Characterization of the olfactory impact around a wastewater treatment plant: optimization and validation of a hydrogen sulphide determination procedure based on passive diffusion

This article was downloaded by: [Héctor Espinós-Morató]On: 10 August 2012, At: 11:02Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Journal of the Air & Waste Management AssociationPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/uawm20

Characterization of the olfactory impact arounda wastewater treatment plant: Optimization andvalidation of a hydrogen sulfide determinationprocedure based on passive diffusion samplingFernando Llavador Colomer a , Héctor Espinós-Morató b , Enrique Mantilla Iglesias b , TatianaGómez Pérez b , Andreu Campos-Candel b & Caterina Coll Lozano ca Entidad Pública de Saneamiento de Aguas Residuales de la Comunidad Valenciana (EPSAR),Valencia, Spainb Instituto Universitario Centro de Estudios Ambientales del Mediterráneo CEAM-UMH,Valencia, Spainc IMECAL S.A. L'Alcúdia, Valencia, Spain

Accepted author version posted online: 21 May 2012. Version of record first published: 18Jul 2012

To cite this article: Fernando Llavador Colomer, Héctor Espinós-Morató, Enrique Mantilla Iglesias, Tatiana Gómez Pérez,Andreu Campos-Candel & Caterina Coll Lozano (2012): Characterization of the olfactory impact around a wastewatertreatment plant: Optimization and validation of a hydrogen sulfide determination procedure based on passive diffusionsampling, Journal of the Air & Waste Management Association, 62:8, 863-872

To link to this article: http://dx.doi.org/10.1080/10962247.2012.686440

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.

TECHNICAL PAPER

Characterization of the olfactory impact around a wastewater treatmentplant: Optimization and validation of a hydrogen sulfide determinationprocedure based on passive diffusion samplingFernando Llavador Colomer,1 Héctor Espinós-Morató,2,⁄ Enrique Mantilla Iglesias,2

Tatiana Gómez Pérez,2 Andreu Campos-Candel,2 and Caterina Coll Lozano31Entidad Pública de Saneamiento de Aguas Residuales de la Comunidad Valenciana (EPSAR), Valencia, Spain2Instituto Universitario Centro de Estudios Ambientales del Mediterráneo CEAM-UMH, Valencia, Spain3IMECAL S.A. L’Alcúdia, Valencia, Spain⁄Please address correspondence to: Héctor Espinós-Morató, Mediterranean Center for Environmental Studies–CEAM, Parque Tecnológico,C/ Charles R. Darwin 14, Paterna 46980, Valencia, Spain; e-mail: [email protected]

A monitoring program based on an indirect method was conducted to assess the approximation of the olfactory impact in severalwastewater treatment plants (in the present work, only one is shown). The method uses H2S passive sampling using Palmes-typediffusion tubes impregnated with silver nitrate and fluorometric analysis employing fluorescein mercuric acetate. The analyticalprocedure was validated in the exposure chamber. Exposure periods of at least 4 days are recommended. The quantification limit ofthe procedure is 0.61 ppb for a 5-day sampling, which allows the H2S immission (ground concentration) level to be measured withinits low odor threshold, from 0.5 to 300 ppb. Experimental results suggest an exposure time greater than 4 days, while recoveryefficiency of the procedure, 93.0 � 1.8%, seems not to depend on the amount of H2S collected by the samplers within theirapplication range. The repeatability, expressed as relative standard deviation, is lower than 7%, which is within the limits normallyaccepted for this type of sampler. Statistical comparison showed that this procedure and the reference method provide analogousaccuracy. The proposed procedure was applied in two experimental campaigns, one intensive and the other extensive, andconcentrations within the H2S low odor threshold were quantified at each sampling point. From these results, it can beconcluded that the procedure shows good potential for monitoring the olfactory impact around facilities where H2S emissionsare dominant.

Implications: Passive samplers are very attractive tools to experimentally tackle a number of air pollution problems, especiallythose related to odor impact. Their small size and cost permit a denser sampling design and thus a more detailed spatialcharacterization than other techniques. On the other hand, the large inherent variability in passive sampler measures requires anuncertainty analysis of the chemical species and analytical procedures used.

Introduction

It is estimated that environmental odors cause annoyance to13–20% of the population of some European countries (Hudonet al., 2000). In fact, the majority of public complaints presentedto regulatory agencies in both Europe and North America arerelated to odor annoyance (Leonardos, 1995).

Hydrogen sulfide (H2S) is a colourless gas that occurs natu-rally during the treatment processes of wastewater, such asthrough bacterial action on organic matter under anaerobic con-ditions, especially in biological reactors (Stuetz and Frechen,2001). In general, the importance of H2S determination in airlies in its toxicity (only indoor ranges) and in the unpleasant odorthat it entails (in the environment, at much lower concentrations)(U.S. National Library of Medicine, n.d.).

H2S has a noxious odor even at trace-level concentrations,with a low odor threshold that ranges from 0.5 to 300 ppb,although 8.1 ppb can be considered the odor threshold, a valuecorresponding with the 50th percentile of the perception distri-bution (Amoore, 1985; Lawrence et al., 2000).

Its presence in the ambient air of inhabited areas can causechronic or acute episodes of high olfactory impact. Thus, to avoidcomplaints related to odor, theWorld Health Organization (WHO)recommended in the year 2000 that 7 mg/m3 should not beexceeded over a 30-min averaging period (World HealthOrganization 2000).

Schiffman et al. speculated on the possibility that odors couldcause harmful effects on health and the environment, but datarelating the incidence of respiratory diseases to odors are scarce(Campagna et al., 2004; Schiffman et al., 2005).

863

Journal of the Air & Waste Management Association, 62(8):863–872, 2012. Copyright © 2012 A&WMA. ISSN: 1096-2247 printDOI: 10.1080/10962247.2012.686440

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

Wastewater treatment plants (WWTP) have been identified aspotential sources of offensive odors, and H2S not only has beenassociated with olfactory impacts, but also has been shown toexhibit a clearly dominant role over other odorants (RWDI AirInc., 2005; Leonardos, 1995; NEDQ, 1997).

