Development Of PM0.1 Personal Sampler For Evaluation Of .
Aerosol and Air Quality Research, 15: 180–187, 2015Copyright Taiwan Association for Aerosol ResearchISSN: 1680-8584 print / 2071-1409 onlinedoi: 10.4209/aaqr.2014.05.0102Development of PM0.1 Personal Sampler for Evaluation of Personal Exposure toAerosol NanoparticlesThunyapat Thongyen1, Mitsuhiko Hata1, Akira Toriba1, Takuji Ikeda2, Hiromi Koyama3,Yoshio Otani1, Masami Furuuchi1*1Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, JapanNitta Cooperation, 172 Ikezawacho, Yamatokōriyama, Nara 639-1085, Japan3Shibata Scientific Technology, Tokyo 113-0034, Japan2ABSTRACTA PM0.1 sampler for the evaluation of the personal exposure to nanoparticles was designed based on a novel approach toa layered mesh inertial filter. Applications to practical environments would include roadsides and highly contaminatedworkplaces. The separation performances of PM0.1 sampler consisting of a layered mesh inertial filter and pre-separatorsfor the removal of coarse particles were evaluated. The influence of particle loading on the pressure drop and separationperformance, which is important from a practical standpoint, was also discussed. The novel personal sampler recorded acutoff size of 100 nm with a small pressure drop of 5 kPa. Through the combination of a layered mesh inertial filter forthe PM0.1 and pre-cut impactors for the removal of huge or coagulated particles (PM1.4-TSP) along with a pre-cut inertialfilter using webbed SUS fibers for the removal of fine particles (PM0.5-PM1.4), the present PM0.1 inlet for the personalsampler was practical for the chemical analysis of collected particles. This sampler was proven effective even under thelimitations of a small-capacity portable battery pump, which was rated at less than the minimum change for separationperformance. The novel PM0.1 personal sampler is compact and lightweight (under 1 kg including a portable batterypump), which is important for the practical application of a personal sampler.Keywords: PM0.1; Nanoparticles; Personal exposure; Inertial filter.INTRODUCTIONDuring the assessment of the health effects of airborneparticulates, it is necessary to determine both theconcentration and composition of the particles in thebreathing zone with regards to aerodynamic particle size,which affects the regional deposition of particles inhaled intothe human respiratory system. This is particularly importantfor ambient nanoparticles ( 100 nm), since they can containa large portion of hazardous chemicals from anthropogenicsources and can penetrate deeply inside lungs, eventuallyreach the alveolar region. Moreover, their chemicalcompositions will be more quickly dispersed throughoutthe human body (Hinds, 1999; Bolch et al., 2001; Warheit,2004; Hussain et al., 2011). Exposure to nanoparticles hasbeen associated with pulmonary inflammation, immunechanges, and a contribution to undesirable cardiovasculareffects (Donaldson et al., 2002; Granum and Lovik, 2002;*Corresponding author.Tel.: 81-76-234-4646; Fax: 81-76-234-4644E-mail address: mfuruch@staff.kanazawa-u.ac.jpBorm and Kreyling, 2004). Moreover, PM0.1 in environmetnsilfluenced by human activities, e.g., powder production ina factory, burning of agricultural crop waste, and cigarettesmoking, is being reported in ever-increasing concentrations(Phillips and Bentley, 2001; Behera et al., 2004; Davidsonet al., 2005; Herner et al., 2005; Morawska et al., 2008; Ngoet al., 2010). In order to evaluate health influences and risks,therefore, the monitoring of environmental nanoparticles iscrucially important.The evaluation of nanoparticle exposure has beenconcerned not only on nanoparticles from daily humanactivities and environments, but also on nanomaterials thatare an inherent part of nanotechnological developments(Kuhlbusch et al., 2011). Although the number of personalexposure studies on fine particles has continually increased(Du et al., 2010; Borgini et al., 2011; Lim et al., 2012;Jahn et al., 2013), relatively few studies have focused onmonitoring the personal exposure to fine particles in thenano-size range via a portable personal sampler (Young etal., 2013). Therefore, the development of a portable personalsampler that could be used to evaluate nanoparticle exposurewould be indispensable in any discussion on the healthrisks and infuluences posed by nanoparticles.Various types of portable personal samplers equipped
