Simultaneous Use of Polystyrene Latex Particles of Different Sizes to Evaluate Performance of a Cyclone and Impactor

Monodisperse and polydisperse aerosols were produced to evaluate the effect of particle size on cyclone and impactor performance. Monodisperse aerosols were generated from polystyrene latex and divinylbenzene particles. Polystyrene aerosols were also generated by mixing several monodisperse aerosols of different sizes. The mixture ratio of monodisperse aerosols was found by trial and error to generate polydisperse aerosols. Generated polydisperse aerosols had multimodal aerosol size distribution, which had the same peak point as shown in the size distribution of monodisperse particles. The results show the collection efficiency curves of a cyclone and impactor, when generating monodisperse particles were coherent with those for polydisperse ones. Our findings show that the size distribution and the size range of test aerosols can be easily determined by mixing monodisperse particles of known particle sizes, using a time saving procedure.     

Influence of Sampling Artefacts on Measured PM,OC, and EC Levels in Carbonaceous Aerosols in an Urban Area

The registration efficiency of the TSI model 3025 ultra-fine condensation particle counter for Ag and NaCl particles of between 2 and 20 nm in diameter was determined. Taking into account the different shapes of the input aerosol size distributions entering the differential mobility analyzer (DMA) and the transfer function of the DMA, the counting efficiencies of condensation nucleus counters (CNC) for monodisperse Ag and NaCl particles were estimated. In addition, the dependence of the CNC registration efficiency on the particle concentration was investigated.     

Narrow size distribution nanoparticle production by electrospray processing of ferritin

Electrospraying and in-flight heating of ferritin, the iron-storage protein, was used to produce controlled size, monodisperse aerosol particles which can be used as size standards for instrument calibration. As aerosol particles can be collected in liquids or on a substrate, standard size aerosol nanoparticles can be used for the calibration and development of not only aerosol instrumentation, but also colloid instrumentation and electron microscopes. Differences in the sizes of apoferritin and ferritin were detectable using scanning mobility particle spectrometry. Apoferritin has a mobility diameter of 11.8 nm, while iron-rich ferritin had a mobility diameter of 13.1 nm and the size distribution function of both apoferritin and ferritin had geometric standard deviations of 1.05. In-flight heating in a furnace aerosol reactor was used to remove the ferritin protein coat and produce monodisperse iron oxide particles 7.9 nm in diameter and a size distribution function geometric standard deviation of 1.07. Ferritin dimers and higher order n-mers, produced from multiple ferritin complexes being present in a single electrospray droplet, remained bound to each other after in-flight heating. Monte Carlo simulations of the electrospray process showed that as long as the electrospray droplets are sufficiently monodisperse, monodisperse standard size nanoparticles can also be produced from ferritin n-mers.     

Simultaneous Production of Two Monodisperse Aerosols Using a Spinning-Top Aerosol Generator

A relatively simple laboratory technique for the simultaneous production of two monodisperse aerosols of different size has been developed and tested. This technique utilizes a standard May spinning-top aerosol generator that has been modified and enclosed under a special dual-cone fractionator. The fractionator efficiently separates the primary and satellite droplets. Illustrative Nacl aerosol generation data, obtained in a series of experiments, show that satellite droplets can provide an important source of the monodisperse aerosol.     

Particle Bounce During Filtration of Particles on Wet and Dry Filters

This paper experimentally examines the bounce and immediate re-entrainment of liquid and solid monodisperse aerosols under a stable filtration regime (precake formation) by wet and dry fibrous filters. PSL and DEHS were the solid and liquid aerosols, respectively, used in four monodisperse sizes of 0.52, 0.83, 1.50, and 3.00 w m. Three different fibrous filters were used to filter the aerosol streams, and the efficiency of the filtration process for each aerosol type under dry and wet regimes was measured. It was found that the solid particles generally exhibited a lower fractional filtration efficiency than liquid particles, although this difference decreased in the smaller size fractions. The difference between solid and liquid efficiencies was found to be greatest in the 1.5 w m size range. As particle sizes of liquid/solid aerosols and filtration parameters were similar, this difference is most likely to be due to the effect of particle bounce and or immediate re-entrainment occurring inside the filter, with the greater efficiency of filtration of the liquid particles being due to their greater capacity to plastically/elastically deform in order to absorb the impact forces. However, for the wet filtration regime (each fibre of the filter was coated by a film of water), no significant difference in filtration efficiency was detectable between solid and liquid aerosols. Therefore, the conclusion can be drawn that the either the bounce effect of the particles is inhibited by the liquid film, or the filtration conditions in the wet filter are so different that the aerosol properties are less significant with respect to capture.     

