Thermophoretic Precipitator Research Articles

Wearable Resonator-Based Respirable Dust Monitor for Underground Coal Mines

Exposure to respirable coal dust and diesel exhaust in underground coal mines can cause detrimental airway diseases such as coal worker’s pneumoconiosis (CWP), silicosis, and lung cancer. In this article, we present the design, fabrication, and experimental evaluation of a low-cost wearable respirable dust monitor (WEARDM) that uses a dual-resonator gravimetric sensing approach for real-time measurement of respirable airborne particulate matter (PM) concentrations. The sensor selects for the ISO-respirable dust fraction using a miniature virtual impactor (VI) and removes moisture from the collected dust to ensure accurate mass measurement. WEARDM uses a novel dual-resonator mass sensor (DRMS) that is composed of a quartz crystal microbalance (QCM) and a film bulk acoustic resonator (FBAR). The QCM measures the mass concentration of particles generated from coal mining operations [typically >2.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> aerodynamic diameter (AD)], separated using inertial impaction. Thermophoretic precipitation is used to deposit the fine and ultrafine particles, such as those emitted from diesel sources [typically <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 0.1~\mu \text{m}$ </tex-math></inline-formula> AD) on FBAR. This allows the WEARDM system to maintain a large dynamic range and uniform collection efficiency (CE) across the entire respirable fraction. The WEARDM system is optimized for a low flow rate of 250 mL/min which results in low power usage and a small form factor and is an order of magnitude smaller and less expensive than currently available devices.

AlN FBAR Particle Sensor With a Thermophoretic Sampling Mechanism

Pollution by particulate matter (PM) poses a serious and growing risk to human health. Film Bulk Acoustic Resonators (FBARs) have been proposed as a low-cost way to monitor particle concentration. This paper presents particle detection by a 1.1 GHz aluminium nitride based FBAR designed and fabricated by SilTerra Malaysia. The FBARs are used in a differential configuration with one sensing and one reference device in a system comprising a microchannel with an electric microfan and a thermophoretic precipitator microhotplate array for improved sampling. A custom-built test chamber was designed to characterise the device at different levels of particulate matter concentration in air. The particle feed rate into the test chamber was varied between 9.5, 19, 43, 66 and 94 μg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> s. The FBAR frequency was found to decrease with increasing particulate matter concentration in the test chamber air. The experiments were conducted with and without the microchannel and it was found that the sampling channel increased sensitivity of FBAR resonant frequency to particle concentration per cubic meter of air from 5 Hz/ μgm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> to 20 Hz/ μgm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The detection limit in this test was estimated at ca. 50 μg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which is around current European limits for PM10 pollution. In addition, the use of the sampling microfan to aid cleaning of FBARs after particle measurement was also investigated and found to be feasible especially for lower particle concentration.

Combustion of Spherical Agglomerates of Titanium in Air. III. Motion of Agglomerates and the Effect of Blowing Velocity on Nanosized Combustion Products and Burning Time

The combustion of monodisperse titanium particles with a characteristic size of 38 and 320 μm moving in air was studied. Pyrotechnic samples generating monodisperse particles were burned in a chamber with a nozzle to impart an initial velocity to the burning particles. The particles were accelerated by the jet of gaseous combustion products discharged from the nozzle. The maximum path-averaged particle velocity relative to the ambient air was 7.9 m/s. Combustion of moving particles was carried out in a quartz tube 2 m long. At the end of the combustion, combustion products (oxide aerosol) were sampled from the tube using a thermophoretic precipitator. Size distribution functions of nanometer-sized spherule particles were determined by processing electron micrographs of samples. The velocity and burning time of burning particles were determined by video recording at a speed of 300 fps. It was found that increasing the velocity of motion of agglomerate particles with a diameter of 320 μm relative to the gas from 0.9 to 7.9 m/s leads to a decrease in the size of the spherules from 28 to 19 nm and to a decrease in the burning time from 0.45 to 0.26 s.

