Aerosol Science 36 (2005) 639–650

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A static water surface sampler to measure bioaerosol depositionand characterize microbial community diversity

Ashish Sahu, Stefan J. Grimberg∗, Thomas M. HolsenDepartment of Civil and Environmental Engineering, Clarkson University, 8 Clarkson Avenue, Potsdam, NY 136995710, USA

Received 1 May 2004; received in revised form 1 October 2004; accepted 4 October 2004

Abstract

A static water surface sampler was developed to quantify bioaerosol deposition rates without the need of culturingprior to enumeration. Measured bioaerosol deposition fluxes upwind and downwind of an activated sludge aerationbasin ranged from 7.7× 106 to 1.4× 107#/m2h. Upwind bioaerosol fluxes were approximately 1.5 times smallerthan downwind fluxes. The mean atmospheric bioaerosol concentrations measured simultaneously with an open-face filter sampler ranged between 1.3 × 105 and 1.4 × 105#/m3 upwind and downwind of the aeration basinrespectively. The deposition velocities derived from the simultaneous measurements (1.5 and 3.2 cm/s upwind anddownwind respectively) were similar to those found for trace elements using similar techniques. Results fromamplified ribosomal DNA restriction analysis confirm that the bacterial composition of the downwind samplescontained DNA fragments consistent with the wastewater, while these fragments do not appear in upwind samples.The sampler will accommodate the inclusion of state-of-the-art biomolecular tools and allow for the generation ofquantitative data needed for fate and transport models.� 2004 Elsevier Ltd. All rights reserved.

Keywords:Bioaerosols

1. Introduction

Bioaerosols are often small particles that can easily penetrate into the lungs (Kenline & Scarpino,1971). However, they are also likely to be associated with larger airborne particles that are likely to

∗ Corresponding author. Tel.: +1 3152686490; fax: +13152687636.E-mail address:grimberg@clarkson.edu(S.J. Grimberg).

0021-8502/$ - see front matter� 2004 Elsevier Ltd. All rights reserved.doi:10.1016/j.jaerosci.2004.10.001

640 A. Sahu et al. / Aerosol Science 36 (2005) 639–650

be deposited higher in the respiratory tract. Some bacteria are of health concern since they may causediseases such as asthma (due to allergens) or other respiratory illnesses (Macher, Ammann, Milton,Burge, & Morey, 1999). Previous studies have found that composting facilities and wastewater treatmentfacilities are large bioaerosol sources and may therefore represent an exposure hazard to workers andpeople living in the vicinity of these locations (Johnson, Camann, Harding, & Sober, 1979; Sawyeret al., 1996). Hryhorczuk et al. (2001)showed a statistically significant pattern of decreasing bioaerosolconcentration with distance from a composting pile, a known source of bioaerosols. The mean bacterialconcentrations were highest 1m downwind (1.9×104 cfu/m3) of the composting pile and second highest10m downwind (1.0×104 cfu/m3) of the composting pile. Mean bacterial concentrations were relativelyconstant (1.3× 105–1.4× 105#/m3).A largevarietyof samplershavebeendeveloped tocollect airbornebacteriaand tostudy thesurvivability

of bacteria in theair (Cox&Wathes, 1995;Hering, 1989).Nostandardizedmethods for outdoor bioaerosolmonitoring are available to date (Cox & Wathes, 1995). More importantly, no techniques have beendeveloped thatwill quantify bioaerosol deposition rates, ameasureneeded for bioaerosol fateand transportmodels. This study focuses on a novel collection technique to determine bioaerosols dry deposition rates.There have been a variety of studies that have attempted to quantify dry deposition of trace metals and

other pollutants (for example seeDavidson, Lindberg, Schmidt, Cartwright, & Landis, 1985; Sofuogloet al., 1998; Paode et al., 1998). These studies include both direct measurements and modeled estimates.Modeled estimates are typically made by multiplying the measured airborne concentrations by a singlemodeled deposition velocity. There are several problemswith this approach.Theseproblemsarise becausedifferent size particles have different deposition velocities and the fact that deposition velocities vary withmeteorological conditions and surface characteristics (Willeke & Baron, 1993).Direct measurements of dry deposition can bemade with aerodynamically designed surrogate surfaces

