Enhancement of collection efficiency of inertial impactors using elliptical concave impaction plates

In this study, elliptical concave impaction plate was suggested for lowering cut-off size and therefore enhancing collection efficiency of the inertial impactor. Statistical Lagrangian Particle Tracking (SLPT) model was employed for calculating impactor collection efficiency and validated by comparing with the experimental data of Tsai, C.J., Cheng, Y.H. ((1995). Solid particle collection characteristics on impaction surfaces of different designs. Aerosol Science Technology, 23, 96–106), for three different shapes of impaction plates. Then, the effect of the ratio of major axis length (A) to minor axis length (B) for determining the curvature of elliptical concave impaction plate, on impactor collection efficiency was numerically investigated using the SLPT model, with nozzle Reynolds numbers ranging from 1440 to 2600. It was found that there existed an optimum range of the A/B ratio for minimizing the cut-off size, i.e. the A/B ratio ranged between 3.2 and 4.2 for the PM10 inertial impactor, or between 3.2 and 3.5 for the PM2.5 inertial impactor. When the elliptical concave impaction plates with the A/B ratio of 4.0 and 3.5 were applied to the MST indoor air sampling impactor having PM10 and PM2.5 stages, the cut-off size was predicted to decrease from 10 to 6.5 μm and from 2.5 to 1.6 μm, respectively, while the impactor collection efficiency curves became less steep.     

Design and evaluation of a low flow personal cascade impactor

A very compact cascade impactor with 2 L/min sampling flow rate has been developed. Its dimensions are 8.5 cm L x 5.0 cm W x 11.4 cm H, and it weighs 0.27 kg, with ten impaction stages with aerodynamic cutpoints in the range of 60 nm to 9.6 μm. The top eight stages, collecting particles down to 170 nm in aerodynamic diameter, can be used as a stand-alone impactor with a portable, battery-powered pump. Particle collection efficiencies were obtained with two types of commonly used substrates, aluminum foil and glass fiber filters. Impactor cutpoints with aluminum foil substrates agree well with conventional impactor theory. The efficiency curves are sharp with minimum overlap between them. Thus, the compact impactor design does not compromise its performance, making it suitable for general purpose applications where a lower sampling flow rate provides adequate mass collection. With glass fiber filter substrates, impactor cutpoints are smaller and the efficiency curves are less steep, in particular for the last stages. Also, the collection efficiency curves do not drop to near zero at small Stokes numbers. Instead, excess particle collection efficiency of around 10% is observed for the top six stages, and becomes higher for the last four stages. This is due to the collection of particles by filtration as the impinging jets penetrate the filter substrate. Thus, using glass fiber filter substrates should generally be avoided due to the non-ideal effect on the impactor collection efficiency curves, especially for the last two stages.

Copyright © 2018 American Association for Aerosol Research     

A Streamlined,High-Volume Particle Impactor for Trace Chemical Analysis

The design and characterization of a streamlined, high-volume particle impactor intended for use with trace chemical analysis is presented. The impactor has a single round jet and is designed to operate at a flow rate of 1000 L/min. Computational fluid dynamics (CFD) was used as a tool to optimize the aerodynamic performance of the impactor by iteratively redesigning the geometry and curvature of the internal walls. By eliminating recirculation zones within the flowfield of the impactor and using flowfield streamlines as new walls, successive designs revealed a significant reduction in the pressure drop across the impactor. Particle trajectories were simulated in the impactor and the 50% cutpoint was determined to be 1.05 μm. The impaction surface itself is easily removed from the body of the impactor assembly, potentially facilitating rapid trace chemical analysis using a variety of chemical detection techniques. A prototype impactor was fabricated with a 3D rapid prototyping printer and characterized in terms of particle cut-off diameter using test aerosols generated by an Ink Jet Aerosol Generator (IJAG) and fluorescence intensity measurements. The experimental particle cut-off diameter was not able to be measured because the smallest aerosol particles that could be tested were 1.86 μm which were collected at 100% efficiency. Particulate contamination from the high-explosive compound C4 was also collected with the impactor to demonstrate operational utility for trace explosives detection.

