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Improved atmospheric sampling of hexavalentchromiumMehdi Amouei Torkmahalleh a b , Chang-Ho Yu c d , Lin Lin b , Zhihua (Tina) Fan c d , Julie L.Swift e , Linda Bonanno f , Don H. Rasmussen a , Thomas M. Holsen b & Philip K. Hopke a ba Department of Chemical and Biomolecular Engineering , Clarkson University , Potsdam ,NY , USAb Center for Air Resource Engineering and Science, Clarkson University , Potsdam , NY , USAc Environmental and Occupational Health Sciences Institute , Piscataway , NJ , USAd Robert Wood Johnson Medical School , University of Medicine and Dentistry of New Jersey(UMDNJ) and Rutgers University , Piscataway , NJ , USAe Eastern Research Group , Morrisville , NC , USAf New Jersey Department of Environmental Protection , Trenton , NJ , USAAccepted author version posted online: 18 Jul 2013.Published online: 16 Oct 2013.

To cite this article: Mehdi Amouei Torkmahalleh , Chang-Ho Yu , Lin Lin , Zhihua (Tina) Fan , Julie L. Swift , Linda Bonanno ,Don H. Rasmussen , Thomas M. Holsen & Philip K. Hopke (2013) Improved atmospheric sampling of hexavalent chromium,Journal of the Air & Waste Management Association, 63:11, 1313-1323, DOI: 10.1080/10962247.2013.823894

To link to this article: http://dx.doi.org/10.1080/10962247.2013.823894

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TECHNICAL PAPER

Improved atmospheric sampling of hexavalent chromiumMehdi Amouei Torkmahalleh,1,2 Chang-HoYu,3,4 Lin Lin,2 Zhihua (Tina) Fan,3,4 Julie L. Swift,5

Linda Bonanno,6 Don H. Rasmussen,1 Thomas M. Holsen,2 and Philip K. Hopke1,2,⁄1Department of Chemical and Biomolecular Engineering, Clarkson University, Potsdam, NY, USA2Center for Air Resource Engineering and Science, Clarkson University, Potsdam, NY, USA3Environmental and Occupational Health Sciences Institute, Piscataway, NJ, USA4Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey (UMDNJ) and Rutgers University,Piscataway, NJ, USA5Eastern Research Group, Morrisville, NC, USA6New Jersey Department of Environmental Protection, Trenton, NJ, USA⁄Please address correspondence to: Philip K. Hopke, Institute for a Sustainable Environment, Clarkson University, P.O. Box 5708, Potsdam, NY13699-5708, USA; e-mail: phopke@clarkson.edu

Hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) are the primary chromium oxidation states found in ambientatmospheric particulate matter. While Cr(III) is relatively nontoxic, Cr(VI) is toxic and exposure to Cr(VI) may lead to cancer, nasaldamage, asthma, bronchitis, and pneumonitis. Accurate measurement of the ambient Cr(VI) concentrations is an environmentalchallenge since Cr(VI) can be reduced to Cr(III) and vice versa during sampling. In the present study, a new Cr(VI) sampler(Clarkson sampler) was designed, constructed, and field tested to improve the sampling of Cr(VI) in ambient air. The new ClarksonCr(VI) sampler was based on the concept that deliquescence during sampling leads to aqueous phase reactions. Thus, the relativehumidity of the sampled air was reduced below the deliquescence relative humidity (DRH) of the ambient particles. The new samplerwas operated to collect total suspended particles (TSP), and compared side-by-side with the current National Air ToxicsTrends Stations (NATTS) Cr(VI) sampler that is utilized in the U.S. Environmental Protection Agency (EPA) air toxics monitoringprogram. Side-by-side field testing of the samplers occurred in Elizabeth, NJ, during the winter and summer of 2012. The averagerecovery values of Cr(VI) spikes after 24-hr sampling intervals during summer and winter sampling were 57 and 72%, respectively,for the Clarkson sampler, while the corresponding average values for NATTS samplers were 46% for both summer and wintersampling, respectively. Preventing the ambient aerosol collected on the filters from deliquescing is a key to improving the samplingof Cr(VI).

Implications: This study describes a sampler that provides cooling and drying of the particle collection filter by reducing theambient air relative humidity to below deliquescence relative humidity of ambient particles. This Clarkson Cr(VI) sampler improvedthe measurement of ambient Cr(VI) concentration. It showed higher Cr(VI) recovery during field tests (71.8 � 4.9% in winter and57.1� 0.2 % in summer) compared to the current EPACr(VI) sampler (46.2� 10.8% in winter and 46.0� 1.6% in summer) that isemployed in the National Air Toxics Trends Stations (NATTS) monitoring program.

Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher’s online edition of the Journal ofthe Air & Waste Management Association.

Introduction

Cr(III) and Cr(VI) are the two common oxidation states ofchromium in the environment. Cr(VI) is toxic and exposure to Cr(VI) may lead to cancer, nasal damage, asthma, bronchitis,pneumonitis, dermatitis, and skin allergies (Barceloux, 1999;Park et al., 2004). In contrast, Cr(III) is a trace element essentialfor the proper function of living organisms (IndependentEnvironmental Technical Group [IETEG], 2005).

Meng et al. (2011) determined the soluble Cr(VI) concentra-tion in ambient air of Paterson, NJ (0.44 U.S. 0.35 ng m�3), and

Chester (0.40� 0.53 ngm�3), NJ, which are an industrial city anda background site, respectively. Swietlik et al. (2011) performedambient air sampling in Radom, Poland, and reported the averagevalues for total Cr and Cr(VI) concentrations to be 25 and 6ng m�3 respectively. They determined the Cr(VI) to total Crratio to be 36%. In total, 1466 Cr(VI) measurements were con-ducted over 22 sites from January 2005 to December 2005 in theUnited States (Eastern Research Group [ERG], 2007). The con-centration of soluble Cr(VI) ranged from 0.001 to 2.97 ng m�3,and the average Cr(VI) concentration was determined to be 0.044ng m�3. The soluble and total Cr(VI) concentrations in ambient

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Journal of the Air & Waste Management Association, 63(11):1313–1323, 2013. Copyright © 2013 A&WMA. ISSN: 1096-2247 printDOI: 10.1080/10962247.2013.823894

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PM10 collected from four locations in New Jersey, that is,Meadowlands, Elizabeth Trailer, and Rahway (with mixed Cremission sources), and Piscataway (a suburb area) were deter-mined by Huang et al. (2013). In the locations with mixed Cremission sources, the mean concentrations were 1.05–1.41 ngm�3 (winter) and 0.99–1.56 ng m�3 (summer) for total Cr(VI),and 0.11–0.19 ng m�3 (winter) and 0.18–0.37 ng m�3 (summer)for soluble Cr(VI). In Piscataway, the mean concentrations were1.07 ng m�3 (winter) and 0.99 ng m�3 (summer) for total Cr(VI),and 0.03 ng m�3 (winter) and 0.12 ng m�3 (summer) for solubleCr(VI). Their results indicate that the ambient PM in these sam-pling locations contain soluble and insoluble Cr(VI), with insolu-ble Cr(VI) being most prevalent.

