Influence of Sampling and Storage Protocol on Fractal Morphology of Soot Studied by Transmission Electron Microscopy

The aim of this work was to compare the fractal characteristics, D_f and k_f, the primary particle diameter, D_pp, the gyration diameter of aggregates, D_g, and the overlap coefficient, C_ov, of carbon nanoparticle aggregates produced by an ethylene diffusion flame and sampled by means of four commonly used techniques. The first method involves a thermophoretic piston probe (TPP) which inserts a TEM grid into the flame. Three other methods were applied at the outlet of a dilution device, also inserted in the flame. The first of these used a nuclepore filtration sampler (NFS), and is based on filtration of particles onto a polycarbonate membrane. The second, post dilution method, the insertion particle sampler (IPS), inserts a TEM grid, perpendicular to the aerosol flow. Similar to TPP, the last method is a thermophoretic particle sampler (TPS) sampling directly onto a TEM grid. After collection, the samples are stored in the dark either, (1) in a nitrogen filled cell at low humidity or, (2) in ambient air for studying atmospheric ageing. Good agreement was observed between TPP, TPS, and IPS indicating that the dilution induced for TPS and IPS does not significantly change the morphology of soot. On the other hand, the NFS protocol tended to overestimate the overlap coefficient and the size of primary particles and aggregates. Finally, with regard to the aging effect, we found that k_f and D_pp evolve slowly during storage in the atmosphere while D_f, was insensitive to the storage conditions. However, the overlap coefficient increased and the gyration diameter decreased as a function of storage duration, while storage under nitrogen tended to reduce these changes.     

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     

A Thermophoretic Precipitator for the Representative Collection of Atmospheric Ultrafine Particles for Microscopic Analysis

In this article, the potential of a thermophoretic sampling device to derive quantitative particle size distributions and number concentrations of aerosols based on microscopic single particle analysis is explored. For that purpose a plate-to-plate thermophoretic precipitator to collect ultrafine atmospheric particles for TEM (transmission electron microscopy) analysis has been calibrated and characterized. The representativeness of the samples has been verified in a series of experiments. Results show that, for particles with diameters of 15 nm to 300 nm, the precipitator's collection efficiency is independent of size, shape, and composition of the particles. Hence, its samples accurately represent the original aerosol.

A numerical model of thermophoretic deposition within the device has been developed and tailored to the specifications of the precipitator. The model has been used to derive the particle number density and size distribution of several calibration aerosols using the TEM analysis of the samples taken with the thermophoretic precipitator as input parameters. The results agree very well with the on-line measurements of the calibration aerosols. This work demonstrates that our thermophoretic sampling device can be used to derive quantitative particle size distributions and number concentrations of ultrafine particles based on microscopic single particle analysis.     

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     

Design Optimization of a Portable Thermophoretic Precipitator Nanoparticle Sampler

Researchers at the National Institute for Occupational Safety and Health (NIOSH) are developing methods for characterizing diesel particulate matter in mines. Introduction of novel engine and exhaust aftertreatment technologies in underground mines is changing the nature of diesel emissions, and metrics alternative to the traditional mass-based measurements are being investigated with respect to their ability to capture changes in the properties of diesel aerosols. The emphasis is given to metrics based on measurement of number and surface area concentrations, but analysis of collected particles using electron microscopy (EM) is also employed for detailed particle characterization. To collect samples for EM analysis at remote workplaces, including mining and manufacturing facilities, NIOSH is developing portable particle samplers capable of collecting airborne nano-scale particles. This paper describes the design, construction, and testing of a prototype thermophoretic precipitator (TP) particle sampler optimized for collection of particles in the size range of 1–300 nm. The device comprises heated and cooled metal plates separated by a 0.8 mm channel through which aerosol is drawn by a pump. It weighs about 2 kg, has a total footprint of 27 × 22 cm, and the collection plate size is approximately 4 × 8 cm. Low power consumption and enhanced portability were achieved by using moderate flow rates (50–150 cm³/min) and temperature gradients (10–50 K/mm with ΔT between 8 K and 40 K). The collection efficiency of the prototype, measured with a condensation particle counter using laboratory-generated polydisperse submicrometer NaCl aerosols, ranged from 14–99%, depending on temperature gradient and flow rate. Analysis of transmission electron microscopy images of samples collected with the TP confirmed that the size distributions of collected particles determined using EM are in good agreement with those determined using a Fast Mobility Particle Sizer.