Copyright 2013 American Association for Aerosol Research     

Design and Calibration of a Multi-Channel Aerosol Sampler for Tropopause Region Studies from the CARIBIC Platform

An aircraft-based, multi-channel aerosol sampler for studies of the upper troposphere and lowermost stratosphere from the CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container) platform was designed and calibrated. The sampler operates with an impaction technique at a flow rate of 10.4 lpm and consists of sixteen sampling channels. Samples are collected in a time sequence. Each channel contains two sample types that are used for quantitative measurement of concentrations, using particle-induced X-ray emission (PIXE), and single particle analysis with electron microscopy. The minimum detection limits for PIXE analysis after 1.5 h sampling are, for example, 2.0, 0.14, and 0.02 ng/m³ STP (standard temperature and pressure) for sulfur, potassium, and nickel. Calibration included penetration studies of a cyclone arrangement used to define the upper size limit in the sampling to 2.0 μ m diameter and the collection efficiency of the impactor. Both components of the sampling system showed penetration and collection efficiency close to 100%, respectively, in the particle size range of interest. The impactor cut-off was found to be dependent on the ratio of the impactor upstream-to-downstream pressure for ratios well below the critical pressure drop (i.e., the pressure where the jet reaches sonic velocity) being 0.15 μ m and 0.08 μ m for ratios 0.41 and 0.2.     

Inertial Separation of Ultrafine Particles Using a Condensational Growth/Virtual Impaction System

ABSTRACT

A system for the separation of ultrafine particles (i.e., particles smaller than 0.1 μm) has been developed and evaluated. Ultrafine particles are first grown by means of supersaturation to a size that can be easily separated in a virtual impactor. Thus, inertial separation of ultrafine particles occurs without subjecting them to a high vacuum. The condensational growth/virtual impaction system has been evaluated using monodisperse 0.05 and 0.1 μm fluorescent PSL particles, as well as polydisperse ultrafine ammonium sulfate and potassium nitrate aerosols. The generated aerosols were first drawn over a pool of warm water (50°C) where they became saturated. Subsequently, the saturated aerosol was drawn through a cooling tube (8°C) where particles grew due to supersaturation to sizes in the range 1.0–4.0 μm. By placing a virtual impactor with a theoretical 50% cutpoint of 1.4 μm downstream of the condenser, ultrafine particles were separated from the majority (i.e., 90%) of the surrounding gas. The sampling flow rate of the virtual impactor was 8 L/min and its minor-to-total flow ratio was 0.1. For these operating conditions, the particle collection efficiency of the virtual impactor averaged to about 0.9 for particle concentrations in the range 7 × 10⁴-5 × 10⁵ particles/cm³. Particle losses through the system were found less than 5%. Increasing the particle concentration to levels in the range 106–107 particles/cm³ resulted in a decrease in the collection efficiency of the virtual impactor to about 50–70%, presumably due to the smaller final droplet size to which the ultrafine particles grew for the available supersaturation.     

Development of a High Volume Cascade Impactor for Toxicological and Chemical Characterization Studies

This paper presents the design and development of a compact high volume cascade impactor (HVCI). The HVCI operates at a flow rate of 900 l/min and consists of 4 impaction stages equipped with circular slit-shaped acceleration nozzles and a backup filter. The backup filter is placed downstream of the fourth stage and is used to collect the ultrafine particles ( d p < 0.1 w m). The major feature of this novel sampler is its ability to collect relatively large amounts of particles (mg-g levels) onto relatively small polyurethane foam substrates without using adhesives. As previously reported, the capacity of the impaction substrate is 2.15 g of collected particles per cm 2 of foam. Although the impaction substrates are not coated with adhesives such as grease or mineral oil, particle bounce and re-entrainment losses were found not to be significant. Particles can be easily recovered from the foam substrates using aqueous extraction. The impactor was calibrated using polydisperse particles. The 50% cutpoints of the 4 stages were 9.90, 2.46, 1.0, and 0.1 w m, respectively. Interstage losses of ultrafine and fine particles were < 10% and for coarse particles were < 20%. The pressure drop across the 4 stages and the backup filter were 0.25, 0.75, 1.25, 19.9, and 3.3 kPa, respectively.     