that minimize air stream disruption and thus provide a measure of the minimum dry deposition flux.Measurements made with surrogate surfaces have been shown to agree well with fluxes modeled using amulti-step method that divides the aerosols into discrete size intervals andmultiplies each size interval byan appropriate deposition velocity (Yi, Holsen, & Noll, 1997; Paode et al., 1998; Sofuoglo et al., 1998;Shahin, Zhu, & Holsen, 1999). Surrogate surfaces can be used for extended periods of time at differentlocations to provide quantitative information on the temporal and spatial variation in dry deposition(Davidson et al., 1985).Collection of bioaerosols by surrogate surfaces containing agar has been used in the past to collect

and analyze bioaerosols (Chang, Hwang, Grinshpun, Macher, & Willeke, 1994; Kenline & Scarpino,1971). In this method deposited bacteria are counted on the surface after incubation of the plates to allowgrowth to occur. These plates are not aerodynamically designed so this technique is not very likely tobe reproducible. Another limitation of this collection technique is counting errors due to the overlappingof colonies of bacteria (Chang et al., 1994). More importantly, this method may only quantify a smallfraction of the deposited organisms since it is well known that only a very small fraction (less than 1%)of all environmental organisms present in the environment will grow on agar plates (Colwell & Grimes,2000).There is, therefore, a need to develop abioaerosol sampler thatwill reproducibly quantify depositedorganisms without the need to grow the organisms prior to enumeration.Inaneffort todevelopbacteria counting techniques forexposureassessmentof airbornemicroorganisms

that does not require culturingKildesZ and Nielsen (1997)proposed the use of fluorescent microscopy.Acridine orange was used in that study as the fluorescent stain. However, this stain cannot be used todistinguish between live and dead bacteria. As an alternativeTerzieva et al. (1996)collected aerosolized

A. Sahu et al. / Aerosol Science 36 (2005) 639–650 641

bacteria using an AGI-30 impinger and enumerated deposited bacteria using the LIVE/DEAD BacLightstaining technique. This technique uses a fluorescentmicroscopic and two fluorescent stains to distinguishbetween “live” (organisms with intact membranes) and “dead” (membrane compromised organisms)bacteria. The advantage of using fluorescent microscopy to enumerate deposited cells lies in the highsensitivity of the stains so that no growth is required before cells can be quantified. Results from thisstudy indicated cells were structurally damaged in the impinger.Recent advances inmolecular biologyallow for the rapid identificationof specificorganismswithout the

need to prior cultivation.Ranalli, Principi, andSorlini (2000)andPascual et al. (2001)applied polymerasechain reaction (PCR) to identify specific bacteria in bioaerosols in the collecting media without the needof cultivation. PCR has been advocated for identification of specific organisms in bioaerosols due toits enhanced sensitivity (Alvarez, Buttner, & Stetzenbach, 1995). PCR, however, does not provide anyquantitative information on the number of organisms present in any given measurement. Therefore, bothenumeration of total organisms andmolecular biological methods need to be used to quantify and identifystrains, respectively.The objective of this study was to develop a novel technique for collecting and analyzing bioaerosols

deposited via dry deposition without the need of culturing.The technique was tested near a known sourcefor bioaerosols, the Potsdam wastewater treatment plant. Upwind and downwind air and depositionsamples from the vicinity of the aeration basin of the wastewater treatment plant were collected andanalyzed for live and dead bacteria using the BacLight staining technique. The dry deposition flux anddeposition velocity of bacteria in air were calculated. Microbial bioaerosol diversity was evaluated usingamplified ribosomal DNA restriction analysis (ARDRA) (Massol-Deya, Odelson, Hickey, & Tiedje,1995). Results indicate that the microbial diversity changed significantly downwind of the aeration basinand the proposed experimental method could be very useful in evaluating the atmospheric transport anddeposition of bioaerosols.

