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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
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    Towards a concentration closure of sub-6 nm aerosol particles and sub-3 nm atmospheric clusters

    Jiang, JingkunKerminen, Veli-MattiKulmala, MarkkuStolzenburg, Dominik...
    11页
    查看更多>>摘要：Atmospheric clusters play a key role in atmospheric new particle formation and they are a sensitive indicator for atmospheric chemistry. Both the formation and loss of atmospheric clusters include a complex set of interlinked physical and chemical processes, and therefore their dynamics is highly non-linear. Here we derive a set of simple equations to estimate the atmospheric cluster concentrations in size ranges of 1.5-2 nm and 2-3 nm as well as 3-6 nm aerosol particles. We compared the estimated concentrations with measured ones both in a boreal forest site (the SMEAR II station in Hyytia center dot la center dot, Finland) and in an urban site (the AHL/BUCT station in Beijing, China). We made this comparison first for 3-6 nm particles, since in this size range observations are more reliable than at smaller sizes, and then repeated it for the 2-3 nm size range. Finally, we estimated cluster concentrations in the 1.5-2 nm size range. Our main finding is that the present observations are able to detect a major fraction of existing atmospheric clusters.
      原文链接:
    • NSTL
    • Elsevier

    Novel inertial impactor for nanoparticle classification without particle loading effect

    Le, Thi-CucLin, Chun-HsuanGong, Wen-ChengZdimal, Vladimir...
    14页
    查看更多>>摘要：Particle size classifiers are widely used to separate particles at a certain aerodynamic diameter below which particles are used for various purposes. However, it is hard for current available classifiers to achieve nanoparticle classification at high particle mass loading conditions in addition to the cost of high pressure drop. In this study, a nanoparticle inertial classifier (NIC) was developed to classify nanoparticles without particle loading effect for the long term. The NIC operated at a 3 L/min flow rate consists of a micro-orifice plate with 163 nozzles and a wetted glass fiber filter substrate through which water is injected upward to wash off deposited particles continuously. This study is the first to achieve a 100 nm cutoff aerodynamic diameter with such a low pressure drop of 8.3 kPa for inertial classification. The NIC showed good number-based and mass-based classification performance for NaCl particles with a narrow nanoparticle size distribution. The NIC also performed well for generating stable nano-TiO2 particles with different feeding mass concentrations up to 92.18 mg/m(3) during a 60-min operation. The current 3 L/min NIC thus can serve as a nanoparticle classifier with high loading mass concentration for future applications such as nanopowder classification or inhalation toxicity testing.
      原文链接:
    • NSTL
    • Elsevier

    Online shape and density measurement of single aerosol particles

    Wang, ShurongZhou, KailiLu, XiaohuiChen, Hong...
    11页
    查看更多>>摘要：Aerosols play crucial roles in affecting air quality, climate and human health. Particle morphology and density would provide critical information on the chemical composition, mixing state and aging process of particles. Many investigations used dynamic shape factor (chi) to quantify particle shape. However, the measurement for chi often requires the knowledge of particle density, which is usually not readily available for atmospheric aerosols. Besides, chi is not a pure geometric descriptor, as it is also dependent on Knudsen number (Kn). Here, a method, consisting of an aerodynamic aerosol classifier (AAC, aerodynamic particle diameter, Da, measurement), a differential mobility analyzer (DMA, electrical mobility particle diameter, Dm, measurement) and a single particle aerosol mass spectrometer (SPAMS, vacuum aerodynamic particle diameter, Dva, measurement), was developed to investigate two geometric descriptors that are solely dependent on particle geometry: the orientationally averaged projected area (AP) and the hydrodynamic radius (RH). The shape indicator, S, was defined as the square root of the ratio AP/pi R2H. To test the performance of the AAC-DMA-SPAMS system, the S and chi of 9 types of laboratory-generated particles with known density were measured with this system, and the quantitative relationship between chi (1<chi <1.05) and S (1<S<1.5) was established at room temperature (T approximate to 300K) and ambient condition. Finally, this method was applied to investigate the S of ambient aerosols in an urban area. A significant fraction of near-spherical aerosols was observed. Thus, their densities can be calculated. Generally, the AAC-DMA-SPAMS system can provide shape, density and the mass spectral information of ambient particle, which can help elucidate their mixing state and aging processes.
      原文链接:
    • NSTL
    • Elsevier

    Particle emissions from mobile sources: Discussion of ultrafine particle emissions and definition

