Monodisperse Aerosol Generator Research Articles

Laboratory evaluation of the Alphasense OPC-N3, and the Plantower PMS5003 and PMS6003 sensors

Ambient levels of particulate matter (PM) are linked to numerous adverse health effects. However, fewer studies have evaluated the effects of coarse PM (larger than 2.5 μm in diameter), and ambient measurements of coarse PM are particularly sparse. Although low-cost PM sensors have been used to complement regulatory measurements of PM2.5, many of these sensors, such as the Plantower PMS5003, are ineffective in measuring coarse PM. The Alphasense OPCs have shown promise in detecting coarse PM and have been used in the field to measure PM10 concentrations. These field evaluations have identified inter-sensor variability. Although field evaluation is critical for understanding sensor performance under environmentally relevant conditions, it provides limited information about sensor response characteristics, which are essential for determining the factors that may affect sensor measurements and contribute to inter-sensor variability. This study aims to understand these factors by conducting a size-selectivity study using monodisperse particles, and evaluating the effect of instrument-specific properties, like flow rate and laser strength, on the sensor-reported sizes and number counts. This study also evaluates a common low-cost sensor, the Plantower PMS5003, and a newer version, the PMS6003, for size selectivity. Monodisperse dioctyl sebacate particles of various diameters (2, 3, 5, 6, 9, and 10 μm) were generated using a flow-focusing monodisperse aerosol generator, and the performance of nine different OPCs was evaluated. For all sizes tested, the nine OPC-N3s detected the particles, showed a peak near the target diameter, and exhibited some inter-sensor variability. The four PMS5003s and four PMS6003s detected all particle sizes but assigned all particles to the smallest size bin i.e., 0.35 μm–1 μm. With an aerodynamic particle sizer (APS) as a reference, the OPCs showed a positive bias for mean particle diameter and a coefficient of variance (CV) of less than 10%. For number concentration, the OPCs showed a negative bias, compared to the APS, and inter-sensor variability increased with the particle diameter. The laser wavelength of the OPC-N3s varied between 600 and 650 nm and appeared to have some effect on inter-sensor variability of the mean size. The flow rate reported by the OPC appeared to affect the inter-sensor variability in the number concentration.

Applicability of the VisiSize D30 shadowgraph system for cloud microphysical measurements

Abstract. A commercial shadowgraph system, the Oxford Lasers VisiSize D30, originally designed to characterize industrial and agricultural sprays, was tested with respect to its application for measuring cloud microphysical properties such as droplet size distribution and number concentration. A laboratory experiment with a dense stream of polydisperse cloud-like droplets indicated a strong dependence of the depth of field, and thus also the sample volume, on particle size. This relationship was determined and a suitable correction method was developed to improve estimations of droplet number concentration and size distribution. The spatial homogeneity of the detection probability inside the sample volume and the minimum droplet diameter providing uniform detection were examined. A second experiment with monodisperse droplets produced by a Flow Focusing Monodisperse Aerosol Generator (FMAG) verified the sizing accuracy and demonstrated reasonable agreement between the instruments. Effects of collisions and the evaporation of droplets produced by the FMAG were observed. Finally, when the instrument was applied to sample atmospheric clouds at a mountain-based observatory, it performed reliably during a 3-week-long field experiment. Based on the laboratory and field tests, recommendations concerning the use of the instrument for cloud droplet measurements were formulated.

Design of a mono-disperse aerosol generator for efficiency testing of HEPA filter

A set of mono-disperse aerosol generator was designed to meet the requirement of efficiency testing for high efficiency particle air filter. The aerosol generation tests and performance tests were conducted by using evaporation–condensation method, with NaCl solutions at different concentrations as the condensation nucleus and respectively using the DEHS, DOP, PAO–4 as reagents. The results show that three reagents can generate mono-disperse aerosol particles by strictly controlling various parameters which affects the aerosol performance, where the particle size range is 0.33–0.36 μm for DEHS, 0.35–0.37 μm for DOP and 0.34–0.36 μm for PAO–4 and the concentrations of the aerosols lager than 106 cm–3. The particle size characteristics and concentrations generated through such method basically conform to the requirements of efficiency testing for high efficiency particle air filter.