Thongyen et al., Aerosol and Air Quality Research, 15: 180–187, 2015with a battery pump have been used for the evaluation of thepersonal exposure in workplaces and in living environments.Few of these personal samplers, however, have beenapplicable to the collection of nanoparticles. This has beendue to the difficulty posed by the large degree of pressuredrop that is needed for the separation of nanoparticles whenusing conventional methods that employ a low-pressureimpactor. In order to overcome this difficulty, the authorsdeveloped a personal sampler based on the “inertial filter”technology (Furuuchi et al., 2010). However, because ofthe difficulty posed by a pressure drop through the inertialfilter under the limited capacity of a portable battery pump,the best cutoff size that could achieved was 140 nm with a6 L/min of a sampling flow rate, which was insufficient fora characterization as “nanoparticles”. Although an impactortype of personal sampler was recently devised with acutoff size of 100 nm (Tsai et al., 2012), its sampling flowrate (2.0 L/min), was not always sufficient for the chemicalanalysis of particles that could be collected in working (6–8hours) and living environments (12–24 hours). Hence, acutoff size of 100 nm must be achieved for a practicalsamplng air-flow rate that should approximate 4-6 L/min,or more. Another difficulty frequently encountered in thepractical application comes from the existence of huge andcoagulated particles, which are typically observed in thehandling of fine powder in workplaces and in the vicinityof roadside environments. The loading of these particles onthe inertial filter for nanoparticle separation increases thepressure drop and also accelerates the rate of bouncingproblems encountered with coarse particles. Hence, giventhe wide range of concentration and size distribution ofparticles, it is very important to overcome these problemsif the practical application of a personal sampler is to beeffective.In this study, the PM0.1 sampler for the evaluation of thepersonal exposure to nanoparticles was designed based ona novel approach that uses a layered mesh inertial filterwhile targeting the application to practical environmentsincluding roadsides and highly contaminated workplaces.Separation performances were evaluated for the PM0.1sampler consisting of the layered mesh filter and other preseparators for the removal of coarse particles. The influenceof particle loading on the pressure drop and separationperformance, which is important for practical applications,was also evaluated.181INERTIAL FILTERS AND PM0.1 PERSONALSAMPLERLayered Mesh Inertial Filter for the PM0.1Fig. 1 shows the structure of the layered mesh inertialfilter used for the PM0.1 separation. It consists ofcommercially available layered square mesh copper TEMgrids (Glider, G600HSS) sandwiched by manufacturedcopper spacers with a circular hole (ϕ 1.9 mm, t 30 µm)stacked in a circular nozzle (ϕ 3 mm, 9 mm nozzle length)with a bell shaped inlet through an aluminum cartridge.The geometry of the original inertial filter used webbedstainless steel fibers (Otani et al., 2007; Eryu et al., 2009;Furuuchi et al., 2010). This new inertial filter was made upof layered TEM grids that provide a uniform structure offibers aligned perpendicular to the flow direction along thenozzle, which maximizes the inertial effect on particlesand provides less pressure drop with no loss in separationperformance. The uniformity of the layered-mesh structureprojected in the flow direction is a key point in the preparationof the layered-mesh inertial filter since the aerosol particlesmay penetrate directly through the opening between meshwires because of a large inertial effect (Eryu et al., 2009).Hence, wire mesh screens must be aligned tangentiallyuniform by shifting each TEM grid for 15 degree in orderto maximize the coverage of the nozzle cross-section bythe mesh wires. The advantages of the layered meshinertial filter cannot be obtained by the original structure ofrandomly orientated SUS fibers packed in a circular nozzlesince it is difficult to make the structure of packed fibersuniform over the cross-section and depth of a nozzle thathas a diameter of less than 2 millimeters. The analysis ofchemical components such as PAHs can be done forparticles collected on TEM grids by the extraction, e.g., byimmersing TEM grids in a solution for the extraction. Thespecifications of the TEM grids are listed in Table 1. FiveTEM grids and spacers were used for each filter based onthe preliminary experiments and numerical analysis (Eryuet al., 2009; Takebayashi, 2012).Pre-cut Inertial Filter for PM0.5In order to prevent clogging and bouncing of coarseparticles on the layered mesh PM0.1 inertial filter, a pre-cutinertial filter consisting of webbed SUS fibers (df 9.8 µm)packed in a ϕ 4.75 mm circular nozzle (5.5 mm length)Fig. 1. Schematic of the main inertial filter.
