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  • Impact of water droplet and humidity interaction with soluble particles on the operational performance of surface filters in gas cleaning applications
    J. Aerosol Sci. (IF 2.24) Pub Date : 2020-01-22
    Almuth D. Schwarz; Leonie König; Jörg Meyer; Achim Dittler

    The behavior of salt particles on a surface filter exposed to a high humidity gas flow and water droplets was studied to gain a better understanding of the influence of water content in its different states on the operational performance of such filters. Two sets of experiments were carried out: in both, polydisperse sodium chloride particles were filtered from a dry air stream onto hydrophobic filter media, which were subsequently exposed to either relative humidity above the deliquescence relative humidity or to water droplets. Results show that the rearrangement of salt particles on the filter face side takes place in both sets of experiments. However, rearrangements resulting from the influence of high humidity can be clearly distinguished from the ones resulting from contact with water droplets. Recordings of the pressure drop across the test filters, as well as scanning electron microscope images of the sodium chloride particles on the face side of the medium, show this difference clearly. No penetration of salt particles through the filter medium occurred under the conditions presented in this study.

    更新日期:2020-01-22
  • Effect of mesoscale inhomogeneity and fibers size distribution on the initial stage of deep-bed filtration process
    J. Aerosol Sci. (IF 2.24) Pub Date : 2020-01-21
    Rafał Przekop; Anna Jackiewicz-Zagórska

    Aerosol filtration in fibrous filters is one of the principal methods of accurate removal of particulate matter from gas stream. The classical theory of depth filtration in fibrous structures is based on the assumption of existence of single fiber efficiency, which may be used for calculation of overall efficiency of the filter. There are several reasons for inappropriate estimation of the single fiber efficiency including assumption of negligible effect of presence of neighboring fibers and perpendicular orientation of the homogenous fibers in filter structure. The aim of this work is to investigate influence of mesoscale inhomogeneity on fibrous filters performance using Digital Fluid Dynamics in models of filters differed by internal structure and to compare obtained results with experimental data. The influence of both, irregularity of structure and fiber size distribution on macroscopic filter performance (initial fractional efficiency, initial pressure drop and their time evolutions) is presented. The neglection of fiber size distribution in theoretical models of filtration efficiency leads to the underestimation of both, filtration efficiency and pressure drop.

    更新日期:2020-01-21
  • Morphological Characterization of Particles Emitted from Monopolar Electrosurgical Pencils
    J. Aerosol Sci. (IF 2.24) Pub Date : 2020-01-09
    Yuechen Qiao; Austin J. Andrews; Chase E. Christen; Bernard A. Olson; Samir Khariwala; Brian MacLachan; Christopher J. Hogan

    Monopolar electrosurgical pencils are used extensively in surgical operations. With such pencils, electric current passes to the tissue, and as such, electrosurgical pencil operation generates a significant amount of thermal energy, which in turn leads to the generation of electrosurgical smoke (ES). The health risks of ES are dependent on the size distributions as well as the morphologies of the produced particles. To better characterize such particles, in this study we utilized (1) differential mobility analysis with acondensation particle counter (DMA-CPC), (2) an aerodynamic particle spectrometer (APS), (3) DMA-transmission electron microscopy analysis (DMA-TEM), and (4) DMA-aerosol particle mass analysis (DMA-APM) to examine the size distribution and morphologies of particles produced during simulated operation of an electrosurgical pencil (Neptune E-SEP, Stryker Corporation) on bovine, porcine, and ovine tissue. We find that under a variety of operating conditions, ES particles are broadly distributed, with a mode mobility diameter in the 150-200 nm size range, and concentrations well above background levels in the 50 nm – 5 μm size range. We also find that the “cut” mode of monopolar electrosurgical pencil operation generates higher particle concentrations than the “coagulate” mode, and that increasing the maximum applied power from 20 W to 50 W also increases ES particle concentrations. TEM images of mobility selected particles reveal both spherical particles and fractal-like agglomerates in ES; these different particle types are produced under the same operation conditions leading to an externally-mixed, morphologically-complex, aerosol. Quantitative analysis of the agglomerate images revealed that agglomerates have an average fractal dimension near 1.93 and that they are structurally similar to agglomerates expected from a diffusion limited cluster aggregation growth mechanism. Despite the presence of both spheres and agglomerates, DMA-APM analysis reveals that all particles have effective densities in the 1000-2000 kg m-3 range, suggesting that they likely contain inorganic components. Finally, we determined that the collection efficiency of the ES capture suction unit attached to the electrosurgical pencil was > 95% for particles in the 50-400 nm mobility diameter range.

    更新日期:2020-01-10
  • 更新日期:2020-01-02
  • Aerosol deposition rates by mass diffusion in laminar boundary layers with an implemented blowing system. Approximate methods for flat plates
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-12-23
    Joaquin Aguirre; Alvaro Perea

    Solid or liquid particles within a carrier gas may be deposited on solid surfaces exposed to the gas stream and, in some practical applications, these aerosol deposits have deleterious effects. In order to mitigate these effects, particle repulsive fields may be applied near the surface to reduce the deposition rate. A current blowing through the exposed surface may play this repulsion role with such a forced stream pushing the aerosol particles away from the surface. The present paper develops a model to analyse and estimate the effect of blowing in reducing particle deposition for laminar flows with high Reynolds numbers over flat surfaces. A classical self-similarity analysis is used to solve the boundary layer equations for mass and momentum conservation. The solution of the particle transport problem provides the self-similarity mass fraction profile and the mass deposition rate in terms of two parameters: the Schmidt number Sc and the dimensionless blowing rate. Moreover, two approximate methods are implemented in two asymptotic limits: for large values of Sc and when the blowing parameter is sufficiently small.

    更新日期:2019-12-23
  • Electrostatic Charging and Precipitation of Nanoparticles in Technical Nitrogen: Highly Efficient Diffusion Charging by Hot Free Electrons
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-12-03
    Patrick Bürger, Ulrich Riebel

    Electrostatic charging and deposition of a liquid nano-aerosol was studied in dry air and in technical (3.6 % O2) nitrogen. The experiments have shown that electronic charging of aerosols can be important in technical scale electrostatic precipitators (ESPs). Already at operation voltages just slightly above the corona onset voltage, the contribution of the free electrons to the overall current is estimated to be around 50 %. Due to the high temperature of free electrons, diffusion charging by free electrons allows to reach exceptionally high particle charge and extremely high precipitation efficiency. A strongly simplified theoretical model was developed, which gives a good prediction of particle charge based on averaged values of particle diameter, current density, electric field strength, electron temperature and residence time. The ion mobilities were determined by fitting the current-voltage characteristics with a modified Townsend (Monrolin et al. 2018) equation and are significantly higher than the values typically used to describe diffusion charging in air. This may be ascribed to the very dry gas phase and the short average lifespan of the ions under ESP conditions, which is in the order of 1 ms. From the practical point of view, electronic charging might be relevant in a number of technical applications, including high temperature ESPs, ESP applications in dry and oxygen-free gases and pulsed corona systems.

    更新日期:2019-12-04
  • Comparison of Particle Size Distributions and Volatile Organic Compounds Exhaled by e-Cigarette and Cigarette Users
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-11-21
    E. Papaefstathiou, S. Bezantakos, M. Stylianou, G. Biskos, A. Agapiou
    更新日期:2019-11-22
  • High Resolution Varying Field Drift Tube Ion Mobility Spectrometer with Diffusion Autocorrection
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-11-19
    Xi Chen, Viraj D. Gandhi, Joshua Coots, Yinghui Fan, Liang Xu, Nobuhiko Fukushima, Carlos Larriba-Andaluz

    Drift tubes (DT) are prominent tools to classify small ions in the gas phase. This is in contrast with its limited use in the aerosol field at atmospheric pressures where the differential mobility analyzer (DMA) has been the tool of choice. While the DMA has been successful, it does not normally achieve the resolution of a common DT. On the other hand, the size range of the DT is limited as well as its sensitivity. Here we propose a variation of the DT where a varying linearly decreasing field is used instead of the constant field commonly used in DT. The Varying Field Drift Tube (VFDT) has the advantage that it allows for diffusion constriction in the axial direction and thus a larger package of ions can be allowed into the system increasing its sensitivity without hampering its resolution. The VFDT also generally outperforms the DT in resolution and this is demonstrated theoretically and empirically reaching resolutions of over 90 in our data although higher resolutions are expected. The diffusion constriction capabilities are also proven theoretically and experimentally by using a mixture of tetraalkylammonium salts while injecting broad packets of ions into the system. The transformation from the raw variable arrival time distribution to Collision Cross Section or mobility diameter is linear making the transformation as simple as with a DMA.

    更新日期:2019-11-20
  • 更新日期:2019-11-11
  • 更新日期:2019-11-07
  • Comparison of the predictions of Langevin Dynamics-based diffusion charging collision kernel models with canonical experiments
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-11-06
    Li Li, Harjindar Singh Chahl, Ranganathan Gopalakrishnan

    Based on the prior work of Chahl and Gopalakrishnan (2019) to infer particle-ion collision time distributions using a Langevin Dynamics (LD) approach, we develop a model for the non-dimensional diffusion charging collision kernel βi or H that is applicable for 0≤ΨE≤60,0≤ΨIΨE≤1,KnD≤2000 (defined in the main text). The developed model for βi for attractive Coulomb and image potential interactions, along with the model for βi for repulsive Coulomb and image potential interactions from Gopalakrishnan et al. (2013b), is tested against published diffusion charging experimental data. Current state of the art charging models, Fuchs (1963) and Wiedensohler (1988) regression for bipolar charging, are also evaluated and discussed. Comparisons reveal that the LD-based model accurately describes unipolar fractions for 10–100nm particles measured in air (Adachi et al., 1985), nitrogen and argon but not in helium (Adachi et al., 1987). Fuchs model and the LD-based model yield similar predictions in the experimental conditions considered, except in helium. In the case of bipolar charging, the LD-based model captures the experimental trends quantitatively (within ±20%) across the entire size range of 4–40nm producing superior agreement than Wiedensohler’s regression. The latter systematically underpredicts charge fraction below ∼20nm in air (by up to 40%) for the data presented in Adachi et al. (1985). Comparison with the data of Gopalakrishnan et al. (2015), obtained in UHP air along with measurements of the entire ion mass-mobility distribution, shows excellent agreement with the predictions of the LD-based model. This demonstrates the capability to accommodate arbitrary ion populations in any background gas, when such data is available. Wiedensohler’s regression, derived for bipolar charging in air using average ion mass-mobility, also describes the data reasonably well in the conditions examined. However, both models failed to capture the fraction of singly and doubly charged particles in carbon dioxide warranting further investigation.