Configuration of Air Microfluidic Chip for Separating and Grading Respirable Dust

Particulate matter (PM) is a category of airborne pollutants, and fine particles that have a diameter of 2.5 μm (PM2.5) or smaller are especially damaging to human health because of their ability to penetrate deep into our respiratory system, Therefore, Monitoring of PM is very important. In this work, an air micro- fluidic PM sensor based on MEMS was proposed, and numerical model of the sensor was simulated accurately. The sensor was able to separate particles according to their sizes, and then transports and deposits the selected particles using thermophoretic precipitation onto the surface of a microfabricated mass-sensitive film bulk acoustic resonator (FBAR), precisely weighing and providing the concentration of PM. The PM sensor has double stage separation function, and the primary separator can separate the particles with size of less 10 μm from the particles, and the secondary can separate particles with size of less 2.5 μm from the particles.

Wafer-Scale Thermophoretic Dry Deposition of Single-Walled Carbon Nanotube Thin Films.

We report the direct and dry deposition of transparent conducting films (TCFs) of aerosol-synthesized single-walled carbon nanotubes (SWNTs) using a thermophoretic precipitator (TP) designed for the uniform and efficient deposition of aerosol-synthesized nanomaterials on 50 mm wafers or similarly sized polymer substrates. The optical and electrical performance of the fabricated TCFs match or surpass the published results achieved using a filter-based collection of aerosol-synthesized SWNTs, and TCFs with sheet resistances of 60 Ω/sq. at 87.8% transmittance and 199 Ω/sq. at 96% transmittance on flexible polymer substrates are demonstrated. The precipitator design is immediately applicable in roll-to-roll fabrication of SWNT TCFs or other functional coatings of aerosol-synthesized nanomaterials.

A Novel Particulate Matter 2.5 Sensor Based on Surface Acoustic Wave Technology

Design, fabrication and experiments of a miniature particulate matter (PM) 2.5 sensor based on the surface acoustic wave (SAW) technology were proposed. The sensor contains a virtual impactor (VI) for particle separation, a thermophoretic precipitator (TP) for PM2.5 capture and a SAW sensor chip for PM2.5 mass detection. The separation performance of the VI was evaluated by using the finite element method (FEM) model and the PM2.5 deposition characteristic in the TP was obtained by analyzing the thermophoretic theory. Employing the coupling-of-modes (COM) model, a low loss and high-quality SAW resonator was designed. By virtue of the micro electro mechanical system (MEMS) technology and semiconductor technology, the SAW based PM2.5 sensor detecting probe was fabricated. Then, combining a dual-port SAW oscillator and an air sampler, the experimental platform was set up. Exposing the PM2.5 sensor to the polystyrene latex (PSL) particles in a chamber, the sensor performance was evaluated. The results show that by detecting the PSL particles with a certain diameter of 2 μm, the response of the SAW based PM2.5 sensor is linear, and in accordance with the response of the light scattering based PM2.5 monitor. The developed SAW based PM2.5 sensor has great potential for the application of airborne particle detection.

Dry and Direct Deposition of Aerosol-Synthesized Single-Walled Carbon Nanotubes by Thermophoresis.

Single-walled carbon nanotubes (SWCNTs) show great potential as an active material in electronic and photonic devices, but their applicability is currently limited by shortcomings in existing deposition methods. SWCNTs can be dispersed from liquid solutions; however, their poor solubility requires the use of surfactants and ultrasonication, causing defects and degradation in device performance. Likewise, the high temperatures required by their chemical vapor deposition growth limit substrates on which SWCNTs can be directly grown. Here, we present a systematic study of the direct deposition of pristine, aerosol-synthesized SWCNTs by thermophoresis. The density of the deposited nanotube film can be continuously adjusted from individual, separated nanotubes to multilayer thin films by changing the deposition time. Depending on the lateral flow inside the thermophoretic precipitator, the angular distribution of the deposited SWCNT film can be changed from uniform to nonuniform. Because the substrate is kept at nearly ambient temperature, deposition can be thus carried out on practically any flat substrate with high efficiencies close to unity. The thermophoretic terminal velocity of SWCNTs, determined by aerosol loss measurements, is found to be approximately one-third of the usual prediction in the free molecular regime and shows a weak dependence on the nanotube diameter. As a demonstration of the applicability of our technique, we have used thermophoretic deposition in the fabrication of carbon nanotube thin-film transistors with uniform electrical properties and a high, over 99.5%, yield.

