Jose, USA) hyphenated to a ThermoFinnigan magnetic sector MAT95XP-TRAP mass spectrometer(Thermo Finnigan, Bremen, Germany).

2.4.1. GC analysisThe concentrated extract was injected in splitless mode via a

BEST PTV injector (Interscience, Louvain-la-Neuve, Belgium), inorder to avoid discrimination between lower and higher boilingtarget compounds. The base temperature was set at 28 �C. One mlwas injected into a 2 mm ID SKY baffled liner (Restek, Bellefonte,PA, USA) and was evaporated during 1 min at 50 �C. The temper-ature was then increased to 320 �C at a rate of 14 �C/s and was heldfor 5 min. Afterward, a cleaning step was implemented byincreasing the temperature to 350 �C at a rate of 14.5 �C/s, and washeld for 10 min (flow 50 ml/min).

Chromatographic separation was performed on a Restek Rxi-17Sil MS column (30 m; 0.25 mm ID; 0.25 mm; Interscience,Louvain-la-Neuve, Belgium). To protect the analytical column, a50 cm guard column was connected in front of the analytical col-umn (deactivated, 0.25 mm ID). The GC (Trace GC Ultra) oventemperature was initially set at 70 �C (2.5 min), and then heated to320 �C at a heating rate of 10 �C/min. The final temperature washeld for 15 min. The MS-transfer line was heated to 240 �C.

2.4.2. Selective accurate mass detectionAfter separation, compounds were subjected to Electron Ioni-

zation (EI; 70 eV). A perfluorokerosene mix, was continuouslyintroduced (1e2 ml per 24 h of analysis) into the source via a heated(150 �C) capillary leak. The mass fragments of the per-fluorokerosene were used as internal reference ions enabling ac-curate mass measurements.

The mass spectrometer was run in multiple ion detection (MID)mode with a mass resolution above 10 000 (10% valley definition).Perfluorokerosene fragments provide each MID window (retentiontime window in which the mass calibration takes place) with aspecific lock and calibration mass (Table S1). In every single MIDmeasurement cycle, i.e. the time between two consecutive mea-surements of the same ion, the instrument automatically carriesout an electric mass calibration taking these two reference massesas calibration points. This principle of high resolutionMIDwith tworeference masses in each MID window is necessary for accurate,selective and sensitive target compound analysis. Eleven MIDwindows were used. The number of data points over a chromato-graphic peak was higher than 10 in all cases.

2.5. Analytical method characteristics

The performance of the entire analytical method was evaluatedby 1) the instrumental characteristics such as linearity, inter andintraday-precision, instrumental detection and quantificationlimits (IDLs and IQLs); 2) the determination of the recovery of thetarget PAHs and oxy-PAHs; 3) the influence of the matrix on therelative response factors; and 4) the determination of (oxy-)PAHsconcentrations on SRM Urban Dust 1649b (NIST, Gaithersburg, MD,

USA).

2.5.1. Recovery of PAHs and oxy-PAHs from Urban Dust 1649bThe methodology used is schematically presented in Fig. 1

(n¼ 3� 4). A first extraction cell, containing diatomaceous earth(DA) and SRM 1649b (massPM¼±25 mg) was extracted using theoptimized PLE methodology. At the end of the concentration step,1 ml of the perdeuterated PAHs solution was added. After analysisthe relative peak area, i.e the ratio of the peak area of the analyte tothe peak area of its corresponding internal standard (see Table S2),was determined for each analyte (RPAPM).

In a second extraction cell, the SRM 1649b dust (masspre-spiked,PM) was additionally spiked with a PAHs and oxy-PAHs solution(containing known amounts: ±500 ng depending on the com-pound), and after analysis, the RPApre-spiked, PM was obtained. Anexperimentwas also conductedwere the spikingwas done onto thediatomaceous earth resulting in a RPApre-spiked, DA. The thirdextraction cell was processed like the other extractions, but aknown amount of PAHs and oxy-PAHs (±500 ng) was spiked intothe final extract and analyzed (RPApost-spiked). The recoveries fromparticulate matter, diatomaceous earth, REPM, and REDA are calcu-lated by Equations (1) and (2) respectively.

The effect of the matrix on the relative response factor, furtherdenoted as matrix effects (ME) is investigated by comparing themass spectrometric response (RPApost-spiked) of a known mass oftarget compounds in a matrix solution to the response in puresolvent (Equation (3)). All concentrations are corrected for bothrecovery and matrix effects.

REPM ¼ RPApre�spiked; PM � RPAPM � masspre�spiked; PM

massPM

RPApost�spiked � RPAPM � masspost�spiked

massPM

� 100 (1)

REDA ¼ RPApre�spiked; DA � RPAPM � masspre�spiked; DA

massPM

RPApost�spiked � RPAPM � masspost�spiked

massPM

� 100 (2)

ME ¼ RPApost�spiked � RPAPM � masspost�spiked

massPMRPAstandard

� 100 (3)

2.5.2. Detection characteristicsThe detector was calibrated using internal standard calibration

with 7 perdeuterated internal standards. Standards were analyzedbefore and intertwined with real sample extracts and relativesample response factors (RSRF: response factor of the compound(peak area/ng injected) divided by the response factor of the in-ternal standard) were determined and used for the calculation ofthe concentrations of the samples. The linearity (R2) and stability ofthe detector was investigated by a six point calibration. Intradayprecision was determined by acquiring three calibration curves atthe same day and by calculating the relative standard deviation(RSD) on the calibration curve’ slopes (n¼ 3). The interday preci-sion is defined as the RSD on the relative sample response factors ofa standard during a 5 week period.