Copyright 2012 American Association for Aerosol Research     

Development and Optimization of the Electrostatic Precipitator with Superhydrophobic Surface (EPSS) Mark II for Collection of Bioaerosols

We recently developed an electrostatic collector for bioaerosols that electrostatically deposits biological particles onto a 3.2 mm electrode covered by a superhydrophobic substance. The deposited biological particles are removed and collected by rolling water droplets (20 or 40 microliter) which results in high concentration rates. The collector has been improved further by integrating it with an electrical charger. Here, we describe the development and optimization of the charger and collection chamber, while maximizing collection efficiency and minimizing particle loss. The resulting sampler is made of static dissipative material (e.g., Delrin), is shaped as a closed half cylinder, and is integrated with a charger. The sampler's round top section contains eight carbon fiber brushes (ion sources to charge particles), while its flat bottom section holds a rectangular collection electrode (254 × 3.2 mm) made of pressed carbon fiber and coated with a superhydrophobic material.

The optimized configuration of the EPSS Mark II had a collection efficiency of up to 84% when sampling airborne Escherichia coli at 10 L/min and for 10 min. The bacteria were accumulated in rolling water droplets as small as 20 microliters, and the sampler achieved sample concentration rates of up to 4.2 × 10⁵/min. When the sampler was operated for a longer time period (60 min), its collection efficiency was 72%. The efficiency decrease was most likely due to a reduced particle removal from the electrode, but the difference was not statistically significant. Since the EPSS Mark II shows satisfactory collection efficiency and high sample concentration rate, it could serve as a basis for developing a field-deployable version of the sampler.

Copyright 2015 American Association for Aerosol Research     

A New Cross-Flow Tube Bundle Heat Exchanger with Staggered Hot and Cold Tubes for Thermophoretic Deposition of Submicron Aerosol Particles

A new tube cross-flow bundle heat exchanger has been designed and tested for thermophoretic deposition of submicron aerosol particles. The present design has five columns of hot and cold square tubes, respectively, arranged in a staggered manner to maintain a nearly constant temperature gradient in the direction of the aerosol flow. Each column has four tubes of 4 mm × 4 mm in cross section and the gap between the tube surfaces is 0.5 mm. The precipitator was tested experimentally using monodisperse NaCl test particles ranging from 38 to 397 nm in diameter at the aerosol flow rate of 0.6 and 1.2 L/min, respectively, at different temperature gradients. Results showed that the thermophoretic deposition efficiency increased with decreasing aerosol flow rate and increasing temperature gradient with the maximum thermophoretic deposition efficiency occurred at the aerosol flow rate of 0.6 L/min. The effect of inlet temperature of the aerosol flow on the efficiency was also tested and showed increasing inlet temperature increased the deposition efficiency. Numerical simulation was further conducted to validate the experimental data and good agreement was obtained. An empirical equation was also validated to facilitate the design and scale-up of the precipitator.     

A New Thermophoretic Precipitator for Collection of Nanometer-Sized Aerosol Particles

A new thermophoretic precipitator (TP) has been designed and used for the collection of nanosized aerosol particles. NaCl and Fe particles, with mean diameters of 55 nm and 3.6 nm, respectively, were used to determine the thermophoretic deposition efficiency as well as the uniformity of the deposition. When the average temperature gradients applied were 2200 K/cm and 2400 K/cm, a high thermophoretic deposition efficiency, close to 100%, was attained at aerosol flow rates below 15 sccm. A gradual decay in the efficiency was observed as the flow rate was increased. Theoretical calculations of particle deposition efficiency were in good agreement with experimental data. The deposition along the TP was shown to be homogenous on a millimeter scale for both NaCl and Fe particles collected on thin foil substrates and microscope grids, respectively. Finally, the thermophoretic precipitator was used to efficiently deposit Fe nanoparticles on a substrate for the subsequent growth of carbon nanotubes.     

Wind Tunnel Evaluation of a Rotating-Element Large-Particle Sampler

A large-particle sampler was tested in an environmental wind tunnel to characterize the efficiency as a function of particle size and type (solid or liquid). The sampler, which had been developed by another organization, has two slotted-cylinder collection elements which are rotated through air at a tangential speed of 39 m/s. Data from wind tunnel tests show the efficiency of liquid droplet collection to increase with particle size to approximately 50% at 25 μm and then decrease with a further increase in particle size. It is suggested that the air flow patterns created by the sampler produce this anomalous behavior. Results of tests with solid particles show higher efficiencies than are obtained with liquid droplets of the same size. It appears that solid particles, which rebound from collection sites other than a slot, can subsequently enter the slots. Supporting data were obtained on the performance of a single slotted cylinder that was fixed in the discharge region of a small free-jet tunnel. Those results show the impaction efficiency of all sizes of liquid droplets in the slotted cylinder follow the type of trend expected for a circular cylinder, i.e., a curve in which efficiency monotonically increases with size. However, 41-μ m diameter solid particles are re-entrained in the air stream and show reduced efficiency in comparison with liquid aerosol particles.     