    Giannelli, RobertKittelson, DavidKhalek, ImadMcDonald, Joseph...
    31页
    查看更多>>摘要：There is no universally agreed upon definition for ultrafine particles (UFP). Commonly used definitions for UFP are either particle number below 100 nm or total particle number, but without an agreed upon lower cut point. For example, a lower cut point of 3 nm compared to 10 nm could result in a substantially higher count. Another definition for UFP is total particle mass but without a commonly agreed upon aerodynamic diameter upper cut point, e.g., below 100 nm, 200 nm, 300 nm, etc. Yet another definition is lung deposited surface area weighted by lung deposition fraction, found mainly in the particle mobility diameter range from 20 to 400 nm. It is clear from these definitions that there are inconsistencies in the way UFP is used and defined in the literature. Sometimes these metrics are well correlated, sometimes not. In this paper we suggest three exposure metrics: UFP-N, UFP-M, and UFP-S, that we believe will add clarity. These metrics represent total number, mass, and surface area below 500 nm, respectively. For surface area and mass, the 500 nm cut point can be either aerodynamic or mobility diameter depending upon measurement methodology. For all metrics, this cut point captures nearly all of the primary particle emissions from mobile sources. Furthermore, UFP-N would include a lower cut point of 3-6 nm and would not require an upper size cut point because there is very little particle number above 500 nm or even above 100 nm. Thus, our definition of UFP-N is consistent with the current definition of ultrafine number except for, importantly, the specification of a lower cut point. These exposure metrics can help facilitate consistency in the characterization of both short- and long-term UFP ambient exposures and associated health effects in epidemiological studies.
      原文链接:
    • NSTL
    • Elsevier

    A molecular dynamics study of collisional heat transfer to nanoclusters in the gas phase

    Yang, HuanSong, GuanyuHogan, Christopher J., Jr.
    13页
    查看更多>>摘要：Nanoclusters in the gas phase grow by condensation and coagulation, which heat up nanoclusters, creating thermal non-equilibrium with the surrounding gas. The extent of non-equilibrium for nanoclusters is dependent upon the rate of heating relative to the rate of cooling brought about by nanocluster-gas molecule collisions, hence the latter process plays an important role in nano cluster energy evolution during growth. We apply molecular dynamics simulations to investigate heat transfer between metal nanoclusters and gas molecules relevant to high temperature aerosol systems. In analysis, we first define a thermal reemission coefficient (TRC), which is a correction factor for the portion of energy possessed by reemitted gas molecules after collision. The TRC differs from the thermal accommodation coefficient (TAC), which is a correction factor for the maximum possible energy transfer rate from nanoclusters to gas molecules based on the diffusive collision model. We find the TRC is insensitive to nanocluster size but is affected by the nano cluster to gas temperature ratio and the nanocluster to gas atomic mass ratio. Comparison to the traditionally-defined TAC shows that the TAC is insensitive to temperature, a phenomenon that has been widely indicated in literature but not quantitatively explained. We show how the temperature insensitivity of the TAC arises because of the manner in which TRCs vary with both nanocluster and gas temperature, i.e. the manner in which the reemitted gas molecule energy from a surface varies with the temperature of that surface relative to that of the gas. In addition, while calculations ultimately reveal temperature insensitive TACs and justify their continued use in modeling gas-phase heat transfer, we argue that the TRC is more appropriate to calculate a priori in analyzing simulations; it is physically more realistic to first introduce a correction factor solely for the energy of reemitted gas molecules after a collision (as TRCs) instead of a correction factor applying to both the reemission energy and the initial energy (as TACs), as the latter is exactly calculable and independent of nanocluster properties. In line with prior work, for monoatomic gases we find the TAC decreases as the nanocluster to gas atomic mass increases, approaching 0.08 for gold nanoclusters in helium.
      原文链接:
    • NSTL
    • Elsevier

    Particulate matter pollution in Hookah lounges in Palestine

    Martin, Randal S.Khader, Abdelhaleem
    9页
    查看更多>>摘要：Hookahs, or water pipes, are ornate glass bowl structures used to smoke tobacco products, often in private or public social settings. Hookah smoking is believed to have originated in ancient India in the 16th century; however, it has seen rapid global expansion over the last two decades. A number of studies using high-cost, regulatory or research grade instruments have found respirable particulate concentrations in hookah lounges up to several hundred micrograms per cubic meter. In the summer of 2018, a study was initiated examining the PM2.5 concentrations in several hookah lounges in Nablus and Tulkarm, Palestine (West Bank). However, rather than using the typical high-cost system, low-cost laser light scattering and detection systems were used. Observed PM2.5 concentrations ranged from 84 to 371 mu g/m(3), concentrations considered to be of notable health concerns in the indoor environment and well within the range of hookah-related particulate matter reported in the literature. Further, examination of the 10-min average temporal PM2.5 concentrations showed variable correlation with the number of active smokers and a seeming dependency on the type of building ventilation. The employed low-cost particulate systems proved capable of reliably quantifying PM2.5 levels in a variety of hookah lounges, as well as being able to characterize the temporal nature of the PM2.5 concentration changes. The results of this study suggest that these systems may be an economic and reliable alternative for particulate studies.
      原文链接:
    • NSTL
    • Elsevier

    Optimization of swirler type dry powder inhaler device design-Numerical investigation on the effect of dimple shape, inlet configuration and mouthpiece constriction