    更新日期:2019-11-06
  • Evaluation of Spray Impact on a Sphere with a Two-Fluid Nozzle
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-11-06
    Ramona Strob, Tejas Babaria, Matthias Rodeck, Gerhard Schaldach, Peter Walzel, Markus Thommes

    The generation of a secondary aerosol after impact, consisting of smaller droplets at a given velocity and mass flow, is relevant for various applications. Thus far, the investigations and modelling approaches on spray impact are based on extrapolation of the single-droplet impingement or empirical correlations. The validity of the models presented is limited to the given experimental setup and conditions such as initial droplet size, velocity and the impact surface characteristics. The aim of this work was to empirically evaluate the spray impact of a two-fluid nozzle on a sphere. A small-scale nozzle was used, which produced a primary aerosol with a mass median diameter of about 12μm (liquid-to-gas mass flow ratio=1, gas pressure: ΔpG=5 bar). After impact on a sphere, a multimodal distribution was observed and a higher mass flowrate of droplets in the small micrometer range (2 and 3μm) was produced for a liquid mass flow rate in the range of 1.2-6 kg/h and an atomizing gas mass flow rate of 1-4 kg/h. For easier observation, a geometrically similar, larger nozzle was used, which produced an aerosol with a mass median diameter of about 80μm (liquid-to-gas mass flow ratio=4, gas pressure: ΔpG=1 bar). The measured droplet size after impact is smaller for a lower liquid-to-gas mass flow ratio and increased atomizing gas inlet pressure. Droplet formation mechanisms such as splashing, crown formation and spreading on the sphere surface were observed. A characteristic film with large variations in thickness was generated.

    更新日期:2019-11-06
  • Transient numerical simulation of airflow and fibrous particles in a human upper airway model
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-11-06
    Morteza Kiasadegh, Homayoun Emdad, Goodarz Ahmadi, Omid Abouali

    In this study, the unsteady airflow field in a realistic model of human upper airways during the breathing cycle and the fibrous particle transport and deposition were investigated using the CFD method. An anatomically realistic model of airway passage including vestibule to the end of the trachea was constructed from the CT images of a 24-year-old healthy woman. Several user-defined functions (UDFs) were developed and incorporated into the discrete phase model (DPM) of ANSYS Fluent code and were used for the evaluation of ellipsoidal particle motion in transient airflows. The developed UDF was used to solve the coupled translational and rotational equations of motion of ellipsoidal fibers and to analyze their dispersion and deposition in the upper airways. The total and regional depositions for a range of fiber sizes were evaluated. The transient particle deposition fraction was compared with those obtained for the equivalent steady flow condition. In addition, the fraction of ellipsoidal fibers that penetrate the lower respiratory tract under cyclic breathing was calculated and compared with the steady flow simulation. The presented results showed that the steady simulation with an appropriate equivalent airflow rate can predict the total fibrous particle deposition during cyclic breathing with reasonable accuracy. The steady simulations, however, cannot properly predict the regional particle deposition under transient flows. In particular, the comparison between steady and transient penetration fraction reveals that the steady breathing model fails to accurately predict the penetration fraction of ellipsoidal fibers into the lower respiratory tract.

    更新日期:2019-11-06
  • On the Coagulation Efficiency of Carbonaceous Nanoparticles
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-11-05
    Dingyu Hou, Diyuan Zong, Casper S. Lindberg, Markus Kraft, Xiaoqing You
    更新日期:2019-11-05
  • Bipolar charging and neutralization of particles below 10 nm, the conditions to reach the stationary charge distribution, and the effect of a non-stationary charge distribution on particle sizing
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-11-02
    I. Ibarra, J. Rodríguez-Maroto, M. Alonso

    Bipolar charging and neutralization of aerosol particles with diameter below 10 nm in a circular tube with uniform ion-pair generation have been studied theoretically to determine the conditions required to reach the stationary charge distribution. In order to reach the stationary distribution the initial ion-to-aerosol number concentration ratio, Nin/nin, and the Ninτ product (τ is the mean aerosol residence time in the charger) must both be sufficiently large. These parameters can be combined in a single dimensionless parameter, βNin2τ/nin, where β is the attachment rate coefficient between a charged particle and an ion of opposite polarity. Attainment of the stationary distribution requires that this dimensionless number be larger than about 800 for neutralization of charged particles, and larger than about 500 for charging of uncharged particles. Experiments have shown that the stationary charge distribution cannot be reached neither using low cost, low activity 241Am sources nor a commercially available and widely used 2 mCi 85Kr neutralizer. When particle sizing by mobility analysis is carried out employing a charger in which the stationary charge distribution is not reached, inversion of the mobility distribution assuming that the charge distribution on the particles is the stationary one yields correct values of the mean particle diameter and the standard deviation, but fails to predict the aerosol number concentration.

    更新日期:2019-11-04
  • Electrospraying an enabling technology for pharmaceutical and biomedical applications: A review.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-01-22
    Sunil Kumar Boda,Xiaoran Li,Jingwei Xie

    Electrospraying (ES) is a robust and versatile technique for the fabrication of micro- and nanoparticulate materials of various compositions, morphologies, shapes, textures and sizes. The physics of ES provides a great degree of flexibility towards the materials design of choice with desired physicochemical and biological properties. Not surprising, this technology has become an important tool for the production of micro- and nanostructured materials, especially in the pharmaceutical and biomedical arena. In this review, a basic introduction to the fundamentals of ES along with a brief description of the experimental parameters that can be manipulated to obtain micro- and nanostructured materials of desired composition, size, and configuration are outlined. A greater focus of this review is to bring to light the broad range of electrosprayed materials and their applications in drug delivery, biomedical imaging, implant coating, tissue engineering, and sensing. Taken together, this review will provide an appreciation of this unique technology, which can be used to fabricate micro- and nanostructured materials with tremendous applications in the pharmaceutical and biomedical fields.

    更新日期:2019-11-01
  • Bridging the gap between exposure assessment and inhalation toxicology: Some insights from the carbon nanotube experience.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2016-08-23
    Aaron Erdely,Matthew M Dahm,Mary K Schubauer-Berigan,Bean T Chen,James M Antonini,Mark D Hoover

    The early incorporation of exposure assessment can be invaluable to help design, prioritize, and interpret toxicological studies or outcomes. The sum total of the exposure assessment findings combined with preliminary toxicology results allows for exposure-informed toxicological study design and the findings can then be integrated, together with available epidemiologic data, to provide health effect relevance. With regard to engineered nanomaterial inhalation toxicology in particular, a single type of material (e.g. carbon nanotube, graphene) can have a vast array of physicochemical characteristics resulting in the potential for varying toxicities. To compound the matter, the methodologies necessary to establish a material adequate for in vivo exposure testing raises questions on the applicability of the outcomes. From insights gained from evaluating carbon nanotubes, we recommend the following integrated approach involving exposure-informed hazard assessment and hazard-informed exposure assessment especially for materials as diverse as engineered nanomaterials: 1) market-informed identification of potential hazards and potentially exposed populations, 2) initial toxicity screening to drive prioritized assessments of exposure, 3) development of exposure assessment-informed chronic and sub-chronic in vivo studies, and 4) conduct of exposure- and hazard-informed epidemiological studies.

    更新日期:2019-11-01
  • Measurement of Transport Properties of Aerosolized Nanomaterials.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2015-12-22
    Bon Ki Ku,Pramod Kulkarni

    Airborne engineered nanomaterials such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), functionalized MWCNT, graphene, fullerene, silver and gold nanorods were characterized using a tandem system of a differential mobility analyzer and an aerosol particle mass analyzer to obtain their airborne transport properties and understand their relationship to morphological characteristics. These nanomaterials were aerosolized using different generation methods such as electrospray, pneumatic atomization, and dry aerosolization techniques, and their airborne transport properties such as mobility and aerodynamic diameters, mass scaling exponent, dynamic shape factor, and effective density were obtained. Laboratory experiments were conducted to directly measure mobility diameter and mass of the airborne nanomaterials using tandem mobility-mass measurements. Mass scaling exponents, aerodynamic diameters, dynamic shape factors and effective densities of mobility-classified particles were obtained from particle mass and the mobility diameter. Microscopy analysis using Transmission Electron Microscopy (TEM) was performed to obtain morphological descriptors such as envelop diameter, open area, aspect ratio, and projected area diameter. The morphological information from the TEM was compared with measured aerodynamic and mobility diameters of the particles. The results showed that aerodynamic diameter is smaller than mobility diameter below 500 nm by a factor of 2 to 4 for all nanomaterials except silver and gold nanorods. Morphologies of MWCNTs generated by liquid-based method, such as pneumatic atomization, are more compact than those of dry dispersed MWCNTs, indicating that the morphology depends on particle generation method. TEM analysis showed that projected area diameter of MWCNTs appears to be in reasonable agreement with mobility diameter in the size range from 100 - 400 nm. Principal component analysis of the obtained airborne particle properties also showed that the mobility diameter-based effective density and aerodynamic diameter are eigenvectors and can be used to represent key transport properties of interest.

