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Journal of Aerosol Science
Pergamon Press
Journal of Aerosol Science

Pergamon Press

0021-8502

Journal of Aerosol Science/Journal Journal of Aerosol ScienceSCIISTPEI
正式出版
收录年代

    Silicon nanocluster anion-argon cation recombination via hybrid continuum-molecular dynamics calculations

    Tamadate, TomoyaHogan, Christopher J. Jr Jr
    14页
    查看更多>>摘要：Prediction of the charge distribution on particles in an aerosol is critical not only in electrical mobility based characterization methods, but also in understanding the role that charging plays in particle growth in gas phase synthesis reactors. The latter is particularly important in non-thermal plasma synthesis reactors, wherein nanoclusters form and grow from vapor phase precursors in a high electron and high ion density environment. In plasmas, because free electrons are much less massive and much more mobile than positive gas ions, nanocluster charge distributions are biased negative. However, neutral or even positively charged nanoclusters may exist, depending on the rate of nanocluster-gas ion recombination, and nanocluster-nanocluster collisions may greatly contribute to nanocluster growth if not Coulombically suppressed. To better understand the charge distribution on nanoclusters in non-thermal plasma synthesis systems, we applied a recently developed collision rate calculation method, i.e. the continuum-molecular dynamics (C-MD) method, to examine recombination of Si-n(z) nanoclusters (n = 47, 91, 266, & 494, z = - 1, & - 2) and Ar+ cations at 300 K and pressures from 10(3.5) - 10(6) Pa, in argon neutral gas. With collision rate coefficients from the C-MD approach, nanocluster steady-state charge distributions were calculated. C-MD determined recombination rate coefficients are found to be higher than those from the traditionally-used limiting sphere theory approach of Fuchs outside of the continuum limit, leading to charge distributions which, although biased towards negative charge levels, are less biased than predicted by the traditional limiting sphere method, with differences particularly noticeable at lower pressures. Application of C-MD recombination coefficients in steady-state charge distribution calculations shows that the fraction of positively charged nanoclusters in a non-thermal plasma would be negligibly small; however, there is an appreciable fraction of neutral nanoclusters, and hence nanocluster-nanocluster collisions cannot be neglected in modeling particle growth in plasma reactors.
      原文链接:
    • NSTL
    • Elsevier

    Passive bioaerosol samplers: A complementary tool for bioaerosol research. A review

    Manibusan, SydoniaMainelis, Gediminas
    16页
    查看更多>>摘要：Bioaerosols consist of airborne particles of biological origin. They play an important role in our environment and may cause negative health effects. The presence of biological aerosol is typically determined using active samplers. While passive bioaerosol samplers are used much less frequently in bioaerosol investigations, they offer certain advantages, such as simple design, low cost, and long sampling duration. This review discusses different types of passive bioaerosol samplers, including their collection mechanisms, advantages and disadvantages, applicability in different sampling environments, and available sample elution and analysis methods. Most passive samplers are based on gravitational settling and electrostatic capture mechanism or their combination. We discuss the agar settle plate, dustfall collector, Personal Aeroallergen Sampler (PAAS), and settling filters among the gravity-based samplers. The described electrostatics-based samplers include electrostatic dust cloths (EDC) and Rutgers Electrostatic Passive Sampler (REPS). In addition, the review also discusses passive opportunity samplers using preexisting airflow, such as filters in HVAC systems. Overall, passive bioaerosol sampling technologies are inexpensive, easy to operate, and can continuously sample for days and even weeks which is not easily accomplished by active sampling devices. Although passive sampling devices are usually treated as qualitative tools, they still provide information about bioaerosol presence and diversity, especially over longer time scales. Overall, this review suggests that the use of passive bioaemsol samplers alongside active collection devices can aid researchers in developing a more comprehensive understanding of biological presence and dynamics, especially over extended time scales and multiple locations.
      原文链接:
    • NSTL
    • Elsevier

    Performance characteristics of a small scale cyclone separator operated in different flow regimes

    Misiulia, DzmitryLiden, GoranAntonyuk, Sergiy
    21页
    查看更多>>摘要：The flow pattern, cyclone pressure drop and particle penetration through a sampling cyclone have been studied at a wide range of flow rate 0.22-7.54 LPM using the LES simulations that have been validated based on experimental penetration data. The cyclone performance has been described by three dimensionless characteristics, the Euler number Eu-out(stat) , cut-size psi(50) and slope of the transformed penetration curve ?1. Three main flow regimes and four sub-regimes have been revealed. The effects of the flow rate (Reynolds number) on the dimensionless cyclone performance characteristics have been described and a one-term power series model has been proposed. Additionally, the effect of the aspiration efficiency on the cyclone cut-size has been determined.
      原文链接:
    • NSTL
    • Elsevier

    Deformation and film formation mechanisms during high velocity impact of silicon carbide nanoparticles