Table 1 reviews the total Cr and Cr(VI) concentrations as wellas Cr(VI) to total Cr ratios determined in previous studies.Table 1 shows that Cr(III) comprises the majority of ambientchromium. Cr(VI) concentrations ranging from 0.001 (ERG,2007) to 70 ng m�3 (Mandiwana et al., 2006), and the averageCr(VI) to total Cr ratios varied from 1 to 30%.

ERG developed a sampler (Figure S1) (ERG, 2007) for theU.S. Environmental Protection Agency National Air ToxicsTrends Stations (NATTS) monitoring program to collect totalsuspended particles (TSP). The sampler operates for 24 hr frommidnight to midnight using a carbonate-impregnated cellulosefilter (see Figure S1 in the supplemental material), and thesamples typically remain in the sampler after the samplinginterval. ERG (2007) has shown that when filters are left in theNATTS sampler for longer than 12–24 hr, conversion of Cr(VI)occurs. When filters are spiked with Cr(VI) solution and left inthe field for 33 to 105 hr, the reduction in Cr(VI) mass valuesranged from 30% to 58% (ERG, 2007).

Meng et al. (2011) found the average Cr(VI) recovery to be 57� 9% for the 24-hr sampling in Paterson, NJ, and Chester, NJ,using filters spiked prior to sampling. This recovery value wassignificantly lower than 67 � 23% average Cr(VI) recovery forfilters spiked after sampling.

The corresponding values for Cr(III) conversion were reportedto be 17� 9% and 11� 5% for filters spiked prior to sampling andafter sampling, respectively. These results suggest that�10%of theCr(VI) and �6% of the Cr(III) were converted during sampling.Huang et al. (2013) studied chromium stability during sampling(NATTS sampler) using the method of filter-spiked prior to andafter sampling such that reduction of Cr(VI) occurred during sum-mer andwinter. However, sampling had no significant influence onthe Cr(III) oxidation. Tirez et al. (2011) determined the Cr(VI)recovery to be 75 � 39%, and the Cr(III) conversion was 1.7 �1.2% during sampling in the Flemish region of Belgium. Theseprevious results regarding chromium reduction and oxidation dur-ing sampling indicate that in general, there is conversion of Cr(VI)toCr(III) during sampling.However, sinceCr(III) ismuch higher inconcentration than Cr(VI) in ambient PM, even a small conversionof Cr(III) to Cr(VI) can lead to a substantial positive bias in Cr(VI)measurements. The observed Cr(VI) and Cr(III) conversion inprevious studies is attributed to the conversion during sampling,filter storage, extraction, and analysis. The differences in thereported Cr(VI) recovery and Cr(III) conversion among previousstudies could be also due to differences in the type of filters and inthe analytical and filter extraction methods.

The conversion of Cr(VI) during sampling could be the resultof deliquescence of the collected ambient particulate matter thatprovides aqueous reaction media, and subsequent reactions withorganic matter, SO2, and other reductants (Huang et al., 2013;

Table 1. Total Cr and Cr(VI) concentration values and Cr(VI) to total Cr ratio reported in previous studies

Reference Total Cr (ng m�3) Cr(VI) (ng m�3) Cr(VI) ratio (%) Location

Puxbaum (1991) 1–40 Nonpolluted areaKrystek and Ritsema (2007) 20 1–20 Close to a foundryMandiwana et al., (2006) 20–70 Ferrochrome smelterNowak and Kwapulinski (1991) 30 Heavy industry regionBem et al. (2003) 5 Central part of PolandNowak and Kwapulinski (1991) 2000 In the vicinity of a power plantTalebi (2003) 27 7 25 Isfahan, IranZereini et al. (2005) 16.3 Frankfurt, GermanyFernández et al. (2000) 7.1 Seville, SpainUtsunomiya et al. (2004) 2.7 Detroit, MIRichter et al. (2007) 5 Santiago, ChileNusko and Heumann (1997) 1 25 Regensburg, GermanyKhlystov and Ma (2006) 0.5 Wilmington, DELi et al. (2002) 0.1–1.3 Sydney Basin, AustraliaMetze et al. (2004) 1–20 City areaBell and Hipfner, (1997) 20 OntarioBorai et al. (2002) 19–6842 20–30 Alexandria and Cairo, EgyptTirez et al. (2011) 34–96 1.2–5.2 2.6–3.5 Near and far from an anthropogenic source,

Flemish region, BelgiumHagendorfer et al. (2007) 0.04–0.23 1 Vienna, Austria

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Amouei Torkmahalleh et al., 2012; Grohse et al. 1988). Undertypical atmospheric conditions, the relative humidity (RH) variesover the 24-hr sampling period. It may exceed the deliquescencerelative humidity (DRH) at least 2 times during the 24 hr samplingperiods commonly employed: after sunset and early in the morn-ing. Once the relative humidity (RH) reaches or exceeds the DRHof the ambient particulate matter (76%) (Amouei Torkmahallehet al., 2012), conversion of Cr(VI) can occur even if the relativehumidity subsequently drops below the DRH. The conversion ofCr(III) during sampling could be attributed to the reaction of Cr(III) with dissolved Mn (Seigneur and Constantino, 1995; Nicoand Zasoski, 2000), or with water-soluble organic compound(WSOC) that include secondary organic aerosol (SOA) (Huanget al., 2013), and also reactions with gaseous oxidants such as O3

and particle-bound reactive oxygen species (ROS) (AmoueiTorkmahalleh et al., 2013; Werner et al., 2006).

The reported Cr(VI) concentrations and Cr(VI) to total Crratios in previous studies may have been biased by the Cr(VI)reduction and Cr(III) oxidation during sampling, filter storage,filter extraction, and analysis.

The goal of the current study was to design, construct, and testa new Cr(VI) sampler (Clarkson sampler) and compare the recov-ery of Cr(VI) using the Clarkson sampler with the NATTS sam-pler. The new sampler preserves Cr(VI) by reducing the humidityof the ambient air during sample collection to avoid deliquescenceand slightly cooling the ambient air during summer.

Experimental Methods

Clarkson Cr(VI) sampler

The Clarkson Cr(VI) sampler was designed such that thesampling filters remain dry (RH < 76%) during the samplingand postsampling intervals. To keep the filter dry, the RH of theair passing through the sampling filter was maintained below 76� 2%, the deliquescence relative humidity (DRH) of the ambientparticles reported by Amouei Torkmahalleh et al. (2012). The dryfilter should slow the reduction reactions of Cr(VI) with ambientparticles by preventing aqueous Cr(VI) chemistry so only solid–gas and solid–liquid reactions can occur (Amouei Torkmahallehet al., 2013; Huang et al., 2013). Thus, a clean and dried airflowwas added to sampled air in an FRM sampler (Rupprecht andPatashnick MODEL 2000H) equipped with TSP inlet (Figure 1).The clean air is also cooled to 10�C in the summer to decrease thetemperature of the sampled air to slow Cr(VI) reactions on thefilter. The clean air is warmed to 10�C in thewinter to decrease therelative humidity. The FRM sampler pump draws air through twopaths, the clean air and the ambient air paths.