2. Materials and methods

Two samplers were employed for onsite collection of airborne bacteria; the static water surface sampler(SWSS), which measures the dry deposition of bioaerosols, and the open face filter (OFF), which wasused to measure ambient bioaerosol concentrations.Samplers.The SWSS was designed at Clarkson University and consists of a deposition plate, a metal

bracket with leveling screws and a tri-pod stand (Fig. 1). The deposition plate consists of an aerodynam-ically designed surrogate surface allowing the formation of thin and uniform laminar boundary layer onthe surface (Davidson &Wu, 1990). The deposition plate is made of Plexi glass and is 41 cm in diameterwith a smooth surface and sharp edges. The plate is 2.54 cm thick and slopes downwards with a 15-degreeangle from the upper edge of the surface.A circular hole 15 cm in diameter and approx 2 cm in depth wascut in the center of the plate to hold a Petri dish with liquid medium for collection of deposited bacteria.The brim of the Petri dishwas level with the surface of the plate. The collectionmedia was filtered through0.22�m white polycarbonate filter and autoclaved at 120◦C for 25min to ensure the media was bacteriaand particle free.The atmospheric concentration of bioaerosols was measured using an OFF by drawing surrounding

air through 0.22�m black polycarbonate filter. Bacteria collected on the filter were then enumeratedusing direct fluorescent microscopy techniques (Hobbie, Daly, & Jasper, 1977). The filter assembly was

642 A. Sahu et al. / Aerosol Science 36 (2005) 639–650

Fig. 1. Sideview of the static water surface sampler. The deposition plate was made of Plexi glass and has a 41 cm diameter witha smooth surface and sharp edges.

supported by clamps and an aluminum rod attached to a wooden base. The filter was connected to theoil-free portable GAST vacuum pump and a dry gas meter using transparent tygon tubing (ID=6.4mm).Sampling locations and collection.Samples were collected from two locations: near a wastewater

treatment plant and on the Clarkson University campus. The wastewater treatment plant facility treatsbetween 1.7–2.5 MGD (6400–9500m3/d) of wastewater using a conventional activated sludge process.For mixing and aeration the aeration basin employs 12 surface aerators of 5 hp each operating at 900 rpm.The volume of the aeration basin is 2500m3. Exact sampling sites were determined daily based on on-site flag directions but were always 10 m upwind and downwind of the aeration basin and 2m above theground surface. Background samples were collected from a rooftop of a three-story building located onClarkson University campus (approximately 2 km from the wastewater treatment plant).

A. Sahu et al. / Aerosol Science 36 (2005) 639–650 643

The SWSS and the OFF sampler were placed side-by-side for collection of airborne bacteria. Typicallyair flow rates for theOFFsamplerwere 24L/min anda collection timeof 5–7hwasused for both samplers.After the predetermined sampling period the liquid media from the SWSS was transferred with sterile25mL disposable plastic pipettes to clean/sterile bottles with rubber stoppers. Field blanks were obtainedby placing the liquidmedium into a clean/sterile Petri dish located in theSWSSand immediately pipettingout the liquid and placing it into a clean sampling bottle.Sample analysis.Two methods were employed to characterize the deposited organisms. Bacteria de-

posited on the OFF and SWSS samplers were enumerated for “live” and “dead” organisms using flu-orescent microscopic methods. In addition some samples from the OFF filter and SWSS were used todetermine the microbial diversity of the bacteria collected upwind and downwind of the aeration basin.Enumeration of organisms was accomplished using the filtration fluorescence direct counting methodas described in the literature (e.g.Moschandreas, Cha, & Qian, 1996). The LIVE/DEAD BacLight as-say (Molecular Probes, Inc., Eugene, OR) was used as the fluorescent stain in that test. The assay usestwo DNA stains (SYTO 9 and propidium iodide) to distinguish between membrane-intact (“live”) andmembrane-compromised (“dead”) cells. SYTO 9 stain generally labels the DNA of all bacteria whilepropidium iodide penetrates only bacteria with damaged membranes, causing a reduction in the SYTO9 stain fluorescence when both dyes are present. While the LIVE/DEAD Bacterial Viability kit has beenused in this research other LIVE/DEAD kits are available that specifically target fungi.Water samples (350mL) were filtered under vacuum through a non-fluorescent 0.22�m polycarbonate

filter (Fisher Scientific, Pittsburgh, PA). Next 1mL of particulate free DI water and 3�L stain were addedand the filter incubated in the dark for 15min.Thebacteria on the filterwere then countedmanually using afluorescentmicroscope (Olympus, Inc.) at 1250×magnification.At least 100 cells per filter were countedat aminimumof five locations on the filter to obtain statistically significantmeasurements. Locationswerechosen so that they did not contain clumps and had a visually relatively uniform distribution. Bacteriacollected on the OFF filter were stained by adding 1mL of particulate free DI water and 3�L of stain,incubated in the dark and then counted as described above.In order to characterize the biodiversity of themicrobial community of the deposited cells in the SWSS