Experimental Study of Particle Deposition on Semiconductor Wafers

A sensitive method for detecting particle deposition on semiconductor wafers has been developed. The method consisted of generating a monodisperse fluorescent aerosol, depositing the known-size monodisperse aerosol on a wafer in a laminar flow chamber, and analyzing the deposited particles using a fluorometric technique. For aerosol particles in the size range of 0.1–1.0 μm, the mobility classification-inertial impaction technique developed by Romay-Novas and Pui (1988) was used to generate the monodisperse test aerosols. Above a particle diameter of 1.0 μm, monodisperse uranine-tagged oleic acid aerosols were generated by a vibrating-orifice generator. The test wafer was a 3.8-cm diameter silicon wafer placed horizontally in a vertical laminar flow chamber which was maintained at a free stream velocity of 20 cm/s. A condensation nucleus counter and an optical particle counter were used to obtain the particle concentration profile in the test cross section and to monitor the stability of aerosol concentration during the experiment. The results show that the measured particle deposition velocities on the wafers agree well with the theory of Liu and Ahn (1987) in the particle size range between 0.15 and 8.0 μm. The deposition velocity shows a minimum around 0.25 μm in particle diameter and increases with both smaller and larger particle size owing to diffusional deposition and gravitational settling, respectively.     

Aerosol measurement by laser doppler spectroscopy—I. Theory and experimental results for aerosols homogeneous

The basic theory, experimental techniques and results are presented describing a technique for sizing aerosol particles in situ using laser Doppler spectroscopy. Unlike conventional light scattering procedures which use average intensity information, this technique utilizes the Doppler shifted frequency of the scattered light produced by the Brownian motion of the aerosol particles to determine particle diffusion coefficients and size. Experiments were carried out using monodisperse dibutylpthalate aerosols and monodisperse polystyrene latex spheres, in concentrations ranging from 10³ to 10⁶ particles per cubic centimeter. Measured particle sizes were within 10 per cent of the size predicted by conventional light scattering methods for the DBP particles and the reported sizes of the PSL particles. Based on these results it is concluded that laser Doppler spectroscopy can be utilized to accurately measure aerosol particle size in situ.     

MEASUREMENTS OF INERTIAL DEPOSITION OF AEROSOL PARTICLES IN REGULAR ARRAYS OF SPHERES

Inertial deposition of aerosol particles on single spheres and regular assemblies of spheres was investigated in the range of Stokes numbers from 0.03 to 5. Measurements were carried out on steel spheres suspended from wires in a 100 mm wide flow channel at air velocities from 5 to 28 m s^-1, using monodisperse DES (Di-II-ethyl-hexyl-sebacate) test aerosol in the size range from 1.5 to 15 μm. Experimentally determined deposition efficiencies on single spheres are in very good agreement with theoretically predicted results based on a potential flow field as well as a numerical flow simulation. Results in various types of arrays consisting of up to 12 equal-sized spheres show substantial variation of deposition efficiency from sphere to sphere which are strongly influenced by Stokes number and geometry.     

Generation of monodisperse aerosols by combining aerodynamic flow-focusing and mechanical perturbation

A novel instrument has been developed for generating highly monodisperse aerosol particles with a geometrical standard deviation of 1.05 or less. This aerosol generator applies a periodic mechanical excitation to a micro-liquid jet obtained by aerodynamic flow-focusing. The jet diameter and its fastest growth wavelength have been optimized as a function of the flow-focusing pressure drop and the liquid flow rate. The monodisperse aerosol generated by this instrument is also charge neutralized with bipolar ions produced by a non-radioactive, corona discharge device. Monodisperse droplet generation in the 15- to 72-μm diameter range from a single 100-micron nozzle has been demonstrated. Both liquid and solid monodisperse particles can be generated from 0.7- to 15-μm diameter by varying solution concentration, liquid flow rate, and excitation frequency. The calculated monodisperse particle diameter agrees well with independent measurements. The operation of this new monodisperse aerosol generator is stable and reliable without nozzle clogging, typical of other aerosol generators at the lower end of the operating particle size ranges.