The sampling flow rate was adjusted to 15 LPM, and clean airwas introduced into the sampler at 5 LPM. The TSP sampler wasoperated from 00:00 to 24:00. The ambient airflow was con-trolled by a solenoid valve installed between the sampler inletand the clean air inlet. The valve was controlled by the sampler’scontroller. The solenoid valve is normally closed. The controllerprovides a signal to open the valve at 00:00 and close the valve at24:00. In the subsequent period, the clean airflow rate increasedto 15 LPM with the pump continuously pulling air through thefilter/dryer/cooler system.

To provide dry air, filtered air was forced through a mechanicaldryer (modelD18IN, Ingersoll Rand, USA) to provide initialwaterremoval. The air stream leaving the dryer was divided into fourpaths; each of them entered the drier enclosure (DE) of eachClarkson sampler. However, the mechanical dryer is required tooperate even oneClarkson sampler because of the amount ofwaterthat needs to be removed from the air in hot and humid weather.

Each DE included two 47-mm cellulose filters, two HEPAfilter capsules, a membrane dryer (Thermo Fisher Scientific,USA), a chiller/heater (TE Technology; model CP-065), twoneedle valves, a vacuum pump, and a vacuum pressure gage.The chiller/heater cooled the air in the summer, and heated the airduring the winter. The set point of the chiller/heater was 10�C,and the actual working temperature was 10 � 0.5�C. The tem-perature reached approximately 5 and 15�C during winter andsummer, respectively, at the end of the line, before mixing withambient air. The needle valve was used to adjust the clean airflow rate as needed. The membrane dryer removed the waterfrom the airflow. To prevent water saturation in the dryer, acounterflow purge air driven by 24 � 1 inches Hg pressuredrop was applied continuously across each dryer. The vacuumpump was used to provide purge airflow in the dryer. The purgeair was passed through the cellulose filter and a HEPA filtercapsule before entering the dryer. The needle valve was used toadjust the flow rate of the purge air to 0.5 LPM (Figure 1).Abrasion-resistant gum rubber tubing (1/4 inch ID, 1/2 inchOD, 1/8 inch wall thickness) was used in the clean air path andthe tubing was insulated by semiflexible polyethylene foamrubber (McMaster Carr) to minimize the temperature drop.Because of heat transfer across the clean air line, the temperatureof the clean air slightly deviated from the cooler/heater set point.Figures S2 and S3 show the FRM sampler with TSP inlet and DEconnected to the sampler. The relative humidity and the tem-perature of the ambient air and clean air were continuouslymonitored using a temperature and relative humidity sensor(iButton, Maxim).

Sampling filters

Cellulose filters were used because they have low chromiumbackground concentrations (ERG, 2007). Cellulose filters spikedwith Cr(VI) solution and then frozen showed no Cr(VI) reductionfor up to 11 days at –18�C (ERG, 2007). The cellulose filters wereleached overnight in 10% nitric acid solutions to remove anychromium contamination. The filters were washed with ultrapurewater, and dried overnight in a clean bench. The pH of the filterswas measured using pH indicator paper, and found to be between5 and 6. To prepare basic cellulose filters, the acid-washed filterswere impregnated with 500 mL of a 0.12 M sodium bicarbonatesolution. The filters were dried in a clean bench producing filterswith pH values between 9 and 10 (ERG, 2007).

Isotopic spiking

Solutions of isotopically enriched Cr(III) (chromium(III)nitrate, Cr(NO3)3) and Cr(VI) (potassium dichromate, Cr2K2O7)standards were purchased from Applied Isotope Technology andrefrigerated at 4�C. 53Cr(VI) and 50Cr(III) isotopeswere spiked on

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the filters to simultaneously monitor the oxidation and reductionof Cr(III) and Cr(VI), respectively, using ion chromatography (IC)coupled with inductively coupled plasma mass spectrometry(ICPMS) (IC/ICPMS).

Cr(VI) standard was spiked on the filters to determine Cr(VI)recovery using ion chromatography-ultraviolet spectroscopy(ICUV) for a positive control study that was performed duringthe field (summer) sampling campaign. All unspiked filtersincluding field and laboratory blank filters were analyzedusing ICUV.

Spiked filters were placed in a laminar flow clean bench for10 min to dry and then stored in a freezer at –20�C. All of thefrozen filters were then dried in vacuum desiccators before beingused for sampling to remove any possible absorbed water.

Analytical methods

To determine Cr(VI) concentration using IC/ICPMS (ThermoX-series, MA) analysis, a CS5A ion-exchange column (DionexIonPac, 250 � 4.0 mm, 5 µm size) was employed. The sampledelivery system consisted of high-performance liquid chromato-graphy (HPLC), a Spectrosystem peristaltic pump, and a quartzspray chamber with a Conikal concentric glass nebulizer.Collision cell technology (CCT) was used to reduce polyatomicinterferences such as 52ArCþ and 53ClOþ. The instrument wasoptimized daily using a Thermo A25 Tune solution. Externalcalibration curves were generated using a blank and Cr(VI)standards of 0.2, 0.5, 1, 2, 5, and 10 ng/mL. The method

detection limit (MDL; 40. CFR 136, Appendix B) was deter-mined as 0.042 ng/mL. The mean of the blank filter extract was0.004 ng/mL (n ¼ 4), which was below the MDL. RelevantHPLC parameters and analytical conditions for HPLC-ICPMSare given in Table S1 (supplemental material).

To determine the concentration of Cr(VI) using ICUVanaly-sis, Cr(VI) is separated by ion chromatograph (IC) using ananion-exchange analytical column (AS7, Dionex) with a sup-porting guard column (NG1, Dionex), and reacted using a post-column derivatization module with diphenylcarbohydrazide(DPC) to form a complex that can be detected at 530 nm witha UV-visible detector.

The conversion of Cr(VI) to Cr(III) cannot be directly com-pared from IC/ICPMS analyses and the ICUV analyses. Thesamples were extracted using an acidic solution when preparedfor IC/ICPMS, and with a slightly basic solution when preparedfor ICUVanalysis.

Data analyses

The relative standard deviations (RSD) of Cr(VI) recovery andCr(III) conversion were calculated as the ratio of the standarddeviation of the group of data to average of the data. Data forsampleswithmore than two repetitions are presented as average�standard deviation, while data from duplicated samples are pre-sented as average� relative percent difference (RDP). Variabilityis defined as absolute (value of sample 1 – value of sample 2)/average (value of sample 1 and value of sample 2).

Filter HEPA

Needle Valve Filters

HEPACooler/heater

Needle Valve

TSP Inlet

Ball Valve vaccumpump

FRMSampler

MembraneDrier

CompressorMechanical

DrierFilter

Figure 1. Clarkson Cr(VI) sampler. The arrows show the direction of ambient airflow.

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One-way analysis of variance (ANOVA) and two-wayANOVA were used for statistical comparisons in the campusand the field studies, respectively.