Thongyen et al., Aerosol and Air Quality Research, 15: 180–187, 2015182Table 1. Specification of TEM grids used for the layered mesh inertial filter.Grid typeCodeMaterialMesh(lines/inch)Pitch(µm)Bar width(µm)square meshGliderG600HSSCu600425through a metal cartridge was used upstream from thelayered mesh inertial filter. This type of inertial filter had arelatively large dust-loading capacity and provides lesspressure drop than that of the impactor. The pre-cut inertialfilter had a geometry that was similar to the original onebut with a different diameter for the nozzle and SUS-fiberloading to decrease the cutoff size from 700 to 450 nm. Thiswas intended to reduce the amount of particles penetrating tothe layered mesh inertial filter to help maintain performance.The specifications of the pre-cut inertial filter are shown inTable 2.Pre-cut ImpactorsThe pre-cut inertial filter was expected to have a largercapacity for particle loading and fewer re-suspended particlescompared with the impaction plate of an impactor.However, the dust loading capacity was suspected to beinsufficient for the measurement in environments highlycontaminated by the huge and coagulated particles that aretypically observed in fine powder handling processes androad-side environments. In order to avoid penetration bythese particles into the pre-cut and layered mesh inertialfilters, therefore, a commercially available two-stage precut impactors (SHIBATA, ATPS-20H) were used for theremoval of particles in the micron size range. Cutoff sizeswere estimated to be 5.6 and 1.4 µm at 5 L/min for the 1stand 2nd stages, respectively, of the pre-cut impactors, asestimated using an equation for inertial separation (Hinds,2009), where the cutoff sizes were originally designed tobe 10 and 2.5 µm at 1.5 L/min. The pre-cut impactors areimportant for practical application in workplaces that arehighly contaminated by coagulated particles in order tomaintain the separation performance of the inertial filtersand to minimize the pressure drop due to particle loading.PM0.1 Inlet for a Personal SamplerFig. 2 shows the geometry of the PM0.1 personal samplerinlet, which consisted of two different types of inertialfilters located downstream from the two-stage pre-cutimpactors and was followed by a backup filter on a thinstainless filter holder. The surface of the impaction plate forthe 1st stage of the pre-cut impactor was covered by silicongrease (Dow Corning, 03253589) to a uniform thickness ofapproximately 0.2 mm while a glass fiber filter 10 mm indiameter (Pallflex, T60A20) was attached to the impactionHole width ThicknessQCutoff size(µm)(µm)(L/min)(nm)3785100plate of the 2nd stage. The outlet of the PM0.1 personalsampler was connected to a portable battery pump (HarioSci., HSP-5000) using a flexible resin tube. The weight ofthe PM0.1 personal sampler was 112 g for the sampler inlet(6.5 cm maximum width and 11.4 cm height) and 700 g forthe portable pump (85 mm width, 60 mm depth and 155mm height), which makes it easy to handle in the field.EXPERIMENTSSeparation Performances of Inertial Filters and Pre-cutImpactorsThe separation performance of the inertial filters wasevaluated using the an experimental setup shown in Fig. 3,which consisted of an evaporation-condensation type ofaerosol generator, a nitrogen gas generator for the carriergas supply, HEPA filters, mass flow controllers, a neutralizer(241Am), a differential mobility analyzer (DMA), a testinertial filter in a holder, a digital manometer and measuringinstruments for particle number concentration. Theperformance was evaluated following an establishedprocedure (Furuuchi et al., 2010). ZnCl2 powder was dosedon an alumina boat in a tubular image furnace, then ZnCl2was heated to 190–320 C followed by cooling to roomtemperature in order to obtain the ZnCl2 particles. Afterclassifying the generated particles by DMA, the particleswere used for the test aerosol ( 20–520 nm in aerodynamicdiameter, geometric standard deviation σg 1.06–1.30). Themono-dispersed ZnCl2 particles were diluted with airthrough a HEPA filter and supplied to the inertial filterplaced in a holder.The collection efficiency was determined based on thenumber concentration measured by a laser aerosolspectrometer (TSI, LAS model 3340), a condensation particlecounter (TSI, CPC model 3785), and a scanning mobilityparticle sizer (TSI, SMPS model 3080). The pressure dropthrough the inertial filter was monitored using a digitalmanometer (EXTECH, HD 750). The mobility equivalentdiameters of the ZnCl2 particles were converted toaerodynamic diameters using a measured density (1508 kg/m3averaged for 40 nm to 350 nm) of generated particles viaan aerosol particle mass analyzer (KANOMAX, APMmodel 3600).The performance of pre-cut impactors was evaluatedusing the configuration shown in Fig. 4. A condensationTable 2. Specification of the pre-cut inertial filter.Inertial Filterdf(µm)Pre-cutinertial .54.75QFiber loadings Fiber volume Cutoff size(L/min)(mg)fraction (-)(nm)5100.0133450