    更新日期:2019-11-01
  • Development of a new test system to determine penetration of multi-walled carbon nanotubes through filtering facepiece respirators.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2013-07-01
    Evanly Vo,Ziqing Zhuang

    Carbon nanotubes (CNTs) are currently used in numerous industrial and biomedical applications. Recent studies suggest that workers may be at risk of adverse health effects if they are exposed to CNTs. A National Institute for Occupational Safety and Health (NIOSH) survey of the carbonaceous nanomaterial industry found that 77% of the companies used respiratory protection. Elastomeric half-mask respirators and filtering facepiece respirators (FFRs) are commonly used. Although numerous respirator filtration studies have been done with surrogate engineered nanoparticles, such as sodium chloride, penetration data from engineered nanoparticles such as CNTs are lacking. The aims of this study were to develop a new CNT aerosol respirator testing system and to determine multi-walled CNT (MWCNT) penetration through FFRs. A custom-designed CNT aerosol respirator testing system (CNT-ARTS) was developed which was capable of producing a sufficient amount of airborne MWCNTs for testing of high efficiency FFRs. The size distribution of airborne MWCNTs was 20-10,000 nm, with 99% of the particles between 25 and 2840 nm. The count median diameter (CMD) was 209 nm with a geometric standard deviation (GSD) of 1.98. This particle size range is similar to those found in some work environments (particles ≤6000 nm). The penetration of MWCNTs through six tested FFR models at two constant flow rates of 30 and 85 LPM was determined. Penetration at 85 LPM (0.58-2.04% for N95, 0.15-0.32% for N99, and 0.007-0.009% for P100 FFRs) was greater compared with the values at 30 LPM (0.28-1.79% for N95, 0.10-0.24% for N99, and 0.005-0.006% for P100 FFRs). The most penetrating particle size through all six tested FFR models was found to be in the range of 25-130 nm and 35-200 nm for the 30-LPM and 85-LPM flow rates, respectively.

    更新日期:2019-11-01
  • Effect of gravitational sedimentation on simulated aerosol dispersion in the human acinus.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2003-05-16
    Chantal Darquenne,G Kim Prisk

    We studied the effect of gravitational sedimentation on the dispersion of 0.5 and 1 micrometer-diameter particle boluses within a two-dimensional symmetric six-generation model of the human acinus. Boluses were introduced at the beginning of a 2-s inspiration immediately followed by a 4-s expiration, in normal gravity (1 G) and in the absence of gravity (0 G). The flow corresponded to a flow rate at the mouth of 500 ml/s. In 0 G, simulated dispersion (Hsim) was 16 ml for both particle sizes. In 1 G, Hsim was 71 and 242 ml for 0.5 and 1 micrometer-diameter particles, respectively, showing the effect of gravitational sedimentation. The difference between experimental data (J. Appl. Physiol. 86 (1999) 1402) and simulations was independent of particle size. This suggests that the residual dispersion was independent of the intrinsic properties of the particles and was more likely due to other mechanisms such as ventilation inhomogeneities, cardiogenic oscillations and alveolar wall motion.

    更新日期:2019-11-01
  • Design of an instrument for real-time detection of bioaerosols using simultaneous measurement of particle aerodynamic size and intrinsic fluorescence.
    J. Aerosol Sci. (IF 2.24) Pub Date : 1997-04-01
    P P Hairston,J Ho,F R Quant

    A prototype instrument has been constructed to measure individual airborne particles based on their aerodynamic size and their intrinsic fluorescence at selected excitation and emission wavelength bands. The instrument combines features of an aerodynamic particle sizing device with capabilities similar to those of a liquid flow cytometer. The goal of the instrument is to provide real-time data indicative of particle characteristics, and it is especially targeted to respond to bioaerosols from 0.5 to 10 micrometers (aerodynamic diameter) with intrinsic fluorescence exited at a wavelength of 325 nm and emitting from 420 to 580 nm. This size range covers individual airborne bacteria and bacteria clusters, and the fluorescence sensitivity is selected for biological molecules commonly found in cellular systems, for example, reduced nicotinamide adenine dinucleotide phosphate [NAD(P)H] and riboflavin. Initial tests with nebulised Bacillus subtilis var. niger (BG, ATCC 9372) spores have shown that, for both individual spores and spore clumps, a low level of fluorescence is detected from 17% of the particles. This detection percentage is on the same order as previous experiments that have measured viability of about 12% for mechanically dispersed BG spores (Ho and Fisher (1993) Defense Research Establishment Suffield Memorandum 1421) and suggests a need for further investigation into the possible relationship between the detected fluorescence and viability of bacterial spores.

    更新日期:2019-11-01
  • Characterization of an Aerosol Microconcentrator for Analysis Using Microscale Optical Spectroscopies.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2017-06-20
    Lina Zheng,Pramod Kulkarni,Konstantinos Zavvos,Huayan Liang,M Eileen Birch,Dionysios D Dionysiou

    Efficient microconcentration of aerosols to a substrate is essential for effectively coupling the collected particles to microscale optical spectroscopies such as laser-induced or spark microplasma, or micro-Raman or infrared spectroscopies. In this study, we present detailed characterization of a corona-based aerosol microconcentration technique developed previously (Diwakar and Kulkarni, 2012). The method involves two coaxial electrodes separated by a few millimeters, one held at a high electrical potential and the other grounded. The particles are collected on the collection (i.e., ground) electrode from a coaxial aerosol flow in a one-step charge-and-collect scheme using corona discharge and electrical precipitation between the two electrodes. Performance of the corona microconcentration method was determined experimentally by measuring collection efficiency, wall losses, and particle deposition density. An intrinsic spectroscopic sensitivity was experimentally determined for the aerosol microconcentrator. Using this sensitivity, we show that corona-based microconcentration is much superior to alternative methods, including filtration, focused impaction using aerodynamic lens, and spot collection using condensational growth. The method offers unique advantages for compact, hand-held aerosol analytical instrumentation.

    更新日期:2019-11-01
  • In Vitro Assessment of Small Charged Pharmaceutical Aerosols in a Model of a Ventilated Neonate.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2017-12-26
    Landon Holbrook,Michael Hindle,P Worth Longest

    Aerosolized medications may benefit infants receiving mechanical ventilation; however, the lung delivery efficiency of these aerosols is unacceptably low. In vitro experiments were conducted to evaluate aerosol delivery through conventional and modified ventilation systems to the end of a 3mm endotracheal tube (ETT) under steady state and realistic cyclic flow conditions. System modifications were employed to investigate the use of small charged particles and included streamlined components, a reduction in nebulizer liquid flow rate, synchronization with inspiration, and implementation of a previously designed low-flow induction charger (LF-IC), which was further modified in this study. Cyclic flow experiments implemented a modern ventilator with bias airflow and an inline flow meter, both of which are frequently excluded from in vitro tests but included in clinical practice. The modified LF-IC system demonstrated superior delivery efficiency to the end of the ETT (34%) compared with the commercial system (~1.3%) operating under cyclic ventilation conditions. These findings indicate that commercial systems still provide very low lung delivery efficiencies despite decades of innovation. In contrast, the modified system increased dose delivery to the end of the ETT by 26-fold. Despite initial concerns, the charged aerosol could be efficiently delivered through the small diameter ETT and reach the lungs. Future studies will be required to determine if the applied particle charge can eliminate expected high exhalation aerosol loss and will require the development of a realistic lung model.

    更新日期:2019-11-01
  • Design and Development of an Electrostatic Screen Battery for Emission Control (ESBEC).
    J. Aerosol Sci. (IF 2.24) Pub Date : 2017-10-07
    Taewon Han,Gediminas Mainelis

    Current diesel particulate filters (DPFs) can effectively capture the exhaust particles, but they add to engine backpressure and accumulate particles during their operation, which results in the need to regenerate the DPFs by burning off the collected particles periodically. This regeneration results in aerosol emissions, especially in the 10-30 nanometer size range and contributes to ultrafine particle pollution. In this research, we designed and developed a prototype of a novel diesel exhaust control device: the Electrostatic Screen Battery for Emissions Control (ESBEC). The device features high particle collection efficiency without adding to the exhaust backpressure and without the need for thermal regeneration of the collected particles. The ESBEC consists of a series of metal mesh screens coated with a superhydrophobic substance and an integrated carbon fiber ionizer to charge the incoming particles. Multiple pairs of screens (e.g., 5 pairs) are arranged in a battery, in which one screen of each pair is supplied with high voltage, and the other is grounded, producing electrostatic field produced across the screens. The application of a superhydrophobic coating onto the screens allows easy removal of the collected particles using liquid without the need for thermal regeneration. The current prototypes of the device were tested with fluorescent polystyrene latex (PSL) particles of 0.2 and 1.2 μm in size and at 25 and 105 L/min sampling flow rates. The average collection efficiency was ~87% for 0.2 μm and ~95% for 1.2 μm PSL particles. In addition, the ESBEC was tested with actual diesel exhaust particles; here its performance was verified by visually inspecting deposition of particles on an after-filter with the device ON and OFF. In the next stages of this work, the ESBEC will be challenged with diesel exhaust at different mass concentrations and for different collection time periods.

    更新日期:2019-11-01
  • Evaluation of consumer monitors to measure particulate matter.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2017-09-06
    Sinan Sousan,Kirsten Koehler,Laura Hallett,Thomas M Peters

    Recently, inexpensive (<$300) consumer aerosol monitors (CAMs) targeted for use in homes have become available. We evaluated the accuracy, bias, and precision of three CAMs (Foobot from Airoxlab, Speck from Carnegie Mellon University, and AirBeam from HabitatMap) for measuring mass concentrations in occupational settings. In a laboratory study, PM2.5 measured with the CAMs and a medium-cost aerosol photometer (personal DataRAM 1500, Thermo Scientific) were compared to that from reference instruments for three aerosols (salt, welding fume, and Arizona road dust, ARD) at concentrations up to 8500 μg/m3. Three of each type of CAM were included to estimate precision. Compared to reference instruments, mass concentrations measured with the Foobot (r-value = 0.99) and medium-cost photometer (r-value = 0.99) show strong correlation, whereas those from the Speck (r-value range 0.88 - 0.99) and AirBeam (0.7 - 0.96) were less correlated. The Foobot bias was (-12%) for ARD and measurements were similar to the medium-cost instrument. Foobot bias was (< -46%) for salt and welding fume aerosols. Speck bias was at 18% salt for ARD and -86% for welding fume. AirBeam bias was (-36%) for salt and (-83%) for welding fume. All three photometers had a bias (< -82%) for welding fume. Precision was excellent for the Foobot (coefficient of variation range: 5% to 8%) and AirBeam (2% to 9%), but poorer for the Speck (8% to 25%). These findings suggest that the Foobot, with a linear response to different aerosol types and good precision, can provide reasonable estimates of PM2.5 in the workplace after site-specific calibration to account for particle size and composition.