Chromatograms and mass spectra were processed using XCali-bur software (Thermo Finnigan, version 2.07). Samples were pro-cessed using Extracted Ion Chromatograms generated using thecharacteristic monitored MID ion of the target compound. Criteriafor detection and quantification are based on a signal-to-noise ratio(S/N) of 3 and 10, respectively. Blank correction of the samples wasdone when the compound could be quantified in the blank extract.

Fig. 1. Schematic overview of the methodology used to determine recoveries of PAHs and oxy-PAHs. A: Extraction cell filled with 50 mg SRM 1649b and 4.5 g diatomaceous earth;B: Spiking of PAHs and oxy-PAHs (±500 ng); C: spiking of the concentrated extract with 1 ml perdeuterated PAHs solution; RPA: relative peak area; see Equations (1)e(3) for thecalculation methodology.

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272 265

3. Results and discussion

3.1. Method development: instrumental analysis

A comprehensive overview of the instrumental characteristics isgiven in Table 1. Regression analysis (statistical software SPSS 22,IBM) on the 6-point calibration curve showed a good linearity andcoefficients of determination (R2) higher than 0.997 (7H-benzo[de]anthracene-7-one) and 0.998 (benzo[k]fluoranthene, dibenz[a,h]anthracene) were obtained for respectively the group of the oxy-PAHs and PAHs. Intercepts with the Y-axis are not significantlydifferent from the origin (a ¼ 0.05). Intraday precision ranges from1% (naphthalene, fluoranthene) to 6% (chrysene) for the group ofthe PAHs. The intraday precision for the oxy-PAHs was slightlylower with RSDs between 6% (napthalene-1-carboxaldehyde, flu-orene-2-carboxaldehyde, phenanthrene-9-carboxaldehyde) and15% (pyrene-1-carboxaldehyde). Interday precision is lower thanintraday precision for all PAHs. Thirteen out of the 16 US-EPA PAHsshow a good interday precision of less than 10%. For 8 oxy-PAHs,RSDs less than 10% are obtained. The stability of the retentiontimes of the target analytes is high, with RSDs ranging from 0.04 to0.15% (n¼ 75) (Table S1).

Instrumental quantification limits less than 1 pg are obtainedfor 12 US-EPA PAHs. For example, the quantification limit fornaphthalene is determined at 0.1 pg, whereas for benzo[ghi]per-ylene it is 0.9 pg. For phenanthrene, anthracene, benzo[b]fluo-ranthene and benzo[k]fluoranthene the quantification limit issomewhat higher but is lower than 5 pg. The quantification limitsobserved for the oxy-PAHs are in the same range as for the PAHs.9H-Fluorene-9-one could be quantified at a level of 0.3 pg injected,whereas fluorene-2-carboxaldehyde could be quantified at 7 pg.The instrumental detection limits are similar to those observed byO'Connell and co-workers using GC-EI-MS (O'Connell et al., 2013).They determined detection limits of 9H-fluorene-9-one (0.2 pg),7H-benzo[de]anthracene-7-one (0.8 pg), benz[a]anthracene-7,12-

dione (0.9 pg), napthacene-5,12-dione (1.3 pg). However, thedetection limit for anthracene-9,10-dione (6.9 pg) is a factor of 70higher when compared to our study (0.1 pg). Detection limitsdetermined by Delgado-Saborit et al. (2013) using GCeMS arehigher than determined in our study, even after derivatization ofthe quinone oxy-PAHs to their diacetyl derivatives using zinc andacetic anhydride (Delgado-Saborit et al., 2013). For benz[a]anthra-cene-7,12-dione they found detection limits of 4 and 6 pg for thederivatized and underivatized compound, respectively, whereasthe detection limit in this study is a factor of 10e15 lower. Themethod developed by Albinet (Albinet et al., 2014) using GCnegative ion chemical ionization (NICI) MS gave similar detectionlimits, ranging between 6 fg (9H-fluorene-9-one) and 4.1 pg (10H-anthracene-9-one).

When comparing the determined detection limits with the re-sults obtained from our previous (Walgraeve et al., 2012) developedmethod using HPLC-APCI(þ)-HRMS it is found that the detectionlimits for benzo[de]anthracene-7-one (1.4 pg), pyrene-1-carboxaldehyde (1.3 pg), napthacene-5,12-dione (0.4 pg) andbenzo[a]anthracene-7,12-dione (0.4 pg) are a factor of 6, 100, 1300and 2300 lower with the current developed method. However, lowdetection limits (7e9 pg) were obtained with our HPLC-HRMSmethod for the benzo[a]pyrenedione isomers, which are prefer-ably analyzed by HPLC.