    Davies, Derek W.Moyers, Aidan H.Gammage, Michael D.Keto, John W....
    18页
    查看更多>>摘要：Molecular dynamics simulations were conducted to study the factors that affect deformation behavior that occurs during high-speed impact of SiC nanoparticles onto flat substrates. For these simulations, a 6 nm particle was impacted onto a (110)-oriented SiC substrate and the particle impact velocity (3000-4000 m/s), particle orientation, and impact angle (0 degrees -75 degrees) were systematically varied. A broad range of impact behaviors were observed and categorized from elastic with no particle sticking to plastic with significant particle deformation and sticking. High impact velocities and near normal impact angles were found to enhance particle sticking. Particle orientation also had an effect. For some impact conditions, disordering of the lattice within the particle was observed and quantified. Particle impacts that resulted in the greatest degree of amorphization also exhibited significant deformation. This suggests that amorphization followed by viscous flow in the disordered region of the particle is the primary deformation mechanism responsible for particle sticking.
      原文链接:
    • NSTL
    • Elsevier

    A new coupling setup of DMA, CPC and sp-ICP-MS with increased versatility

    Bierwirth, MalteOlszok, VinzentWollmann, AnnettWeber, Alfred P....
    11页
    查看更多>>摘要：Accurate mass measurements of aerosol nanoparticles are inherently challenging. Beyond pure mass determination, such as can be realized using centrifugal particle mass analysis, aerosol mass spectrometry also enables material-specific analysis. In this work, the hyphenation of an inductively coupled plasma mass spectrometer working in single particle mode (sp-ICP-MS) with a scanning mobility particle sizer (SMPS) is presented. The coupling of the instruments is described, with special attention to the position of the gas exchange device, which allows flexible interconnection of DMA and ICP-MS while maintaining the full classification range of the DMA. The mass calibration of the ICP-MS signal and the limits in terms of particle concentration were studied on spherical gold nanoparticles. As an application example, the structure of gold nanoparticle agglomerates was characterized as a function of a preceding temperature treatment. The fractal dimension and the effective density of the agglomerates is directly determined after sintering at various temperatures. In addition, a new approach to derive the primary particle diameter from the measurement of agglomerate mass is outlined. Finally, the possibility of analyzing the particle charge is shown in perspective.
      原文链接:
    • NSTL
    • Elsevier

    Retrieval of aerosol properties from in situ, multi-angle light scattering measurements using invertible neural networks

    Boiger, RomanaModini, Rob L.Moallemi, AlirezaDegen, David...
    20页
    查看更多>>摘要：Atmospheric aerosols have a major influence on the earth's climate and public health. Hence, studying their properties and recovering them from light scattering measurements is of great importance. State of the art retrieval methods such as pre-computed look-up tables and iterative, physics-based algorithms can suffer from either accuracy or speed limitations. These limitations are becoming increasingly restrictive as instrumentation technology advances and measurement complexity increases. Machine learning algorithms offer new opportunities to overcome these problems, by being quick and precise. In this work we present a method, using invertible neural networks to retrieve aerosol properties from in situ light scattering measurements. In addition, the algorithm is capable of simulating the forward direction, from aerosol properties to measurement data. The applicability and performance of the algorithm are demonstrated with simulated measurement data, mimicking in situ laboratory and field measurements. With a retrieval time in the millisecond range and a weighted mean absolute percentage error of less than 1.5%, the algorithm turned out to be fast and accurate. By introducing Gaussian noise to the data, we further demonstrate that the method is robust with respect to measurement errors. In addition, realistic case studies are performed to demonstrate that the algorithm performs well even with missing measurement data.
      原文链接:
    • NSTL
    • Elsevier

    Mobility analysis of nanocluster formation and growth from titanium tetraisopropoxide in a flow tube reactor

    Qiao, YuechenLi, LiChen, JustinYang, Suo...
    13页
    查看更多>>摘要：In an effort to understand the earliest stages of nanocluster growth in gas phase synthesis systems, we apply a flow tube reactor with a differential mobility analyzer-Faraday cage electrometer system to examine nanocluster formation and growth in the sub-3.0 nm mobility diameter range from the decomposition of titanium tetra-isopropoxide (TTIP) in air. Measured mobility distributions are inverted accounting for the DMA transfer function, tubing losses, and the charging efficiency, estimated from a non-steady state charge model within a bipolar ion source. Measurements reveal two types of species in spectra. First, we detect discrete (narrow) peaks falling in the 0.5 nm-1.5 nm size range which appear at different locations for positive and negative measurement modes. Second, we observe a larger, broadly distributed peak, which is similar in intensity for both positive and negative modes after data inversion, and which increases in intensity (concentration) and peak diameter with increasing precursor flow rate, increasing reactor temperature, and increasing residence time. We conclude that the latter broad peak arises from growing nanoclusters in the reactor. The narrower, sub 1.5 nm peaks, are most likely attributable to specific reactive intermediates from the decomposition of TTIP. We find that increasing TTIP concentration, reactor temperature, or increasing residence time, which furthers the extent of nanocluster formation, leads to the depletion of the sub 1.5 nm ions. Because of the large step size in diameter between neighboring sub 1.5 nm peaks, we also find it is unlikely that these peaks arise from small TiO2 clusters. Therefore, our measurements suggest that nanocluster growth from TTIP is facilitated by surface growth of reactive intermediates from TTIP decomposition, with reactive intermediates detectable via mobility analysis. Furthermore, while nanocluster formation and growth is clearly detected, measurements do not make clear that the nanoclusters are fully oxidized TiO2 nanoclusters for the synthesis temperature range examined.
      原文链接:
    • NSTL
    • Elsevier