    更新日期:2019-11-01
  • Calculating Compound Dependent Gas-Droplet Distributions in Aerosols of Propylene Glycol and Glycerol from Electronic Cigarettes.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2017-05-01
    James F Pankow

    Aerosols created by electronic cigarettes are suspensions of liquid droplets in a gas phase. All of the volatile or semi-volatile compounds in the system will partition between both phases; among these compounds are the "e-liquid" constituents plus the degradation products such as formaldehyde produced during "vaping". This partitioning affects deposition in the respiratory tract and optimal analytical method design. Theory can be used to predict the particle- vs. gas-phase distribution of each compound as a function of the composition of the aerosol droplets, temperature, and the vapor pressure of the compound. As an example, even at the highest total particulate matter (TPM, μg/m3) levels for e-cigarette aerosols, formaldehyde as CH2O will be mostly in the gas phase; two important adducts of formaldehyde will be mostly in the aerosol droplets even at the lowest TPM levels.

    更新日期:2019-11-01
  • Recommendations for Simulating Microparticle Deposition at Conditions Similar to the Upper Airways with Two-Equation Turbulence Models.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2018-10-24
    Karl Bass,P Worth Longest

    The development of a CFD model, from initial geometry to experimentally validated result with engineering insight, can be a time-consuming process that often requires several iterations of meshing and solver set-up. Applying a set of guidelines in the early stages can help to streamline the process and improve consistency between different models. The objective of this study was to determine both mesh and CFD solution parameters that enable the accurate simulation of microparticle deposition under flow conditions consistent with the upper respiratory airways including turbulent flow. A 90° bend geometry was used as a characteristic model that occurs throughout the airways and for which high-quality experimental aerosol deposition data is available in the transitional and turbulent flow regimes. Four meshes with varying degrees of near-wall resolution were compared, and key solver settings were applied to determine the parameters that minimize sensitivity to the near-wall (NW) mesh. The Low Reynolds number (LRN) k-ω model was used to resolve the turbulence field, which is a numerically efficient two-equation turbulence model, but has recently been considered overly simplistic. Some recent studies have used more complex turbulence models, such as Large Eddy Simulation (LES), to overcome the perceived weaknesses of two-equation models. Therefore, the secondary objective was to determine whether the more computationally efficient LRN k-ω model was capable of providing deposition results that were comparable to LES. Results show how NW mesh sensitivity is reduced through application of the Green-Gauss Node-based gradient discretization scheme and physically realistic near-wall corrections. Using the newly recommended meshing parameters and solution guidelines gives an excellent match to experimental data. Furthermore, deposition data from the LRN k-ω model compares favorably with LES results for the same characteristic geometry. In summary, this study provides a set of meshing and solution guidelines for simulating aerosol deposition in transitional and turbulent flows found in the upper respiratory airways using the numerically efficient LRN k-ω approach.

    更新日期:2019-11-01
  • DESIGN AND OPTIMIZATION OF A COMPACT LOW-COST OPTICAL PARTICLE SIZER.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2018-10-03
    Tomas Njalsson,Igor Novosselov

    Direct measurements of time- and size-resolved particulate matter (PM) concentrations are of major importance in air quality studies and pollution monitoring. Low-cost, compact optical particle counters (OPCs), which provide accurate PM measurements independent of the particle complex index of refraction (CRI), can be useful in personal exposure monitoring and distributed sensor network studies applications. A methodology is presented for the optimization of the sensor design and operation parameter space aimed at reducing the effect of the CRI on particle sizing errors. The Monte Carlo numerical simulation, which utilizes Mie scattering calculations, is used to determine the optimal detector angle for the specific set of constraints described by the weighting coefficients. The optimized detector position (θ = 48°) has the lowest dependency on CRI over the entire particle size range of 0.5-10 microns. The near-forward, optimized, and perpendicular detector angles are compared experimentally using monodisperse 2 μm and 4 μm particles of silica, PSL, and alumina; the light collection cone angle is set at α = 20° in all experiments. The data agree well with the numerical results for all tested scenarios. Overall, the perpendicular detector location has the best precision and worst accuracy related to the CRI variations. The optimized detector position has the best accuracy for both silica and alumina particles. The use of low-cost components, such as laser diodes, photodiodes, miniaturized integrated electronics, and simple component layouts allows for the development of compact OPCs capable of accurately sizing PM. The number of sizing bins, sizing accuracy and precision, and other parameters of interest can be used as an input to an optimization algorithm.

    更新日期:2019-11-01
  • Comparison of multiple X-ray fluorescence techniques for elemental analysis of particulate matter collected on air filters.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-01-22
    Fabjola Bilo,Laura Borgese,Anne Wambui,Ahmad Assi,Annalisa Zacco,Stefania Federici,Diane M Eichert,Kouichi Tsuji,Roberto G Lucchini,Donatella Placidi,Elza Bontempi,Laura E Depero

    This work reports on qualitative and semi-quantitative elemental analysis of particulate matter (PM) collected on PTFE membrane filters, for a source apportionment study conducted in Brescia (Italy). Sampling was undertaken in a residential area where an increase in Mn emissions has been highlighted by previous studies. Filters are measured by means of X-ray Fluorescence (XRF) based techniques such as micro-XRF and grazing incidence XRF using synchrotron radiation, Mo or W excitation sources, after applying an automatized sample preparation method. A heterogeneous distribution in PM shape, size and composition was observed, with features typical of anthropogenic sources. XRF measurements performed at various incidence angle, on large areas and different experimental setup were reproducible. The results demonstrate a successful comparison of the various XRF instrumentation, and the decrease in Mn content with the distance away from the identified emission source. This work highlights the potentialities of the presented approach to provide a full quantitative analysis, and ascertain its suitability for providing a direct, fast, simple and sensitive elemental analysis of filters in source apportionment studies and screening purposes.

    更新日期:2019-11-01
  • Comparison of diffusion charging and mobility-based methods for measurement of aerosol agglomerate surface area.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2012-05-01
    Bon Ki Ku,Pramod Kulkarni

    We compare different approaches to measure surface area of aerosol agglomerates. The objective was to compare field methods, such as mobility and diffusion charging based approaches, with laboratory approach, such as Brunauer, Emmett, Teller (BET) method used for bulk powder samples. To allow intercomparison of various surface area measurements, we defined 'geometric surface area' of agglomerates (assuming agglomerates are made up of ideal spheres), and compared various surface area measurements to the geometric surface area. Four different approaches for measuring surface area of agglomerate particles in the size range of 60-350 nm were compared using (i) diffusion charging-based sensors from three different manufacturers, (ii) mobility diameter of an agglomerate, (iii) mobility diameter of an agglomerate assuming a linear chain morphology with uniform primary particle size, and (iv) surface area estimation based on tandem mobility-mass measurement and microscopy. Our results indicate that the tandem mobility-mass measurement, which can be applied directly to airborne particles unlike the BET method, agrees well with the BET method. It was also shown that the three diffusion charging-based surface area measurements of silver agglomerates were similar within a factor of 2 and were lower than those obtained from the tandem mobility-mass and microscopy method by a factor of 3-10 in the size range studied. Surface area estimated using the mobility diameter depended on the structure or morphology of the agglomerate with significant underestimation at high fractal dimensions approaching 3.

    更新日期:2019-11-01
  • A Scanning Transmission Electron Microscopy Method for Determining Manganese Composition in Welding Fume as a Function of Primary Particle Size.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2011-06-01
    Julie D Richman,Kenneth J T Livi,Alison S Geyh

    Increasing evidence suggests that the physicochemical properties of inhaled nanoparticles influence the resulting toxicokinetics and toxicodynamics. This report presents a method using scanning transmission electron microscopy (STEM) to measure the Mn content throughout the primary particle size distribution of welding fume particle samples collected on filters for application in exposure and health research. Dark field images were collected to assess the primary particle size distribution and energy-dispersive X-ray and electron energy loss spectroscopy were performed for measurement of Mn composition as a function of primary particle size. A manual method incorporating imaging software was used to measure the primary particle diameter and to select an integration region for compositional analysis within primary particles throughout the size range. To explore the variation in the developed metric, the method was applied to 10 gas metal arc welding (GMAW) fume particle samples of mild steel that were collected under a variety of conditions. The range of Mn composition by particle size was -0.10 to 0.19 %/nm, where a positive estimate indicates greater relative abundance of Mn increasing with primary particle size and a negative estimate conversely indicates decreasing Mn content with size. However, the estimate was only statistically significant (p<0.05) in half of the samples (n=5), which all had a positive estimate. In the remaining samples, no significant trend was measured. Our findings indicate that the method is reproducible and that differences in the abundance of Mn by primary particle size among welding fume samples can be detected.

    更新日期:2019-11-01
  • Effects of Surface Smoothness on Inertial Particle Deposition in Human Nasal Models.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2011-02-23
    Jeffry D Schroeter,Guilherme J M Garcia,Julia S Kimbell

    Computational fluid dynamics (CFD) predictions of inertial particle deposition have not compared well with data from nasal replicas due to effects of surface texture and the resolution of tomographic images. To study effects of geometric differences between CFD models and nasal replicas, nasal CFD models with different levels of surface smoothness were reconstructed from the same MRI data used to construct the nasal replica used by Kelly et al. (2004) [Aerosol Sci. Technol. 38:1063-1071]. One CFD model in particular was reconstructed without any surface smoothing to preserve the detailed topology present in the nasal replica. Steady-state inspiratory airflow and Lagrangian particle tracking were simulated using Fluent software. Particle deposition estimates from the smoother models under-predicted nasal deposition from replica casts, which was consistent with previous findings. These discrepancies were overcome by including surface artifacts that were not present in the reduced models and by plotting deposition efficiency versus the Stokes number, where the characteristic diameter was defined in terms of the pressure-flow relationship to account for changes in airflow resistance due to wall roughness. These results indicate that even slight geometric differences have significant effects on nasal deposition and that this information should be taken into account when comparing particle deposition data from CFD models with experimental data from nasal replica casts.