The odor intensity of binary, ternary, and quaternary mixturesprepared with odorants characteristic of a WWTP is very close tothat of the dominant component in the mixture; consequently, thiscompound can give an indication of the total olfactory impact(Laing et al., 1994). As H2S is often present in higher concentra-tions than other odorants in the air around aWWTP, it can be usedas a valid marker for the odors arising from such facilities. A studycarried out with 70 air samples collected from several industrialenvironments under strong source activity concluded that theodorant concentration data measured via an instrumental methodcould be used effectively to account for the odor intensity esti-mated by the sensory method (Kim and Park, 2008). Literaturedescribes the variety of procedures used to quantify H2S concen-trations in ambient air. Among the continuous procedures, auto-matic analyzers like gold-film or ultraviolet (UV)–fluorescenceanalyzers are widely employed. The former is based on resistancechanges of a thin gold film as a result of adsorption of H2Smolecules, whereas the latter actually measures sulfur dioxide(SO2) concentrations but can be converted by first scrubbingSO2 out of the sample and then catalytically oxidizing H2S toSO2 (Stuetz and Frechen, 2001). These instruments are very stableand reproducible, and they have been applied to H2S measure-ments in both urban and sewage ambient air (Kourtidisa et al.,2008; McIntyre, 2000). Their main drawback is their high cost;thus, using them to monitor analyte concentration spatial varia-tions at several points simultaneously is not economically feasible.

Discontinuous procedures involve laboratory analysis of asample previously collected in the field. Sampling can be activeor passive, depending on whether the air is forced to passthrough the sampler by means of a pump or diffuses throughthe device.

Spectroscopic, chromatographic, and electrochemical techni-ques are widely used in sulfide (S2-) determination (Lawrenceet al., 2000). The standard wet method for environmental H2Sdetermination entails its active collection in a Cd(OH)2 suspen-sion followed by colorimetry through formation ofmethylene bluedye. This procedure is sensitive and selective but requires hand-ling solutions and glassware in the field (Natusch et al., 1974).

Other reagents, such as silver–gelatin complex, lead acetate,mercuric chloride, silver nitrate, or zinc acetate, have also beenused for sampling. Silver nitrate has been considered the mostsuitable reagent for the active sampling on paper filters of H2S inthe 0.001–50 ppm range. Silver–gelatin complex and lead sul-fide are sensitive to photoreduction, whereas working with mer-curic chloride is time-consuming. Stainless steel meshes andsilica gel have been employed as solid supports as well (hhtp://www.radiello.com/english/h2s_en.htm).

Impregnated supports have the important advantages of easeof preparation, simplicity of adaptation to active and passivesampling, and portability.

Silver sulfide (Ag2S) is formed from H2S adsorption ontosilver nitrate (AgNO3). It can be quantified by a fluorometricmethod employing fluorescein mercuric acetate (FMA)

complexes which are quenched by the presence of sulfide. Thismethod is highly sensitive, with a detection limit of the order of50 ppt, as it combines the low detection limits for fluorescentcompounds offered by this analytical technique with the precon-centration of the analyte on the sampler. It can also be consideredspecific because notable interferences with AgNO3 have notbeen described throughout the selective sampling stage. It hasbeen applied successfully in outdoor and indoor environments(De Santis et al., 2006; Natusch et al., 1972; Shooter et al., 1995).

Other alternative procedures are based on the use of separationtechniques, like gas chromatography (GC)—appropriate becauseof H2S volatility—ion chromatography (IC), or high-performanceliquid chromatography (HPLC) (Bramante et al., 2006; Lawrenceet al., 2000). GC has been applied to the determination of sulfurcompounds in ambient air or in relation to animal feeding opera-tions. Air samples are usually collected in closed containers likecanisters or bags, preconcentrations are made in the laboratory, andthe analyte is then quantified by means of a suitably sensitivedetector, for example, a mass spectrometer (MS) or a pulsedflame photometric detector (PFPD) (Li and Shooter, 2004;Trabuea et al., 2008). The procedure recommended by theU.S. Occupational Safety and Health Administration (OSHA)involves active sampling with silver nitrate-coated silica gel andanalysis by ICusing a conductivity detector (Bramante et al., 2006).

Direct reading systems, which are able to quantify H2S con-centrations in air of a few parts per million, are employed mainlyin occupational environments. These are based on colorimetricor luminescent reactions, among other phenomena (McKee andMconnaughey, 1986).

Impregnated solid supports can be adapted easily to passivesampling systems, as in the case of Palmes-type dosimeters andradial geometry samplers (Palmes and Gunnison, 1976; Wattset al., 2003). Moreover, passive samplers have several advan-tages over active techniques: lower cost, permitting the simulta-neous deployment of a large number of samplers at differentsites; greater simplicity, because the flow does not have to beadjusted; and greater autonomy, since an electrical supply is notrequired and sampling periods can be extended. On the otherhand, passive samplers generally perform poorly with respect totemporal variability because they provide averaged concentra-tions over the entire sampling period instead of instantaneousones. Nevertheless, a strategy based on this sampling methodcould be useful for characterizing the olfactory impact around aWWTP, as it could maximize the cost/performance ratio.

This paper describes the optimization and validation of ananalytical procedure for determining the atmospheric concentra-tion of H2S. The procedure involves diffusive sampling usingPalmes-type dosimeters equipped with AgNO3-impregnatedsupports and analysis by the FMA fluorometric method. Theresults obtained from using this procedure to monitor the olfac-tory impact around a WWTP are also reported.

Experimental Work

Diffusive sampler

Palmes-type diffusion tubes were used to sample H2S(Shooter et al., 1995). They consisted of hollow acrylic tubes

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872864

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

with a length (L) of 70 mm and an internal diameter (d) of 10mm, fitted on one end with polypropylene caps containing anadsorbent support with a 12 mm internal diameter. The samplerswere mounted vertically, with the adsorbent end upward, on aholder with capacity for up to four tubes. In the case of ambientmeasurements, the holders with the exposed samplers weresheltered by means of a cylindrical frame at a height of approxi-mately 2.5 m above the ground for ventilation and protectionagainst bad weather, as can be seen in Figure 1. To ensureadequate preservation of the diffusive sampler, its lower endwas sealed both before and after sampling with a polypropylenecap that contained no adsorbent support. Then the sampler wasplaced in a hermetic plastic bag that was kept in a refrigerator andprotected from light. All the components of the sampler, theholder, and the shelter were manufactured from industrial mate-rials at the facilities of the Mediterranean Center forEnvironmental Studies–CEAM.