Thongyen et al., Aerosol and Air Quality Research, 15: 180–187, 2015183Fig. 2. PM0.1 personal sampler inlet and inertial filters used: (a) an outside picture and structure of PM0.1 personal samplerinlet, (b) the pre-cut inertial filter and stainless steel (SUS) fibers used, and (c) the main inertial filter (layered meshgeometry).Fig. 3. An experimental setup for the inertial filter performance test.aerosol generator (TOPAS, SLG 270) was used to obtain ahigh number concentration of mono-dispersed NaCl coarseparticles ( 540–2840 nm in aerodynamic diameter, σg 1.22–1.29), which are electrically neutral and correspondto the heating temperature between 220 and 280 C.Generated mono-dispersed NaCl particles were diluted bymixing with filtered air via a HEPA filter, then them to thepre-cut impactor filters. The collection efficiency of the pre-cut impactor filters was determined based on the numberconcentration measured by an aerosol particle sizer (TSI,APS model 3321). A pressure drop through the inertial filterwas also monitored using a digital manometer (EXTECH,HD 750).Effect of Surface Coating of the Inertial FiltersThe influence of the surface treatment of the inertial filter
184Thongyen et al., Aerosol and Air Quality Research, 15: 180–187, 2015Fig. 4. An experimental setup for the pre-cut impactors performance test.fibers to reduce the bouncing effect of coarse particles wasalso investigated. Fiber surfaces of the pre-cut and themain inertial filters were coated by glue, or, by dropping 1wt% water solution of water soluble glue (Tombo, HCA122) onto the pre-cut and main inertial filters, which heldthem on the PM0.1 inlet, followed by drying via flowing aHEPA filtered air through each inertial filter for 1 hour.Based on observation using an optical microscope, therewas no remaining water glue solution or dried glue at anyof the corners or edges of the mesh grids, which may haveinfluenced the flow and particle motion.Influence of Particle Loading on Pressure DropThe influences of particle loading on the pressure dropand separation performance of the PM0.1 inlet wereinvestigated for different size ranges of particles: coarseparticles on the order of microns that may be predominantin some workplaces or roadsides, and fine particles that arethe main fraction of smoke particles including cigarettesmoke and automobile exhaust particles, etc. As coarseloading test dust, JIS No. 5, which is a mineral dust of 85 5% as the coarse particles ( 5 µm) in mass, was used. Asfine loading test particles, incense smoke particles, whichranged concentrations between 100–200 nm, were used.The JIS No.5 dust was dispersed by an ejector (Sympatec,RODOS type) to a mixing box then introduced to the PM0.1inlet. Incense smoke particles were diluted by filtered airthrough a HEPA filter then introduced to the PM0.1 inlet. Inorder to obtain various particle loadings on the filters, thesampling was adjusted between 60 and 120 min for the JISNo. 5 dust and between 5 and 10 min for the incense smokeparticles. The pressure drop was measured using a digitalmanometer (EXTECH, HD 750) before and after sampling.Validation of the PM0.1 Personal SamplerFor the validation of measurement by the PM0.1 personalsampler, the concentration and size distribution of ambientaerosol particles were compared between the PM0.1 personalsampler and the Nanosampler (NS, KANOMAX, Model3180; Furuuchi et al., 2010) after the same period of aerosolsampling. The validation was conducted on a balcony ofthe 6th floor in a 7-story building at Kanazawa Universityon the Kakuma campus, Kanazawa. Binder-less quartzfibrous filters (Pallflex, 2500QAT- UP) were used for thevalidation. They were weighed after the conditioning at20 C and 50% RH in a weighing chamber for 48 hoursboth before and after the sampling.RESULTS AND DISCUSSIONSeparation Performance of the Inertial FiltersFig. 5 shows the collection efficiency curves for the precut and main inertial filter along with a combination ofthose filters and pre-cut impactors measured at an airflowrate of 5 L/min. The cutoff size of the pre-cut filter wasestimated at 450 nm with a pressure drop of 0.6 kPa. Thecutoff size of the main filter could be adjusted by 100 nmby changing the filtration velocity, or, the size of a spacerhole, with an acceptable steepness of the efficiency curveat 4.6 kPa of pressure drop. The dashed curve in Fig. 5denotes a prediction based on the filtration theory alongwith a numerical simulation for a fiber with a square crosssection (Hinds, 1999; Otani et al., 2007; Eryu et al., 2009),where the fiber volume fraction α was adjusted to fit a dp50 100 nm (α 0.21). Although there was good consistencyin the separation tendency between measured and predictedefficiencies, the measured collection efficiency for coarseparticles larger than 200 nm was slightly lower than thatfrom the prediction. This may have been the influence ofbouncing or a re-suspension on the TEM grid mesh fiberswhen dealing with this size range of particles. Because ofBrownian diffusion, the collection efficiency for particlesin the 10–20 nm range increased both in the pre-cut inertialfilter and in the main inertial filter. This increase may begreater for particles for smaller than 10 nm, but from thepoint view of particle mass, it may not be so important.The pre-cut inertial filter just has only a slight influence onthe main filter performance. Values of the total pressure
Thongyen et al., Aerosol and Air Quality Research, 15: 180–187, 2015Fig. 5. Collection efficiency curves for th
monitoring the personal exposure to fine particles in the nano-size range via a portable personal sampler (Young et al., 2013). Therefore, the development of a portable personal sampler that could be used to evaluate nanoparticle exposure would be indispensable in any discussion on
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