Development of a PM2.5 sampler with inertial impaction for sampling airborne particulate matter

A simple and low cost PM_2.5 impactor for sampling airborne particulate matter was developed, designed and evaluated. The design was an assembly of an acceleration nozzle and an impaction plate. Particles with sufficient inertia were unable to follow air streamlines and impacted on the plate. Smaller particles followed the streamlines, avoided being captured by the plate and could then be collected on a downstream filter. Analytical and numerical models were formulated to predict collection efficiency, flow fields and vectors, and particle trajectories in the impactor. The modeling suggested that an optimal operational domain exists for the PM_2.5 impactor. A prototype was then built and tested. The collected particles on the impaction plate and downstream of the PM_2.5 impactor were analyzed by using scanning electron microscopy. Experimental results agreed well with the theoretical predictions. Testing of the PM_2.5 impactor prototype showed promising results for this airborne particulate matter sampler.     

Design and development of a self-contained personal electrostatic bioaerosol sampler (PEBS) with a wire-to-wire charger

Here, we present a concept of a personal electrostatic bioaerosol sampler (PEBS), which is an open channel collector consisting of a novel wire-to-wire particle charger and a collection section housing a double-sided and removable metal collection plate and two quarter-cylinder ground electrodes. The charger consists of a tungsten wire (25.4 mm long and 0.076 mm in diameter) connected to high voltage and positioned in the center of the charging section (a cylinder 50.8 mm long and 25.4 mm in diameter); a ring of stainless steel wire 0.381 mm in diameter surrounds the hot electrode at its midpoint and is grounded. The newly designed wire-to-wire charger produces lower ozone concentrations compared to traditional wire-to-plate or wire-to-cylinder charger designs. The particles captured on the collection plate are easily eluted using water or other fluids. The sampler was iteratively optimized for optimum charging and collection voltages, and collection electrode geometry. When tested with polystyrene latex particles ranging from 0.026 µm to 3.1 µm in diameter and 10 L/min collection flow rate, the sampler's collection efficiency was approximately 70%–80% at charging and collection voltages of +5.5 kV and ?7 kV, respectively. The PEBS showed this collection efficiency at sampling times ranging from 10 min to 4 h. Preliminary tests with Bacillus atrophaeus bacterial cells and fungal spores of Penicillium chrysogenum showed similar collection efficiency. The use of a unique wire-to-wire charger resulted in ozone production below 10 ppb. Due to low ozone emissions, this sampler will allow maintaining desirable physiological characteristics of the collected bioaerosols, leading to a more accurate sample analysis.

© 2017 American Association for Aerosol Research     

High-Volume Aerosol Filtration and Mitigation of Inertial Particle Rebound

The performance of electrostatically charged blown microfiber filter media was characterized for high-volume sampling applications. Pressure drop and aerosol collection efficiency were measured at air pressures of 55.2 and 88.7 kilopascals (kPa) and filter face velocities ranging from 2.5 to 11.25 meters per second (m/s). Particle penetration was significant for particles above 0.5 micrometers (μm) in aerodynamic diameter where the onset of particle rebound was observed as low as 200 nanometers (nm). Particle retention was enhanced by treating filters in an aqueous solution of glycerol. Adding this retention agent eliminated electrostatic capture mechanisms but mitigated inertial rebound. Untreated filters had higher nanoparticle collection efficiencies at lower filter face velocities where electrostatic capture was still significant. At higher filter face velocities, nanoparticle collection efficiencies were higher for treated filters where inertial capture was dominant and particle rebound was mitigated. Significant improvements to microparticle collection efficiency were observed for treated filters at all air flow conditions. At high air pressure, filter efficiency was greater than 95% for particles less than 5 μm. At low air pressure, performance enhancements were not as significant since air velocities were significantly higher through the fiber mat. Measured single fiber efficiencies were normalized by the theoretical single fiber efficiency to calculate adhesion probability. The small fiber diameter (1.77 μm) of this particular filter gave large Stokes numbers and interception parameters forcing the single fiber efficiency to its maximum theoretical value. The adhesion probability was plotted as a function of the ratio of Stokes and interception parameter similar to the works of others. Single fiber efficiencies for inertial nanoparticle collection were compared to existing theories and correlations.