FLAME PROPAGATION IN LIQUID FUEL DROPLETS SPRAY

Taking into account the significant volumes of liquid fuels consumption in the world fuel balance, one of the most urgent tasks of our time is to reduce the anthropogenic impact on the biosphere by completely or partially replacing mineral fuels with their renewable plant origin analogues. In this paper we present the experimental studies results of the flame propagation process in a one-dimensional set of ethanol droplets with water addition up to 50% by volume. In contrast to studies of processes accompanying the combustion of a single liquid fuel droplet, the combustion of their aggregate, in the form of a jet, has been studied to a lesser extent. The proposed scheme of a jet generator with a vibrating needle makes it possible to obtain a chain of monodisperse fuel droplets with a diameter d=490±5 μm, which is sufficiently stable over time (within 10 min), with the possibility of varying the inter-drop distance. As control parameters for changing this distance, the vibration frequency of the membrane and the value of constant pressure on the reservoir with liquid were used. Using the developed experimental procedure, dependences of the relative distance between the droplets, on the value of constant pressure on the reservoir with liquid fuel, at different monodisperse aerosol generator needle oscillation frequencies were obtained.The whole process of the flame front propagation along the monodisperse aerosol chain was recorded with a frequency of 300 fps. The video capturing results analysis of the flame propagation process made it possible to determine the dependence of flame propagation velocity on the distance between the droplets. A qualitative picture process analysis showed the flame propagation velocity decrease along the inter-droplet distance increase. The critical distance between droplets that is an order of magnitude greater than the droplet size under experimental conditions, at which the flame propagation stopped, was determined experimentally. The obtained results are explained with a sufficient degree of reliability within the framework of the proposed relay flame propagation mechanism within a one-dimensional monodisperse aerosol system.

Characterization of the Vitrocell® 24/48 aerosol exposure system for its use in exposures to liquid aerosols

BackgroundThe Vitrocell® 24/48 is an advanced aerosol exposure system that has been widely used and characterized for exposure studies of cigarette smoke, but not for exposure to liquid aerosols with a low gas-vapor phase content such as the ones generated by electronic cigarettes. An experimental system characterization for this specific application was therefore performed. MethodsGlycerol model aerosols of different particle size distributions, produced by a condensation monodisperse aerosol generator, were used for exposing small volumes of phosphate-buffered saline in the Vitrocell® 24/48. Disodium fluorescein, added as a tracer in the aerosol, allowed the exact aerosol mass deposition to be quantified fluorometrically. ResultsThe aerosol mass delivery efficiency within the system showed variations in the range of ±25%. Aerosol dilution was not fully reflected in aerosol delivery, the achieved aerosol delivery should therefore be determined experimentally. Quartz crystal microbalances underestimated the deposition of liquid aerosols. Unequal delivery of particles of different sizes was detectable, although this effect is unlikely to be relevant under applied experimental conditions. ConclusionsThe Vitrocell® 24/48 aerosol exposure system can be used for exposures to liquid aerosols, such as those generated by electronic cigarettes. However, our results indicate that, compared with aerosol studies of cigarettes, a higher variability is to be expected.

Condensation-type quasi monodisperse aerosol generator with WOx nanoparticles as nuclei produced by glowing wire method

A new condensation-type quasi monodisperse aerosol generator with WOx nanoparticles as condensation nuclei is investigated in this research. The nuclei are produced by glowing wire method. Compared with the traditional condensation-type aerosol generator reported previously, the new condensation-type aerosol generator does not use a high-pressure air source and aerosol dryer, as well as extends the lower limit of the final aerosol size to 50nm. All technical parameters are discussed, and the values of electrical current through tungsten wire, nuclei and vapor concentrations, and reheater and condensation temperatures are obtained. The current values of 5.0A to 5.2A produce sustainable and stable nuclei. A substantially higher nuclei concentration can depress the aerosol homogeneous condensation. Vapor concentration can adjust the size distribution of the final aerosol and change the saturation temperature; vapor flow rate can have equal advantage. A critical reheater temperature is noted to completely evaporate the condensated vapor. Condensation temperature between 15°C and 21°C hardly influences the size distribution of the final aerosol. Finally, stability, sustainability, and reproducibility of the nuclei, as well as the final aerosol, are all successfully verified.

A new fluorescence-based method for characterizing in vitro aerosol exposure systems

Knowledge of how an in vitro aerosol exposure system delivers a test aerosols to the biological test system is among the most crucial prerequisites for the interpretation of exposure experiments and relies on detailed exposure system characterization. Although various methods for this purpose exist, many of them are time consuming, require extensive instrumentation, or offer only limited ability to assess the performance of the system under experimental settings. We present the development and evaluation of a new, highly robust and sensitive fluorometry-based method for assessing the particle size specific delivery of liquid aerosols.Glycerol aerosols of different mean particle sizes and narrow size distributions, carrying the fluorophore disodium fluorescein, were generated in a condensation monodisperse aerosol generator. Their detailed characterization confirmed their stability and the robustness and reproducibility of their generation. Test exposures under relevant experimental settings in the Vitrocell® 24/48 aerosol exposure system further confirmed their feasibility for simulating exposures and the high sensitivity of the method.Potential applications of the presented method range from the experimental confirmation of computationally simulated particle dynamics, over the characterization of in vitro aerosol exposure systems, to the detailed description of aerosol delivery in test systems of high complexity.