During exposure, gaseous pollutants diffuse up the tubetoward the support impregnated with AgNO3. There, the H2Smolecules are specifically adsorbed and converted intoAg2S. The diffusion is controlled by the H2S molecular diffusioncoefficient in air, the geometry of the sampler, and the gradientbetween the H2S concentration in ambient air and in the sur-roundings of the adsorbent support. The pollutant concentrationin ambient air (standardized at a temperature of 293 K and apressure of 101.3 kPa) is calculated by applying eq (1), derivedfrom Fick’s first law by assuming that the concentration at theend of the tube is very close to zero due to efficient eliminationof pollutants by the adsorbent:

Cð�g=m3Þ ¼ ðmð�gÞ � mBð�gÞÞ � zðcmÞR� Dðcm2= secÞ � p� r2ðcm2Þ � tðsecÞ

� TambðKÞ293ðKÞ � 101:3ðKPaÞ

PambðKPaÞ� 106

(1)

where R is the recovery efficiency,D the coefficient of moleculardiffusion (D ¼ 0.160 cm2/sec) (Gudzhedzhiani, 1978), r theradius of the dosimeter (r ¼ 0.5 cm), t the sampling time, z thediffusion length in the tube (z¼ 7cm), m andmB the H2S massesmeasured in the exposed sampler and in the blank, respectively,and Tamb and Pamb the mean ambient temperature and the meanatmospheric pressure over the exposure period. The nominaluptake rate (UR) of the diffusion tube for H2S was estimated to

be 0.018 mL air per second, calculated from the values of D andthe geometry of the sampler, z and r2. Equation (1) is thenconverted to the following equation:

Cð�g=m�3Þ ¼ mð�gÞ � mBð�gÞR� URðcm3=sÞ � tðsÞ �

TambðKÞ293ðKÞ

� 101:3ðKPaÞPambKPa

� 106(2)

Exposure chamber system

To carry out the experiments described in this paper, batchesof diffusive samplers were placed inside an exposure chamberwhere the H2S concentration was controlled (Figure 2). Thischamber consists of a semispherical Teflon compartment witha capacity of 1 m3. An internal Teflon cover ensures its inertperformance, while a slight overpressure is also applied to pre-vent pollutants entering from outside. Homogeneity is achievedby a fan installed inside the chamber. Diffusive samplers andprobes are inserted or removed through openings with caps ontheir base.

Figure 1. View of the dosimeter and the device used for ambient sampling.

Figure 2. View of the equipment employed: chamber, automatic analyzer,dilution system, and H2S/N2 gas cylinder.

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872 865

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

Several controlled atmospheres containing different H2S con-centrations, from 2 to 500 ppb, were generated by diluting anH2S/N2 standard mixture inside a compressed gas cylinder withpurified air N2/O2. This air is produced by a compressor, and it isdried and chemically filtered in an air purification system thatincludes adsorption driers of type HEA 1400 (Zander, Essen,Germany) filled with a molecular sieve ECO 30%/MOL 70%(Sogimair, Barcelona, Spain). The relative humidity of the air islower than 2%.

The mean concentration of H2S during the different exposuretimes of the diffusive samplers was measured independently byan automatic analyzer, designated as an automatic equivalentmethod by the U.S. Environmental Protection Agency(U.S. EPA, 2009). For this purpose, a modified commercialUV fluorescence SO2 analyzer (model 4108, DasibiEnvironmental Corporation, Glendale, CA) continuously mon-itored the H2S concentration in the exposure chamber. Thisinstrument was originally designed to measure sulfur dioxide,but for our experiment it was modified by first scrubbing sulfuroxides (SOx) from the air and then catalytically oxidizing H2S toSO2 in an oven. The analyzer was also calibrated under anatmosphere with a controlled H2S concentration. This instru-ment recorded 10-min average concentration data, which wereaveraged for comparison with the diffusion tube measurementdata.

Diffusion tubes were assembled and disassembled under apurified air atmosphere and protected from light.

Sampler analysis

The H2S collected on the adsorbent support was determinedby the FMA fluorometric method. After the samples werecollected, the tubes were opened and, using tweezers, the sup-ports were placed inside polypropylene test tubes with caps.Alkaline cyanide solutions were employed to extract Ag2Sfrom the adsorbent because cyanide forms a complex withsilver, releasing S2-. Solutions of 0.1 M NaCN/0.1 M NaOHare used to extract filters and meshes exposed to environmentswith low H2S concentrations, parts per trillion or low parts perbillion (Natusch et al., 1972; Shooter et al., 1995), whereasmore concentrated solutions, for example, 0.5 M NaCN/0.1 MNaOH, are necessary to remove the sulfide when samples comefrom occupational environments where the expected concen-trations are higher, parts per billion or parts per million (OSHA,2006). In this study, 3 mL of 0.2 M NaCN/0.1 M NaOH wasadded to the tubes before treatment in an ultrasonic bath for 15min. Then 2 mL of the extract was transferred to a stopperedquartz cell, with 0.1 mL of 10-6 M FMA/0.1 M NaOH added,and the solution was mixed and the fluorescence intensitymeasured using a Hitachi F-4500 fluorescence spectrophot-ometer (lex ¼ 499 nm and lem ¼ 519 nm) (Natusch et al.,1972). Seven fresh sulfide standards in the 0–1.5 � 10-7 Mrange were used to establish the calibration curve (Shooteret al., 1995). These were prepared by dilution of a 10-6 Msolution of sodium sulfide (Na2S) using the NaCN extractingsolution. The use of S2- aqueous standards instead of gaseousones is adequate, although there is a risk of underestimating theprecision of the method (Farwell et al., 1987).

Preliminary experiments

To study the performance of the diffusive sampler and theanalytical method, several preliminary tests were carried out.Their results were compared with the ones provided by theautomatic analyzer. Each batch was composed of six replicates(n ¼ 6) and three blanks.

To evaluate the influence of different kinds of supports on thediffusion tube measurement, two of the most commonly usedones were tested: stainless-steel meshes and cellulose acetatefilters (Millipore, Bedford, MA), both with a 12-mm diameter.For this, two batches of tubes were exposed to a controlledatmosphere of 20 ppb H2S, representative of the concentrationaround aWWTP, for 4 days. In the first batch, two stainless-steelmeshes were fitted into the cap and impregnated with 50 µL of1% AgNO3/10% glycerol in 20/80 EtOH/H2O (Shooter et al.,1995). In the second batch, however, the silver nitrate-impregnated filters were prepared by soaking cellulose acetatefilters in HNO3 0.01 M/2% AgNO3/2% glycerol in 20/80 EtOH/H2O (Natusch et al., 1974). After 2 hr of immersion, the filterswere removed and inserted into the caps.