Clarkson campus study

Basic pH filters were spiked with 10 ng Cr(VI) and 20 ng Cr(III). Four FRM samplers either were used for the NATTSsamplers or were assembled for the Clarkson samplers. Thesamplers were operated simultaneously using spiked basic cel-lulose filters prepared a day before the sampling day, fromNovember 2010 to February 2011. Sampling was performedwith flow rates of 15 L min�1 on the roof of an academicbuilding on the Clarkson University campus in Potsdam,NY. After sampling, the filters were transferred to petri dishesand stored in a freezer at –20�C until analysis.

To examine the precision of the four Clarkson samplers on Cr(VI) recovery and Cr(III) conversion, four samplers were oper-ated simultaneously for 24 hr, and the sampling was repeated for4 days to collect a total of 16 filters.

NATTS and Clarkson samplers were operated side by side tocompare the performance of both types of the samplers torecover Cr(VI). The experiments were performed by operatingtwo Clarkson samplers and two NATTS samplers simulta-neously with 15 LPM flow rate. The comparison was made ontwo different days to duplicate the study. Overall, four filterswere collected per sampler type.

Field study

Field sampling was conducted at the New Jersey Departmentof Environmental Protection (NJDEP) air toxics monitoring sitein Elizabeth, NJ. The site is downwind from a number of poten-tial sources of hexavalent chromium emissions, and is locatedadjacent to interchange 13 on the New Jersey Turnpike(Figure 2). The site has power, and is easily accessible by fieldsampling crews 24 hr/day, 7 days/week. In total, eight samplers(four Clarkson samplers and two dual-channel NATTS samplers)were deployed in the field for the sampling at average flow ratesof 13.1 (NATTS) and 15.2 (Clarkson) LPM. To minimize poten-tial airflow interferences, the collocated samplers were placed atleast 1 m apart from each other at the monitoring site, but closeenough to ensure that there were no significant differences(<20%) in the collected PM mass by the samplers. The massprecision tests were conducted for four rounds, from August 1,2011, to August 4, 2011. The sampling was performed 14 � 1LPM for 24 hr on Teflon filters, with no Cr spiking. The sampledfilters were kept in petri dishes in a weighing room (20 � 2�Cand 35� 5%) at least 24 hr until gravimetric analysis. The massof the filters before and after sampling was monitored using amicrobalance to determine the collected PM mass.

During the sampling campaign, field blank samples wereplaced in all samplers for 24 hr and then were collected withfield samples to store in the freezer until analyses. After samplecollection, the field and field blank samples were shipped

Figure 2. Sampling location at Elizabeth, NJ.

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overnight to the designated laboratories for analysis by mail ondry ice (without weekend delivery). Accordingly, laboratoryblank samples were shipped from either ERG or RutgersUniversity laboratories to the designated laboratories. Sampleswere kept at –20�C in freezers at each laboratory until analysis.Samples were analyzed by each laboratory soon after receipt.

Tables S2 and S3 (supplemental material) present the detailsof field samples during winter and summer 2012, respectively.Tables S4 and S5 (supplemental material) show the samplinginformation for field and laboratory blank samples during winterand summer sampling campaigns, respectively. Rounds 5 and 6in Table S3 are considered as positive control study.

Winter and summer sampling were performed in January2012 (eight rounds) and June 2012 (six rounds), respectively.During winter sampling, in each round, eight samplers (fourClarkson and four NATTS samplers) were operated side byside except during round 1. During round 1, six samplers includ-ing four Clarkson samplers and two NATTS samplers wereoperated. Day 1 pickup represents 24-hr sampling plus the sub-sequent overnight field storage period, and Day 3 pickup refersto 24-hr sampling plus subsequent 48 hr and an overnight fieldstorage period. During the winter sampling, sample analysis wasperformed by ICUVat Clarkson University, Rutgers University,and ERG, and also by IC/ICPMS at Clarkson University andRutgers University, under the same sampling and analysis con-ditions per analytical method. All recovery and conversion cal-culations were made using the determined concentrations by IC/ICPMS.

During summer sampling, four NATTS and three Clarksonsamplers (one sampler had failed) were operated side by side.Rounds 3 and 4 were designed to monitor Cr(VI) recovery andCr(III) conversion using IC/ICPMS, while rounds 5 and 6 (posi-tive control study) were performed to monitor only the Cr(VI)recovery using ICUV. During the summer campaign, sampleanalysis was performed by ICUV at ERG and IC/ICPMS atRutgers University.

Table S6 (supplemental material) shows the method detectionlimit (MDL) for each analytical method at each laboratory.

Ambient Cr(VI) concentration was defined as the mass of thecollected Cr(VI) after 24-hr sampling divided by the samplingvolume. For laboratory and field blank samples, the Cr(VI)concentration was estimated by the mass of the determined Cr(VI) divided by the average sampling volume (20.2 m3 for wintersampling and 20.5 m3 for summer sampling) during the sam-pling period. The precision in sampling flow rate was higher forClarkson samplers compared to NATTS samplers.

Results and Discussion

All of the laboratories analyzed quality assurance/qualitycontrol (QA/QC) samples before field sampling as well as dur-ing field campaign to ensure the accuracy for each method ateach laboratory. All of the laboratories showed acceptable resultsfor Cr(VI) and Cr(III) audit samples during winter sampling.During summer sampling, Clarkson laboratory and RutgersUniversity laboratory (for ICUV method) did not show accep-table results and thus were not included for analyses. Auditsamples were prepared and distributed by an independent third

party (Wibby Environmental, Golden, CO), as well as by thethree laboratories.

The ratio of the measured 53Cr(VI) mass in the sample extractsubtracted from the portion of 53Cr(VI) in the ambient airdivided by the spiked 53Cr(VI) mass was defined as “recovery”of 53Cr(VI) when IC/ICPMSwas used for analysis. Likewise, theratio of the measured natural Cr(VI) mass in the sample extractsubtracted from the portion of natural Cr(VI) in the ambient airdivided by the spiked Cr(VI) standard mass was defined as“recovery” of Cr(VI) when ICUV was used for analysis. Theconversion of 50Cr(III) to 50Cr(VI) was defined as the measuredmass of 50Cr(VI) in the sample extract subtracted by the portionof 50Cr(VI) in the ambient air divided by the spiked 50Cr(III)mass. To estimate the mass of 50Cr(VI) and 53Cr(VI) in theambient air, the determined mass of 52Cr(VI) using IC/ICPMSwas corrected by the abundance isotopic ratio of each chromiumisotope.

Campus study

Evaluation of the membrane dryerThis section examines the performance of the DE in drying

the clean air, as all of the data presented in this section wereobtained when the mechanical dryer was off. The pressure of thepurge air strongly affects the intensity of the drying by themembrane dryer. Increasing the pressure drop of the purge airdecreases the relative humidity of the clean air. Therefore, thepressure of the purge air was adjusted at the lowest possiblepressure (24 inches Hg vacuum), maintained by the vacuumpump.