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

ABSTRACTA 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 ...

A method for in vitro regional aerosol deposition measurement in a model of the human tracheobronchial tree by the positron emission tomography.

Researchers have been studying aerosol transport in human lungs for some decades. The overall lung deposition can be predicted with sufficient precision nowadays. However, the prediction of local deposition remains an unsolved problem. Numerical modeling of aerosol transport can provide detailed data with such precision and spatial resolution which were unavailable in the past. Yet, the necessary validation of numerical results represents a difficult task, as the experimental data in a sufficient spatial resolution are hardly available. This article introduces a method based on positron emission tomography, which allows acquisition of detailed experimental data on local aerosol deposition in a realistic model of human lungs. The method utilizes the Condensation Monodisperse Aerosol Generator modified for a safe production of radioactive aerosol particles and a special measuring rig. The scanning of the model is performed on a positron emission tomography-computed tomography scanner. The evaluation of aerosol deposition is based on a volume radioactivity analysis in a specialized, yet publicly available software. The reliability of the method was tested and its first results are discussed in the article. The measurements performed using the presented method can serve for validation of numerical simulations, since the presented lung model digital geometry is available.

Performance Evaluation of Four Commercial Optical Particle Counters

The performances of four optical particles counters, Aerosol Spectrometer (Grimm 1.108), Enviro Check (Grimm 1.107), DustMonit and ParticleScan, were evaluated in laboratory tests employing monodisperse aerosol particles. The study focused on how commercial instruments perform during routine measurements respect to OPC scientific understanding, because it is important for users of such instruments to be aware of their limitations. Measurements were performed using aerosol generated by a Monodisperse Aerosol Generator (MAGE), which produced carnauba wax particles of diameter (1.00 ± 0.08) μm and (1.40 ± 0.15) μm, and monodisperse Polystyrene Latex (PSL) aerosol with nominal diameter of 1.0mm. The results show comparable total particle number concentrations for all the counters, when the count of the first size channel (0.3 - 0.4 μm) for the 1.108 Grimm counter was left out. In the said channel the Grimm counter 1.108 always showed much higher particle counts than those inferred from the tested aerosols. The overcount was proved by the fact that the aerosol sampled in each test on a Nuclepore filter showed no particles in the 0.3 - 0.4 μm range when examined under Scanning Electronic Microscope (SEM). The presence of an artefact produced by the counter was assumed as a likely explanation. For all the counters, the Count Median Diameters (CMDs) of aerosol size distributions, were far below the expected value for the aerosol used. The nearest CMD values to the expected ones were shown by the Grimm 1.107 counter.

Application of Positron Emission Tomography to Aerosol Transport Research in a Model of Human Lungs

Positron Emission Tomography (PET) is a convenient method for measurement of aerosol deposition in complex models of lungs. It allows not only the evaluation of regional deposition characteristics but also precisely detects deposition hot spots. The method is based on a detection of a pair of annihilation photons moving in opposite directions as a result of positron – electron interaction after the positron emission decay of a suitable radioisotope. Liquid di(2-ethylhexyl) sebacate (DEHS) particles tagged with fluorine-18 as a radioactive tracer were generated by condensation monodisperse aerosol generator. Aerosol deposition was measured for three different inhalation flowrates and for two sizes of particles. Combination of PET with Computed Tomography (CT) in one device allowed precise localisation of particular segments of the model. The results proved correlation of deposition efficiency with Stokes number, which means that the main deposition mechanism is inertial impaction. As a next task the methodology for tagging the solid aerosol particles with radioactive tracer will be developed and deposition of porous and fiber aerosols will be measured.