Design and development of an electrostatic sampler for bioaerosols with high concentration rate

Integration of bioaerosol sampling methods with modern analysis techniques, such as the polymerase chain reaction as well as our ability to detect low concentrations of airborne agents require samplers that are able not only to efficiently collect the biological particles, but also to concentrate them in small amounts of fluids. In this research, we began development of a novel bioaerosol sampler, where a combination of electrostatic collection mechanism with superhydrophobic (“Lotus leaf” type) collection surface allows for efficient particle collection, removal and concentration in water droplets as small as 5 μL. This new sampling concept allowed achieving very high sample concentration rates (up to 1 million and higher) and could be applied to detect low concentrations of bioaerosols in various environments.The prototype electrostatic precipitator with superhydrophobic surface had a shape of a half-pipe, where a top plate served as the ground electrode, while the collecting surface was 3.2 mm wide rectangular electrode coated with a superhydrophobic substance and positioned in a groove in the flat bottom surface. Airborne particles drawn into the sampler were positively charged and then by the action of an electrostatic field deposited onto the negatively charged electrode. The sampler was positioned at a ∼1° inclination angle to the horizontal, and the injected water droplets rolled off of electrode's surface removing deposited particles. Sampler's performance has been analyzed with polystyrene latex particles of five aerodynamic diameters (0.5, 1.2, 1.9, 3.2, and 5.1 μm), collecting droplet volumes ranging from 5 to 60 μL, and sampling flow rates of 2, 5, and 10 L/min. It was determined that vast majority of particles deposited onto the electrode are removed by the first rolling droplet, which for 3.2 μm particle and 20 μL droplet translated into a concentration rate of 3×10⁵. By narrowing the electrode to 2.1 mm and lowering the droplet volume to 5 μL we achieved the concentration rate as high as 1.2×10⁶. These concentration rates were sustained for sampling times as long as 60 min. This novel sampling concept demonstrates a great potential for sampling and detecting airborne microorganisms in low concentration environments.     

Thermophoretic Deposition of Particles in Laminar and Turbulent Tube Flows

Thermophoretic deposition of aerosol particles (particle diameter ranges from 0.038 to 0.498 μm) was measured in a tube (1.18 m long, 0.43 cm inner diameter, stainless steel tube) using monodisperse NaCl test particles under laminar and turbulent flow conditions. In the previous study by Romay et al., theoretical thermophoretic deposition efficiencies in turbulent flow regime do not agree well with the experimental data. In this study, particle deposition efficiencies due to other deposition mechanisms such as electrostatic deposition for particles in Boltzmann charge equilibrium and laminar and turbulent diffusions were carefully assessed so that the deposition due to thermophoresis alone could be measured accurately. As a result, the semiempirical equation developed by Lin and Tsai in laminar flow regime and the theoretical equation of Romay et al. in turbulent flow regime are found to fit the experimental data of thermophoretic deposition efficiency very well with the differences of less than 1.0% in both flow regimes. It is also found that Talbot's formula for the thermophoretic coefficient is accurate while Waldmann's free molecular formula is only applicable when Kn is greater than about 3.0.     

DESIGN AND EXPERIMENTAL CHARACTERIZATION OF A PM1 AND A PM2.5 PERSONAL SAMPLER

This paper presents the development, laboratory and field evaluation of two personal particle samplers (PPS). Both samplers operate at a flow rate of 4 l min^-1, and collect particles smaller than 1.0 and 2.5 μm in aerodynamic diameter, respectively, on 3.7 cm Teflon filters. In each sampler, particles larger than 2.5 or 1.0 μm are retained by impaction onto a coated porous metal disk, which minimizes particle bounce. Using the substrates without any coating results in a substantial reduction of the collection efficiency for particles larger than the 50% cutpoint of the sampler. Particle losses in each sampler are quite low (e.g., on the order of 10% or less) and do not depend significantly on aerodynamic particle diameter. Both samplers display sharp particle cut characteristics, with the ratio of the aerodynamic particle diameter corresponding to 84% collection efficiency to the 50% cutpoint being approximately 1.18 and 1.27 for the PM₁ and the PM_2.5 samplers, respectively. Field tests showed that the mass, sulfate and nitrate concentrations measured by the PM_2.5 PPS and a collocated PM_2.5 Personal Exposure Monitor (PEM) agreed within 10% or less. Such agreement, however, was not observed between the PM_2.5 PPS and the Harvard/EPA Annular Denuder System (HEADS), with the HEADS nitrate concentrations being on the average higher by a factor of 2.1. The particle mass, sulfate and nitrate concentrations obtained with a modified MOUDI sampler collecting all particles smaller than 1 μm in aerodynamic diameter on a filter and the PM₁ PPS were also in very good agreement (e.g., within 7% or less). The two personal particle samplers will be used in field studies in different locations of the U.S. to provide better estimates of human exposures to exclusively particles of the accumulation mode. (e.g., without incorporating the contribution of the coarse mode).     