Copyright 2014 American Association for Aerosol Research     

惯性分离装置的性能分析及结构优化

通过搭建惯性分离装置测试平台，结合相关检测设备的数据采集，进行某型惯性除雾器的性能分析。实验发现，两通道折流惯性分离装置的分离效率与液滴直径成正比。对于微小粒径5～10μm的液滴分离效果不佳，风速对分离效率的影响不大。对于30μm以上的液滴分离效果较好，效率整体超过80%。系统进出口压降损失方面，粒径的变化相对于整个装置可以近似忽略，不同粒径条件下压降曲线变化基本相同，风速是压降变化的主要影响变量。为突破小粒径液滴分离效果不佳的限制，分别从板间距、底面高度及板型等方面入手，分析不同尺寸参数条件下分离效率与压降的变化规律。计算结果表明，板间距数值越大，分离效率越低，系统压降越小；底面高度与效率变化并不是总体相关，存在波动并呈现局部相关性；高度增加到30mm时达到最佳，系统压降也较小；通道级数越多，分离效率越高，但压降增加较大；流线型壁面分离效果较好，控制压降的能力也较强。     

A Cylindrical Thermal Precipitator with a Particle Size-Selective Inlet

We designed a thermal precipitator in a cylindrical configuration with a size-selective inlet, and investigated its performance in experiments using differential mobility analyzer (DMA)-classified particles of sodium chloride (NaCl) and polystyrene latex (PSL). Our investigation was performed in two parts: (1) using the size-selective inlet to determine the best inlet-to-wall distance for optimal impaction of 1 μm particles; (2) using a simple inlet tube to measure particle collection via thermophoresis over a size range from 40 nm to 1000 nm. The results showed that the inlet had a particle cut-off curve, with a 50% particle cut-off Stokes number of 0.238, resulting in removing particles with sizes larger than 1 μm at an aerosol flow rate of 1.5 lpm. The thermophoretic particle collection efficiency in the prototype was measured without the size-selective inlet installed. The size dependence of the collection efficiency was negligible for particles with diameters ≤300 nm and became noticeable for those with diameters >300 nm. An analytical model was further developed to estimate the particle collection efficiency due to thermophoresis of the prototype under various aerosol flow rates and temperature gradients. For particles with diameters less than 400 nm, reasonable agreement was obtained between the measured data and the collection efficiency calculated from the developed analytical model. It was further concluded that the derived formula for the calculation of thermophoretic particle collection efficiency could serve as the backbone for future design of thermal precipitators in any configuration, when combined with the proper formula for the dimensionless thermophoretic particle velocity.

Copyright 2012 American Association for Aerosol Research     

Mechanism of Particle Impaction and Filtration by the Dry Porous Metal Substrates of an Inertial Impactor

This study has investigated numerically the particle collection efficiency curves of inertial impactors with a dry porous metal substrate covering a wide range of particle diameters. The results show that the penetrating air causes higher inertial force for particles near the surface of the dry porous metal substrate than that of the flat plate, which increases the collection efficiency due to inertial impaction mechanisms. The calculated collection efficiency curve will be sharper than that assuming 100% filtration efficiency (ideal filtration) and there is a minimum value of <2% at $\sqrt {\bf St}$ = 0.05 ～ 0.07 (corresponding to d p = 0.1 ～ 0.5 w m) for different Re and K. The collection efficiency increases to 15% for the ultrafine particles with a diameter of 0.01 w m when Re = 3,000 and K = 568,000 cm m 2 . When $\sqrt {\bf St}$ M 0, the collection efficiency will approach the curve considering ideal filtration due to diffusion mechanisms.     