3.2. Method development: extraction temperature

In order to select the appropriate extraction temperature, 20 mgof SRM 1649b was extracted using three extraction temperatures(50 �C, 100 �C and 150 �C). The results are presented in Fig. 2 as therecovery ratio, i.e. the ratio of the relative peak area to themaximum relative peak area obtained for that compound (RPAmax).The extraction at 50 �C is clearly insufficient for most compoundswith 63% of the PAHs having a ratio less than 80%. For the oxy-PAHs,none has a ratio higher than 80% at 50 �C. The ratio increases by

Table 1Intraday precision (RSD of the slopes of the calibration curves), interday precision (RSD of the relative peak area of a standard), linearity (R2) and instrumental detection (IDL)and quantification limits (IQL) of the target PAHs and oxy-PAHs.

Intraday precision (n¼ 3)Average slope± SD (RSD)

R2 Interday precision (n¼ 33)Average RPA± SD (RSD)

IDL (fg, n¼ 18)Average IDL

IQL (fg,n¼ 18)Average IQL

PAHsNaphthalene 5.14± 0.03 (1) 0.9998 0.48± 0.03 (5) 39 131Acenaphthylene 2.39± 0.06 (3) 0.9996 0.19± 0.03 (15) 106 354Acenaphthene 1.42± 0.04 (3) 0.9996 0.11± 0.02 (14) 183 609Fluorene 1.93± 0.05 (3) 0.9995 0.14± 0.01 (7) 75 250Phenanthrene 4.82± 0.12 (3) 0.9996 0.41± 0.02 (4) 471 1570Anthracene 4.08± 0.09 (2) 0.9998 0.33± 0.02 (6) 669 2229Fluoranthene 4.13± 0.05 (1) 0.9996 0.33± 0.01 (4) 78 261Pyrene 4.52± 0.13 (3) 0.9998 0.38± 0.02 (4) 68 228Benz[a]anthracene 5.01± 0.19 (4) 0.9996 0.41± 0.03 (8) 78 261Chrysene 5.89± 0.35 (6) 0.9994 0.44± 0.04 (8) 73 243Benzo[b]fluoranthene 5.87± 0.21 (4) 0.9994 0.44± 0.03 (7) 1336 4453Benzo[k]fluoranthene 7.85± 0.14 (2) 0.998 0.55± 0.05 (9) 894 2980Benzo[a]pyrene 5.12± 0.10 (2) 0.9997 0.42± 0.02 (5) 177 590Dibenz[a,h]anthracene 3.57± 0.17 (5) 0.998 0.25± 0.03 (11) 209 696Indeno[1,2,3-cd]pyrene 4.69± 0.23 (5) 0.9998 0.34± 0.03 (10) 241 803Benzo[ghi]perylene 4.13± 0.09 (2) 0.9999 0.34± 0.03 (8) 275 917Oxy-PAHsNapthalene-1,4-dione 0.28± 0.02 (8) 0.9994 0.02± 0 (18) 243 811Napthalene-1-carboxaldehyde 0.62± 0.04 (6) 0.9994 0.05± 0.01 (17) 86 2879H-Fluorene-9-one 1.99± 0.14 (7) 0.9996 0.21± 0.01 (5) 83 276Fluorene-2-carboxaldehyde 0.46± 0.03 (6) 0.998 0.04± 0.01 (15) 2130 710110H-Anthracene-9-one 1.02± 0.07 (7) 0.998 0.09± 0.02 (21) 1494 4980Anthracene-9,10-dione 0.72± 0.08 (10) 0.9995 0.07± 0.01 (8) 101 3371,8-napthalic anhydride 0.48± 0.03 (7) 0.9994 0.04± 0 (9) 213 710Phenanthrene-9-carboxaldehyde 0.49± 0.03 (6) 0.999 0.04± 0 (6) 173 5767H-benzo[de]anthracene-7-one 1.56± 0.12 (8) 0.997 0.09± 0.01 (10) 1413 4709Pyrene-1-carboxaldehyde 0.91± 0.14 (15) 0.999 0.08± 0.01 (10) 1304 4347Benz[a]anthracene-7,12-dione 0.98± 0.09 (10) 0.998 0.04± 0 (9) 395 1317Napthacene-5,12-dione 0.98± 0.11 (11) 0.998 0.07± 0.01 (9) 419 1398

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272266

performing the extraction at 100 �C with ratios between 27%(naphthalene) and 85% (benzo[a]pyrene) for the PAHs, and be-tween 28% (naphthalene-1,4-dione) and 100% (pyrene-1-carboxaldehyde) for the oxy-PAHs. At 100 �C only 25% of the

Fig. 2. Recovery ratio (ratio of the relative peak area (RPA) to the maximum relative peak areand 150 �C) for target A) PAHs and B) oxy-PAHs.