Porous polyurethane foam for use as a particle collection substrate in a nanoparticle respiratory deposition sampler

Porous polyurethane foam was evaluated to replace the eight nylon meshes used as a substrate to collect nanoparticles in the Nanoparticle Respiratory Deposition (NRD) sampler. Cylindrical (25 mm diameter by 40 mm deep) foam with 100 pores per inch was housed in a 25-mm-diameter conductive polypropylene cassette cowl compatible with the NRD sampler. Pristine foam and nylon meshes were evaluated for metals content via elemental analysis. The size-selective collection efficiency of the foam was evaluated using salt (NaCl) and metal fume aerosols in independent tests. Collection efficiencies were compared to the nanoparticulate matter (NPM) criterion and a semi-empirical model for foam. Changes in collection efficiency and pressure drop of the foam and nylon meshes were measured after loading with metal fume particles as measures of substrate performance. Substantially less titanium was found in the foam (0.173 µg sampler^?1) compared to the nylon mesh (125 µg sampler^?1), improving the detection capabilities of the NRD sampler for titanium dioxide particles. The foam collection efficiency was similar to that of the nylon meshes and the NPM criterion (R² = 0.98, for NaCl), although the semi-empirical model underestimated the experimental efficiency (R² = 0.38). The pressure drop across the foam was 8% that of the nylon meshes when pristine and changed minimally with metal fume loading (～19 mg). In contrast, the pores of the nylon meshes clogged after loading with ～1 mg metal fume. These results indicate that foam is a suitable substrate to collect metal (except for cadmium) nanoparticles in the NRD sampler.

Copyright © 2016 American Association for Aerosol Research     

A Granular Bed for Use in a Nanoparticle Respiratory Deposition Sampler

A granular bed was designed to collect nanoparticles as an alternative to nylon mesh screens for use in a nanoparticle respiratory deposition (NRD) sampler. The granular bed consisted of five layers in series: a coarse mesh, a large-bead layer, a small-bead layer, a second large-bead layer, and a second coarse mesh. The bed was designed to primarily collect particles in the small-bead layer, with the coarse mesh and large-bead layers designed to hold the collection layer in position. The collection efficiency of the granular bed was measured for varying depths of the small-bead layer and for test particles with different shape (cuboid, salt particles; and fractal, and stainless steel and welding particles). Experimental measurements of collection efficiency were compared to estimates of efficiency from theory and to the nanoparticulate matter (NPM) criterion, which was established to reflect the total deposition in the human respiratory system for particles smaller than 300 nm. The shape of the collection efficiency curve for the granular bed was similar to the NPM criterion in these experiments. The collection efficiency increased with increasing depth of the small-bead layer: the particle size associated with 50% collection efficiency, d₅₀, for salt particles was 25 nm for a depth of 2.2 mm, 35 nm for 3.2 mm, and 45 nm for 4.3 mm. The best-fit to the NPM criterion was found for the bed with a small-bead layer of 3.2 mm. Compared to cubic salt particles, the collection efficiency was higher for fractal-shaped particles larger than 50 nm, presumably due to increased interception.

Copyright 2015 American Association for Aerosol Research     

Thermophoretic Coating with Molybdenum Oxide Nanoparticles

Thermophoretic and electrophoretic coatings are the main viable mechanisms for the coating of objects with nanoparticles. Unlike electrophoretic coating, thermophoretic coating has the advantage that electrically conductive substrates are not a requirement. This paper investigates the thermophoretic deposition and uniformity of molybdenum oxide nanoparticles, generated by a glowing wire generator, on various surfaces at three different flow rates (0.3, 1 and 1.5 L min^–1). The quantitative evidence of the presence of particles collected by a suggested thermophoretic precipitator at different flow rates has shown that a uniform distribution of the particles could be achieved across the whole area of the precipitator. SEM and TEM micrographs of the film confirmed that a homogeneous densely packed network of molybdenum oxide nanoparticles was built across the precipitation area at the flow rate of 1.5 L min^–1.     