    更新日期:2019-11-01
  • Airflow and nanoparticle deposition in rat nose under various breathing and sniffing conditions: a computational evaluation of the unsteady effect.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2010-11-16
    Jianbo Jiang,Kai Zhao

    Accurate prediction of nanoparticle (1~100 nm) deposition in the rat nasal cavity is important for assessing the toxicological impact of inhaled nanoparticles as well as for potential therapeutic applications. A quasi-steady assumption has been widely adopted in the past investigations on this topic, yet the validity of such simplification under various breathing and sniffing conditions has not been carefully examined. In this study, both steady and unsteady computational fluid dynamics (CFD) simulations were conducted in a published rat nasal model under various physiologically realistic breathing and sniffing flow rates. The transient airflow structures, nanoparticle transport and deposition patterns in the whole nasal cavity and the olfactory region were investigated and compared with steady state simulation of equivalent flow rate. The results showed that (1) the quasi-steady flow assumption for cyclic flow was valid for over 70% of the cycle period during all simulated breathing and sniffing conditions in the rat nasal cavity, or the unsteady effect was only significant during the transition between the respiratory phases; (2) yet the quasi-steady assumption for nanoparticle transport was not valid, except in the vicinity of peak respiration. In general, the total deposition efficiency of nanoparticle during cyclic breathing would be lower than that of steady state due to the unsteady effect on particle transport and deposition, and further decreased with the increase of particle size, sniffing frequency, and flow rate. In the contrary, previous study indicated that for micro-scale particles (0.5~4μm), the unsteady effect would increase deposition efficiencies in rat nasal cavity. Combined, these results suggest that the quasi-steady assumption of nasal particle transport during cycling breathing should be used with caution for an accurate assessment of the toxicological and therapeutic impact of particle inhalation. Empirical equations and effective steady state approximation derived in this study are thus valuable to estimate such unsteady effects in future applications.

    更新日期:2019-11-01
  • Characterizing the performance of two optical particle counters (Grimm OPC1.108 and OPC1.109) under urban aerosol conditions.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2010-11-13
    J Burkart,G Steiner,G Reischl,H Moshammer,M Neuberger,R Hitzenberger

    The performance of Grimm optical particle counters (OPC, models 1.108 and 1.109) was characterized under urban aerosol conditions. Number concentrations were well correlated. The different lower cut-off diameters (0.25 and 0.3 μm) give an average difference of 23.5%. Both detect less than 10% of the total particle concentration (0.01-1 μm; Differential Mobility Analyzer), but in the respective size ranges, differences are <10%. OPC number size distributions were converted to mass concentrations using instrument-specific factors given by the manufacturer. Mass concentrations for OPC1.108 were 60% higher than for OPC1.109 and (in case of OPC1.109) much lower than those measured with an impactor in the relevant size range or a TSP filter. Using the C-factor correction suggested by the manufacturer, OPC1.109 underestimated mass concentrations by 21% (impactor) and by about 36% (TSP filter), which is in the range of comparability of co-located different mass concentration methods (Hitzenberger, Berner, Maenhaut, Cafmeyer, Schwarz, & Mueller et al., 2004).

    更新日期:2019-11-01
  • CFD simulations of enhanced condensational growth (ECG) applied to respiratory drug delivery with comparisons to in vitro data.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2010-09-14
    P Worth Longest,Michael Hindle

    Enhanced condensational growth (ECG) is a newly proposed concept for respiratory drug delivery in which a submicrometer aerosol is inhaled in combination with saturated or supersaturated water vapor. The initially small aerosol size provides for very low extrathoracic deposition, whereas condensation onto droplets in vivo results in size increase and improved lung retention. The objective of this study was to develop and evaluate a CFD model of ECG in a simple tubular geometry with direct comparisons to in vitro results. The length (29 cm) and diameter (2 cm) of the tubular geometry were representative of respiratory airways of an adult from the mouth to the first tracheobronchial bifurcation. At the model inlet, separate streams of humidified air (25, 30, and 39 °C) and submicrometer aerosol droplets with mass median aerodynamic diameters (MMADs) of 150, 560, and 900 nm were combined. The effects of condensation and droplet growth on water vapor concentrations and temperatures in the continuous phase (i.e., two-way coupling) were also considered. For an inlet saturated air temperature of 39 °C, the two-way coupled numerical (and in vitro) final aerosol MMADs for initial sizes of 150, 560, and 900 nm were 1.75 μm (vs. 1.23 μm), 2.58 μm (vs. 2.66 μm), and 2.65 μm (vs. 2.63 μm), respectively. By including the effects of two-way coupling in the model, agreements with the in vitro results were significantly improved compared with a one-way coupled assumption. Results indicated that both mass and thermal two-way coupling effects were important in the ECG process. Considering the initial aerosol sizes of 560 and 900 nm, the final sizes were most influenced by inlet saturated air temperature and aerosol number concentration and were not largely influenced by initial size. Considering the growth of submicrometer aerosols to above 2 μm at realistic number concentrations, ECG may be an effective respiratory drug delivery approach for minimizing mouth-throat deposition and maximizing aerosol retention in a safe and simple manner. However, future studies are needed to explore effects of in vivo boundary conditions, more realistic respiratory geometries, and transient breathing.

    更新日期:2019-11-01
  • GAS-PHASE FLAME SYNTHESIS AND PROPERTIES OF MAGNETIC IRON OXIDE NANOPARTICLES WITH REDUCED OXIDATION STATE.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2010-03-17
    Benjamin M Kumfer,Kozo Shinoda,Balachandran Jeyadevan,Ian M Kennedy

    Iron oxide nanoparticles of reduced oxidation state, mainly in the form of magnetite, have been synthesized utilizing a new continuous, gas-phase, nonpremixed flame method using hydrocarbon fuels. This method takes advantage of the characteristics of the inverse flame, which is produced by injection of oxidizer into a surrounding flow of fuel. Unlike traditional flame methods, this configuration allows for the iron particle formation to be maintained in a more reducing environment. The effects of flame temperature, oxygen-enrichment and fuel dilution (i.e. the stoichiometric mixture fraction), and fuel composition on particle size, Fe oxidation state, and magnetic properties are evaluated and discussed. The crystallite size, Fe(II) fraction, and saturation magnetization were all found to increase with flame temperature. Flames of methane and ethylene were used, and the use of ethylene resulted in particles containing metallic Fe(0), in addition to magnetite, while no Fe(0) was present in samples synthesized using methane.

    更新日期:2019-11-01
  • CFD Simulation and Experimental Validation of Fluid Flow and Particle Transport in a Model of Alveolated Airways.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2010-02-18
    Baoshun Ma,Vincent Ruwet,Patricia Corieri,Raf Theunissen,Michel Riethmuller,Chantal Darquenne

    Accurate modeling of air flow and aerosol transport in the alveolated airways is essential for quantitative predictions of pulmonary aerosol deposition. However, experimental validation of such modeling studies has been scarce. The objective of this study is to validate CFD predictions of flow field and particle trajectory with experiments within a scaled-up model of alveolated airways. Steady flow (Re = 0.13) of silicone oil was captured by particle image velocimetry (PIV), and the trajectories of 0.5 mm and 1.2 mm spherical iron beads (representing 0.7 to 14.6 mum aerosol in vivo) were obtained by particle tracking velocimetry (PTV). At twelve selected cross sections, the velocity profiles obtained by CFD matched well with those by PIV (within 1.7% on average). The CFD predicted trajectories also matched well with PTV experiments. These results showed that air flow and aerosol transport in models of human alveolated airways can be simulated by CFD techniques with reasonable accuracy.

    更新日期:2019-11-01
  • Aggregate Morphology Evolution by Sintering: Number & Diameter of Primary Particles.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2013-05-10
    Max L Eggersdorfer,Dirk Kadau,Hans J Herrmann,Sotiris E Pratsinis

    The structure of fractal-like agglomerates (physically-bonded) and aggregates (chemically- or sinter-bonded) is important in aerosol synthesis of nanoparticles, and in monitoring combustion emissions and atmospheric particles. It influences also particle mobility, scattering, and eventually performance of nanocomposites, suspensions and devices made with such particles. Here, aggregate sintering by viscous flow of amorphous materials (silica, polymers) and grain boundary diffusion of crystalline ceramics (titania, alumina) or metals (Ni, Fe, Ag etc.) is investigated. A scaling law is found between average aggregate projected area and equivalent number of constituent primary particles during sintering: from fractal-like agglomerates to aggregates and eventually compact particles (e.g. spheres). This is essentially a relation independent of time, material properties and sintering mechanisms. It is used to estimate the equivalent primary particle diameter and number in aggregates. The evolution of aggregate morphology or structure is quantified by the effective fractal dimension (Df ) and mass-mobility exponent (Dfm ) and the corresponding prefactors. The Dfm increases monotonically during sintering converging to 3 for a compact particle. Therefore Dfm and its prefactor could be used to gauge the degree or extent of sintering of agglomerates made by a known collision mechanism. This analysis is exemplified by comparison to experiments of silver nanoparticle aggregates sintered at different temperatures in an electric tube furnace.

    更新日期:2019-11-01
  • Continuous flame aerosol synthesis of carbon-coated nano-LiFePO(4) for Li-ion batteries.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2011-10-01
    Oliver Waser,Robert Büchel,Andreas Hintennach,Petr Novák,Sotiris E Pratsinis

    Core-shell, nano-sized LiFePO(4)-carbon particles were made in one step by scalable flame aerosol technology at 7 g/h. Core LiFePO(4) particles were made in an enclosed flame spray pyrolysis (FSP) unit and were coated in-situ downstream by auto thermal carbonization (pyrolysis) of swirl-fed C(2)H(2) in an O(2)-controlled atmosphere. The formation of acetylene carbon black (ACB) shell was investigated as a function of the process fuel-oxidant equivalence ratio (EQR). The core-shell morphology was obtained at slightly fuel-rich conditions (1.0

    更新日期:2019-11-01
  • The effect of carrier gas contaminants on the charging probability of aerosols under bipolar charging conditions.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2012-12-05
    Gerhard Steiner,Georg P Reischl

    This work concentrates on the experimental determination of the properties of ionic molecular clusters that are produced in the bipolar ionic atmosphere of a radioactivity based (241)Am charger. The main scope of this study was to investigate the dependency of the ions' properties on carrier gas contaminants caused by the evaporation of trace gases from different kinds of frequently encountered tubing materials. A recently developed high resolution mobility spectrometer allows the precise determination of the ions' electrical mobility; an empirical mass-mobility relationship was used to approximate the corresponding ion masses. It was found that impurities in the carrier gas dramatically change the pattern of the ion mobility/size distribution, resulting in very different ion properties that strongly depend on the carrier gas composition. Since the ion properties control the charging process of aerosols, it was further investigated how the different ion properties affect the calculation of the charging probabilities of aerosols. The results show that despite large variations of the ions' properties, only a minor effect on the calculated charging probabilities can be found.