PAHs had a ratio less than 80%, in contrast to 80 percent of the oxy-PAHs. It is clear that the maximum extraction efficiency for nearlyall compounds is obtained by using an extraction temperature of150 �C. Only the ratio of pyrene-1-carboxaldehyde (94%) was

a (n¼ 1) obtained for that compound (RPAmax) at different temperatures (50 �C, 100 �C

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272 267

slightly lower than 100% at the extraction temperature of 150 �C. Sothe extraction temperature of 150 �C is selected.

3.3. Method development: extraction recovery and matrix effect

The extraction recovery is one of the most important methodcharacteristics. The optimization of the extraction temperature wasdone by the evaluation of the recovery ratio, i.e a methodology tofind local maxima (but does not specify the actual recoveries). Theprocedure used to determine the actual recoveries is described inSection 2.5.1 and the results are presented in Table 2. For the PAHs,excellent recoveries between 87% (naphthalene) to 98% (benzo[a]pyrene) are obtained together with low RSDs between 3.6%(naphthalene) and 10.5% (chrysene). Recoveries of the PAHs spikedon diatomaceous earth were similar with values between 89%(fluorene) and 98% (acenapthene). Precision ranged from 0.1 to5.5%. For the oxy-PAHs, good recoveries between 74% (naphtha-lene-1,4-dione) and 110% (anthracene-9,10-dione) were obtained.Only for 1,8-napthalic anhydride and 10H-anthracene-9-one ratherlow recoveries of 14 and 29% were found, respectively. Recoveriesfrom diatomaceous earth showed similar recoveries between 77%(naphthalene-1,4-dione) and 107% (anthracene-9,10-dione) for allcompounds except for 1,8-napthalic anhydride (13%) and anthra-cene-9-one (26%). For PAHs the matrix effects (ME) are between76% (benzo[k]fluoranthene) and 97% (fluoranthene). For oxy-PAHsME values between 96% (anthracene-9-one) and 170% (fluorene-2-carboxaldehyde) are observed.

3.4. Method development: analysis of SRM 1649b

A certified reference material, SRM 1649b, was analyzed for thetarget compounds in order to evaluate the performance of thedeveloped analytical method. The results are graphically presented

Table 2Matrix effects (ME), recovery (%) of the target PAHs and oxy-PAHs spiked

Recovery on DA% (n¼ 2)

PAHsNaphthalene 94.8± 1.6 (1.6)Acenaphthylene 92.1± 3.2 (3.4)Acenaphthene 98.0± 1.2 (1.2)Fluorene 88.9± 0.5 (0.5)Phenanthrene 90.7± 0.1 (0.1)Anthracene 92.6± 1.1 (1.2)Fluoranthene 91.4± 0.2 (0.2)Pyrene 89.9± 1.2 (1.4)Benz[a]anthracene 90.9± 0.3 (0.3)Chrysene 91.8± 0.1 (0.1)Benzo[b]fluoranthene 90.1± 3.1 (3.5)Benzo[k]fluoranthene 96.2± 5.3 (5.5)Benzo[a]pyrene 94.1± 0.01 (0.01)Dibenz[a,h]anthracene 91.8± 1.3 (1.4)Indeno[1,2,3-cd]pyrene 90.3± 1.4 (1.6)Benzo[ghi]perylene 90.1± 2.7 (3)Oxy-PAHsNapthalene-1,4-dione 76.8± 1 (1.3)Napthalene-1-carboxaldehyde 92.6± 1 (1.1)9H-Fluorene-9-one 89.6± 0.03 (0.04)Fluorene-2-carboxaldehyde 89.3± 3.1 (3.5)10H-Anthracene-9-one 25.6± 4.2 (16.3)Anthracene-9,10-dione 107.1± 2.9 (2.7)1,8-Napthalic anhydride 12.8± 0.6 (4.5)Phenanthrene-9-carboxaldehyde 92.4± 1.2 (1.3)7H-Benzo[de]anthracene-7-one 88.7± 0.4 (0.4)Pyrene-1-carboxaldehyde 94.8± 4.6 (4.9)Benz[a]anthracene-7,12-dione 89.3± 3.3 (3.7)Napthacene-5,12-dione 94.6± 3.2 (3.4)