Particle Sampling by TEM Grid Filtration

Transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX) offers a very comprehensive tool for individual particle analysis allowing the determination of size, morphology, specific surface, and elemental composition. This information is needed in aerosol studies, especially in the field of nanomaterials. However, observations with TEM require a controlled sampling on an adapted analysis support, namely TEM grid. Techniques allowing sampling on TEM grids are of great interest to aerosol analysis. Indeed, sample preparation is not required, thereby gaining time and avoiding a risk for the sample to be altered. The present study evaluates the efficiency of a new particle collection technique based on filtration through one class of TEM-dedicated supports, namely TEM porous grids. Two types of porous grids, considered as the best on the market for this application, have been put to the test: the “Quantifoil” type porous grid, which has a regular structure, and the “Holey” type (Agar Scientific, Stansted, Essex, England). A filter holder has been developed specifically for this application, the MPS® (Mini-Particle Sampler®, Ecomesure, Janvry, France). Experimental tests have been carried out with a flow rate of 0.3 L·min^?1. They show that the collection is operational in the 5-nm to 150-nm size range, with a minimum efficiency of 15–18% around 30 nm. Simulation confirms these results and shows an increased efficiency even below 5 nm and beyond 150 nm. The filter holder MPS® designed in this study is a low-cost, portable, versatile, and easy-to-use tool.

Copyright 2013 American Association for Aerosol Research     

Investigation of Cut-Off Sizes and Collection Efficiencies of Portable Microbial Samplers

This research investigated the physical collection efficiencies and cut-off sizes of SMA MicroPortable, BioCulture, Microflow, Microbiological Air Sampler (MAS-100), Millipore Air Tester (MAT), SAS Super 180, and RCS High Flow portable microbial samplers when collecting Polystyrene Latex particles ranging from 0.5 to 9.8 μm in aerodynamic size. Traditional collection efficiency measurements often directly compare particle concentrations upstream and downstream of the sampler without considering the particle losses. Here, we developed a new approach which tests collection efficiencies of the sampler with and without agar collection plate loaded. This method thus allows estimating the effective collection efficiency, i.e., the fraction of incoming particles deposited onto the agar collection medium only. The experimental cut-off sizes, or d ₅₀, of the investigated samplers ranged from 1.2 μm for the RCS High Flow, 1.7 μm for the MAS-100, 2.1 μm for SAS Super 180, to 2.3 μm for MAT; for other three samplers they were close to or above 5 μm. In most cases the theoretical d ₅₀ was lower than the experimental value, which was likely due to the dissipation of impactor jets and the influence of cross-flow in the multi-nozzle impactors. For most samplers, we observed a notable difference between the collection efficiency obtained by the traditional measurement method and the effective collection efficiency. In general, all samplers collected 10% or less of 0.5 μm particles onto the agar medium. This study indicates that the use of most of the tested bioaerosol samplers may result in a substantial underestimation of bacterial concentrations, especially of single bacterial cells with diameter 0.5–1.0 μm. On the other hand, most of the investigated samplers would be more efficient when collecting larger fungal spores.     

Design and Characterization of a New Coarse Particle Collector Based on Microtrap Impactor Technology

A microtrap inertial impactor has been developed and characterized for use as an area or personal sampler. The microtrap impactor utilizes a high-density multijet plate to direct airflow and a matched multiwell plate to impact and collect particles for extraction with a reduced pressure drop relative to inertial impactors with fewer jets. Reported here is the characterization of the microtrap impactor using a fluidized bed aerosol generator and a small volume nebulizer to generate particles of Arizona Road Dust, potassium chloride, and oleic acid. Collection efficiency was determined by measuring particle size distributions with an aerodynamic particle sizer. Two geometries of the microtrap were tested suitable for a two-stage coarse particle sampler, with 1–4 μm and a 4–10 μm stages. The 1 μm cut-point microtrap stage has a collection efficiency above 97% for particles greater than 2 μm in diameter (at a 10 L/min flow rate and a pressure drop of 0.12 kPa). This stage's collection efficiency was constant for a period of time up to 10 h under typical ambient conditions without any coating on the impaction surface. The microtrap impactor provides an improvement in area sampling due to its high collection efficiency at a low pressure drop across the device, and its use of an uncoated impaction surface allowing for the extraction and analysis of biological samples.

© 2013 American Association for Aerosol Research