and OFF samples as well as in one wastewater sample, the DNA of all the organisms were extracted,amplified using polymerase chain reaction (PCR) and analyzed usingARDRA (Massol-Deya et al., 1995)as described below. DNA was extracted from the filter deposited cells using an Ultra Clean Soil DNAIsolation Kit (Mo Bio Laboratories, Inc., Solana Beach, CA) following the manufacturer’s laboratoryprocedure. Briefly, the filter paper was cut and vortexed with five different solutions to obtain DNA.DNA was stored at−20◦C until it was amplified using PCR with non-specific primers (obtained byIntegrated DNA Technologies, Inc.) pHr (reverse) and p23SRO1 and following experimental methodsas described byMassol-Deya et al. (1995). Briefly, 45�L of super mix, 1�L of primer 1 (pHr reverse),1�L of primer 2 (p23SRO1) and 1�L of DNA sample was added to 2mL PCR vials for amplification.Amplified DNAwas then subjected to the restriction enzymeHinfl in order to break the amplified DNA inorganism-representative subunits. The DNA fragment mixture was then subjected to gel electrophoresisusing 1.5% agarose gels. Electrophoresis was carried out with 10× TAE buffer at 70V DC for 45min.The gel was then placed in 2mL ethidium bromide and 50mL IC water in a constant shaker at 35 rpm andobserved under UV light. The resulting pattern was analyzed using ONE-Dscan (Scanalytics, Fairfax,VA) and used as a fingerprint of the mixed bacterial population.Field blanks were obtained routinely at all sites and bacterial concentrations for the SWSS blanks

as a percent of the sample concentrations averaged 3% for upwind, 5% for downwind to 13% for the

644 A. Sahu et al. / Aerosol Science 36 (2005) 639–650

0.0E+00

5.0E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

Live Dead TotalTotal bacteria

Flu

x (#

/ m

2 h

r)

Upwind Downwind Science center

Fig. 2. Mean flux of live, dead and total bacteria upwind, downwind of the aeration basin in Potsdam, NY and at a backgroundsite on the Science Center of Clarkson University, Potsdam, NY. Error bars represent± one standard deviation.

background site. These small blank values were subtracted from measured values. Field blanks for theOFF sampler never yielded any bacterial counts.

3. Results

To test the SWSS sampler, bioaerosol fluxes and atmospheric concentrations were measured upwindand downwind of the wastewater treatment plant and at the background site for a two-month period (MayandJune, 2003).Themean total bacteria fluxesmeasuredby theSWSSwere7.7×106and1.4×107#/m2hupwind and downwind of the plant, respectively (Fig. 2). Themean flux at the background site was similarto the upwind site (7.5× 106#/m2h).The deposition ratesmeasured in this study around the aeration basin of an activated sludge wastewater

treatment plant are similar to the only previous study found in the literature.Kenline and Scarpino (1971)reported a flux of 1.5×106 cfu/m2h bacteria deposited from the air near an aeration basin of an activatedsludge plant. They used soy agar collection media in petri dishes as their surrogate surface. Since thistechnique only counts bacteria that can grow in this media it likely underestimated the total amount ofdeposited bacteria.The ratio of the upwind to downwind flux varied from 0.16 to 1.0 but was below 1.0 for all but one

sampling day (Fig. 3). During this day the wind speed was very low. Results from pairedt-tests indicatethat for the upwind anddownwind samples there is a significant difference (at the 95%confidence interval)in the measured fluxes (p = 0.009<0.05).The viability of the collected bacteria (percent live) varied between sampling sites. The largest percent

of live bacteria were found downwind of the aeration basin (78%). A smaller percentage of live bacteriawere found upwind of the basin, (65%) and at the background site (57%).The larger percentage of bacteriadownwind of the site suggests that many of the bacteria that were emitted from the aeration basin wereviable.

A. Sahu et al. / Aerosol Science 36 (2005) 639–650 645

0

0.5

1

1.5

19-May 29-May 8-Jun 18-Jun 28-Jun

Dates in 2003

up

win

d f

lux

/ do

wn

win

d f

lux

Fig. 3. Ratio of upwind to downwind flux for total bacteria 10m from the aeration basin of the wastewater treatment facility,Potsdam, NY. Error bars represent± one standard deviation due to bacterial enumeration variations.