Thus, it was considered necessary to investigate severalpotential effects: the effects of drying the supports after theirimpregnation and before sealing the samplers for storage, theeffects of changing the composition of the AgNO3 solution, andthe effects of exposing the samplers to different H2S concentra-tion levels, including one associated with polluted environments.For this, three batches of samplers were exposed to 15 ppb andalso to 500 ppb for a period of 4 days using two stainless-steelmeshes as supports. Two batches were impregnated with a solu-tion of 1% AgNO3/10% glycerol in 20/80 EtOH/H2O. In one ofthem, the tubes were sealed immediately after the support wasimpregnated, and in the other the meshes were left to dry insidethe chamber under a purified air atmosphere. For the remainingbatch, a solution that did not contain glycerol was used, 1%AgNO3 in 20/80 EtOH/H2O, and the supports were dried beforesealing the samplers.

Optimization of exposure time and H2S ambientconcentration

These two variables, exposure time and H2S ambient concen-tration, usually have a significant influence on the developmentof passive diffusion sampling. Therefore, to study their effectand the result of their interaction on the performance of thesampler and to establish their optimal levels, a factorial experi-ment was designed (Miller and Miller, 2000). Factorial experi-ments not only detect and estimate any interaction; they alsorequire fewer tests than the classical approach to obtain theoptimal levels.

In this case, each batch was composed of six replicates (n¼ 6)and one blank and, again, the results were compared with thoseprovided by the reference method.

A full factorial two-level experiment with two factors (22) wasdesigned. Three replicates of a center point were added to test forthe presence of curvature in the response and to obtain indepen-dent error estimates (Montgomery, 1991). A broad range of H2Sconcentrations can be found in the ambient air around a WWTP

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872866

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

(Lee et al., 2006). For this reason, the optimization was carriedout at two concentration ranges, one low (experiment I) and theother high (experiment II), since the use of two distant levels tocover such a broad experimental domain could cause a differencein response that would not be significant (Miller and Miller,2000). As shown in Table 1, it was decided that the exposuretime should be less than 8 days to achieve results with a shortenough temporal representativeness and to avoid possible satura-tion of the device, which determines the upper limit of applic-ability of the procedure; it was also considered that 2 days ofsampling would be sufficient if the dosimeter performance wasadequate, with 5 days as the center point. For experiment I, 6 ppbwas chosen as the center point, with 2 ppb and 10 ppb as theendpoints, whereas for experiment II, 275 ppb was chosen as thecenter with 225 ppb of distance between levels, which generated50 ppb and 500 ppb as the extremes. Recovery, calculated as theratio of the concentrations provided by the diffusion tubes to thevalues of the analyzer, was selected as the response. This value iscomplementary to the relative error, which is calculated as thedifference between 1 and recovery.

Batches were simultaneously exposed inside the chamber for2 days and 8 days for each concentration level studied. Diffusivesamplers with an exposure time of 2 days were introduced at theend of the sixth day after the start of the test. Both batches wereremoved at the end of the eighth day and simultaneouslyanalyzed.

Validation of the procedure

Limit of detection and limit of quantificationThe limit of detection (LOD) of the procedure is expressed as

the minimum mass of H2S collected onto the adsorbent supportof the dosimeter which provides a signal significantly differentfrom the mean signal of the blank. A blank is a passive diffuserthat is prepared in the same way as the dosimeters tested andaccompanies them during storage and transportation; however, itremains closed for the entire sampling time. The LOD wascalculated as the ratio of 3.29 times the standard deviation of

the blank (sb) to the slope of the calibration curve. A conservativecriterion (a ¼ b ¼ 5%) was used instead of others with 3 sb(Massart et al., 1997).

Two sets of blanks were prepared to establish the LOD. Bothconsisted of 10 independent sample blanks (n¼ 10), which wereeach measured once (Eurachem n.d.). The blanks of one batchwere exposed unopened to external ambient conditions for 8days (exposure blanks), whereas the ones in the other batchwere kept stored in the refrigerator during that time (preparationblanks). The limit of quantification (LOQ), which determinesthe lower limit of applicability of the procedure, was expressedas 3.04 times the LOD (IUPAC, 1997).

Accuracy and precisionThe broad range of H2S concentrations that can be found in

ambient air causes variations in the amount collected onto theadsorbent. To evaluate the accuracy of the procedure underdifferent concentration levels, five series of samplers wereexposed to different conditions within the previously optimizedrange for exposure time and ambient H2S concentration. Thus,every set of dosimeters should have sampled a different amountof H2S within the limits of application of the procedure. Therecovery efficiency of the procedure, R in eq (2), was establishedby comparing the diffusion results with the analyzer measure-ments. Each batch consisted of six replicates (n¼ 6) and a blank.

Moreover, in order to establish the possible presence of sys-tematic errors in the procedure, its results were compared bysimple least-squares regression with those provided by the refer-ence method (experimental values¼ f(theoretical values)) for 10samplers (n¼ 10) exposed for different periods of time at a widerange of ambient concentrations of H2S (Miller and Miller,2000). The statistical study of the slope and the intercept allowsus to determine whether they are significantly different from 1and 0, respectively, for a specific confidence level, and thus howaccurate the method is.

The coefficient of variation (CV), or relative standard devia-tion (RSD), is a statistical measurement of the repeatability of theprocedure. It was calculated for each of the five series as the ratioof the standard deviation of the concentrations provided by sixreplicate samplers and their averaged concentration.Additionally, the average CV over the studied range was calcu-lated to estimate the overall precision of the procedure.

Experimental campaigns

A monitoring program designed to evaluate the olfactoryimpact by means of the proposed procedure was carried out atthe Rincón de León WWTP, which is located relatively close toboth the city of Alicante (Spain) and the coast.