Depositional arrangement of non-spherical atmospheric particles on impaction plate of a multi-nozzle impactor

Abstract

Aerosols and dust particles as a main component of atmospheric composition are of different shapes and sizes and affect the human health. Over the recent decades, the sampling, analysis and characterization of aerosol and dust particles have been a significant challenge. Finding a relationship between the location of particle deposition on impaction plate and its size and shape is very important for mineralogical and geochemical analysis. Hence, in this investigation, a common multi-nozzle impactor was taken and the arrangement of collected particles with different shapes and diameters on impaction plate was analyzed. Because of the highly priced geochemical and mineralogical analysis of atmospheric particles collected by the impactor, the results of this study can be used as a preliminary classifier for analyzing the accumulated atmospheric particles. In this study, a multi-nozzle impactor was three-dimensionally simulated. The simulation was carried out by applying Eulerian-Lagrangian approach. The experimental tests were also accomplished for sampling of the atmospheric particles. As the results of this study, the collection efficiency curve for the atmospheric particles with different shape factors was numerically obtained. As the most important result of this study, the location of particles deposited with diameters 2.5?µm and 5?µm and with shape factor of 1, 0.5 and 0.3 on impaction plate was numerically calculated. Due to these results, on one hand the central/outer parts of primary deposits mostly contain relatively coarse/fine-sized particles with high sphericity. On the other hand, the linear/low-cumulative deposits between adjacent jets mostly contain relatively fine/coarse-sized particles with low sphericity and angular shapes. Three-dimensional simulation results matched well with experimental sampling data.

Copyright © 2019 American Association for Aerosol Research     

A novel quartz crystal cascade impactor for real-time aerosol mass distribution measurement

A quartz crystal microbalance (QCM) based instrument has been developed for real-time aerosol mass distribution measurement. It includes two key components: a six-stage QCM micro-orifice cascade impactor and a novel relative humidity (RH) conditioner. This instrument operates at a flow rate of 10 L·min^?1 and measures the mass of the collected particles in six aerodynamic diameter channels between 45 nm and 2.5 μm. The RH conditioner ensures that the aerosol particles are collected at an RH between 40% and 65%, which is critical for eliminating particle bounce and for ensuring optimal particle coupling with the QCM. The nozzles of the impactors are clustered in the center of the nozzle plates. Therefore, particles are deposited on the central electrode of the QCM, where the mass calculated from first principles (i.e., Sauerbrey equation) agrees with the actual collected mass. The QCM response is linear up to around 130 μg for solid particles and up to around 2 μg for liquid particles. The collection efficiency curves of the QCM impactor stages were measured experimentally with monodisperse aerosols, and the results agree with the predictions of established impactor theory. This QCM-based instrument has also been tested with ambient aerosols with varying temperature and relative humidity. The aerosol distributions measured by this new instrument are in good agreement with simultaneous independent measurements carried out with a wide-range particle spectrometer (MSP Model 1000XP WPS).

Copyright © 2016 American Association for Aerosol Research     

Air sampling filtration media: Collection efficiency for respirable size-selective sampling