Copyright © 2016 American Association for Aerosol Research     

A wind tunnel evaluation of the physical sampling efficiencies of three bioaerosol samplers

The physical sampling efficiency of three commonly used samplers for bioaerosols has been determined under controlled conditions in a wind tunnel. Non-biological, monodisperse test aerosols of aerodynamic diameters up to 23 μm were used in a range of wind speeds up to 5 m s⁻¹. The performance of each sampler type was different. For the Andersen Microbial Sampler and the Casella Slit Sampler, sampling efficiency dropped both with increasing wind speed and particle size, while for the Aerojet General Glass Cyclone, performance was generally independent of windspeed and particle size. This work is part of a larger study to determine both the physical and the biological sampling efficiencies of currently used samplers for bioaerosols. The results highlight the importance of understanding the performance of aerosol monitoring equipment, if results obtained in the field are to be interpreted correctly.     

Inkjet Aerosol Generator as Monodisperse Particle Number Standard

The AIST-inkjet aerosol generator (IAG) can generate highly monodisperse solid or liquid aerosol particles in the particle diameter range from 0.3 to 20 μm at precisely known particle generation rates. The device has been developed for evaluating the counting efficiencies of optical and condensation particle counters. Particle generation efficiency of the IAG is defined as the number of aerosol particles generated by one voltage pulse sent to an inkjet head. The 95% confidence interval of the efficiency were 0.998 ± 0.006 within the 0.4 to 10 μm particle diameter range. The efficiencies remained close to unity when the droplet generation rates were within 20–500 s^?1 and 100–900 s^?1 using ultrapure-water and isopropyl alcohol (IPA) as the solvent of the inkjet solution, respectively. The operating aerosol flowrate range of the IAG is currently 0.5 and 1.0 L/min. The coefficients of variations (C.V.) of the size distributions were 2 to 3% indicating the generated particles were highly monodisperse. The generated particle sizes were defined as the volume equivalent diameter, D_ve. The uncertainty analysis on the factors affecting D_ve indicated that 95% confidence interval of the D_ve is expected to be ±5%. The uncertainty of D_ve was entirely caused by the uncertainty of the average mass of a droplet. The reproducibility of particle sizes within 0.5 to 10 μm was evaluated using an aerodynamic particle sizer. The C.V. of the measured particle sizes were less than 6% and 4% when NaCl particles and ionic liquid droplets were generated, respectively.

Copyright 2014 American Association for Aerosol Research     

System design and test method for measuring respirator filter efficiency using mycobacterium aerosols

Recently, the protection of health care workers from tuberculosis-containing aerosols has been the subject of considerable debate. An experimental apparatus and test protocol were developed to measure the collection efficiency of surgical mask and respirator filter media using a microbial aerosol challenge. Mycobacterium chelonae (M. chelonae), used as a surrogate for Mycobacterium tuberculosis, was generated from liquid suspension using a Collison nebulizer. Upstream and downstream concentrations of viable aerosol particles were measured using Andersen cascade impactors, while total particle concentrations were measured with an aerodynamic particle sizer (APS). A monodisperse polystyrene latex (PSL) sphere aerosol (0.804 μm) was used in separate experiments to measure filter efficiency; concentrations were determined with the APS. The mycobacterial aerosol ranged in size from 0.65 to 2.2 μm when measured with the cascade impactor. A similar size range was found with the APS, yielding a count median diameter of about 0.8 μm. Samples of the mycobacterial aerosol were collected on glass slides, stained M. chelonae, as determined by environmental scanning electron microscope, were found to be rod shaped with an average length of 2 μm and average width of 0.3 μm. To evaluate the apparatus over a range of filter efficiencies (10–100%), different layers of fiberglass filter paper were tested for penetration using a 0.12 μm dioctyl phthalate (DOP) aerosol measured with a light scattering photometer, in addition to the mycobacterial and PSL aerosols. For the range of efficiencies tested it was shown that filter collection of DOP was linearly related to that of both mycobacterial and PSL sphere aerosols (r² = 0.99), demonstrating that an inert aerosol may be used to predict the collection of biological aerosols by such filter media.     