Intensive sampling was conducted inside and outside theplant for 5 days during the summer period. Fifteen internalmeasurement points were set up according to a geometric criter-ion. Passive samplers were placed at the perimeter of the plantand at intermediate points in relation to the potential focus, all ofthem out of the direct influence of the emissions. Nine externalpoints, covering several kilometers around the plant, were dis-tributed on the basis of the wind pattern and orography in thearea under study. Results could reveal the spatial structure of the

Table 1. A two-factor two-level full factorial design: runs, plan of experimenta-tion, and observed response

MatrixPlan of

experimentationResponse

Experiment X1 X2 Conc. (ppb) Days recovery (%)

I 1 –1 –1 2 2 572 –1 þ1 2 8 753 þ1 –1 10 2 744 þ1 þ1 10 8 94

5, 6, 7 0 0 6 5 92II 1 –1 –1 50 2 73

2 –1 þ1 50 8 903 þ1 –1 500 2 924 þ1 þ1 500 8 95

5, 6, 7 0 0 275 5 94

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872 867

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

impact field, which is usually strongly dependent on the prevail-ing weather conditions. A 1-yr extensive campaign was con-ducted inside the facility to systematically monitor H2S levels,after four internal points were considered representative of theimmission (ground-level concentration) field. The passive sam-plers were deployed once a month for 5 days. Measurements atfixed points over long periods of time reflect the seasonal varia-bility of H2S concentrations. At each sampling point, threedosimeters and one blank were exposed.

Meteorological information was provided by a tower installedin the plant. This infrastructure consists of a 15-m-tall mast withwind measurements (speed and direction) at the highest level andtemperature measurements at two heights (3 and 15 m, thusproviding a direct measure of the surface thermal gradient).The measurement system operates continuously and averagesthe data at 10-min intervals.

Results and Discussion

Experiments were carried out in six replicates because the useof single tubes is problematic (Ankersmit et al., 2005) andbecause Dixon’s Q-test can be correctly used to eliminate out-liers at a 95% confidence level with samples of this size (Millerand Miller, 2000). The values provided by each series of repli-cates were then considered. Subsequently, the results obtainedafter subtracting the corresponding blank were compared withthose provided by the reference method. Finally, the series pre-senting the lowest relative error in each experiment was chosen(Er) so as to achieve the most effective sampling.

Preliminary experiments

A t-test was applied to compare the means of the two batchesof samplers equipped with different kinds of supports (Millerand Miller, 2000), one with two stainless-steel meshes and theother with cellulose acetate filters. It showed a statistically sig-nificant difference between using one or the other (t0¼ 2.52, tc¼2.45, p ¼ 0.05). Two stainless-steel meshes were selected as theadsorbent support because their Er (relative error), 1%, waslower than the filter one, 13%, although their CV was slightlyhigher, 13% vs. 4%. Stainless-steel meshes have generally beenused for dosimeters with this geometry (Glasius et al., 1999;Heal et al., 1999). Nevertheless, one study reported that bothsupports had performed similarly in their experiments althoughextraction had not been carried out using an ultrasonic bath(Shooter et al., 1995). In our case, the difference could be dueto degradation of the cellulose acetate filter during the sonicationstep.

Neither the drying of the meshes after their impregnation withthe AgNO3 adsorbent solution nor the absence of glycerol in thesolution influenced the performance of the sampler. Analysis ofvariance (ANOVA) (Miller and Miller, 2000) of these threeseries did not reveal any statistically significant differencesbetween their means, both at low and high concentrations ofH2S (F0 (15 ppb)¼ 0.03; F0 (500 ppb)¼ 2.08, Fc¼ 4.77; p¼ 0.05).This contradicts a preceding paper that considered the presenceof glycerol in the composition of the solution to be necessary toachieve quantitative sampling with filters when the relative

humidity is low (Natusch et al., 1974). The relative humidity ofthe air used to fill up the exposure chamber in this study waslower than 2% and the mean recovery obtained using twomeshesas the support was approximately 91%. Therefore, glycerol canbe eliminated from the composition of the adsorbing solutionunder low relative humidity conditions if this type of support isused. In practice, to achieve the shortest preparation time the twomeshes were not allowed to dry after their impregnation with 50µL of a solution of 1% AgNO3, 10% glycerol in 20/80 EtOH/H2O and before sealing the tubes for preservation. Although thedifferences between this method and the other two were not verysignificant, this method exhibited the lowest Er for both concen-tration levels, 5%, and also the smallest CV, 9% and 3% for 15ppb and 500 ppb, respectively. It can be seen that the CVof theseries exposed to 15 ppb was slightly higher than that of theseries exposed to 500 ppb, whereas the Er remained approxi-mately constant.

Optimization of exposure time and H2S ambientconcentration

It is necessary to determine the minimum period of time that asampler has to be exposed to the environment for it to accuratelymeasure H2S with respect to the reference method. For this, afactorial experiment 22 with three center points was designed.The results were statistically analyzed using Statgraphics soft-ware. One outlier was eliminated from the replicates of thecentral point in experiment I.

Analysis of variance (ANOVA) showed that exposure timeand ambient concentration were statistically significant variables(p-value < 0.05), although not their interaction (p-value > 0.05),for both the low range and the high range of H2S concentrations.For both ranges, these variables had a similar positive effect onthe recovery of the procedure, with exposure time showing aslightly greater influence. The tests carried out at any lower pointin experiment I exhibited Er equal to or higher than 25%,whereas in experiment II only the point (–1, –1) presented anequivalent value. Consequently, the lower the ambient concen-tration of H2S, the greater is the magnitude of the effect of eachvariable. Significantly higher relative errors were found for thosetests conducted for short exposure times. These values decreasedwhen the time ranged from the low level to the high one, as canbe seen in Table 1. This effect was more pronounced for thelowest studied concentration of H2S, 2 ppb. Similarly, as theconcentration increased, the Er decreased and the recoveryslightly improved. This tendency was not as pronounced forhigh concentration levels, which generally provided lower Er

than the experiments conducted at low concentrations.Thus, the recovery was considerably worsened for short

exposure times (2 days), but, on the other hand, the influenceof the concentration on the procedure was not as marked, exceptfor low levels (2 ppb). For this reason, Er for exposure times of 5and 8 days is lower than 10% except for an ambient concentra-tion of 2 ppb H2S.