Microfabricated air-microfluidic sensor for personal monitoring of airborne particulate matter: Design, fabrication, and experimental results

We present the design and fabrication of a micro electro mechanical systems (MEMS) air-microfluidic particulate matter (PM) sensor, and show experimental results obtained from exposing the sensor to concentrations of tobacco smoke and diesel exhaust, two commonly occurring PM sources. Our sensor measures only 25mm×21mm×2mm in size and is two orders of magnitude smaller than commercially available direct mass PM sensors. The small shape allows our sensor to be used for continuous recording of personal PM exposure levels. The sensor contains an air-microfluidic circuit that separates the particles by size (virtual impactor) and then transports and deposits the selected particles using thermophoretic precipitation onto the surface of a microfabricated mass-sensitive film bulk acoustic resonator (FBAR). The mass-loading of the FBAR causes a change in its resonant frequency, and the rate of the frequency change corresponds to the particle concentration in the sampled air volume. We present experimental results that demonstrate the performance of our sensor for measuring PM mass emitted from diesel exhaust and tobacco smoke, and show that it exhibits sensitivity approaching 2μg/m3 with up to 10min integration time.

Thermophoretic Coating with Molybdenum Oxide Nanoparticles

AbstractThermophoretic 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.

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 after treatment 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.

Conductivity for Soot Sensing: Possibilities and Limitations

In this study we summarize the possibilities and limitations of a conductometric measurement principle for soot sensing. The electrical conductivity of different carbon blacks (FW 200, lamp black 101, Printex 30, Printex U, Printex XE2, special black 4, and special black 6), spark discharge soot (GfG), and graphite powder was measured by a van der Pauw arrangement. Additionally the influence of inorganic admixtures on the conductivity of carbonaceous materials was proven to follow the percolation theory. Structural and oxidation characteristics obtained with Raman microspectroscopy and temperature programmed oxidation, respectively, were correlated with the electrical conductivity data. Moreover, a thermophoretic precipitator has been applied to deposit soot particles from the exhaust stream between interdigital electrodes. This combines a controlled and size independent particle collection method with the conductivity measurement principle. A test vehicle was equipped with the AVL Micro Soot Sensor (photoacoustic soot sensor) to prove the conductometric sensor principle with an independent and reliable technique. Our results demonstrate promising potential of the conductometric sensor for on-board particle diagnostic. Furthermore this sensor can be applied as a simple, rapid, and cheap analytical tool for characterization of soot structure.

On Line Characterization of SiC Nanoparticles Produced by Laser Pyrolysis

On Line Measurements campaigns have been carried out for the first time in IRAMIS/SPAM CEA's laser gas-phase pyrolysis nanoparticles production facilities. The produced aerosol is composed of Argon and/or Helium laden with SiC nanoparticles concentrated up to ∼14 mg/l.Different commercial apparatus were used for sampling, and characterisation of size, and morphology of the particles. A series of experiment is performed by IRSN with a DMS500 from Cambustion Ltd™, which gives electrical mobility equivalent diameter distribution in real time. Particles are sampled with an ejector-diluter VKL-10 from Palas™. On the same sampling line, APTL performed aerodynamic equivalent diameter mass distribution using a Nanomoudi from MSP Corp.™ and TEM post analysis, as well as post elemental analysis (EDS) after collection on TEM grid with a Thermophoretic Precipitator (TP). A previously developed model is used to obtain the aggregate morphology and primary particles sizes.In addition to these commercial or well-known techniques, a new patent-pending technique called RFPM (Radio Frequency Plasma Metrology developed by CILAS + GREMI in the frame of NANOCARA program) is tested for the first time off the lab. The principle is based on levitation of particles in plasma RF. The entire set up is a prototype, including the sampling line. Experiments showed that this technique is very promising for on line gas phase monitoring, even though future improvements are needed, especially on the direct injection of the sample in the measuring chamber.First results of size distribution on pyrolysis line were obtained: three modes of different geometric mean diameter D50 were measured. Further analysis of TEM micrographs gave insight on these three modes, they can be interpreted as primary particles, aggregated particles, and a third one which could be composed of silica oxide nanoparticles issued from the combustion of the remaining silane initiated by an air leak in the exhaust of the reactor.Furthermore, a parametric study was undertaken. Helium addition in reactor and laser power were authorized to vary within a significant range. There was an evidence of influence of these parameters on the size distributions.Thus, we have demonstrated the high interest of implementing a size monitoring set up on gas phase nanoparticles production line for safety, yield improvement, and cost reduction purposes. This set up can run in a safe and non invasive way, and require low maintenance.