0.0E+00

5.0E+04

1.0E+05

1.5E+05

2.0E+05

2.5E+05

Live Dead Total

Bacteria

Co

nce

ntr

atio

n (

# /

m3

)

Upwind Downwind Science center

Fig. 4. Mean concentration of live, dead and total bacteria upwind and downwind of the aeration basin in Potsdam, NY and at abackground site on the Science Center of Clarkson University, Potsdam, NY. Error bars represent± one standard deviation.

The mean atmospheric bioaerosol concentrations measured by the OFF samplers ranged between1.3× 105 and 1.4× 105#/m3 upwind and downwind of the aeration basin respectively (Fig. 4). At thebackground site an average bioaerosol concentration of 1.25× 105#/m3 was measured. Results froma pairedt-test indicate that there is no statistical difference (within the 95% confidence level) in themeasured bioaerosol concentrations at the upwind and downwind sites (p = 0.52>0.05). The finding ofno difference in airborne concentration upwind and downwind of the treatment plant in combination with

646 A. Sahu et al. / Aerosol Science 36 (2005) 639–650

increased flux downwind of the plant may indicate that a significant number of the bacteria generated byaerating the mixing basin were associated with particles that were too large to be collected by the OFFfilter. Large particles (> approximately 20�m) can have significant inertia and would not be collected bythe open-face filter sampler since these particles cannot cross streamlines (Lighthart, Shaffer, Marathi, &Ganio, 1991). During surface aeration it is likely that water droplets of this size would be generated andemitted to the downwind atmosphere.Mean ambient bioaerosol concentrations measured in this study were within the lower range of the

values reported byDurand, Muilenberg, Burge, and Seixas (2002)near a composting facility using aculturing technique. In their study total bacterial concentration in air measured by filtration followed byincubation with agar media ranged from 1.17× 104 to 1.0 × 106 cfu/m3 for 2–5h sampling periods.These concentrations were likely less than the true concentration since some bacteria will not grow onthe agar media and colony masking may occur if too much growth occurred on the agar plate (Changet al., 1994).The viability of the bioaerosols in the atmosphere near the wastewater treatment plant was approxi-

mately 48% at both sites while 80% of the total bacteria at the background site were live. Bioaerosolviability hasbeenshown todependonsamplingmethodandsampling time.Terzievaet al. (1996)collectedaerosolized bacteria using anAGI-30 impinger and analyzed them using BacLight staining technique andfound the ratio of live to total bacteria dropped from initially 100% to only 20% after 60min of sampling.The ratio of live to total bacteria obtained by SWSS was about 80% for downwind samples after 7 h ofsampling indicting that the SWSS seems to maintain the integrity of the microbial community.One important factor in determining the fate of the bioaerosols in the atmosphere is their deposition

velocity. The overall apparent best-fit deposition velocity of the bioaerosols at each sitewas determined byregressing themeasured deposition flux with themeasured atmospheric concentration. (Since the upwindand background site appeared to be similar based on the measured fluxes and concentrations these datasets were combined to increase the sample number.) The overall apparent best-fit deposition velocity atthe upwind and background sites was 1.5 cm/s (r2 = 0.61) (Fig. 5a) and is somewhat smaller than thevalue found downwind of the treatment plant (3.2 cm/s; r2=0.36) (Fig. 5b). The larger value downwindof the treatment plant may be due to the presence of bioaerosols associated with large water dropletsemitted from the twelve surface aerators in the aeration basin. These measured deposition velocities (andr2 values) are similar to those found for trace elements in the atmosphere (Yi, Shahin, Sivadechathep,Sofuoglu, & Holsen, 2001). The upwind and background deposition velocity is similar to those foundfor anthropogenic elements that are generally associated with smaller particles in the atmosphere whilethe velocity downwind of the treatment plant is similar to those found for crustal elements which aregenerally associated with larger particles in the atmosphere (Yi et al., 2001).The velocities measured in this study are similar to a bacterial deposition velocities of 1.0 and 3.8 cm/s

that was reportedKenline and Scarpino (1971). They used a combination of Anderson impactors tomeasure concentrations and petri dishes containing media to measure fluxes. Both these techniquesrequired culturing to obtain bacterial numbers and likely underestimated the total number of bacteriapresent; however since the same bacteria were measured for both concentration and deposition flux theirtechnique should yield reasonable values.Results of theARDRA indicate that the microbial population of the deposited organisms was different

downwind of the wastewater treatment plant than it was upwind and at the background site (Fig. 6). Toquantify the relative abundanceofDNA fragments in each sample gel electrophoresis resultswere scannedusing ONE-DScan, resulting in chromatograms for each sample. The fingerprints produced, which is an