in Fig. 3. Obtained concentrations for the PAHs are in good agree-ment with the certified concentrations (NIST, 2009), showing rela-tive differences [(concNIST � concdetermined)/concNIST� 100]between 4% (benzo[b]fluoranthene) and 17% (dibenz[a,h]anthra-cene). Only for benzo[k]fluoranthene a relative difference of 25%was found. However, the certified concentrations were obtained at alower extraction temperature (100 �C) using Soxhlet or PLE,whereas our method consisted of a PLE extraction at 150 �C (100 �Cwas insufficient for our target compounds, see Section 3.2).Therefore, the obtained PAHs concentrations are also compared tothe concentrations obtained by Schantz and co-workers who haveused PLE extraction with toluene at 150 �C (they found no differ-ences in extraction recoveries between toluene and dichloro-methane) (Schantz et al., 2012). Lower relative differences between4% (benz[a]anthracene) and 15% (benzo[a]pyrene) are found for allcertified US-EPA PAHs when our results are compared to the studyof Schantz. For the other PAHs, lower concentrations than thereference values are obtained for acenapthene (0.12± 0.02 mg/kg)and fluorene (0.18± 0.02 mg/kg), whereas higher concentrationsare found for naphthalene (1.49± 0.27 mg/kg), acenapthylene(0.34± 0.03 mg/kg) and anthracene (0.85± 0.07 mg/kg). For theoxy-PAHs, the obtained results are in agreement with the infor-mation values for 9H-fluorene-9-one (1.35± 0.05 mg/kg), anthra-cene-9,10-dione (1.64± 0.08 mg/kg) and benz[a]anthracene-7,12-dione (3.50± 0.06 mg/kg) with relative differences of 1.4, 1.6 and3.6%, respectively. For 7H-benzo[a]anthracene-7-one a concentra-tion of 3.61± 0.23 mg/kg is obtained, which is higher than the in-formation value of 1.6 mg/kg provided by NIST. Other authors alsoobtained also higher values: 3.13± 0.40 mg/kg (Nocun and Schantz,2013), 4.46± 0.50 mg/kg (Layshock et al., 2010), 7.60± 0.31 mg/kg(Ekstrand-Hammarstrom et al., 2013), and 7.15± 0.53 mg/kg(Albinet et al., 2014). For 1,8-napthalic anhydride a concentration of43.43± 5.82 mg/kg is found, which is higher than the concentration

on diatomaceous earth (DA) and SRM 1649b (PM).

Recovery on PM% (n¼ 6)

Matrix effects% (n¼ 6)

87.1± 3.1 (3.6) 85.4± 8.5 (9.9)91.0± 7.6 (8.4) 91.6± 8.3 (9.0)93.2± 5.2 (5.6) 80.8± 3.43 (4.3)94.1± 6.4 (6.9) 87.0± 6.8 (7.8)92.7± 4.5 (4.8) 87.9± 5.3 (6.1)94.8± 4.2 (4.4) 79.1± 2.5 (3.2)93.0± 5.9 (6.3) 97.3± 4.8 (5.0)93.6± 6.4 (6.8) 89.1± 3.3 (3.7)97.4± 9.8 (10.0) 83.0± 5.0 (6.0)

97.3± 10.2 (10.5) 84.3± 4.1 (4.8)93.9± 7.2 (7.7) 85.3± 2.8 (3.3)93.8± 7.5 (8.0) 75.6± 3.2 (4.3)97.7± 5.9 (6.0) 83.9± 2.4 (2.9)95.1± 4.5 (4.7) 97.0± 2.3 (2.3)95.1± 5.6 (5.8) 93.5± 2.8 (3.0)95.0± 6.2 (6.6) 88.2± 2.2 (2.5)

74.4± 12.5 (16.8) 117.2± 10.1 (8.6)92.3± 4.7 (5.1) 118.4± 6.9 (5.9)91.4± 5.4 (5.9) 120.9± 6.9 (5.7)92.9± 6.1 (6.5) 170.3± 4.3 (2.5)28.8± 8.8 (30.5) 95.6± 19.1 (19.9)

110.0± 9.9 (9.0) 169± 15.1 (9.0)13.7± 1.1 (8.0) 137.8± 7.7 (5.6)93.6± 6.3 (6.7) 158.2± 4.1 (2.6)

97.4± 13.4 (13.8) 182.1± 6.9 (3.8)99.2± 9.7 (9.8) 155.6± 6.2 (4.0)94.6± 8.2 (8.6) 147.6± 6.3 (4.3)93.9± 6.1 (6.5) 157.1± 3.9 (2.5)

Fig. 3. Concentrations of target A) PAHs and B) oxy-PAHs in SRM 1649b determined by this method compared to certified (C), reference (R), or informative (I) values provided byNIST (NIST, 2009) and recent literature. (Ref. A: (Schantz et al., 2012); Ref. B: (Nocun and Schantz, 2013); Ref. C: (Layshock et al., 2010); Ref. D: (Delgado-Saborit et al., 2013); Ref. E:(Ekstrand-Hammarstrom et al., 2013); Ref. F: (O'Connell et al., 2013); Ref. G: (Albinet et al., 2014). [1]: chrysene þ triphenylene, [2]: benzo[b þ j]fluoranthene, [3]: dibenzo[a,h þ a,c]anthracene.

Table 3Repeatability (n¼ 5) and reproducibility for the target PAHs and oxy-PAHs. (P25:25 th percentile; P50: 50 th percentile; P75: 75 th percentile).