Penetration of charged particles through metallic tubes

Several theoretical studies have shown that charged particles increased the particle deposition efficiency in cylindrical tubes by image force. Some experimental investigations have also found that the deposition loss increased with increasing aerosol charge. However, the amount of charges on the aerosols or the electrical mobility was relatively low in these previous experimental studies. In order to extend to higher aerosol charge, a TSI vibrating orifice monodisperse aerosol generator was modified to generate 1-μm DEHS aerosols with charge up to 24,000 elementary units. Metallic tubes were employed to exclude the effect of Coulombic force. Tube diameter, tube length, and average velocity in tubes were among the major operating parameters. Aerosol charge was monitored using a TSI electrometer, while a TSI aerodynamic particle sizer was utilized to measure both aerosol concentrations and size distributions upstream and downstream of the tubes. Aerosol deposition loss in the sampling train of the TSI electrometer was measured to back-calculate the average aerosol charge. A closed-form theoretical model, showing the deposition efficiency as a function of particle charge, was validated by the experimental data produced.The aerosol deposition efficiency increased with increasing aerosol charge and tube length, due to stronger image force and longer retention time, respectively. The deposition efficiency decreased with increasing average velocity because of shorter retention time. Under the same average velocity, the deposition loss decreased with increasing tube diameter because the fraction of aerosols near the inner wall was higher for small-diameter tube than for large-diameter tube. The model developed from parabolic flow showed good agreement with most of the experimental data, except for data of highly charged particles. The discrepancy was probably due to the space charge effect.

The Generation And Properties Of Solid Monodisperse Aerosols Of Stearic Acid And Carnauba Wax

A monodisperse aerosol generator (MAGE) was used to generate calibration or monodisperse aerosols containing stearic acid and carnauba wax. Some of the factors affecting the size of aerosol particles generated with the MAGE were determined. The factors include: temperature of operation of the MAGE, type and purity of coating material used. The reproducibility of aerosol particles and stability of the aerosol generated were evaluated. The performance characteristics of the MAGE over an extended period of time of operation were also established. The calibration aerosols generated with the MAGE can be used in situ for studies of aerosol deposition measurement equipment. Keywords: Generation, Calibration aerosols, Monodisperse aerosol generator, Performance characteristics

Effect of particle spatial distribution on particle deposition in ventilation rooms

We used simulations and experimental tests to investigate indoor particle deposition during four commonly used ventilation modes, including ceiling supply, side-up supply, side-down supply and bottom supply. We used a condensation monodisperse aerosol generator to generate fine diethylhexyl sebacate (DEHS) particles of different sizes along with two optical particle counters that measured particle concentration at the exhaust opening and inside a three-dimensional ventilated test room. We then simulated particle deposition using the same ventilation modes with computational fluid dynamics (CFD) method. Our simulated results indicate that mean deposition velocity/rate for particles 0.5–10 μm (aerodynamic diameter) is not affected by different ventilation modes. However, both our experimental and simulated results indicate that the deposition loss factor, a parameter defined based on mass balance principle to reflect the influence of particle distribution on deposited particle quantity, differ significantly by ventilation mode. This indicates that ventilation plays an important role in determining particle deposition due to the apparent differences in the spatial distribution of particles. The particle loss factor during ventilation modes characterized by upward air flow in the room is smaller than that of mixing ventilation; however this trend was strongly influenced by the relative location of the inlets, outlets and aerosol source.

Determination of Uniformity of Filter Deposits

Certain measurement techniques (such as the asbestos method using phase contrast microscopy) require uniform deposits of the sample on a filter. The asbestos fiber analytical methods require such uniform deposition because the analysis only observes small, randomly chosen locations on the filter. In this study, a vibrating orifice monodisperse aerosol generator was used to generate methylene blue particles. The aerosols were dried by filtered compressed air and then neutralized by inducing a charge on the droplet stream that emerged from the vibrating orifice. An Aerodynamic Particle Sizer was used to measure the number concentration and size distribution of the generated aerosol particles. Meanwhile, the filter deposits were examined via image processing, combined with statistical methods for defining uniformity. In order to better define uniformity and make the indicator more universal, the uniformity was defined as the exponential of the negative CV (coefficient of variation) value which was a transfor...

Application of induction charging to mono-disperse aerosol generator and electric field measurement

Charged droplets passing in an AC electric field vibrate in response to its charge. If only we know the charge of a droplet in advance, we can estimate the field strength from the amplitude of the droplet oscillation at the measuring point because the size is readily calculable from the phase lag of the droplet oscillation. The droplets, which were generated from the vibrating orifice aerosol generator, can be charged by a charging electrode which is set over the orifice. The charge of droplets depends on several parameters like the condition of a liquid jet. The relationship between some of the parameters and charge of droplets has been examined. In this experiment, we applied the method of simultaneous measurements of size and charge of droplets by using laser Doppler system. As an example of electric field measurements, we measured the electric field distribution near the surface of a high-voltage-insulated cable positioned at the center of a metal disk. A reasonable agreement between the measured values and the calculated values was obtained.