Natural and anthropogenic environmental nanoparticulates: Their microstructural characterization and respiratory health implications

A wide range of environmental particulate matter (PM) both indoor and outdoor and consisting of natural and anthropogenic PM was collected by high volume air filters, electrostatic precipitation, and thermophoretic precipitation directly onto transmission electron microscope (TEM) coated grid platforms. These collected PM have been systematically characterized by TEM, energy-dispersive X-ray spectrometry (EDS) and scanning electron microscopy (SEM). In the El Paso, TX, USA/Juarez, Mexico metroplex 93% of outdoor PM 1 is crystalline while 40% of PM 1 is carbonaceous soot (including multiwall carbon nanotubes (MWCNTs) and multiconcentric fullerenes) PM. Multiply-replicated cytotoxicity ( in vitro) assays utilizing a human epithelial (lung model) cell line (A549) consistently demonstrated varying degrees of cell death for essentially all PM which was characterized as aggregates of nanoparticulates or primary nanoparticles. Cytokine release was detected for Fe 2O 3, chrysotile asbestos, BC, and MWCNT PM while reactive oxygen species (ROS) production has been detected for Fe 2O 3, asbestos, BC, and MWCNT aggregate PM as well as natural gas combustion PM. Nanoparticulate materials in the indoor and outdoor environments appear to be variously cytotoxic, especially carbonaceous nano-PM such as multiwall carbon nanotubes, black carbon, and soot nano-PM produced by natural gas combustion.

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 sam...

Size and morphology of the nanooxide aerosol generated by combustion of an aluminum droplet

The increasing recent interest in characteristics ofsubmicron oxide smoke generated by combustion ofaluminum droplets stems from environmental problemsassociated with application and utilization of alumi-nized propellant rocket motors and from the develop-ment of technologies of production of metal nanoox-ides in aerodisperse flames [1, 2]. Oxide particles rang-ing from nanometer to submicrometer size form andgrow in the flame zone surrounding a burning particle,this process being the starting point for their furtherevolution. Rational design of particle combustion pro-cesses in technical devices is based on an understand-ing of physicochemical processes that occur duringcombustion of a particle and on knowledge of how theircharacteristics depend on combustion conditions. Oneof the challenges in studying the aluminum particlecombustion mechanism is to study the formation andproperties of oxide nanoparticles. In this work, we stud-ied how the size distribution and morphology of theoxide aerosol formed by combustion of aluminum par-ticles in atmospheric air depends on the size of a burn-ing droplet. We intend to extend the pressure range inthe future.Burning droplets were produced by combustion of asmall sample (from 2 × 2 × 20 to 2 × 4 × 40 mm in size)of aluminized solid propellant, which was burnt in a20-L container in air filtered from aerosols. Duringcombustion, the sample expelled burning aluminumdroplets (agglomerates), which fell freely under grav-ity. The combustion lasted a few seconds. During thistime, the container was filled with “oxide smoke,” a fineaerosol. After completion of combustion, aerosol parti-cles coagulated, sedimented, and were partially depos-ited on the walls of the container. To study the evolutionof particles after burning, the resulting aerosol wasperiodically sampled. The aerosol sample was fedeither into a thermophoretic precipitator, to collect par-ticles for subsequent dispersion and morphologicalanalysis based on their electron microscopic images, orinto a Millikan cell, to observe aerosol particles andrecord their motion by a video camera with a micro-scope lens and a laser illuminator. The cell constructionimplies that a homogeneous electric field can beapplied. This, in combination with video recording ofparticle motion, makes it possible to determine the elec-tric charge of the particles. The sampling, video record-ing, and image processing techniques were describedelsewhere [1, 3].We carried out four series of experiments with pro-pellants differing in the size of generated burning drop-lets.In series 1, a model solid propellant containing25 wt % ammonium perchlorate (AP), 35 wt %cyclotetramethylenetetranitramine (HMX), 20 wt %binder, and 20 wt % aluminum was used. Inasmuch asaluminum droplets are agglomerated as the propellantburns, the distribution function of burning droplets gen-erated by the propellant was estimated in the followingmanner. The size distribution of agglomerates, as wellas the fraction of the metal involved in agglomeration(≈0.6), was determined using the technique in [4]. If weassume that the metal not involved in agglomerationpasses into the gas phase in the same form as it has inthe propellant, the set of particles generated by combus-tion consists of agglomerates and particles of initialaluminum. The distribution function of initial alumi-num was preliminarily determined on a Malvern 3600Eparticle size analyzer. Table 1 summarizes the charac-teristics of the set of polydisperse particles calculatedtaking into account the weight fractions. Hereinafter,D