    An integrated electrical condensation particle counter for compact and low-cost ultrafine particle measurement system

    Jeon, Jae-WanYoo, Seong-JaeKim, Yong-Jun
    13页
    查看更多>>摘要：In this study, we developed a compact and low-cost measurement system that can measure the real-time number concentration of airborne ultrafine particles (UFPs, particles smaller than 100 nm). Our system is based on the condensation nucleation method; however, it counts particles based on their electrostatic properties (i.e., dielectric constant) to overcome the limitations of complex optical systems that have traditionally been employed. The new system consists of two components: a microfluidic particle growth channel to grow UFPs into micron-sized water droplets and a capacitive particle counter to count the grown droplets. To effectively reduce the size and cost of the system, each system was fabricated into a single module using a semiconductor manufacturing process prior to integration. Super-hydrophilic micropillar wicks were monolithically integrated with Printed Circuit Board substrate channels to use water as the condensing working fluid. A glass substrate interdigitated electrode chip with a 3 mu m gap was fabricated and placed on the impaction plate of an inertial impactor to be used as a sensor. Numerical calculations were performed to verify the dimensions of the channel required for efficient supersaturated vapor generation. Quantitative experiments using NaCl, (NH4)(2)SO4, and Ag2O UFPs showed that our system could grow particles larger than 50 nm into micron-sized droplets and count up to 10,300 N cm(-3) particles with linear electrostatic properties.
      原文链接:
    • NSTL
    • Elsevier

    A collision-dominated regime in electrodynamic particulate suspension

    Ling, H.Higuera, F. J.
    13页
    查看更多>>摘要：Electrodynamic particulate suspension is a technique to generate suspensions of electrically conducting particles by overcoming their weight with the electric force that acts on the particles when they are enclosed in the gap between two horizontal electrodes to which a high voltage is applied. The particles move then up and down in the gap, colliding with the electrodes and with other particles. A collision-dominated regime is analyzed in which the time between interparticle collisions is short compared with the time it takes for a particle to cross the gap. Conservation equations for the number and charge densities of particles in the gap are derived neglecting the inertia of the particles. These equations are coupled with a Poisson equation for the electric potential and with mass and momentum conservation equations for the gas in the gap, which is set in motion by the drag of the particles. In agreement with experimental results (Shoshin and Dreizin, 2002), solutions of this problem display a transition between stationary suspensions and non-stationary suspensions characterized by the continuous generation of electrohydrodynamic plumes at the lower electrode. The transition occurs when the number of suspended particles per unit electrode area in the stationary state becomes larger than a certain value.
      原文链接:
    • NSTL
    • Elsevier

    Infection control measures for public transportation derived from the flow dynamics of obstructed cough jet

    Chao, Christopher Y. H.Fu, S. C.Wang, C. T.Xu, J. C....
    13页
    查看更多>>摘要：During the COVID-19 pandemic, WHO and CDC suggest people stay 1 m and 1.8 m away from others, respectively. Keeping social distance can avoid close contact and mitigate infection spread. Many researchers suspect that suggested distances are not enough because aerosols can spread up to 7-8 m away. Despite the debate on social distance, these social distances rely on unobstructed respiratory activities such as coughing and sneezing. Differently, in this work, we focused on the most common but less studied aerosol spread from an obstructed cough. The flow dynamics of a cough jet blocked by the backrest and gasper jet in a cabin environment was characterized by the particle image velocimetry (PIV) technique. It was proved that the backrest and the gasper jet can prevent the front passenger from droplet spray in public transportation where maintaining social distance was difficult. A model was developed to describe the cough jet trajectory due to the gasper jet, which matched well with PIV results. It was found that buoyancy and inside droplets almost do not affect the short-range cough jet trajectory. Infection control measures were suggested for public transportation, including using backrest/gasper jet, installing localized exhaust, and surface cleaning of the backrest.
      原文链接:
    • NSTL
    • Elsevier