The optimum point for the experimental domain of bothexperiments, Table 1, is [(1,1) ” maximum ambient concentra-tion, maximum exposure time], which corresponds to an 8-daysampling period and to the highest concentration studied. The

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872868

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

contours of the estimated response surface (not included)showed that recoveries close to 100% can be obtained with a 5-day sampling for an ambient concentration of 10 ppb H2S. Toconfirm this, an additional test was carried out and the diffusiontubes were exposed for 2, 4, 8, and 16 days to 10 ppb H2S. Theresults obtained supported the previous hypothesis becausequantitative recoveries were achieved for both the 4-day andthe 8-day exposure, approaching 93% and 96%, respectively. Asignificant difference between the mean of the 2-day series andthe others was also observed using the Tukey test (Miller andMiller, 2000).

Therefore, exposure times shorter than 4 days were not con-sidered suitable for this type of sampler. This duration is verysimilar to the 3.5 days reported in literature to validate theaccuracy of the device (Shooter et al., 1995).

Proposed procedure

The procedure involves H2S passive sampling using Palmes-type diffusion tubes that house two stainless-steel meshesimpregnated with 50 µL of a solution of 1% AgNO3, 10%glycerol in 20/80 EtOH/H2O. The samplers are exposed to theatmosphere for periods equal to or longer than 4 days and thenthe S2- collected onto the meshes is extracted with 3 mL of 0.2MNaCN/0.1 M NaOH by means of an ultrasonic bath for 15 min.Finally, the extract obtained is analyzed as described earlier andthe concentration of H2S in ambient air calculated with eq (2).

Validation of the procedure

Limit of detection and limit of quantificationOne outlier was eliminated from the replicates of the prepara-

tion blank. To check whether both types of blanks were equiva-lent or not, a t-test was applied. It showed statistically significantdifferences between the mass of S2- collected by exposing theclosed dosimeters to ambient air and by not exposing them (t0 ¼15.61, tc ¼ 2.23; p ¼ 0.05). The LOD calculated with exposureblanks is 2.2 ng, almost six times higher than that calculatedfrom preparation blanks, 0.4 ng. Following the conservativeapproach used previously, 2.2 ng of H2S was preferred as theLOD of the procedure, and hence 6.7 ng was established as theLOQ. This LOD is approximately twice the value obtained byShooter et al. using blanks exposed to air for a week, but it wasnot specified whether indoors or outdoors (Shooter et al., 1995).This fact might explain the difference, since both the procedureand the type of sampler used in both studies are similar.

Using eq (2) the LOD and the LOQ can be expressed in theH2S ambient air concentration, which can be detected or quanti-fied, respectively, as summarized in Table 2.

These values depend on the exposure period and facilitate thecomparison of different procedures. The ambient concentrationof H2S detectable by this procedure can also be represented as afunction of the length of the sampling period, as shown inFigure 3. According to this, as the exposure time increases, theprocedure is able to detect lower concentrations of H2S. Thus,concentrations of around 1 ppb can be detected after a 1-dayexposure. But, in practice, sampling periods appreciably longerthan the theoretical ones are recommended to ensure good arepresentation of the measurements (Glasius et al., 1999; Healet al., 1999). This has been demonstrated previously since theresults obtained from a 2-day sampling at different concentrationlevels presented high Er values with respect to the referencemethod.

Accuracy and precisionIn order to experimentally confirm the accuracy and repeat-

ability of the proposed procedure in its application range, 5 sets ofdosimeters were exposed for between 4 and 8 days to H2S con-centrations from 6 to 500 ppb. Thus, variable amounts of H2Swere sampled by the tubes. Table 3 shows that the recoveryefficiency of the procedure approaches 93% and does not dependon the amount of H2S collected by the dosimeters in the applica-tion range. The recovery depends, to a large extent, on the extrac-tion efficiency of the sulfur collected on the meshes with thecyanide solution. These results confirm that quantitative deso-rption was obtained using 3 mL of a solution of 0.2M NaCN/0.1M NaOH. Since there was no risk of degradation of the stainless-steel meshes, their immersion in an ultrasonic bath for 15 minutesensures a more intimate contact between Ag2S and CN-.

The populations of values obtained by the proposed proce-dure (corrected with R, as stated in eq (2)) for 10 samplersexposed to several H2S ambient concentrations for differentexposure times were compared with the results provided by theautomatic analyzer. The confidence intervals calculated at a 95%level for the intercept (b) and the slope (a) include the idealvalues of 0 and 1, respectively (y¼ 1.0028x – 0.0023; a between0.996 and 1.010; b from –0.016 to 0.011). So a and b are notsignificantly different from those values and, therefore, the pro-posed procedure is free from systematic errors.

The CVof the six samplers was lower than 7% in every series,with an average of 5%, largely within the limits normallyaccepted for this type of device, between 10 and 20% (DeSantis et al., 2006).

Table 2. LOD and LOQ of the procedure expressed as mass of H2S and ambientconcentration for 5 days or 1 hr sampling

H2S ng ppb/5 days ppb/hr

LOD 2.2 0.20 24LOQ 6.7 0.61 73

Figure 3. Theoretical H2S concentration that can be detected in ambient air bythis procedure as a function of the length of the sampling period.

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872 869

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

Experimental campaigns

The already-described procedure was applied to evaluate theolfactory impact around a WWTP, which is expressed as the

time-weighted average H2S concentration for a 5-day sampling,as summarized in Figure 4 and Figure 5.

Five days was selected for the exposure period because thiswould allow the greatest possible homogeneity in atmospheric

Table 3. Recovery of the procedure obtained for a confidence level of 95%

µg H2S per sampleraRecovery (%)

1 2 3 4 5 6 Average CV

0.07 88.7 90.3 98.4 83.9 96.8 90.3 91.4 5.90.20 92.4 89.0 96.6 94.9 89.8 99.2 93.6 4.20.89 96.4 91.9 90.5 93.7 82.7 97.8 92.2 5.83.37 92.9 85.5 91.0 96.8 93.2 97.4 92.8 4.78.51 84.9 95.3 93.1 99.4 103.3 94.3 95.0 6.6

aValue provided by the reference method.

Figure 4. Location of sampling points and H2S concentrations outside and inside the WWTP.

Figure 5. Monthly H2S variation observed at ground level inside the plant.

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872870

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

conditions to be achieved and because H2S concentrations closeto the olfactory threshold can be quantified throughout this time.