Carbon nanotubes in wood soot

AbstractMultiwall carbon nanotubes were observed in a small fraction of soot collected by thermophoretic precipitation from Texas piñon pine wood burning in air. Transmission electron microscopy showed the carbon nanotubes to be aggregated with other fullerene‐like nanoforms and graphite fragments. Copyright © 2006 Royal Meteorological Society

Combustion-Generated Nanoparticulates in the El Paso, TX, USA / Juarez, Mexico Metroplex: Their Comparative Characterization and Potential for Adverse Health Effects

In this paper we report on the collection of fine (PM1) and ultrafine (PM0.1), or nanoparticulate, carbonaceous materials using thermophoretic precipitation onto silicon monoxide/formvar-coated 3 mm grids which were examined in the transmission electron microscope (TEM). We characterize and compare diesel particulate matter (DPM), tire particulate matter (TPM), wood burning particulate matter, and other soot (or black carbons (BC)) along with carbon nanotube and related fullerene nanoparticle aggregates in the outdoor air, as well as carbon nanotube aggregates in the indoor air; and with reference to specific gas combustion sources. These TEM investigations include detailed microstructural and microdiffraction observations and comparisons as they relate to the aggregate morphologies as well as their component (primary) nanoparticles. We have also conducted both clinical surveys regarding asthma incidence and the use of gas cooking stoves as well as random surveys by zip code throughout the city of El Paso. In addition, we report on short term (2 day) and longer term (2 week) in vitro assays for black carbon and a commercial multiwall carbon nanotube aggregate sample using a murine macrophage cell line, which demonstrate significant cytotoxicity; comparable to a chrysotile asbestos nanoparticulate reference. The multi-wall carbon nanotube aggregate material is identical to those collected in the indoor and outdoor air, and may serve as a surrogate. Taken together with the plethora of toxic responses reported for DPM, these findings prompt concerns for airborne carbonaceous nanoparticulates in general. The implications of these preliminary findings and their potential health effects, as well as directions for related studies addressing these complex issues, will also be examined.

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.

A TEM study of soot, carbon nanotubes, and related fullerene nanopolyhedra in common fuel-gas combustion sources

Nanoparticle aggregates collected by thermophoretic precipitation from natural gas–air and propane–air kitchen stove top flame exhausts, natural gas–air water heater roof-top exhausts, and other common fuel-gas combustion sources were observed by transmission electron microscopy to consist of occasional aggregates of mostly turbostratic carbon spherules, aggregates of crystalline graphite nanoparticles mixed with other fullerene nanoforms; and aggregates of various sizes of multiwall carbon nanotubes and other multishell, fullerene polyhedra for optimal blue-flame combustion. The carbon nanotube structures and end cap variations as well as fullerene polyhedral structures were observed to be the same as those for arc-evaporation produced nanoaggregates. Nanoparticle aggregation or the occurrence of carbon nanoforms always occurred as aggregates with nominal sizes ranging from about 0.5 μm to 1.5 μm.

Utilization of Selected Area Electron Diffraction Patterns for Characterization of Air Submicron Particulate Matter Collected by a Thermophoretic Precipitator

A thermophoretic precipitator (TP) that uses a novelty of direct sampling of ambient air particulate matter (PM) onto transmission electron microscopy (TEM) grids was designed and utilized to determine its potential applicability for the collection and consequent qualitative analyses of representative PM in the air, especially those with aerodynamic diameter less than 1 µm (PM1.0 ). After a calibration process, preliminary field tests were performed under different weather conditions, locations, and time frames. TEM, selected area electron diffraction (SAED), and electron energy-dispersive X-ray spectrometry (EDS) analyses were performed on individual samples, and chemical species were analyzed. During this investigation, individual air PM with different sizes ranging from 10 [H9262]m to 10 nm for TEM analysis was collected. Two observations were made: (1) a large fraction of collected particulates were aggregates of very small particles of both organic and inorganic origin, and (2) a large fraction of the collected particulates were crystalline or polycrystal-line. This study has demonstrated, by utilization of SAED patterns from TEM on air particles collected by a TP, the potential to analyze and identify individual air PM in a nanometer regime qualitatively by combining SAED and EDS data.