Concentration (pg/m3)Average±SD (RSD), n¼ 5

RSD (%) betweenfilters (n¼ 31)

P25 P50 P75

PAHsNaphthalene 130± 4 (3) 7 13 18Acenaphthylene 28± 2 (5) 4 8 19Fluorene 24± 2 (8) 6 13 18Phenanthrene 189± 5 (3) 4 9 14Anthracene 55± 2 (3) 5 7 13Fluoranthene 148± 4 (3) 3 7 14Pyrene 222± 24 (11) 2 6 9Benz[a]anthracene 115± 1 (1) 7 11 14Chrysene 183± 2 (1) 4 10 17Benzo[b]fluoranthene 418± 17 (4) 2 4 10Benzo[k]fluoranthene 228± 10 (5) 4 6 10Benzo[a]pyrene 499± 12 (2) 3 6 8Dibenz[a,h]anthracene 120± 5 (4) 5 10 14Indeno[1,2,3-cd]pyrene 1126± 11 (1) 4 6 10Benzo[ghi]perylene 2053± 16 (1) 5 6 8Oxy-PAHsNapthalene-1,4-dione 51± 6 (12) 5 10 17Napthalene-1-carboxaldehyde 42± 2 (5) 6 10 179H-Fluorene-9-one 77± 4 (5) 6 10 18Anthracene-9,10-dione 232± 4 (2) 2 6 131,8-Napthalic anhydride 844± 18 (2) 25 37 47Phenanthrene-9-carboxaldehyde 13± 2 (13) 9 22 327H-benzo[de]anthracene-7-one 279± 4 (1) 3 7 12Pyrene-1-carboxaldehyde 71± 4 (5) 6 13 20Benz[a]anthracene-7,12-dione 84± 3 (3) 4 6 13Napthacene-5,12-dione 72± 2 (3) 4 8 14

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272268

observed by Albinet and co-workers (Albinet et al., 2014) being0.17± 0.35 and 13.59± 3.28 for PLE extraction and the QuEChERSapproach respectively.

Napthalene-1,4-dione and naphthalene-1-carboxaldehyde isobserved at a concentration of 0.51± 0.05 mg/kg and0.44± 0.03 mg/kg respectively. Phenanthrene-9-carboxaldehydeand pyrene-1-carboxaldehyde is determined at 0.10± 0.01 mg/kgand 0.41± 0.06 mg/kg, whereas Albinet and co-workers (Albinetet al., 2014) found values of 0.050± 0.004 mg/kg and0.16± 0.02 mg/kg using PLE extraction. The napthacene-5,12-dioneconcentration (1.09± 0.04 mg/kg) is higher than determined byO'Connell et al. (2013) (0.72 mg/kg) but lower than that of Nocunand Schantz (2013) (1.25± 0.14 mg/kg) and Layshock et al. (2010)(2.2± 0.15 mg/kg). Fluorene-9-carboxaldehyde and antracene-9-one could not be quantified.

3.5. Method development: repeatability and reproducibility

The repeatability was checked by repeatedly injecting a partic-ulate matter extract (n¼ 5). The results are given in Table 3. TheRSD on the determined concentrations varied between 1% (7H-benzo[de]anthracene-7-one) and 13% (phenanthrene-9-carboxaldehyde) for the oxy-PAHs and between 1% (benz[a]anthracene, chrysene, indeno[1,2,3-cd]pyrene and benzo[ghi]per-ylene) and 11% (pyrene) for the PAHs.

Thirty-one sets of 2 quartz fiber filters, which were sampled atthe same time and location, were independently extracted andanalyzed. The comparison is presented in Fig. S2 (PAHs) and S3(oxy-PAHs) as scatter plots with the first bisector giving 100% cor-responding concentrations. The RSD of the determined concen-trations can be used as a quantitative measure of the

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272 269

reproducibility (Table 3). For example, for the PAHs 75% of the RSDsdetermined are lower than 8% for benzo[ghi]perylene and lowerthan 19% for acenapthylene. For higher molecular weight com-pounds the reproducibility is higher and thus RSDs are lower. Goodresults are obtained for the oxy-PAHs, given that 75% of thedetermined RSDs (n¼ 31) are lower than 20% for 10 oxy-PAHs. For7H-benzo[de]anthracene-7-one, 75% of the RSDs are even lowerthan 12%. Only for 1,8-napthalic anhydride and phenanthrene-9-carboxaldehyde RSDs are higher (only 25% of the RSDs (n¼ 30)are lower than 25% and 9% respectively).

3.6. Method application: case study in Chiang Mai, Thailand

The optimized method is applied to PM10 samples collected inChiang Mai, Thailand. An overview of the concentration of thesamples is given in Table S3. The results are shown in Fig. 4A asboxes for the

PPAHs and

Poxy-PAHs concentrations. The median

PPAHs concentration is a factor of 1.5 (PH; Faculty of Pharmacy),

1.7 (NP; Nakorn Ping Hospital) and 1.8 (KW; Kowit Thamrongschool) higher when compared to median

PPAHs concentration

(2.4 ng/m3) observed at Mae Faek Municipal (MF). The concentra-tions are in the lower range of the levels observed by Chantara,Pengchai and colleagues who found an average

PPAHs concen-

tration between 2.7 and 16.6 ng/m3 in the wet season (JuneeSep-tember) at several locations in the Chiang Mai and Lamphunprovince (Chantara and Sangchan, 2009; Chantara et al., 2009;Pengchai et al., 2009). The observed concentrations of benzo[a]pyrene are between 158 and 555 pg/m3, 63e461 pg/m3,58e518 pg/m3 and 194e391 pg/m3 for respectively the KW, MF, NP,PH site and are well below the EU target value of 1 ng/m3.