    Kim, Yun HwanLi, Darson DezhengYeoh, Guan HengAbbas, Ali...
    24页
    查看更多>>摘要：Dry powder inhalers (DPIs) are recognized as one of the most convenient drug delivery devices via the respiratory tract. However, there is a large variation in their dispersion efficiencies due to the cohesive nature of the inhalable pharmaceutical powders. This paper presents a thorough numerical investigation of the effect of various design modifications in swirler type DPI devices. One-way coupled Computational Fluid Dynamics-Discrete Phase Modeling simulations were implemented to evaluate the flow field and particle behaviour in DPIs under 60 L/min inhalation condition. The dispersion behaviour of entrained particles in relation to the particle-wall impactions was evaluated in six different in-house designed and one commercial DPI devices, with variations in dimple shape, inlet orientation, inlet numbers, and mouthpiece pipe constriction. We found that the shape of dimples varies the swirling capability of both fluid and particles and mouthpiece pipe constriction reduced the turbulence kinetic energy. Meanwhile, the axial velocity and impaction frequency are increased as the size of particles are increased. The constriction of mouthpiece pipe did not show significant improvement on the frequency of particle-wall impactions for particles smaller than 10 mu m, whilst higher impaction frequencies were observed for particles larger than 10 mu m. Overall, the sphere shape dimples with mouthpiece pipe constricted design is optimal in terms of device efficiency.
      原文链接:
    • NSTL
    • Elsevier

    Stochastic population balance methods for detailed modelling of flame-made aerosol particles

    Boje, AstridKraft, Markus
    47页
    查看更多>>摘要：Particle formation and growth by chemical reactions and physical processes has implications spanning properties of industrial chemicals, human health, and environmental impact. It has been the subject of scientific scrutiny for many years with incremental developments in understanding driven by both experimental and numerical characterisation. Of the developed numerical methods, this review paper will focus on Monte Carlo methods, which are best suited to simultaneous, extensive characterisation of both chemistry and particle geometry in organic and inorganic systems, with other population balance modelling strategies discussed to contextualise the stochastic approach. We outline the high-dimensional particle models used to resolve the typically fractal-like, complex aggregate structure of particles produced by flame synthesis, and describe key features, advancements and limitations of the stochastic numerical methods that can accommodate practically arbitrarily many internal particle coordinates. We summarise a decade of our work in this area, and show how this so-called detailed population balance modelling approach provides close agreement with experimental flame measurements under a range of conditions and enables study of industrially relevant systems. Challenges remain, for example in treating flow-chemistry-particle coupling, and these are discussed in the context of the existing simulation strategies and future directions.
      原文链接:
    • NSTL
    • Elsevier

    The standard operating procedure for Airmodus Particle Size Magnifier and nano-Condensation Nucleus Counter

    Jokinen, T.Lehtipalo, K.Ahonen, L. R.Baalbaki, R....
    20页
    查看更多>>摘要：Measurements of aerosol particles and clusters smaller than 3 nm in diameter are performed by many groups in order to detect recently formed or emitted nanoparticles and for studying the formation and early growth processes of aerosol particles. The Airmodus nano-Condensation Nucleus Counter (nCNC), consisting of a Particle Size Magnifier (PSM) and a Condensation Particle Counter (CPC) is a versatile tool to detect aerosol particles and clusters as small as ca. 1 nm in mobility diameter. It offers several different operation modes: fixed mode to measure the total particle number concentration with a fixed, but adjustable lower cut-off size and stepping and scanning modes for retrieving size-resolved information of ca. 1-4 nm particles. The size analysis is based on changing the supersaturation of the working fluid (diethylene glycol) inside the instrument, which changes the lowest detectable size. Here we present a standard operating procedure (SOP) for setting up, calibrating and operating the instrument for atmospheric field measurements. We will also present recommendations for data monitoring and analysis, and discuss some of the uncertainties related to the measurements. This procedure is the first step in harmonizing the use of the PSM/nCNC for atmospheric field measurements of sub-3 nm clusters and particles.
      原文链接:
    • NSTL
    • Elsevier

    An analytical solution for aerosol penetration in the slip flow regime

    Jia, FengHuang, WeiPui, David Y. H.Tsai, Chuen-Jinn...
    12页
    查看更多>>摘要：The classical theory for the diffusional loss of aerosol particles in a fully developed laminar flow through a circular tube derived by Gormley and Kennedy (1949) did not consider the slip-flow condition. However, the non-slip condition for the gas velocity boundary condition may not be appropriate for the gas flow in microgeometries such as microchannels and microtubes. This paper extends the work of Gormley and Kennedy (GK) to include the effect of slip-flow, which often occurs in the gas flow at low pressure or with a small characteristic length scale. In the present solution, the separation of variables was applied to solve the convection-diffusion equation, then confluent hypergeometric function was used to solve for the number concentration as a function of radial distance analytically. Eigenvalues were evaluated for Knudsen numbers ranging from 0.001 to 0.1. Finally, a simple power series correlation was developed to describe aerosol penetration in the slip flow regime as a function of the dimensionless deposition factor and Knudsen number (Kn). In the slip flow regime, the penetration decreases with increasing Kn. The correlation is reduced to GK's solution when Kn = 0. The present solution of aerosol penetration calculated at Kn = 0 shows good agreement with GK's solution and validates the applicable range of the approximate solution by Alonso et al. (2016).
      原文链接:
    • NSTL
    • Elsevier