    更新日期:2019-11-01
  • Production of Inhalable Submicrometer Aerosols from Conventional Mesh Nebulizers for Improved Respiratory Drug Delivery.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2012-06-19
    P Worth Longest,Benjamin M Spence,Landon T Holbrook,Karla M Mossi,Yoen-Ju Son,Michael Hindle

    Submicrometer and nanoparticle aerosols may significantly improve the delivery efficiency, dissolution characteristics, and bioavailability of inhaled pharmaceuticals. The objective of this study was to explore the formation of submicrometer and nanometer aerosols from mesh nebulizers suitable for respiratory drug delivery using experiments and computational fluid dynamics (CFD) modeling. Mesh nebulizers were coupled with add-on devices to promote aerosol drying and the formation of submicrometer particles, as well as to control the inhaled aerosol temperature and relative humidity. Cascade impaction experiments were used to determine the initial mass median aerodynamic diameters of 0.1% albuterol aerosols produced by the AeroNeb commercial (4.69 μm) and lab (3.90 μm) nebulizers and to validate the CFD model in terms of droplet evaporation. Through an appropriate selection of flow rates, nebulizers, and model drug concentrations, submicrometer and nanometer aerosols could be formed with the three devices considered. Based on CFD simulations, a wire heated design was shown to overheat the airstream producing unsafe conditions for inhalation if the aerosol was not uniformly distributed in the tube cross-section or if the nebulizer stopped producing droplets. In comparison, a counter-flow heated design provided sufficient thermal energy to produce submicrometer particles, but also automatically limited the maximum aerosol outlet temperature based on the physics of heat transfer. With the counter-flow design, submicrometer aerosols were produced at flow rates of 5, 15, and 30 LPM, which may be suitable for various forms of oral and nasal aerosol delivery. Thermodynamic conditions of the aerosol stream exiting the counter-flow design were found be in a range of 21-45 °C with relative humidity greater than 40% in some cases, which was considered safe for direct inhalation and advantageous for condensational growth delivery.

    更新日期:2019-11-01
  • Evaluation of Exposure to Brevundimonas diminuta and Pseudomonas aeruginosa during Showering.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2018-10-16
    Sandip Chattopadhyay,Sarah D Perkins,Matthew Shaw,Tonya L Nichols

    This study experimentally assessed bacterial water-to-air partitioning coefficients resulting from showerhead aerosolization of water contaminated with Brevundimonas diminuta or Pseudomonas aeruginosa, and estimated human exposure through inhalation. Dechlorinated tap water was spiked with two cell densities (109 and 1010 CFU l-1) and cycled at three temperatures (10, 25, and 37 or 40ºC) through a full-scale shower system. For reproducibility, spiked water concentrations were intentionally higher than found in natural environments. Three types of samplers measured size distribution and viable concentrations throughout the system. Results indicate low levels of respirable bioaerosols were generated. The ratio of bacterial contaminant that was effectively aerosolized (bacterial water-to-air partitioning coefficient, PC bwa ) was low - averaging 1.13×10-5 L m-3 for B. diminuta and 8.31×10-6 L m-3 for P. aeruginosa. However, the respirable fraction of aerosolized organisms was high, averaging above 94% (in shower) and above 99% (downstream) for both organisms. This study found no significant difference in bioaerosol load for a forward facing versus reverse facing individual. Further, for the average hot shower (33-43°C) the total number of respirable bioaerosols is higher, but the observed culturability of those aerosolized cells is lower when compared to lower temperatures. Bacterial water to air partitioning coefficients were calculated to predict microbial air concentration and these empirical parameters may be used for assessing inhalation as a route of exposure to pathogens in contaminated waters.

    更新日期:2019-11-01
  • Effect of static vs. dynamic imaging on particle transport in CT-based numerical models of human central airways.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2017-01-17
    Shinjiro Miyawaki,Eric A Hoffman,Ching-Long Lin

    Advances in quantitative computed tomography (CT) has provided methods to assess the detailed structure of the pulmonary airways and parenchyma, providing the means of applying computational fluid dynamics-based modeling to better understand subject-specific differences in structure-to-function relationships. Most of the previous numerical studies, seeking to predict patterns of inhaled particle deposition, have considered airway geometry and regional ventilation derived from static images. Because geometric alterations of the airway and parenchyma associated with regional ventilation may greatly affect particle transport, we have sought to investigate the effect of rigid vs. deforming airways, linear vs. nonlinear airway deformations, and step-wise static vs. dynamic imaging on particle deposition with varying numbers of intermediate lung volume increments. Airway geometry and regional ventilation at different time points were defined by four-dimensional (space and time) dynamic or static CT images. Laminar, transitional, and turbulent air flows were reproduced with a three-dimensional eddy-resolving computational fluid dynamics model. Finally, trajectories of particles were computed with the Lagrangian tracking algorithm. The results demonstrated that static-imaging-based models can contribute 7% uncertainty to overall particle distribution and deposition primarily due to regional flow rate (ventilation) differences as opposed to geometric alterations. The effect of rigid vs. deforming airways on serial distribution of particles over generations was significantly smaller than reported in a previous study that used the symmetric Weibel geometric model with smaller flow rate. Rigid vs. deforming airways were also shown to affect parallel particle distribution over lobes by 8% and the differences associated with use of static vs. dynamic imaging was 18%. These differences demonstrate that estimates derived from static vs. dynamic imaging can significantly affect the assessment of particle distribution heterogeneity. The effect of linear vs. nonlinear airway deformations was within the uncertainty due to mesh size.

    更新日期:2019-11-01
  • Incorporation of dosimetry in the derivation of reference concentrations for ambient or workplace air: a conceptual approach.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2016-10-11
    Adriana R Oller,Günter Oberdörster

    Dosimetric models are essential tools to refine inhalation risk assessments based on local respiratory effects. Dosimetric adjustments to account for differences in aerosol particle size and respiratory tract deposition and/or clearance among rodents, workers, and the general public can be applied to experimentally- and epidemiologically-determined points of departure (PODs) to calculate size-selected (e.g., PM10, inhalable aerosol fraction, respirable aerosol fraction) equivalent concentrations (e.g., HEC or Human Equivalent Concentration; REC or Rodent Equivalent Concentration). A modified POD (e.g., HEC) can then feed into existing frameworks for the derivation of occupational or ambient air concentration limits or reference concentrations. HECs that are expressed in terms of aerosol particle sizes experienced by humans but are derived from animal studies allow proper comparison of exposure levels and associated health effects in animals and humans. This can inform differences in responsiveness between animals and humans, based on the same deposited or retained doses and can also allow the use of both data sources in an integrated weight of evidence approach for hazard and risk assessment purposes. Whenever possible, default values should be replaced by substance-specific and target population-specific parameters. Assumptions and sources of uncertainty need to be clearly reported.

    更新日期:2019-11-01
  • Total and regional deposition of inhaled aerosols in supine healthy subjects and subjects with mild-to-moderate COPD.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2016-08-06
    Chantal Darquenne,Wayne J Lamm,Janelle M Fine,Richard A Corley,Robb W Glenny

    Despite substantial development of sophisticated subject-specific computational models of aerosol transport and deposition in human lungs, experimental validation of predictions from these new models is sparse. We collected aerosol retention and exhalation profiles in seven healthy volunteers and six subjects with mild-to-moderate COPD (FEV1 = 50-80%predicted) in the supine posture. Total deposition was measured during continuous breathing of 1 and 2.9 μm-diameter particles (tidal volume of 1 L, flow rate of 0.3 L/s and 0.75 L/s). Bolus inhalations of 1 μm particles were performed to penetration volumes of 200, 500 and 800 mL (flow rate of 0.5 L/s). Aerosol bolus dispersion (H), deposition, and mode shift (MS) were calculated from these data. There was no significant difference in total deposition between healthy subjects and those with COPD. Total deposition increased with increasing particle size and also with increasing flow rate. Similarly, there was no significant difference in aerosol bolus deposition between subject groups. Yet, the rate of increase in dispersion and of decrease in MS with increasing penetration volume was higher in subjects with COPD than in healthy volunteers (H: 0.798 ± 0.205 vs. 0.527 ± 0.122 mL/mL, p=0.01; MS: -0.271±0.129 vs. -0.145 ± 0.076 mL/mL, p=0.05) indicating larger ventilation inhomogeneities (based on H) and increased flow sequencing (based on MS) in the COPD than in the healthy group. In conclusion, in the supine posture, deposition appears to lack sensitivity for assessing the effect of lung morphology and/or ventilation distribution alteration induced by mild-to-moderate lung disease on the fate of inhaled aerosols. However, other parameters such as aerosol bolus dispersion and mode shift may be more sensitive parameters for evaluating models of lungs with moderate disease.

    更新日期:2019-11-01
  • INHALED AEROSOL DOSIMETRY: SOME CURRENT RESEARCH NEEDS.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2016-08-06
    Chantal Darquenne,Mark D Hoover,Robert F Phalen

    After the presentation of 60 papers at the conference "Advancing Aerosol Dosimetry Research" (October 24-25, 2014 in Irvine, CA, USA), attendees submitted written descriptions of needed research. About 40 research needs were submitted. The suggestions fell into six broad categories: 1) Access to detailed anatomic data; 2) Access to subject-specific aerosol deposition datasets; 3) Improving current inhaled aerosol deposition models; 4) Some current experimental data needs and hot topics; 5) Linking exposure and deposition modeling to health endpoints; and 6) Developing guidelines for appropriate validation of dosimetry and risk assessment models. Summaries of suggestions are provided here as an update on research needs related to inhaled aerosol dosimetry modeling. Taken together, the recommendations support the overarching need for increased collaborations between dose modelers and those that use the models for risk assessments, aerosol medicine applications, design of toxicology experiments, and extrapolation across species. This paper is only a snapshot in time of perceived research needs from the conference attendees; it does not carry the approval of any agency or other group that plans research priorities or that funds research.