For theP

oxy-PAHs, a similar trend is found with the lowestmedian concentration observed at MF (0.9 ng/m3), whereas theconcentration at PH, NP and KWwas respectively a factor of 1.8, 1.3and 1.3 higher. This can be explained by the fact that MF is a remotelocation outside the city center, surrounded by rice fields and awayfrom direct emission sources. In Fig. 4B the ratio of the

Poxy-PAHs

toP

PAHs is given as boxes. The median ratio is the highest at thelocation PH (0.4) followed by location MF (0.3), location KW (0.2)and location NP (0.2). Although the

PPAHs and

Poxy-PAHs

Fig. 4. A: Concentrations (pg/m3) ofP

PAHs andP

oxy-PAHs (pg/m3) observed at the differand Mae Faek Municipal (MF, n¼ 26). Data from Faculty of Pharmacy Chiang Mai UniversityP

PAHs at the different locations. The box plots represent the 25, 50 (median) and 75 perc

concentration is lower at location MF when compared to otherlocations, a higher ratio is observed. This might be explained byolder air masses inwhich the PAHsmight undergo (photo)chemicaltransformation to oxy-PAHs compounds.

The contribution of the individual PAHs to theP

PAHs isinvestigated, showing a major contribution of benzo[ghi]perylene(30e44%; median: 36%), > indeno[1,2,3-cd]pyrene (17e27%; me-dian: 22%), > benzo[a]pyrene (4e12%; median: 9%) and > benzo[b]fluoranthene (4e10%; median: 7%). High contributions of benzo[ghi]perylene are also observed in Ho Chi Minh City, Vietnam (Hienet al., 2007); Bangkok, Thailand (Oanh et al., 2000); and KualaLumpur, Malaysia (Jamhari et al., 2014).

The dominant presence of high molecular weight compounds(Fig. 5) is indicative of a higher contribution of gasoline poweredvehicles. It was found by Perrone et al. (2014) that 5 and 6 ring PAHs(benzo[b þ j þ k]fluoranthene, benzo[aþe]pyrene, dibenzo[a,h]anthracene, benzo[ghi]perylene) accounted for 55% of the

PPAHs

in gasoline powered vehicles, whereas for Diesel cars this per-centage was only 15% (Perrone et al., 2014). This is explained by thelubrication oil in gasoline vehicles which absorbs and concentratesheavy molecular weight PAHs formed during combustion. ThesePAHs are finally released in the environment as a component ofunburned lubrication oil. The PAHs profile of Diesel car emissions issimilar to the content of Diesel fuel, and is characterized by lowmolecular weight PAHs (Perrone et al., 2014).

Diagnostic ratios are often used in literature for source appor-tionment, but should be used with caution since the PAHs patternmight alter during the transport from emission source to samplingpoint (Krumal et al., 2013). For example, the ratios can be affectedby the presence of atmospheric species (O3, �OH, NO2) or photolyticand thermal decomposition (Teixeira et al., 2012). The ratio of thesum of 9 major non-alkylated compounds (or combustion PAHs)(fluorene, pyrene benzo[a]anthracene, chrysene, benzo[b]fluo-ranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene) to the

PPAHs is indicative of PAHs

produced by combustion activities when it is close to unity(Tobiszewski and Namiesnik, 2012). The median ratio observed inour study was 0.9 (P25: 0.89; P75: 0.91). A median fluorene/(fluorene þ pyrene) ratio of 0.1 (P25: 0.09; P75: 0.11) is observed,

ent locations: Kowit Thamrong school (KW, n¼ 20), Nakornping Hospital (NP, n¼ 23)(PH) are not shown given the limited sample number (n¼ 3). B: Ratio of

Poxy-PAHs to

entiles. Whiskers are representing the 10th and 90th percentiles.

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272270

which is indicative of a contribution of gasoline powered vehicles(<0.5) (Ravindra et al., 2008b; Alves et al., 2012). The observedmedian ratio of benzo[b]fluoranthene to benzo[k]fluoranthene is1.88 (P25: 0.80; P75: 0.94) and indicative of a contribution of Dieselvehicles (Ravindra et al., 2008b).

The biggest contributors to theP

oxy-PAHs are 1,8-napthalicanhydride (26e78%; median: 51%), > anthracene-9,10-dione

Fig. 5. Concentration levels of the individual PAHs and oxy-PAHs. The box plots representpercentiles. The numeric data can be found in Table S2.

(4e27%; median: 10%) and > 7H-benzo[de]anthracene-7-one(6e26%; median: 14%). A possible explanation for the relativehigh contributions of 1,8-napthalic anhydride is the photochemicaldegradation of acenapthylene (which was never detected in ourstudy) (Barbas et al., 1994).