The Clarkson sampler efficiently reduced the RH of the cleanair below 30% during 24-hr sampling (Figure 3), even during theearly morning around 3 a.m. when the ambient RH reached 94%.The average temperature for the ambient air and the clean airwere 5.1 � 1.2�C and 5.0 � 1.3�C, respectively.

The RH of the clean air increased as its flow rate increased to15 LPM (Figure 4). During the postsampling period, the increase

Figure 3. RH variations for the ambient air and the clean air during 24 hr, purgeair pressure¼ 24 inches Hg vacuum, purge air flow rate¼ 0.5 LPM, and the cleanair flow rate ¼ 5 LPM.

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in the clean air flow rate decreased its residence time inside themembrane, and thus at constant ambient RH, purge airflow rate,and membrane pressure drop, the RH of the clean air increasedcompared to the sampling period (Figure 4). The RH of the cleanair was below 60% during the most humid condition when theRH of the ambient air exceeded 85%. During the post-samplingtime, the sampling filter faced only the clean stream with a RHvalue below 76%, indicating that the Clarkson sampler will keepthe filter dry during the postsampling period.

Evaluation of final RH. To examine the RH of ambient air aftermixing with the clean air produced by the mechanical andmembrane dryers, an experimental study was conducted withthe Clarkson sampler during summer. In this study, the RH of theclean air, ambient air and the ambient air passing through thefilter were monitored simultaneously for 24 hr (Figure 5). The

final RH after mixing was below the DRH of ambient particlesindicating that the Clarkson sampler design works to reduce RH.

During winter sampling, the clean air was slightly heated bythe heater to reduce its RH. However, heating the clean airincreases the ambient temperature by 1�C after mixing. Thischange in temperature is negligible and should not affect thecollection of the particulate matter on the filter.

Campus sampling. The samplers showed good precision(<20%), in particular for Cr(III) conversion (Table 2).Sampling during a windy day (round 2) resulted in higher Cr(VI) recovery (over 95%) compared to the rainy day (round 3).This result is in agreement with our recent finding showing thatrelative humidity plays an important role in the reduction of Cr(VI) during sampling (Amouei Torkmahalleh et al., 2012).During a rainy day, the average and maximum humidity valueswere found to be higher compared to a windy day. During round1, the ambient RH exceeded the DRH for only 6 hr, and duringround 2, the ambient RH never exceeded the DRH (data notshown). During round 3, the ambient RH exceeded the DRH ofambient particles for approximately 16 hr (data not shown). Thedifference in the Cr(VI) recovery between rounds 2 and 3 wasdetermined to be statistically significant (P ¼ 0.014).

The average and maximum temperature values were lower inround 3 compared to round 2 (Table 2). Round 3 with the lowertemperature that slows Cr(VI) conversion resulted in lowerrecovery compared to round 2. This result suggests that therole of humidity might be more important than the role oftemperature for the temperature range of this study. It isassumed that the difference in collected PM mass among dif-ferent sampling events is low such that the Cr conversion is notbiased by this difference. The data presented by Swietlik et al.(2011) show the importance of humidity in Cr(VI) to total Crratio in the atmosphere. For example, sampling at the samelocation in Radom, Poland but different days showed Cr(VI) tototal Cr ratio to be 27.6 � 15.5% (n ¼ 3) at cold and humidatmospheric conditions (average T ¼ 3–6�C, average RH ¼90%, PM concentration ¼ 116.5 mg.m�3, and Cr total concen-tration ¼ 14.3 � 2.5 ng m�3) and 38.3 � 5.7% (n ¼ 3) formoderate temperature and humidity conditions (average T ¼22–25�C, average RH ¼ 57%, PM concentration ¼ 100.0 mgm�3 and Cr total concentration ¼ 15.3 � 2.3 ng m�3).

Cr(III) conversion was found to be consistent with higherprecision independent of meteorological conditions. Oxidantssuch as ozone and reactive oxygen species (AmoueiTorkmahalleh et al., 2013; Huang et al., 2013) can oxidize Cr(III) to Cr(VI).

Side-by-side comparison between NATTS and Clarkson sam-plers showed no statistical difference in the Cr(VI) recovery. Theaverage Cr(VI) recovery values after 24-hr sampling were deter-mined to be 87� 2 (n¼ 4) and 89� 13 (n¼ 4) for Clarkson andNATTS samplers, respectively. The Clarkson samplers had bet-ter precision compared to NATTS samplers. Potsdam, NY, is aclean rural areawhere PMmass concentrations are low providinglittle to react with spiked Cr(VI) during campus sampling.Therefore, it was expected that there would be no difference inthe Cr(VI) recovery between the two sampling trains.

Figure 4. RH variations for the ambient air and the clean air during 24 hr, purgeair pressure ¼ 24 inches Hg vacuum, purge air flow rate ¼ 0.5 LPM, and theclean air flow rate ¼15 LPM.

Figure 5. RH variations for the ambient air, the clean air, and the ambient airmixed with the clean air.

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Field study

Overall, both types of the samplers showed a good precisionindividually, on each sampling day (Table S7). Also, the precisionamong all eight samplers on each sampling daywas found to be 14� 5%, which is better than the acceptable range (<20%).

Cr(VI) concentration. The average (n ¼ 61) Cr(VI) concentra-tions during the laboratory and field blank study for winter andsummer sampling campaigns were below the analytical MDL(Table S6). The very low Cr(VI) concentrations suggest that nochromium contamination was introduced by the samplers andsampling filters and during the analyses. However, for somesamples, IC/ICPMS analysis showed chromium backgroundcontamination that could cause the results to be biased.

The average 53Cr(VI) recovery and 50Cr(III) conversion forthe laboratory blank samples (n ¼ 8) were determined to be102.8 � 9.1% and 3.0 � 2.4% . The average 53Cr(VI) recoveryand 50Cr(III) conversion for the winter field blank samples (n ¼4) were 113.5� 27.2% and 14.0� 15.0%, respectively, on day 1pickup. One sample with 153% Cr(VI) recovery and 36% Cr(III)conversion among those field blank samples markedly increasedthe standard deviation values. The average 53Cr(VI) recovery and50Cr(III) conversion for the winter field blank samples (n ¼ 6)were determined to be 88.2 � 8.7% and 8.5 � 3.5%, respec-tively, on day 3 pickup. The average 53Cr(VI) recovery and 50Cr(III) conversion for the summer field blank samples (n¼ 2) were77.0� 0.1% and 6.0� 0.0%, respectively, on day 1 pickup. Theaverage 53Cr(VI) recovery and 50Cr(III) conversion for the sum-mer field blank samples (n ¼ 2) were found to be 67.0 � 0.04%and 11.5 � 0.08%, respectively, on day 3 pickup. Decreases inCr(VI) recovery values were observed for summer and winterfield blank samples when the blank filters were left in the fieldfor 3 days compared to 1 day field blank samples. Also, spikedfield blank filters showed lower Cr(VI) during summer com-pared to winter demonstrating the negative effect of temperatureon Cr(VI) recovery.