    更新日期:2019-11-01
  • Deposition of Particles in the Alveolar Airways: Inhalation and Breath-Hold with Pharmaceutical Aerosols.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2014-11-11
    Navvab Khajeh-Hosseini-Dalasm,P Worth Longest

    Previous studies have demonstrated that factors such as airway wall motion, inhalation waveform, and geometric complexity influence the deposition of aerosols in the alveolar airways. However, deposition fraction correlations are not available that account for these factors in determining alveolar deposition. The objective of this study was to generate a new space-filling model of the pulmonary acinus region and implement this model to develop correlations of aerosol deposition that can be used to predict the alveolar dose of inhaled pharmaceutical products. A series of acinar models was constructed containing different numbers of alveolar duct generations based on space-filling 14-hedron elements. Selected ventilation waveforms were quick-and-deep and slow-and-deep inhalation consistent with the use of most pharmaceutical aerosol inhalers. Computational fluid dynamics simulations were used to predict aerosol transport and deposition in the series of acinar models across various orientations with gravity where ventilation was driven by wall motion. Primary findings indicated that increasing the number of alveolar duct generations beyond 3 had a negligible impact on total acinar deposition, and total acinar deposition was not affected by gravity orientation angle. A characteristic model containing three alveolar duct generations (D3) was then used to develop correlations of aerosol deposition in the alveolar airways as a function of particle size and particle residence time in the geometry. An alveolar deposition parameter was determined in which deposition correlated with d2t over the first half of inhalation followed by correlation with dt2, where d is the aerodynamic diameter of the particles and t is the potential particle residence time in the alveolar model. Optimal breath-hold times to allow 95% deposition of inhaled 1, 2, and 3 μm particles once inside the alveolar region were approximately >10, 2.7, and 1.2 s, respectively. Coupling of the deposition correlations with previous stochastic individual path (SIP) model predictions of tracheobronchial deposition was demonstrated to predict alveolar dose of commercial pharmaceutical products. In conclusion, this study completes an initiative to determine the fate of inhaled pharmaceutical aerosols throughout the respiratory airways using CFD simulations.

    更新日期:2019-11-01
  • Three-dimensional computational fluid dynamics modeling of particle uptake by an occupational air sampler using manually-scaled and adaptive grids.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2016-03-08
    Andrea C Landázuri,A Eduardo Sáez,T Renée Anthony

    This work presents fluid flow and particle trajectory simulation studies to determine the aspiration efficiency of a horizontally oriented occupational air sampler using computational fluid dynamics (CFD). Grid adaption and manual scaling of the grids were applied to two sampler prototypes based on a 37-mm cassette. The standard k-ε model was used to simulate the turbulent air flow and a second order streamline-upwind discretization scheme was used to stabilize convective terms of the Navier-Stokes equations. Successively scaled grids for each configuration were created manually and by means of grid adaption using the velocity gradient in the main flow direction. Solutions were verified to assess iterative convergence, grid independence and monotonic convergence. Particle aspiration efficiencies determined for both prototype samplers were undistinguishable, indicating that the porous filter does not play a noticeable role in particle aspiration. Results conclude that grid adaption is a powerful tool that allows to refine specific regions that require lots of detail and therefore better resolve flow detail. It was verified that adaptive grids provided a higher number of locations with monotonic convergence than the manual grids and required the least computational effort.

    更新日期:2019-11-01
  • Variability in Nose-to-Lung Aerosol Delivery.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2014-10-14
    Ross L Walenga,Geng Tian,Michael Hindle,Joshua Yelverton,Kelley Dodson,P Worth Longest

    Nasal delivery of lung targeted pharmaceutical aerosols is ideal for drugs that need to be administered during high flow nasal cannula (HFNC) gas delivery, but based on previous studies losses and variability through both the delivery system and nasal cavity are expected to be high. The objective of this study was to assess the variability in aerosol delivery through the nose to the lungs with a nasal cannula interface for conventional and excipient enhanced growth (EEG) delivery techniques. A database of nasal cavity computed tomography (CT) scans was collected and analyzed, from which four models were selected to represent a wide range of adult anatomies, quantified based on the nasal surface area-to-volume ratio (SA/V). Computational fluid dynamics (CFD) methods were validated with existing in vitro data and used to predict aerosol delivery through a streamlined nasal cannula and the four nasal models at a steady state flow rate of 30 L/min. Aerosols considered were solid particles for EEG delivery (initial 0.9 μm and 1.5 μm aerodynamic diameters) and conventional droplets (5 μm) for a control case. Use of the EEG approach was found to reduce depositional losses in the nasal cavity by an order of magnitude and substantially reduce variability. Specifically, for aerosol deposition efficiency in the four geometries, the 95% confidence intervals (CI) for 0.9 and 5 μm aerosols were 2.3-3.1 and 15.5-66.3%, respectively. Simulations showed that the use of EEG as opposed to conventional methods improved delivered dose of aerosols through the nasopharynx, expressed as penetration fraction (PF), by approximately a factor of four. Variability of PF, expressed by the coefficient of variation (CV), was reduced by a factor of four with EEG delivery compared with the control case. Penetration fraction correlated well with SA/V for larger aerosols, but smaller aerosols showed some dependence on nasopharyngeal exit hydraulic diameter. In conclusion, results indicated that the EEG technique not only improved lung aerosol delivery, but largely eliminated variability in both nasal depositional loss and lung PF in a newly developed set of nasal airway models.

    更新日期:2019-11-01
  • Application of ATP-based bioluminescence for bioaerosol quantification: effect of sampling method.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2016-01-26
    Taewon Han,Melody Wren,Kelsey DuBois,Jennifer Therkorn,Gediminas Mainelis

    An adenosine triphosphate (ATP)-based bioluminescence has potential to offer a quick and affordable method for quantifying bioaerosol samples. Here we report on our investigation into how different bioaerosol aerosolization parameters and sampling methods affect bioluminescence output per bacterium, and implications of that effect for bioaerosol research. Bacillus atrophaeus and Pseudomonas fluorescens bacteria were aerosolized by using a Collison nebulizer (BGI Inc., Waltham, MA) with a glass or polycarbonate jar and then collected for 15 and 60 min with: (1) Button Aerosol Sampler (SKC Inc., Eighty Four, PA) with polycarbonate, PTFE, and cellulose nitrate filters, (2) BioSampler (SKC Inc.) with 5 and 20 mL of collection liquid, and (3) our newly developed Electrostatic Precipitator with Superhydrophobic Surface (EPSS). For all aerosolization and sampling parameters we compared the ATP bioluminescence output per bacterium relative to that before aerosolization and sampling. In addition, we also determined the ATP reagent storage and preparation conditions that that do not affect the bioluminescence signal intensity. Our results show that aerosolization by a Collison nebulizer with a polycarbonate jar yields higher bioluminescence output per bacterium compared to the glass jar. Interestingly enough, the bioluminescence output by P. fluorescens increased substantially after its aerosolization compared to the fresh liquid suspension. For both test microorganisms, the bioluminescence intensity per bacterium after sampling was significantly lower than that before sampling suggesting negative effect of sampling stress on bioluminescence output. The decrease in bioluminescence intensity was more pronounces for longer sampling times and significantly and substantially depended on the sampling method. Among the investigated method, the EPSS was the least injurious for both microorganisms and sampling times. While the ATP-based bioluminescence offers a quick bioaerosol sample analysis method, this works demonstrates that the method output depends on bioaerosol generation and sampling methods, as well as reagent storage.

    更新日期:2019-11-01
  • Influence of secondary aspiration on human aspiration efficiency.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2014-09-01
    K R Anderson,T Renee Anthony

    Computational fluid dynamics (CFD) was used to evaluate the contribution of secondary aspiration to human aspiration efficiency estimates using a humanoid model with realistic facial features. This study applied coefficient of restitution (CoR) values for working-aged human facial skin to the facial regions on the humanoid CFD model. Aspiration efficiencies for particles ranging from 7 to 116 μm were estimated for bounce (allowing for secondary aspiration) and no-bounce (CoR=0) simulations. Fluid simulations used the standard k-epsilon turbulence model over a range of test conditions: three freestream velocities, two breathing modes (mouth and nose breathing, using constant inhalation), three breathing velocities, and five orientations relative to the oncoming wind. Laminar particle trajectory simulations were used to examine inhaled particle transport and estimate aspiration efficiencies. Aspiration efficiency for the realistic CoR simulations, for both mouth- and nose-breathing, decreased with increasing particle size, with aspiration around 50% for 116 μm particles. For the CoR=0 simulations, aspiration decreased more rapidly with increasing particle size and approached zero for 116 μm compared to realistic CoR models (differences ranged from 0% to 80% over the particle sizes and velocity conditions). Differences in aspiration efficiency were larger with increasing particle size (>52 μm) and increased with decreasing freestream velocity and decreasing breathing rate. Secondary aspiration was more important when the humanoid faced the wind, but these contributions to overall aspiration estimates decreased as the humanoid rotated through 90°. There were minimal differences in aspiration between uniform CoR values of 0.5, 0.8, 1.0 and realistic regionally-applied CoR values, indicating differences between mannequin surfaces and between mannequin and human skin will have negligible effect on aspiration for facing-the-wind orientation.

    更新日期:2019-11-01
  • Generating Charged Pharmaceutical Aerosols Intended to Improve Targeted Drug Delivery in Ventilated Infants.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2015-08-15
    Landon Holbrook,Michael Hindle,P Worth Longest

    The delivery of pharmaceutical aerosols to infants receiving mechanical ventilation is extremely challenging due to small diameter flow passages, low tidal volumes, and frequent exhalation of the aerosol. The use of small charged particles is proposed as a novel method to prevent deposition in ventilator components and foster deposition in the lower infant airways. The objective of this study was to compare the performance of multiple new devices for generating small charged particles that are expected to maximize respiratory drug delivery in ventilated infants. Criteria used to select a leading device included production of a charged aerosol with a mass median aerodynamic diameter (MMAD) ≤ approximately 1.8 μm; low device depositional loss of the aerosol (<20%); particle charge in the range of the Rayleigh limit/100; and high drug output with low performance variability. Proposed new devices were a wick electrospray (WES) system with accelerated cross-flow air; a condensational vapor (CV) system with a charged solution and strong field gradient; and a low flow - induction charger (LF-IC) designed to operate with a modified commercial mesh nebulizer. Based on infant ventilation conditions, flow rates through the devices were in a range of 2-5 L/min and the devices were assessed in terms of depositional drug loss and emitted drug mass; droplet size distribution (DSD) using a Mini-MOUDI; and DSD and net charge with a modified ELPI. Considering the WES, primary limitations were (i) low and variable aerosol production rates and (ii) high device depositional losses. The CV device produced a high quality aerosol with a MMAD of 0.14 μm and a drug delivery rate of 25 μg/min. However, the device was excluded because it failed to produce a charged aerosol. In contrast, the LF-IC produced a 1.6 μm aerosol with high net charge, low device depositional loss (<15% based on recovery), and low variability. In the ELPI size fraction bin nearest the MMAD, the LF-IC produced >100 elementary charges per particle, which was an order of magnitude increase compared to the case of zero charging voltage. In conclusion, the LF-IC was selected as a leading system that is expected to improve aerosol delivery efficiency in ventilated infants through the use of small charged particles.