When the concentrations of oxy-PAHs are summed according totheir ring numbers (

Poxy-PAH2,

Poxy-PAH3,

Poxy-PAH4) and

the 25, 50 (median) and 75 percentiles. Whiskers are representing the 10th and 90th

Fig. 5. (continued).

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272 271

divided by the corresponding sum of PAHs concentrations with thesame ring number (

PPAH2,

PPAH3,

PPAH4) a site specific dif-

ference is observed. The ratioP

oxy-PAH2/P

PAH2 was for all sitessimilar with median values of 1 (P25: 0.9; P75: 1.1), 0.9 (P25: 0.8;P75: 1.1), 0.9 (P25: 0.7; P75: 1.1) and 1 (P25: 0.9; P75: 1) for KW,MF,NP, PH respectively. Also, for

Poxy-PAH4/

PPAH4 similar median

ratios are observed between all locations (KW: 0.6 (P25: 0.6; P75:0.7); MF: 0.7 (P25: 0.6; P75: 0.7); NP:0.7 (P25: 0.6; P75: 0.8); PH:0.7 (P25: 0.6; P75: 0.7)). This in contrast to the

Poxy-PAH3/

PPAH3

ratio which shows a higher median ratio of 6.0 (P25: 5.2; P75: 9.2)at the background MF location when compared to 3.2 (P25: 2.5;P75: 3.9), 3.9 (P25: 3.1; P75: 4.6) and 4.7 (P25: 4.3; P75: 4.7) forsites KW, NP and PH respectively. This might be caused by thedegradation of PAHs and the formation of oxy-PAHs during trans-port from emission source to the background location. The con-centration levels of individual oxy-PAHs (Fig. 5) are in accordancewith literature data for PM collected in the summer months. Forexample, Alam and co-workers observed average concentrations atWeybourne, England for naphthalene-1,4-dione (33 pg/m3),anthracene-9,10-dione (44 pg/m3), benzo[a]anthracene-7,12-dione(14 pg/m3) and napthacene-5,12 dione (15 pg/m3) (Alam et al.,2014). We observed median concentrations of 37 pg/m3, 118 pg/m3, 50 pg/m3 and 47 pg/m3 respectively. At a background locationclose to Douai, France, average concentrations for anthracene-9,10-dione, 7H-benzo[de]anthracene-7-one and benz[a]anthracene-7,12-dione of 55 pg/m3, 104 pg/m3 and 116 pg/m3 were found(Mirivel et al., 2010). Ringuet et al. (2012) determined concentra-tions between 5 and 6 pg, 71 and 76 pg, 194 and 222 pg, 661 and658 pg, 44 and 50 pg, 37 and 52 pg at a traffic site near Paris fornaphthalene-1-carboxaldehyde, 9H-fluorene-9-one, phenan-threne9-carboxaldehyde, anthracene-9,10-dione, 7H-benzo[de]anthracene-7one and benz[a]anthracene-7,12-dione respectively.

Finally, a correlation analysis was conducted between theobserved concentration levels of the PAHs and oxy-PAHs andmeteorological data (average temperature, humidity and windspeed) obtained from a meteorological station in Chiang Mai (seeFig. S1). The results are given as supplementary information

(Table S3). Significant positive Pearson correlation coefficients forsampling site MF were found between the temperature and 70% ofthe individual oxy-PAHs concentrations and 94% of the individualPAHs concentrations. The average relative humidity negativelycorrelated at this sampling site with 50% of the oxy-PAHs and 60%of the PAHs. At the other sampling sites however few significantcorrelations were found. The sites however are characterized bydirect sources from traffic.

4. Conclusions

An advanced analytical method was developed employing PTV-GC coupled to high resolution mass spectrometry for the deter-mination of the 16 US-EPA PAHs and 12 oxy-PAHs on PM10. Lowinstrumental detection limits were obtained for all compounds(0.04e213 pg injected), demonstrating the strength of the methodto analyze trace levels. Pressurized liquid extraction (at 150 �C)using dichloromethane proved to be successful, given the high re-coveries (>74%) for most compounds. Furthermore, SRM 1649bwasanalyzed for PAHs and oxy-PAHs concentrations. It should be notedhowever that no certified concentrations of oxy-PAHs in SRM ma-terials are available today, so continuing efforts have to be made inthis regard. The study also provides the first data on oxy-PAHsconcentration levels in Thailand. Given that 1) the concentrationlevel of oxy-PAHs (

Poxy-PAHs: 1.1 ng/m3) is pronounced when

compared to the PAHs (P

PAHs: 3.4 ng/m3) and 2) the indicatednegative health effects related to oxy-PAHs in other studies, makesit invaluable to include oxy-PAHs in future investigations. Furtherresearch is necessary, both to determine their concentration levelsand extent the knowledge on their formation pathways.

Acknowledgments

We acknowledge financial support from the Flemish Govern-ment in the framework of the Flemish investment support forheavy research equipment and FWO-funding (1.5.062.09.N.00) foranalytical equipment support.

C. Walgraeve et al. / Atmospheric Environment 107 (2015) 262e272272

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.atmosenv.2015.02.051.

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