A. Sahu et al. / Aerosol Science 36 (2005) 639–650 647

0 0.1 0.2 0.3 0.4 0.5

Concentration [# /cm3] Concentration [# /cm3]

0

0.2

0.4

0.6

0.8

0

0.2

0.4

0.6

0.8

Flu

x [#

/ cm

2 s]

Flu

x [#

/ cm

2 s]

Y = 1.50 * X + 0.02, R2 = 0.61

0 0.05 0.1 0.15 0.2 0.25

Y = 3.30 * X + 0.03, R2 = 0.36

(a) (b)

Fig. 5. Bioaerosol deposition flux as a function of concentration for (a) the combined measurements 10m upwind of the aerationbasin of the Potsdamwastewater treatment plant and the background site on the Clarkson University campus. (b) 10m downwindof the aeration basin. The slope represents the apparent best-fit deposition velocity.

indicator of the atmospheric bioaerosol composition, as expected is different downwind of the treatmentplant (Fig. 6a). For example, the peak at 15 Rf increased significantly between the upwind and downwindOFF samples from an optical density of 0.03–0.07, respectively. Similarly, the same peak increased inthe downwind SWSS sample and could be found in the wastewater collected from the aeration basin(Fig. 6b). Other fractions seem to appear in both upwind and downwind samples indicating that thesemay be DNA fragments not associated with wastewater organisms. While the resolution and opticalquality of the gels is relatively poor, the presented results demonstrate clearly the potential use of thistechnique for future bioaerosol characterization experiments in the vicinity of potential sources.Ranalli et al. (2000)used PCR to determine the presence of fecal coliforms in bioaerosols. Thismethod

was rapid (less than 8h) and provided a very high sensitivity. The ARDRA method used in this researchprovides a qualitative tool to determine the contributions of potential bioaerosol sources on microbialcomposition. This method could also be adapted to identify the presence of specific target organisms inthe mixed population without the need of culturing and at a very high sensitivity.

4. Conclusions

Results obtained in this study have demonstrated the ability of the SWSS to quantify bioaerosoldeposition fluxes. The measured bioaerosol deposition fluxes ranged from 7.7× 106 to 1.4× 107#/m2hwith the larger fluxesmeasureddownwindof awastewater treatment plant. Upwind bioaerosol fluxeswereapproximately 1.5 times smaller than downwind fluxes and similar to thosemeasured at a background site.The deposition velocities derived from the simultaneously measured ambient concentrations and fluxes

648 A. Sahu et al. / Aerosol Science 36 (2005) 639–650

Fig. 6. Agarose gel electrophoresis of upwind and downwind samples taken at the wastewater treatment plant in Potsdam, NY.(a) Atmospheric samples taken by the OFF sampler upwind and downwind and (b) samples collected by the SWSS samplerupwind and downwind of the aeration basin and from the wastewater.

were similar to those found for trace elements in the atmosphere. The results indicate that bioaerosolsare generated during aeration of activated sludge tanks with surface aerators, that many of the generatedbioaerosols are viable and that they are associatedwith large atmospheric particles. Results fromamplifiedribosomal DNA restriction analysis confirm that the bacterial composition of the downwind samplecontains DNA fragments consistent with the wastewater, while these fragments do not appear in upwindsamples.

A. Sahu et al. / Aerosol Science 36 (2005) 639–650 649

Acknowledgements

The authors would like to thank Dr. Treves, Assistant Professor in the Biology Department of theIndiana University Southeast, and Dr. Woodworth, Associate Professor in the Biology Department atClarkson University, for their assistance in the ARDRA procedures. The authors are further grateful toManjiang Chen, graduate student in the Department Civil and Environmental Engineering at ClarksonUniversity, for the ONE-DScan analysis of the agarose gels. This research was supported in part by aseed grant of the Clarkson Center for the Environment.

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