Unceta et al. (2010) stated that reduction of Cr(VI) can occurby reaction of Cr(VI) with the polymeric materials used insampling filters such as cellulose and glass during Cr(VI) sam-pling. In addition, filter holders may add to Cr(VI) conversion asa results of the presence of plasticizers materials. However, thehigh recovery of Cr(VI) in the laboratory blank samples as well

as winter field blank samples at day 1 pickup implies very lowimpact of cellulose filter and filter holder on Cr(VI) conversion.This observation is in agreement with findings of Huang et al.(2013).

Twenty-four-hour samples showed no statistically significantdifferences between Cr(VI) concentrations determined byNATTS and Clarkson samplers for each campaign (Table 3).The observed ambient Cr(VI) concentration during our winterand summer sampling campaigns in Elizabeth, NJ, was muchless than previous findings (Table 1). The average ambient Cr(VI) concentrations, 0.03 � 0.01 ng m�3 (summer) and 0.02 �0.01 ng m�3 (winter) determined in this study are lower thanthe average Cr(VI) concentration of 0.044 ng m�3 determinedover 22 locations in the United States (ERG, 2007). The differ-ence in the total Cr(VI) concentrations between the current studyand previous investigations could also be due to difference inanalytical methods. The results of this study show statisticallyhigher levels of Cr(VI) concentration during the summer sam-pling compared to the winter sampling (P ¼ 0.0003) inElizabeth, NJ.

Cr(VI) recovery and Cr(III) conversion. All of the data reportedin this section were obtained using IC/ICPMS analysis unlessotherwise stated.

(1) Cr(VI) recovery. The average Cr(VI) recovery on day 1 forClarkson sampler during summer and winter sampling periodswas found to be 57.1� 0.2 and 71.8� 4.9%, respectively, whilethe corresponding average values for the NATTS samplers were46.0 � 1.6 and 46.2 � 10.8% for the summer and wintersampling campaigns, respectively (Table 4). The average Cr(VI)recovery on day 3 for the Clarkson sampler during summer andwinter sampling were found to be 43.9 �17.6 and 72.3 � 4.3%,

Table 3. Ambient Cr(VI) concentration determined in this study, field study

Summer WinterSampler type Day Cr(VI) (ng m�3) (n) Cr(VI) (ng m�3) (n)

NATTS 1 0.03 � 0.01 (11) 0.02 � 0.01 (9)Clarkson 1 0.03 � 0.01 (5) 0.02 � 0.01 (6)Average 1 0.03 � 0.01 (16) 0.02 � 0.01 (15)

Table 2. The 53Cr(VI) recovery and 50Cr(III) conversion determined by four Clarkson samplers (precision study), campus study

Samplinground

Cr(VI) recovery(average � STD),

RSD

Cr(III) conversion(average� STD, n¼4),

RSD

Ambient RH(average � STD),

highest RH

Ambient temperature(average � STD), highest

temperature Event

1 95.1 � 8.54% (n ¼4),(8.9%)

11 � 0.20% (n ¼4),(1.81%)

59.6 � 19.5%,(92.62%)

15.3 � 10.8�C, (33.66�C) No wind,no rain

2 101 � 6.44% (n ¼4),(6.34%)

11 � 0.35% (n ¼4),(3.14%)

42.1 � 23.4%,(71.46%)

18.6 � 10.1�C, (36.06�C) Windy

3 85.6 � 2.20% (n ¼4),(2.57%)

9.3 � 1.2% (n ¼4),(12.87%)

68.2 � 21.6%,(87.46%)

10.3 � 4.68�C, (21.91�C) Rainy

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while the corresponding average values for the NATTS samplerswere 32.4 � 2.1 and 33.9 � 7.6% for the summer and wintersampling programs, respectively. No statistically significant dif-ference was observed between day 1 and day 3 for both samplersduring the winter sampling campaign. This result could be due tothe low ambient temperature during winter. During summer sam-pling, a statistically significant difference (P ¼ 0.038) wasobserved between day 1 and day 3 Cr(VI) recovery for the bothsamplers. The reduction inCr(VI) recovery between day 1 to day 3was found to be 23 and 30% for Clarkson and NATTS samplersduring summer, respectively. The statistical analyses of the resultsrevealed that Cr(VI) recovery by Clarkson sampler was greatercompared to NATTS sampler during winter sampling for both day1 and day 3 pickup (P� 0.001), while no statistical differencewasobserved during summer. Only two filters were sampled duringsummer by the Clarkson sampler, so these results may not trulyreflect its performance. The results from positive control studythat were obtained using ICUV analysis showed that the averageCr(VI) recovery values by Clarkson and NATTS samplers werefound to be 75.5 � 0.3 and 17.8 � 15.8%, respectively.

The improvement in Cr(VI) recovery by Clarkson samplersindicates that drying was influential in preserving Cr(VI) duringsampling. Clarkson samplers keep the filters dry until the end ofthe postsampling period to prevent deliquescence of ambientparticles, while NATTS samplers may experience deliquescenceof ambient particles resulting in the conversion of Cr(VI).

(2) Cr(III) conversion. The average Cr(III) conversion on day 1for the Clarkson sampler during the summer and winter sam-pling periods was determined to be 8.6 � 0.2 and 12.7 � 2.1%,respectively, while the corresponding average values for NATTSsamplers were 5.1 � 0.8 and 8.4 � 5.9% for the summer andwinter sampling, respectively. However, only duplicate sampleswere taken for Clarkson samplers during the summer campaignto determine the Cr(III) conversion on day 1.

The average Cr(III) conversion by day 3 for the Clarksonsampler during summer and winter sampling campaigns wasfound to be 10.6 � 2.0 and 9.2 � 2.0%, respectively, while thecorresponding average values for NATTS samplers were 9.8 �1.4 and 2.8 � 1.8%, respectively. Statistically significant differ-ences were observed between day 1 and day 3 for the twosampler types during winter sampling (P¼ 0.008). The observedlower Cr(III) conversion by day 3 compared to day 1 duringwinter sampling could be due to reconversion of 50Cr(VI) duringthe postsampling period. The Cr(III) conversion during summerat day 3 was statistically higher compared to day 1 for both

samplers (P ¼ 0.004). The statistical analyses of the results ofboth sampling seasons showed statistically significant differ-ences between the two samplers (P ¼ 0.017 for summer and P¼ 0.003 for winter). The observed conversion of Cr(III) to Cr(VI) during field sampling could be the results of the either offollowing cases:(1) Limited deliquescence of soluble Cr(III) salts such as Cr

(NO3)3 that deliquesce at 52% (Amouei Torkmahalleh et al.,2012), as the Clarkson samplers keeps the ambient RHbelow 76% and not necessarily below 52%.

(2) Solid–gas and solid–liquid reactions of soluble Cr(III) withpotential oxidants in the atmosphere (Amouei Torkmahallehet al., 2013) available during field sampling that result in theformation of soluble Cr(VI).This study investigated the concentration and conversion of

soluble Cr(VI) since the methods for the filter extraction andconversion monitoring are applicable only for soluble Cr(V).Huang et al. (2013) showed that insoluble Cr(VI) constitutesthe majority of the total ambient Cr(VI). No conclusions canbe obtained regarding the concentration and conversion of inso-luble Cr(VI) during sampling in the present study.