    更新日期:2019-11-01
  • Evaluation of particle resuspension in young children's breathing zone using stationary and robotic (PIPER) aerosol samplers.
    J. Aerosol Sci. (IF 2.24) Pub Date : 2015-05-16
    Jessica A Sagona,Stuart L Shalat,Zuocheng Wang,Maya Ramagopal,Kathleen Black,Marta Hernandez,Gediminas Mainelis

    Development of asthma in young children may be associated with high exposure to particulate matter (PM). However, typical stationary samplers may not represent the personal exposure of children ages 3 and younger since they may not detect particles resuspended from the floor as children play, thus reducing our ability to correlate exposure and disease etiology. To address this, an autonomous robot, the Pretoddler Inhalable Particulate Environmental Robotic (PIPER) sampler, was developed to simulate the movements of children as they play on the floor. PIPER and a stationary sampler took simultaneous measurements of particle number concentration in six size channels using an optical particle counter and inhalable PM on filters in 65 homes in New Jersey, USA. To study particle resuspension, for each sampler we calculated the ratio of particle concentration measured while PIPER was moving to the average concentration of particles measured during a reference period when PIPER remained still. For all investigated particle sizes, higher particle resuspension was observed by PIPER compared to the stationary sampler. In 71% of carpeted homes a more significant (at the α = 0.05 level) resuspension of particles larger than 2.5 μm was observed by PIPER compared to the stationary sampler. Typically, particles larger than 2.5 μm were resuspended more efficiently than smaller particles, over both carpeted and bare floors. Additionally, in carpeted homes estimations of PM10 mass from the particle number concentrations measured on PIPER while it was moving were on average a factor of 1.54 higher compared to reference period when PIPER was not moving. For comparison, the stationary sampler measured an increase of PM2.5 mass by a factor of only 1.08 when PIPER was moving compared to a reference period. This demonstrates that PIPER is able to resuspend particles through movement, and provide a better characterization of the resuspended particles than stationary samplers. Accurate measurement of resuspended PM will improve estimates of children's total PM exposure.

    更新日期:2019-11-01
  • Numerical modeling of thermophoretic deposition on cylinder liner of a diesel engine using a sectional soot model
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-10-04
    Pavan Prakash Duvvuri, Rajesh Kumar Shrivastava, Sujith Sukumaran, Sheshadri Sreedhara

    Soot deposition on combustion chamber walls of a diesel engine is one of the key concerns among diesel engine manufacturers as it affects the durability and wear of the power cylinder components. The deposition of soot on the liner also gets scraped to the crank case and leads to soot in the lubrication oil. In this work, a modeling framework is presented to estimate the deposition of soot on the liner walls. Three-dimensional computational fluid dynamic combustion simulations are performed at two operating loads for a direct injection heavy duty diesel engine. A sectional soot model coupled with gas phase chemical kinetics is used to model soot in the combustion chamber. The combustion and soot models are validated by comparing in-cylinder pressure, heat release rate and soot mass from simulations with the experimental data. A thermophoretic soot deposition model is presented which transports soot from combustion to the liner walls. Detailed in-cylinder soot mass fraction contours are used to explain the deposition phenomenon. The deposition of soot on the liner is qualitatively compared to measured soot in the lubrication oil and a good agreement is observed. The proposed modeling framework shall be helpful for optimizing combustion systems to reduce degradation of lubrication oil.

    更新日期:2019-10-23
  • Characterization and source apportionment of black carbon aerosol in the Nanjing Jiangbei New Area based on two years of measurements from Aethalometer
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-09-26
    Sihan Xiao, Xingna Yu, Bin Zhu, K. Raghavendra Kumar, Mei Li, Lei Li

    Black carbon (BC) aerosols were measured using a seven channel Aethalometer at a suburban site of Nanjing, East China from January 2015 to December 2016 to study its temporal variations and quantify the magnitude of BC from fossil fuel (BCff) and biomass burning (BCbb) sources. The mean BC mass concentration was observed to be 2200 ± 1309 ng/m3 at the sampling site during the entire observation period, with the highest (lowest) concentrations found in the winter (summer and spring). A distinct diurnal variations in BC revealed with two maximum peaks occurred between 06:00 and 09:00 local time (LT) and 19:00 and 22:00 LT in all four seasons, was correlated with source emissions, meteorology, and dynamics of the atmospheric boundary layer. A significant seasonality was observed in the absorption Ångström exponent (α) with higher in spring and winter seasons, and lower during the summer. Further, it is evident that the contribution of BCff (BCff%) dominated during the observation period with the mean contributions of BCff % and BCbb% to the BC were found to be ~81% and 19%, respectively. Similar to α, BCbb% also exhibited high fractions in spring and winter suggests an enhanced contribution from biomass burning sources, and a low in summer. The results from both the potential source contribution function (PSCF) and concentration weighted trajectory (CWT) models indicated that the air masses originating from the northern Zhejiang and Anhui provinces were the potential source areas responsible for the high BC concentrations attributed from agricultural waste burning in Nanjing.

    更新日期:2019-10-23
  • An improved model for prediction of the cone-jet formation in electrospray with the effect of space charge
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-09-30
    Zhengwei Jiang, Yunhua Gan, Yanling Shi

    The presence of space charge can cause a non-negligible effect in some electrospray applications, which, however, was ignored in previous numerical studies. In the present study, the formation of the cone-jet in the electrospray process is investigated with considering the space charge effects. The governing equations of fluid flow and electrostatics are coupled in the numerical method. The charge transport equation is implemented with no simplification and the volume of fraction (VOF) method is employed to track the liquid-gas interface. An improved model of considering the effect of charged droplet emitted from the tip of cone-jet on the external electric field is proposed. By considering the space charge effects, the improved model can achieve better accuracy in predicting the shape of the cone-jet by reducing the mean relative error from 12.5% to 4.2%. The flow field in the cone-jet is obtained and the vortices are found to play an important role in the cone-jet formation. In terms of the current produced by the cone-jet, the prediction error is reduced from 19 %-39% to 10 %-16% by considering the space charge. Further validation is conducted by comparing the simulated results with the prediction of the scaling laws. It was found that the prediction of the improved model fits better with the scaling laws based on both the analytical and experimental results. The new model can provide more reliable and detailed information for the simulation of other processes in the electrospray, i.e., the jet breakup and droplets motion.

    更新日期:2019-10-23
  • Droplet detachment behavior from a rough hydrophilic surface
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-10-14
    C.T. Wang, W.T. Leung, J.C. Xu, S.C. Fu, Christopher Y.H. Chao

    Understanding of the droplet detachment behavior from rough hydrophilic surfaces is important in many biological and industrial applications such as biomedicine, surface coating, and pathogen-laden aerosol resuspension. Due to the partial detachment of the droplet on hydrophilic surfaces, leaving behind some droplet residues, the adhesion behavior is extremely complicated. Here we reveal a new adhesion mechanism between a droplet and a rough hydrophilic surface. The adhesion behavior is controlled by a liquid film stuck in the surface microstructure. We establish a model to describe the contributions of liquid film and naked solid peaks, to the work of adhesion and verify the model experimentally. We also find that the normal adhesion force is about 3.35 ± 0.25 times of the lateral adhesion force for different surface roughness, meaning that the separation direction is an important factor affecting adhesion due to the different separation mechanisms. The results of this work shed new insights on the understanding of droplet detachment and adhesion to a rough surface.

    更新日期:2019-10-23
  • Acoustically enhanced evaporation of a polydisperse stream of micro water droplets
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-10-09
    Ata Meshkinzar, Ahmed M. Al-Jumaily

    This work investigates the effect of focused acoustic field on a stream of polydisperse micro water droplets generated by a nebulizer. The acoustic field is induced by a customized axially stepped-thickness piezoelectric circular cylindrical transducer. Exposure of the droplets to the acoustic field while passing through the transducer improves the relative movement between the air and droplets, which results in an enhanced heat transfer and facilitates evaporation. Larger droplets in the stream are affected more than small ones by the acoustic field. A noticeable reduction in the size of 90% of droplets has been observed. This improves and narrows the droplet size distribution in the stream, which is of practical importance for some drug delivery applications or humidification in lung supportive devices.

    更新日期:2019-10-23
  • Local experimental methodology for the study of microparticles resuspension in ventilated duct during fan acceleration
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-10-22
    Félicie Theron, Djihad Debba, Laurence Le Coq

    The purpose of this study is to develop an experimental methodology with relevant space and time resolutions to track the velocity properties responsible for the resuspension of microparticles during the acceleration stage of a fan start. Microparticles release is investigated over a time period of several seconds, i.e. at short time. This methodology involves velocity signal measurements thanks to Hot Wire Anemometry, and an optical counting method to build resuspension kinetics curves. During the fan acceleration the velocity evolution is characterized by two stages: a first increase without fluctuations, and then the acceleration with fluctuations. The same behavior is observed whatever the distance to the wall at which velocity is considered. The resuspension phenomenon seems to be initiated by a threshold turbulent kinetic energy, i.e. by turbulent events powerful enough to release microparticles having the lowest adhesion forces. For the studied particles properties/wall properties/aeraulic conditions, a significant fraction of particles remains on the duct wall at the end of experiments, despite the fact that the remaining fraction is stabilized. This may reveal that the highest energy levels of flow events seen by microparticles were not powerful enough to release particles having the highest adhesion forces.

    更新日期:2019-10-23
  • An optimized evaluation strategy for a comprehensive morphological soot nanoparticle aggregate characterization by electron microscopy
    J. Aerosol Sci. (IF 2.24) Pub Date : 2019-10-18
    Michael Altenhoff, Simon Aßmann, Christian Teige, Franz J.T. Huber, Stefan Will
    更新日期:2019-10-23
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