Atmospheric Size Distributions Measured by Differential Mobility Optical Particle Size Spectrometry

ABSTRACT

A differential mobility and optical particle size spectrometer (DMOPSS) was developed to measure ambient size distributions based on geometric particle diameter in the size range of 0.1 to 1.0 μm diameter. The DMOPSS consists of a high-flow differential mobility analyzer (HF-DMA) followed by an optical particle counter (OPC) and condensation nucleus counter (CNC) operating in parallel. The OPC and CNC sample monodisperse aerosol of known geometric diameter from the HF-DMA output or, alternatively, polydisperse aerosol with known dilution directly from the ambient air. The monodisperse samples are used to create time-dependent calibrations of the OPC, providing optical response versus geometric size for the ambient aerosol under study. The direct ambient measurements are then reduced, using this ambient-based calibration. A field test of the DMOPSS system was performed in the summer of 1992 at Meadview, Arizona, where more than 12,000 size spectra were collected; they consisted of roughly one-third direct ambient samples and two-thirds HF-DMA sized samples. Measured aerosol volumes and calculated particle scattering coefficients were strongly correlated with nephelometer measurements, with a mean scattering-to-volume ratio of 5 m²/cm³. With the ambient aerosol calibration, the measured aerosol volumes were 47% larger, and volume geometric mean diameters were 12% larger, than would have been obtained using a polystyrene latex calibration.     

Particle Charging and Transmission Efficiencies of Aerosol Charge Neutralizes

ABSTRACT

Diffusion losses and charging efficiency were measured for three types of charge neutralizers commonly used in aerosol research: two with ⁸⁵Kr and one with ²¹⁰Po as radiation sources. The diffusion losses were characterized at flows of 0.5 -6 1 min^?1 typically used in atmospheric aerosol physics measurements. All of the neutralizers tested exhibited high transmission efficiencies, with losses up to 25% at the smallest tested size of 3 nm, varying with size and flow in general agreement with diffusion loss theory. Charging efficiency was measured for a singly charged, monodisperse aerosol at the same flows and at concentrations of 10³-10⁴ particles cm^?3. Neither of the ⁸⁵Kr chargers brought the charge distribution close to equilibrium at 2 1 min^?1, except at concentrations ≤ 10³ cm^?3. The ²¹⁰Po charger produced the theoretically expected fraction of singly charged particles within the uncertainty of the experiment.     

Aerosol classification by electric mobility: apparatus, theory, and applications

An improved version of the Hewitt (differential) electric mobility analyzer was developed and its classifying characteristics were determined theoretically. The central mobility of the classified aerosol was found to be (q_c + q_m)/4πΛV, where q_c and q_m are the clean air and main outlet flows, respectively, Λ is a geometric factor, and Λ is the center rod voltage. The half-width of the mobility band was found to be (q_a + q_s)/4πΛV, where q_a and q_s are the aerosol and sampling outlet flows, respectively. These expressions were verified by the tests with a monodisperse aerosol of known size and low charge.

A major advantage of this device is that the classified aerosol fraction remains airborne, ready for further use or analysis. Thus, one application of the device is the production of monodisperse test aerosols of known size, charge, and concentration by classification of a polydisperse aerosol. Other current applications include accurate measurement of particle electric mobility moments and high-resolution particle size analysis for polydisperse aerosols in the 0.005–1.0 μm size range.     