Outside the plant, the concentrations ranged between 0.74and 11.19 ppb. The only exceptions were two sampling pointsthat presented concentrations lower than the LOQ but higherthan the LOD. Figure 4 shows the normal concentration range aswell as the estimated values of these two exceptions. Markedlyhigher values, from 4.9 to 225.2 ppb, were found inside theWWTP, where there was also a strong concentration gradientbetween nearby points. Typical summer atmospheric conditionspersisted throughout the intensive campaign, with a predomi-nance of local breeze-type regimes. There is an axis of max-imums in roughly the east–west direction, which coincides withthe preferred air flow transport direction along the watercourse.Moreover, a clear gradient, which causes a decrease in concen-trations with distance from the plant, can also be observed inFigure 4. This gradient is more intense leeward of the night flow.Therefore, the immission values considerably decrease as thedistance from the potential emission sources increases, reachingthe lower range of the low odor threshold.

The evolution of the time series is very similar. The highestconcentrations were obtained for the summer and spring monthsduring the extensive campaign, as can be seen in Figure 5. Thistrend was more pronounced at the RI11 and RI15 points,whereas RI07 and RI12 showed more homogeneous values.RI11 values ranged between 10.5 and 144.9 ppb, which arelower than the RI15 concentrations, ranging from 29.5 to 309.1ppb, whereas RI07 and RI12 showed the lowest levels, from 1.7to 17.8 ppb and from 2.3 to 39.0 ppb, respectively. All theseconcentrations were higher than 0.5 ppb, the low odor threshold.RI07 always exhibited concentrations lower than 8.1 ppb, theodor threshold, whereas all the RI15 monthly values were higherthan 8.1 ppb. These results are logical since the samplers arelocated inside the influence area of potential emission sources.RI11 is placed south of the sludge line and west of the dewateringfacility, whereas the primary clarifiers are very close to RI15,which is situated east of the sludge line. RI07 and RI12 arepositioned to the east of the WWTP, rather far from the H2Spotential emissions.

Conclusions

The proposed procedure has been optimized and validatedagainst a laboratory reference method. It has been found toprovide an ideal platform for a cost-efficient monitoring programat either a large number of sampling points or a small number ofpoints with high temporal frequency. However, as averagedconcentrations for sampling periods shorter than 4 days cannotbe correctly obtained, any comparison against short-term con-centration limits is not feasible.

The applicability of this procedure to the determination of H2Sin real ambient air has also been verified with satisfactory results.The highest concentrations have been found at the points locatedinside the wastewater treatment plant. A concentration gradient isalso observed because H2S concentrations decrease considerablyas the distance from the potential emission sources increases. Thevalues from interior points located near emission sources show amarked seasonal variation, with maximums in summer and

minimums in winter, thus confirming the importance of meteor-ological conditions in emission-dispersion-immission processes.Five-day sampling permits the quantification of H2S concentra-tions close to the low odor threshold. All the points exhibit con-centrations within this threshold, from 0.5 to 300 ppb, althoughonly the interior values are higher than the odor threshold of H2Sconcentration detectable by the human nose, i.e., 8.1 ppb.

Thus, this procedure shows good potential for monitoring theolfactory impact from wastewater treatment plants, where H2Semissions are dominant.

Acknowledgments

This work is the result of a collaboration agreement betweenEPSAR (Entidad Publica de Saneamiento de la ComunidadValenciana) and the Valencian Instituto Universitario CEAM-UMH, having been financially supported by EPSAR. CEAM-UMH is partly supported by Generalitat Valenciana and theProjects GRACCIE (CSD2007-00067), CONSOLIDER-INGENIO 2010 Program-Spanish Ministry of Science andInnovation and FEEDBACKS (Prometeo/2009/006-GeneralitatValenciana).

ReferencesAmoore, J.E. 1985. The Perception of Hydrogen Sulfide Odor in Relation to

Setting an Ambient Standard. Berkeley, CA: Olfacto-Labs. Prepared for theCalifornia Air Resources Board.

Ankersmit, H.A., N.H. Tennent, and S.F. Watts 2005. Hydrogen sulfide andcarbonyl sulfide in the museum environment—Part 1 . Atmos. Environ.39:695–707.

Bramante, E., L. D’Ulivo, C. Lomontea, M. Onora, R. Zambonic, G. Raspi, andA. D’Ulivo 2006. Determination of hydrogen sulfide and volatile thiols in airsamples by mercury probe derivatization coupled with liquid chromatogra-phy–atomic fluorescence spectrometry. Anal. Chim. Acta 579:38–46.

Campagna, D., S.J. Kathman, R. Pierson, S.G. Inserra, B.L. Phipher, D.C.Middleton, G.M. Zarus, and M.C. White 2004. Ambient hydrogen sulfide,total reduced sulfur, and hospital visits for respiratory diseases in northeastNebraska, 1998–2000. J. Expos. Anal. Environ. Epidemiol. 14:180–187.

De Santis, F., I. Allegrini, R. Bellagotti, F. Vichi, and D. Zona 2006. Developmentand field evaluation of a new diffusive sampler for hydrogen sulfide in theambient air. Anal. Bioanal. Chem. 384:897–901.

Eurachem. n.d. The Fitness for Purpose of Analytical Methods: A LaboratoryGuide to Method Validation and Related Topics. Eurachem Guide. http://www.eurachem.org/guides/valid.pdf.

Farwell, S.O., W.H. Chatham, and C.J. Barinaga 1987. Performance characteriza-tion and optimization of the AgNO3-filter/FMA fluorometric method foratmospheric H2S measurements. J. Air Pollut. Assoc. Am. 37:1052–1059.

Glasius, M., M.F. Carlsen, T.S. Hansen, and C. Lohse 1999. Measurementsof nitrogen dioxide on funen using diffusion tubes. Atmos. Environ. 33:1177–1185.

Gudzhedzhiani, E.N. 1978. Effective coefficient of diffusion of acid gases incement material. Akad. Nauk. Gruz. 89:165–168.

Heal, M.R., M.A. O�Donoghue, and J.N. Cape 1999. Overestimation of urbannitrogen dioxide by passive diffusion tubes: A comparative exposure andmodel study. Atmos. Environ. 33:513–524.

Hudon, G., C. Guy, and J. Hermia 2000. Measurement of odor intensity by anelectronic nose. J. Air Waste Manage. Assoc. 50:1750–1758.