Monodisperse Nanoparticle Synthesis by an Atmospheric Pressure Plasma Process: An Example of a Visible Light Photocatalyst

An atmospheric pressure plasma-enhanced nanoparticle synthesis (APPENS) process was proposed to produce a titania-based visible light photocatalyst. The titanium tetraisopropoxide (TTIP) precursor was vaporized with a N2 carrier gas and entered a nonthermal AC plasma system. The N2 gas was dissociated into N atoms by the plasma energy, and then they were doped into the precursor vapors. The produced TiO2-xNx nanoparticles were highly uniform and adjustable in size. The titania-based particle sizes ranged from 25 to 40 nm, and they depended on the precursor ratio of TTIP/H2O. In addition to producing the photocatalytic particles, the APPENS process has a potential application as a continuous-flow nanosize monodisperse aerosol generator.

Obtaining the monodisperse droplets during the gas penetration through a thin liquid film

The principle of monodisperse aerosol generation based on spraying liquid during the gas bubble destruction near the liquid surface is considered. The synchronization of the bubble growth and collapse processes with capillary oscillations of the thin liquid film is proposed to provide the stability and reproducibility of the droplet formation conditions. On this basis, the possibility of creating the streams of nearly identical droplets without external periodic stimulation is shown. In essence, they can be realized in very wide conditions and only demand a source of low pressure for their implementation. Simple constructions of the monodisperse droplet generator and its operation modes are described.

Monodisperse and Polydisperse Aerosol Deposition in a Packed Bed

Although polydisperse aerosols in ambient and occupational settings have been associated with adverse health effects, researchers have mostly used monodisperse aerosols to investigate particle deposition in the human lung. The objective of this work was to determine whether the deposition of a series of monodisperse aerosols is reasonable to simulate the deposition of a polydisperse aerosol. A packed bed was used as an approximate surrogate to the human lung. Polydisperse and monodisperse sebacate aerosols were generated by nebulizers and a Monodisperse Aerosol Generator (MAGE), respectively. A Harvard respirator pump and aerosol through the packed bed. Complete size distributions of inhaled and exhaled aerosol were measured by an Aerodynamic Particle Sizer (APS) and a Scanning Mobility Particle Sizer (SMPS). The deposition for discrete sections of polydisperse aerosols was compared with the deposition of monodisperse aerosols. Also, the total deposition of a polydisperse aerosol was c...

Experimental Study on the Loading Characteristics of Needlefelt Filters with Micrometer-Sized Monodisperse Aerosols

In this work, three types of needlefelt filters, made of Polyester (PE), Ryton Sulfar (RS), and Polyaramid (PA), were tested to in- vestigate the aerosol loading characteristics of fabric filters when challenged with micrometer-sized monodisperse potassium sodium tartrate (PST) particles. A fibrous filter with packing density of 9%, thickness of 0.38 mm, and fiber diameter of 5.1 θ m was included for comparison. A vibrating orifice monodisperse aerosol generator was used to produce three different sizes (5, 10, and 20 θ m) of PST particles for aerosol loading experiment. An ultrasonic atomizing nozzle and a TSI constant output nebulizer were used to generate polydisperse PST particles for the aerosol penetration test. The aerosol penetration of submicrometer-sized particles through the filters was measured by using a Scanning Mobility Particle Sizer. An Aerodynamic Particle Sizer was used to measure the penetration fraction of aerosol particles larger than 0.8 θ m. The pressure drop across the filter was monitored by using pressure transducers, which were calibrated against an inclined manometer. Airflows of 5, 10 , 20, and 30 cm/s were used to study the flow dependency. The aerosol penetration results showed that the particles larger than 3 θ m did not penetrate the clean fabric filters tested in the present study. The loading curves (plots of pressure drop against sampling time) displayed three regions: an initial region of fast increase, a transition region, and a final linear region after the dust formation point. After the formation point of the dust cake, both fabric and fibrous filters shared the same slope (of the loading curves). The slope of different regions of the loading curves was determined by many factors, such as size of challenge aerosol, face found to be critical to the performance of the fabric filters. In order lower porosity, which caused an extra rise in pressure drop across velocity, surface treatment, and the compressibility of the dust cake forming on the filter. The method of final surface treatment was to avoid the unnecessary rise in air resistance, the melting clumps formed during final surface treatment should be as thin and narrow as possible, just enough to support the filter bag cleaning. From the standpoint of filter quality and energy consumption, the low filtration velocity has to be adopted whenever possible, because high filtration velocity not only led to lower filter quality (in particular for submicrometer-sized particles) but also created dust cake of lower porosity, which caused an extra rise in pressure drop across thet dust cake.