Detection and Analysis of Aerosol Particles by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was evaluated as a means for quantitative analysis of the size, mass, and composition of individual micron-to submicron-sized aerosol particles over a range of well-characterized experimental conditions. Conditional data analysis was used to identify LIBS spectra that correspond to discrete aerosol particles under low aerosol particle loadings. The size distributions of monodisperse particle source flows were measured using the LIBS technique for calcium- and magnesium-based aerosols. The resulting size distributions were in good agreement with independently measured size distribution data. A lower size detection limit of 175 nm was determined for the calcium- and magnesium-based particles, which corresponds to a detectable mass of approximately 3 femtograms. In addition, the accuracy of the LIBS technique for the interference-free analysis of different particle types was verified using a binary aerosol system of calcium-based and chromium particles.     

Mechanisms of aerosol deposition in a nasal model

Total and regional aerosol deposition were investigated in a model of a normal human nasal airway. Contributions of fluid turbulence and particle inertia were evaluated using monodisperse aerosols. At fixed turbulent flow conditions, deposition percentage increased with particle size greater than 1 μm, suggesting that turbulent inertial deposition is a primary mechanism.

With same size aerosol, deposition increased with increasing fluid turbulence but its contribution was less with larger size aerosol. Turbulent diffusion was the dominant transport mechanism for particles less than 1 μm, where deposition decreased with particle size. Two major deposition sites were visualized with radio-aerosol in the anterior region of the nasal airway. One is close to the ostium internum where turbulent eddies are well developed, and the other is the anterior region of the middle turbinate where direction of airflow changes from upward to horizontal.     

Counting Efficiency of the TSI Model 3020 Condensation Nucleus Counter

The counting efficiency of the TSI model 3020 condensation nucleus counter (CNC) was determined as a function of aerosol flow rate and trigger level using aerosols of known size and an aerosol electrometer. When the aerosol flow rate dropped from 300 to 200 mL/min, counting efficiencies increased significantly in the single-particle counting mode for particles with diameter < 20 nm while those for larger particles remained constant. However, the photometric mode counting efficiency for particles with diameter > 20 nm increased and exceeded unity. When the aerosol flow rate was reduced to 100 mL/min, the counting efficiencies for both counting modes decreased regardless of particle size. Varying the trigger level of the CNC did not influence the photometric mode counting efficiency. However, the counting efficiency of the single-particle counting mode increased with decreasing trigger level, especially for particles < 20 nm in diameter. Characteristics for individual instruments need to be measured because counting efficiencies of two CNCs with the same trigger level and flow rate were not identical.     

Experimental Study of Aerosol Filtration by the Granular Bed Over a Wide Range of Reynolds Numbers

The collection performance of granular bed filters consisting of uniform spheres with diameters of 0.5–2.0 mm was experimentally studied by using monodisperse aerosol particles ranging from 0.02 to 2 μm in diameter at superficial velocity from 0.4 to 120 cm/s. Based on the experimental data, prediction equations of collection efficiency due to individual mechanical collection mechanisms were obtained, elucidating the influence of the Reynolds number on the particle collection. Furthermore, by assuming the additivity of the individual mechanical collection efficiencies, a prediction equation applicable to the wide range of filtration conditions is proposed.     

Charge distributions and coagulation of radioactive aerosols

The self-charging of radioactive aerosols will be reduced by background ions, such as those produced by radioactive gases. The sources of these background ions and their production rates are specified for a reactor containment atmosphere during a possible nuclear accident. Previous theory is extended to calculate the charging of a polydisperse radioactive aerosol. Gaussian approximations to charge distributions on an aerosol of a given size, and are shown to give a good representation of the exact numerical charge distributions of a Cs aerosol at normal temperatures, and also for highly radioactive aerosol containing ¹³¹I in a containment atmosphere.

Extensive calculations are performed for charge-induced modifications to Brownian coagulation rates between steady-state size distributions of these radioactive aerosols, and also between small-sized radioactive aerosol and larger (non-radioactive) aerosol. The results show considerable enhancements of the coagulation rates between large and small-sized aerosol, but also a strong suppression of coagulation between large particles. Rate modifications calculated using the Gaussian approximations are generally close to the exact values. Time-dependent calculations for a monodisperse -decaying aerosol reveal enhancements in coagulation rates even when the average charge on the aerosol is positive. Our results are relevant to behaviour in a dusty plasma.