The collection efficiencies of commonly used membrane air sampling filters in the ultrafine particle size range were investigated. Mixed cellulose ester (MCE; 0.45, 0.8, 1.2, and 5 μm pore sizes), polycarbonate (0.4, 0.8, 2, and 5 μm pore sizes), polytetrafluoroethylene (PTFE; 0.45, 1, 2, and 5 μm pore sizes), polyvinyl chloride (PVC; 0.8 and 5 μm pore sizes), and silver membrane (0.45, 0.8, 1.2, and 5 μm pore sizes) filters were exposed to polydisperse sodium chloride (NaCl) particles in the size range of 10–400 nm. Test aerosols were nebulized and introduced into a calm air chamber through a diffusion dryer and aerosol neutralizer. The testing filters (37 mm diameter) were mounted in a conductive polypropylene filter-holder (cassette) within a metal testing tube. The experiments were conducted at flow rates between 1.7 and 11.2 l min^?1. The particle size distributions of NaCl challenge aerosol were measured upstream and downstream of the test filters by a scanning mobility particle sizer (SMPS). Three different filters of each type with at least three repetitions for each pore size were tested. In general, the collection efficiency varied with airflow, pore size, and sampling duration. In addition, both collection efficiency and pressure drop increased with decreased pore size and increased sampling flow rate, but they differed among filter types and manufacturer. The present study confirmed that the MCE, PTFE, and PVC filters have a relatively high collection efficiency for challenge particles much smaller than their nominal pore size and are considerably more efficient than polycarbonate and silver membrane filters, especially at larger nominal pore sizes.     

Design of a Glass Impactor for an Annular Denuder/Filter Pack System

A glass impactor for an annular denuder/filter pack system was developed, to further the application of denuder technology in sampling atmospheric gases and particles. The glass impactor consists of an entrance section containing the inlet tube, the acceleration jet, and the impaction plate, which is mounted at the entrance to the annular denuder. The impaction plate is a removable porous glass disk which can be impregnated with mineral oil to minimize bounce-off of the collected particles during sampling. Calibration tests showed that the impactor has a 50% aerodynamic particle cutoff size of 2.1 μm, at a flow of 10 L min^?1. Particle loss experiments were conducted. Total losses on surfaces inside the impactor, annular denuder, and filter pack, determined for particle sizes ranging between 1.50 and 2.77 μm, were lower than 3%. Co-located air sampling was conducted using the glass impactor and the Harvard impactor. Mass concentrations determined using the Harvard impactor were about 10% higher than for the glass impactor because the glass impactor has a slightly lower aerodynamic particle cutoff point, while sulfate concentrations obtained from the two systems were in excellent agreement.     

Surface Chemical Composition of Size-Fractionated Urban Walkway Aerosols Determined by X-Ray Photoelectron Spectroscopy

Most aerosol chemical characterization studies to date involve bulk particle analysis. The surface chemical and physical properties of aerosol particles have rarely been analyzed, despite the particles’ potential health impacts and interactions with gas in the atmosphere. Aerosol particles ranging from 0.056 to 10 μm in size collected using a 10-stage impactor sampler from a busy walkway in a downtown area of Hong Kong were analyzed using X-ray photoelectron spectroscopy (XPS), a technique providing both elemental and chemical state information about the particle surfaces. Six key elements were detected: nitrogen (N), sulfur (S), calcium (Ca), silicon (Si), oxygen (O), and carbon (C). Carbon was the dominant species on the surfaces of all particles regardless of their sizes. A higher carbon concentration was found on the surfaces of the 0.056–0.32 μm particles. The N, Si, Ca, and O concentrations were higher on the surface of the 3.2–10 μm particles than in the smaller size fractions. Sulfur was mainly found on the surface of the 0.32–1.8 μm particles. High-resolution scans of C, N, and S were obtained to provide chemical state information about these elements. Aromatic C-H and aliphatic C-H were found to be the major carbon chemical states. Fullerenic carbon was detected on the surfaces of the finest (0.056–0.32 μm) particles. Oxygen- and nitrogen-containing organics were found on the surfaces of the 0.32–1.8 μm particles. Sulfur was present in the form of sulfates as expected. Ammonium salts, amide, and nitrate were found to form especially on the surfaces of aerosol particles in the nucleation, accumulation, and coarse modes, respectively. Silicates and carbonates were only discovered on the surfaces of coarse-mode particles (3.2–10 μm). The results suggest that both the chemical elements and their chemical states were significantly dependent on the size of the aerosol particles.