See and Balasubramanian (2008) found insoluble Cr in indoorPM. Chromium speciation in indoor environments would be aninteresting topic for future study. In particular, outdoor originparticles in indoor environment could be important sources ofCr(VI) since they account for a major part of indoor particles.

The availability of the soluble and insoluble Cr(III) in theambient PM samples depends on the source of the chromium.However, there are studies that showed that insoluble Cr(III)dominates the ambient Cr(III) in PM. A field test conducted byHuang et al. (2013) showed that soluble Cr(III) in ambient PM ofthe sampling locations was negligible, and thus the Cr(III) con-version is expected to be insignificant for these soluble Crspecies. This conclusion was also reached by Tirez et al.(2011) and Werner et al. (2007). Insoluble Cr(III) was reportedto be inert under the temperature and pH of the filter extractionprocess in this study (Huang et al., 2013). Thus, the observedconversion of Cr(III) during the field study that was obtainedfrom the conversion of soluble spiked Cr(III) does not reflect theconversion of Cr(III) in ambient PM during sampling. Thisconclusion suggests that the conversion of ambient Cr(III),which is one of the major challenges for the measurement ofCr(VI) using the current filter extraction procedure, may be aconcern only if the insoluble Cr(III) such as Cr(OH)3(s) convertsto soluble Cr(VI) such as CrO4

�2(aq) in the presence of gaseous

and particle oxidants.

Table 4. Average Cr(VI) recovery and Cr(III) conversion determined by Clarkson and NATTS samplers, field study, with all data presented as average � standarddeviation except data for Clarkson sampler during summer and positive control, which are presented as average � variability

Samplertype

Winter percent Cr(VI) recovery (n)

Winter percent Cr(III) conversion (n) Day

Summer percent Cr(VI) recovery (n)

Summer percent Cr(III) conversion (n)

Positive controlstudy (n)

NATTS 46.2 � 10.8 (4) 8.4 � 5.9 (4) 1 46.0 � 1.6 (4) 5.1 � 0.8 (4) 17.8 � 15.8 (4)33.9 � 7.6 (6) 2.8 � 1.8 (6) 3 32.4 � 2.1 (4) 9.8 � 1.4 (4) NA

Clarkson 71.8 � 4.9 (4) 12.7 � 2.1 (4) 1 57.1 � 0.2 (2) 8.6 � 0.2 (2) 75.5 � 0.3 (2)72.3 � 4.3 (5) 9.2 � 2.0 (5) 3 43.9 � 17.6 (4) 10.6 � 2.0 (4) NA

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Conclusion

Drying the filter during sampling of Cr(VI) below DRH ofambient particles is a key to improving the sampling of Cr(VI).Drying slows the chemistry of chromium by preventing thesystem from forming an aqueous phase through deliquescence.The Clarkson Cr(VI) samplers were designed and constructedbased on this principle. Even though only a small amount ofsamples was collected, the Clarkson Cr(VI) samplers showedbetter Cr(VI) recovery compared to the current NATTS sam-plers during sampling at Elizabeth, NJ. Because of the lowchromium concentrations found during the field sampling inNew Jersey, a study performed where Cr(VI) concentrationsmay be higher would allow a better evaluation of Clarksonsamplers. However, based on the limited results presentedhere, it appears likely that the current NATTS sampling systemis systematically underestimating the ambient concentrationsof Cr(VI) in ambient PM. The extent of this underestimationdepends on the fraction of soluble Cr(VI) as well as on thehandling practices for the collection of the samples from thesamplers following the sampling period. There is thus a needfor serious consideration of upgrading of the current samplersto incorporate the drying and cooling that were included in theClarkson samplers to provide better sampling and preservationof the collected PM to produce more accurate estimates of thepopulation exposure to Cr(VI).

Acknowledgment

This work has been supported by the U.S. EnvironmentalProtection Agency under grant XA-97247301. Although theresearch described in this work has been partly funded by theEPA, it has not been subjected to the agency’s required peer andpolicy review and therefore does not necessarily reflect the viewsof the agency and no official endorsement should be inferred.The views expressed herein are also not necessarily those of NJDepartment of Environmental Protection. Dr. Fan is supported inpart by the NIEHS sponsored Rutgers University Center forEnvironmental Exposures and Disease, Grant # NIEHSP30ES005022.

ReferencesAmouei Torkmahalleh, M., L. Lin, T.M. Holsen, D.H. Rasmussen, and P.K.

Hopke. 2012. The impact of deliquescence and pH on chromium speciationin ambient PM. Aerosol Sci. Technol. 46(6): 690–96. doi:10.1080/02786826.2011.654285

Amouei Torkmahalleh, M., L. Lin, T.M. Holsen, D.H. Rasmussen, and P.K.Hopke. 2013. Cr speciation changes in the presence of ozone and reactiveoxygen species at low relative humidity. Atmos. Environ. 71:92–94.doi:10.1016/j.atmosenv.2013.02.005

Barceloux, D.G. 1999. Chromium. Journal of Toxicol. Clin. Toxicol. 37:173–94.doi:10.1081/CLT-100102418

Bell, R.W., and J.C. Hipfner. 1997. Airborne hexavalent chromium in south-western Ontario. J. Air Waste Manage. Assoc. 47:905–10. doi:10.1080/10473289.1997.10464454

Bem, H., M. Gallorini, E. Rizzio, andM. Krzeminska. 2003. Comparative studieson the concentrations of some elements in the urban air particulate matter in

Lodz City of Poland and Milan, Italy. Environ Int. 29:423–28. doi:10.1016/S0160-4120(02)00190-3

Borai, E.H., E.A. El-Sofany, and A.S. Abdel-Halim. 2002. Speciation of hex-avalent chromium in atmospheric particulate samples by selective extractionand ion chromatographic determination. Trends Anal. Chem. 21:741–45.doi:10.1016/S0165-9936(02) 01102-0

Eastern Research Group. 2007. Collection and Analysis of HexavalentChromium in Ambient Air. Morrisville, NC: Eastern Research Group, Inc.

Fernández, A.J., M. Ternero, F.J. Barragán, and J.C. Jiménez. 2000. An approachto characterization of sources of urban airborne particles through heavy metalspeciation.Chemosphere Global Change Sci. 2:123–36. doi:10.1016/S1465-9972(00)00002-7

Grohse, P. M., W.F.L. Hodson, and B. M. Wilson. 1988. The Fate of HexavalentChromium in the Atmosphere. California Air Resources Board Sacramento,CARB contract no. A6-096-32. Research Traingle, NC: Research TriangleInstitute.

Hagendorfer, H., and M. Uhl. 2007. Speciation of Chromium in Particulate Matter(PM10): Development of a Routine Procedure, Impact of Transport andToxicological Relevance. Vienna, Austria: Umwelbundesamt, REP-0111.