International Union of Pure and Applied Chemistry (IUPAC), 1997.Compendium of Chemical Terminology, 2nd ed. Eds. A.D. McNaught andA. Wilkinson. New York: IUPAC.

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872 871

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012

Kim, K.-H., and S.-Y. Park 2008. A comparative analysis of malodor samplesbetween direct (olfactometry) and indirect (instrumental) methods. Atmos.Environ. 42:5061–5070.

Kourtidisa, K., A. Kelesisb, and M. Petrakakisb 2008. Hydrogen sulfide (H2S) inurban ambient air. Atmos. Environ. 42:7476–7482.

Laing, D.G., A. Hedí, and D.J. Best 1994. Perceptual characteristics of binary,ternary and quaternary odor mixtures consisting of unpleasant constituents.Physiol. Behav. 56:81–93.

Lawrence, S.N., J. Davis, and G.R. Compton 2000. Analytical strategies for thedetection of sulphide: A review. Talanta 52:771–784.

Lee, J.A., J.C. Johnson, S.J. Reynolds, P.S. Thorne, and P.T. O’Shaughnessy.2006. Indoor and outdoor quality assessment of four wastewater treatmentplants. J. Occup. Environ. Hyg. 3:36–43.

Leonardos, G. 1995. Review of odor control regulations in the USA. In Odors.Indoor and Environmental Air Proceedings of a Specialty Conference of theA&WMA. Bloomington, MN: A&WMA, 73–84.

Li, K.-C., and D. Shooter. 2004. Analysis of sulphur-containing compoundsin ambient air using solid-phase microextraction and gas chromatography withpulsed flame photometric detection. Int. J. Environ. Anal. Chem. 84:749–760.

Massart, D.L., B.G.M. Vandeginste, S. de Jong, L.M. C, P.J. Lewi, and J.Smevers-Verbeke. 1997. Handbook of Chemometrics and Qualimetrics.Amsterdam: Elsevier.

McIntyre, A. 2000. Odour modelling and monitoring: The use of marker com-pounds such as hydrogen sulphide. In Proceedings of CIWEM/SouthernWater Approaches to Setting Odour Planning Conditions Workshop.

McKee, E.S., and P.W. McConnaughey. 1986. Laboratory validation of a passivelength-of-stain dosimeter for hydrogen sulfide. Am. Ind. Hyg. Assoc. J.47:475–481.

Miller, N.J., and J.C. Miller. 2000. Statistics and Chemometrics for AnalyticalChemistry. Harlow, England: Pearson Education Limited.

Montgomery, D.C. 1991. Design and Analysis of Experiments. New York: JohnWiley & Sons.

Natusch, D.F.S., H.B. Klonis, H.D. Axelrod, R.J. Teck, and J.P. Lodge. 1972.Sensitive method for measurement of atmospheric hydrogen sulfide. Anal.Chem. 44:2067–2070.

Natusch, D.F.S., J.R. Sewell, and R.L. Tanner. 1974. Determination of hydrogensulfide in air—An assessment of impregnated paper tape methods. Anal.Chem. 46:410–415.

Nebraska Department of Environmental Quality. 1997. Technical Basis for aTotal Reduced Sulfur Ambient Air Quality Standard. Lincoln, NE: NDEQ.

Palmes, E.D., and A.F. Gunnison. 1976. Personal sampler for nitrogen dioxide.Am. Ind. Hyg. Assoc. J. 37:570–577.

RWDI Air, Inc. 2005. Odour Management in British Columbia: Review andRecommendations. Final Report. Surrey: British Columbia Ministry ofWater, Land and Air Protection.

Schiffman, S.S., and C. Williams. 2005. Science of odor as a potential healthissue. J. Environ. Qual. 34:129–138.

Shooter, D., S.F. Watts, and A.J. Hayes. 1995. A passive sampler for hydrogensulphide. Environ. Monit. Assess. 38:11–23.

Stuetz, R., and F.-B. Frechen. 2001. Odours in Wastewater Treatment.Measurement, Modelling and Control. London: IWA Publishing.

Trabuea, S., K. Scoggina, F. Mitloehnerb, H. Lic, R. Burnsc, and H. Xinc. 2008.Field sampling method for quantifying volatile sulphur compounds fromanimal feeding operations. Atmos. Environ. 42:3332–3341.

U.S. Environmental Protection Agency, 2009. List of Designated Reference andEquivalent Methods; EQSA-1086-061.www.epa.gov/ttn/amtic/criteria.html

U.S.National Library of Medicine. n.d. Toxicology Data Network (TOXNET).http://toxnet.nlm.nih.gov

U.S.Occupational Safety and Health Administration. 2006. Method 1008:Hydrogen Sulfide. OSHA Sampling and Analytical Methods, Salt LakeCity, UT. http://www.osha.gov/dts/sltc/methods/validated/1008/1008.html

Volkan, M., T. Eroglu, A.E. Eroglu, O.Y. Ataman, and H.B. Mark. 1998. A novelsorbent tube for ambient hydrogen sulphide determination. Talanta 47:585–593.

Watts, S.F., L. Ridge, A.R. Rendell, P.D. Grebenik, A. Miller, and A.J. Reid.2003. The use of diffusion tubes (Palmes tubes) for assessing air quality inindoor and outdoor environments. In Proceedings of the 4th InternationalConference on Urban Air Quality-Measurement, Modelling andManagement, Prague.

World Health Organization. 2000. Air Quality Guidelines for Europe. WHORegional Publications, European Series 91. Copenhagen, Denmark: WHORegional Office for Europe.

About the AuthorsAndreu Campos-Candel andHéctor Espinós-Morató are scientific collabora-tors at the Mediterranean Center for Environmental Studies–CEAM.

Enrique Mantilla Iglesias is senior researcher at the Mediterranean Center forEnvironmental Studies–CEAM.

Fernando Llavador Colomer is the head of the Quality Control Department atthe Public Entity of Wastewater Treatment (EPSAR).

Caterina Coll Lozano is the Plant Manager of a Bioethanol Plant at IMECAL,S.A., and she worked at the Mediterranean Center for Environmental Studies–CEAM until March 2007.

Tatiana Gómez Pérez is a laboratory technician at CEAM.

Colomer et al. / Journal of the Air & Waste Management Association 62 (2012) 863–872872

Dow

nloa

ded

by [

Héc

tor

Esp

inós

-Mor

ató]

at 1

1:02

10

Aug

ust 2

012