Copyright 2013 American Association for Aerosol Research     

Surface-collection efficiency of Nuclepore filters for nanoparticles

The flat surface of Nuclepore filters is suitable for observing collected particles with a scanning electron microscope (SEM). However, experimental data on surface-collection efficiency are limited because surface-collection efficiencies cannot be measured directly using aerosol measuring instruments. In this study, the surface-collection efficiencies of Nuclepore filters were determined by establishing the ratio of the number of particles deposited on the surface of the filter visually counted with an SEM to the number of inflow particles counted by a condensation particle counter, using monodispersed polystyrene latex particles (30–800 nm) and silver particles (15–30 nm). Because Nuclepore filters with smaller pore sizes would be expected to produce higher minimum surface-collection efficiency and a higher pressure-drop, 0.08 and 0.2 µm Nuclepore filters were chosen as the test filters in view of both collection efficiency and pressure drop. The results showed that the minimum surface-collection efficiencies of the 0.08 µm pores at face velocities of 1.9 and 8.4 cm·s^?1 were approximately 0.6 and 0.7, respectively, and those of the 0.2 µm pores at face velocities of 1.5 and 8.6 cm·s^?1 were approximately 0.8 and 0.6, respectively. Because the pressure drop of the 0.2 µm pore filter was lower than that of the 0.08 µm pore filter under the same flow-rate conditions, the 0.2 µm pore filter would be more suitable considering the pressure drop and collection efficiency. The obtained surface collection efficiencies were quantitatively inconsistent with theoretical surface-collection efficiencies calculated using conventional theoretical models developed to determine the collection efficiency of filters with larger pores.

© 2016 American Association for Aerosol Research     

Numerical Study of the RespiCon Sampler Performance in the Calm Air

Results of a numerical study of the RespiCon sampler performance in the calm air are presented. The air flow is described by the Navier–Stokes equations of axisymmetric stationary viscous flow of incompressible fluid that are numerically integrated by the computational fluid dynamics (CFD) software FLUENT. The collection efficiencies of RespiCon impactor stages agree quite well with experimental data and curves of the European standards for the thoracic and respirable dust fractions. The aspiration efficiencies derived from the numerical model overestimate the experimental data in the range of particle sizes of 10 μm < d_p < 40 μm; however, they correctly predict the value of maximal size of aspirated particles. A new design of the RespiCon sampler with a higher volume flow rate was developed.

Copyright 2014 American Association for Aerosol Research     

Reducing Particle Bounce and Loading Effect for a Multi-Hole Impactor

Aerosol sampling is used to evaluate the health hazards associated with particles deposited in the human breathing system. Impactors, which are extensively employed as aerosol samplers, have low collection efficiency because of particle bounce. The impaction plate is typically coated with oil or grease to prevent particle bounce. However, such coating materials cannot sustain long-term heavy particle loading.

In this study, the impaction plate was recessed, forming a cavity filled with Trypticase Soy Agar (TSA) to reduce particle bounce and re-entrainment. An ultrasonic atomizing nozzle was employed to generate challenge aerosols. An Aerodynamic Particle Sizer (APS) was utilized to measure the number concentrations and the size distributions upstream and downstream of the size-selective devices. A multi-hole impactor and Personal Environmental Monitor PM _2.5 (PEM–PM _2.5 ) were used to evaluate particle bounce and heavy particle loading. Liquid type-Dioctyl phthalate (DOP), soluble solid type-potassium sodium tartrate tetrahydrate (PST) and insoluble solid type-polymethyl methacrylate (PMMA) were investigated, as were different impaction surfaces/surface combinations. The multi-hole impactor coated with silicone oil was compared with a TSA-filled plate. Laboratory results demonstrate that the solid PST particles bounced off the TSA-filled plate less than off the silicone-coated aluminum plate. This study also used a 700-μm-thick layer of silicone oil to prevent TSA dehydration. The experimental results revealed that the silicone-TSA double layer minimized PST particle bounce during the two-hour heavy sampling (mass concentration was around 7.22 mg/m ³ ). Moreover, the PEM-PM _2.5 impactor yielded consistent results when the silicone-TSA double layer method was used. These results are useful for designing bounce-free impaction substrates during heavy load sampling.