Huang, L., X. Fan, C.-H. Yu, P.K. Hopke, P. Lioy, B. Buckley, L. Lin, and Y. Ma.2013. Inter-conversion of chromium species during air sampling: Effects ofO3, NO2, SO2, particle matrices, temperature and humidity. Environ. Sci.Technol. 47:4408–15. doi:10.1021/es3046247

Independent Environmental Technical Group. 2005. Chromium (VI) Handbook,ed. J. Guertin, J.A. Jacobs, and C.P. Avakian. Boca Raton, FL: CRC Press.

Khlystov, A., and Y. Ma. 2006. An on-line instrument for mobile measurementsof the spatial variability of hexavalent and trivalent chromium in urban air.Atmos. Environ. 40:8088–93. doi:10.1016/j.atmosenv.2006.09.030

Krystek, P., and R. Ritsema. 2007. Monitoring of chromium species and 11selected metals in emission and immission of airborne environment. Int.J. Mass Spectrom. 265:23–29. doi:10.1016/j.ijms.2007.05.003

Li, Y., N.K. Pradhan, R. Foley, and G.K.C. Low. 2002. Selective determination ofairborne hexavalent chromium using inductively coupled plasma mass spec-trometry. Talanta. 57:1143–53. doi:10.1016/S0039-9140(02)00196-0

Mandiwana, K.L., N. Panichev, and T. Resane. 2006. Electrothermal atomicabsorption spectrometric determination of total and hexavalent chromiumin atmospheric aerosols. Hazard Mater. B136:379–82. doi:10.1016/j.jhazmat.2005.12.030

Meng, Q., Z. Fan, B. Buckley, L. Lin, L. Huang, C. Yu, H. Stiles, and R.L.Bonanno. 2011. Development and evaluation of a method for hexavalentchromium in ambient air using IC ICP-MS. Atmos. Environ. 45:2021–27.doi:10.1016/j.atmosenv.2011.02.009

Metze, D., H. Herzog, B. Gosciniak, D. Gladtke, and N. Jakubowski. 2004.Determination of Cr(VI) in ambient airborne particulate matter by a species-preserving scrubber-sampling technique. Anal. Bioanal. Chem. 378:123–28.doi:10.1007/s00216-003-2250-1

Nico, P.S., and R.J. Zasoski. 2000. Importance of Mn(II) availability of Cr(III)oxidation on birnessite. Environ. Sci. Tecnol. 38:5253–60. doi:10.1080/01490450590945988

Nowak, B., and J. Kwapulinski. 1991. Occurrence of selected metals in dustsuspended around the “Qagisza” power plant.Ochrona Powietrza i ProblemyOdpadów 21:38–42 (in Polish).

Park, R.M., J.F. Bena, L.T. Stayner, R.J. Smith, H.J. Gibb, and P.S. Lees. 2004.Hexavalent chromium and lung cancer in the chromate industry: a quantita-tive risk assessment. Risk Anal. 24:1099–108. doi:10.1111/j.0272-4332.2004.00512.x

Nusko, R., and K.G. Heumann. 1997. Cr(III)/Cr(VI) speciation in aerosol parti-cles by extractive separation and thermal ionization isotope dilution massspectrometry. Fresenius J. Anal. Chem. 357:1050–55. doi:10.1007/s002160050303

Puxbaum, H. 1991. Metal compounds in the atmosphere. In Metals and TheirCompounds in the Environment, ed. E. Merian, 257–86. Weinheim,Germany: VCH.

Richter, P., P. Grino, I. Ahumada, and A. Giordano. 2007. Total element concen-tration and chemical fractionation in airborne particulate matter from Santiago,Chile. Atmos. Environ. 41:6729–38. doi:10.1016/j.atmosenv.2007.04.053

Torkmahalleh et al. / Journal of the Air & Waste Management Association 63 (2013) 1313–13231322

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nloa

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by [

67.8

7.29

.143

] at

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2015

See, S.W., and R. Balasubramanian. 2008. Chemical characteristics of fineparticles emitted from different gas cooking methods. Atmos. Environ.42:8852–62. doi:10.1016/j.atmosenv.2008.09.011

Seigneur, C., and E. Constantino. 1995. Chemical kinetic mechanism for atmo-spheric chromium. Environ. Sci. Technol. 29:222–31. doi:10.1021/es00001a029

Swietlik, R., A. Molik, M. Molenda, M. Trojanowska, and J. Siwiec. 2011.Chromium(III/VI) speciation in urban aerosol. Atmos. Environ. 44:1364–68. doi:10.1016/j.atmosenv.2010.12.001

Talebi, S.M. 2003. Determination of total and hexavalent chromium concentra-tions in the atmosphere of the city of Isfahan. Environ. Res. 92:54–56.doi:10.1016/S0013-9351(02)00036-1

Tirez, K., G. Silversmit, N. Bleux E. Adriaensens, E. Roekens, K. Servaes, C.Vanhoof, L. Vincze, and P. Berghmans. 2011. Determination of hexavalentchromium in ambient air: A story of method induced Cr(III) oxidation.Atmos. Environ. 45:5332–41. doi:10.1016/j.atmosenv.2011.06.043

Yang, M. 2007. Sampling and Analysis of Hexavalent Chromium in AirborneAmbient Particular Matter. Master’s thesis, Clarkson University, Potsdam, NY.

Unceta, N., F. Seby, J. Malherbe, and O.F.X. Donard. 2010. Chromium speciationin solid matrices and regulation: A review. Anal. Bioanal. Chem. 397:1097–111. doi:10.1007/s00216-009-3417-1

Utsunomiya, S., K.A. Jensen, G.J. Keeler, and R.C. Ewing. 2004. Direct identi-fication of trace metals in fine and ultrafine particles in the Detroit urbanatmosphere. Environ. Sci. Technol. 38(8): 2289–97. doi:10.1021/es035010p

Zereini, F., F. Alt, J. Messerschmidt, C. Wiseman, I. Feldmann, A. Bohlen,J. Müller, K. Liebl, and W. Püttmann. 2005. Concentration and distributionof heavy metals in urban airborne particulate matter in Frankfurt am Main,Germany. Envir. Sci. Technol. 39:2983–89. doi:10.1021/es040040t

About the AuthorsMehdi Amouei Torkmahalleh is a research assistant in the Department ofChemical and Biomolecular Engineering at Clarkson University.

Chang-Ho Yu is a postdoctoral associate and Zhihua (Tina) Fan is an associateprofessor in Exposure Science Division, Environmental and Occupational HealthSciences Institute, Rutgers University.

Lin Lin was the director of the Analytical Laboratory, Center for Air ResourcesEngineering and Science at Clarkson University.

Julie L. Swift is a programmanager/chemist at the Eastern Research Group, Inc.,Morrisville, North Carolina.

Linda Bonanno is a research scientist I, Division of Air Quality/Office ofScience, New Jersey Department of Environmental Environmental Protection.

Don H. Rasmussen is a professor of chemical and biomolecular engineering atClarkson University.

Thomas M. Holsen is a professor of civil and environmental engineering atClarkson University.

Philip K. Hopke is the Bayard D. Clarkson Distinguished Professor, Director ofthe Center for Air Resources Engineering and Science and Director, Institute for aSustainable Environment, Clarkson University.

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