Real-Time Characterization of the Composition of Individual Particles Emitted From Ultrafine Particle Concentrators

Particle concentrators are commonly used for controlling exposure levels to ambient ultrafine, fine, and coarse aerosols over a broad range of concentrations. For ultrafine aerosols, these concentrators require water condensation technology to grow and enrich these smaller sized particles (D _a < 100 nm). Because the chemistry of the particles is directly related to their toxicity, any changes induced by ultrafine concentrators on ambient particles need to be better characterized in order to fully understand the results obtained in health exposure studies. Using aerosol time-of-flight mass spectrometry (ATOFMS), the size-resolved chemistry was measured of concentrated ultrafine and accumulation mode (50–300 nm) particles from several particle concentrators with different designs. This is the first report detailing the size-resolved distributions of elemental carbon (EC) and organic carbon (OC) particles sampled from concentrators. Experimental measurements of the single particle mixing state of particles in concentrated versus non-concentrated ambient air show transformations of ultrafine EC particles occur as they become coated with organic carbon (OC) species during the concentration process. Based on relative ion intensities, concentrated ultrafine particles showed a 30% increase in the amount of OC on the EC particles for the same aerodynamic size. An increase in the number fraction of aromatic- and polycyclic aromatic hydrocarbon-containing particles was also observed in both the ultrafine and fine size modes. The most likely explanation for such changes is gas-to-particle partitioning of organic components (e.g., water-soluble organic compounds) from the high volume of air used in the concentrator into aqueous phase ultrafine and fine aqueous particles created during the particle enrichment process.     

Detailed Microphysical Modeling of the Formation of Organic and Sulfuric Acid Coatings on Aircraft Emitted Soot Particles in the Near Field

The development of a detailed microphysical model that describes the complex multicomponent interactions between organic vapors and soot particles emitted from aircraft gas turbine engines is presented. Our model formulation includes both soot surface activation by organic vapors and organic vapor condensation on the activated part of the soot surfaces. To enable this formulation, approaches to estimate chemical and physical properties of aerosols containing complex mixtures of sulfuric acid, water, and organic molecules were developed. Relevant distributions of a list of organic surrogates at the engine exit plane were used to represent complex organic emissions from aircraft engines. A parametric study was performed using this new formulation to understand the effects of ambient conditions, organic emissions levels, and mass accommodation coefficient values on the evolution of near field volatile particulate matter emissions from aircraft engines at ground level.

Copyright 2014 American Association for Aerosol Research     

A Thermophoretic Precipitator for the Representative Collection of Atmospheric Ultrafine Particles for Microscopic Analysis

In this article, the potential of a thermophoretic sampling device to derive quantitative particle size distributions and number concentrations of aerosols based on microscopic single particle analysis is explored. For that purpose a plate-to-plate thermophoretic precipitator to collect ultrafine atmospheric particles for TEM (transmission electron microscopy) analysis has been calibrated and characterized. The representativeness of the samples has been verified in a series of experiments. Results show that, for particles with diameters of 15 nm to 300 nm, the precipitator's collection efficiency is independent of size, shape, and composition of the particles. Hence, its samples accurately represent the original aerosol.

A numerical model of thermophoretic deposition within the device has been developed and tailored to the specifications of the precipitator. The model has been used to derive the particle number density and size distribution of several calibration aerosols using the TEM analysis of the samples taken with the thermophoretic precipitator as input parameters. The results agree very well with the on-line measurements of the calibration aerosols. This work demonstrates that our thermophoretic sampling device can be used to derive quantitative particle size distributions and number concentrations of ultrafine particles based on microscopic single particle analysis.     

Measurements of Morphology Changes of Fractal Soot Particles using Coating and Denuding Experiments: Implications for Optical Absorption and Atmospheric Lifetime

Mobility-selected fractal and non-fractal soot particles (mobility diameters d _m = 135 to 310 nm) were produced at three controlled fuel equivalence ratios (φ = 2.1, 3.5, and 4.5) by an ethylene/oxygen flame. Oleic acid (liquid) and anthracene (solid) coatings were alternately applied to the particles and removed. Simultaneous measurements with an Aerodyne aerosol mass spectrometer and a scanning mobility particle sizer yielded the particle mass, volume, density, composition, dynamic shape factor, fractal dimension, surface area, and the size and number of the primary spherules forming the fractal aggregate. For a given φ, the diameters of the primary spherules are approximately the same, independent of d _m (15 nm, 35 nm, and 55 nm for φ = 2.1, 3.5, and 4.5, respectively). As the coating thickness on a particle increases, the dynamic shape factor decreases but d _m remains constant until the particle reaches a spherical (for oleic acid) or non-fractal but irregular (for anthracene) shape. Under some conditions, liquid oleic acid coating causes the internal BC framework to rearrange into a more compact configuration. The surface area of fractal particles is up to 2.4 times greater than that of a sphere with the same d _m . Using the surface area determinations, the time for a fractal particle to obtain a monolayer of coating material is compared to that of spheres. If it is assumed that the fractal particle is a sphere with the same d _m as the fractal particle, the monolayer coating time is underestimated by a factor of up to 1.7.     

Laboratory Study of Simulated Atmospheric Transformations of Chromium in Ultrafine Combustion Aerosol Particles

While atmospheric particles can have adverse health effects, the reasons for this toxicity are largely unclear. One possible reason is that the particles can contain toxic metals such as chromium. Chromium exists in the environment in two major oxidation states: III, which is an essential nutrient, and VI, which is highly toxic and carcinogenic. Currently little is known about the speciation of chromium in airborne particles or how this speciation is altered by atmospheric reactions. To investigate the potential impacts of atmospheric aging on the speciation and toxicity of chromium-containing particles, we collected chromium and chromium-iron combustion ultrafine particles on Teflon filters and exposed the particles to a combination of light, ozone, water vapor, and, in some cases, basic or acidic conditions. After the aging process, the aged and not-aged samples were analyzed for Cr oxidation state using X-ray Absorption Near Edge Spectroscopy (XANES). We found that the aging process reduced Cr(VI) by as much as 20% in chromium particles that had high initial Cr(VI)/Cr(total) ratios. This reduction of Cr(VI) to Cr(III) appears to be due to reactions primarily with light and hydroperoxyl radical (HO ₂ ) in the chamber. Particles that had low initial Cr(VI)/Cr(total) ratios experienced no significant change in Cr oxidation states after aging. Compared to particles containing only Cr, the addition of Fe to the flame decreased the Cr(VI)/Cr(total) ratio in fresh Cr-Fe particles by ～60%. Aging of these Cr-Fe particles had no additional effects on the Cr(VI)/Cr(total) ratio.     

焦炉装煤逸出含尘烟气成分的监测与计算

本课题以6m焦炉为例,分析了装煤逸出烟尘的来源,计算了焦炉装煤逸出烟尘量,在检测装煤焦炉逸出烟尘主要成分浓度的基础上,计算了主要污染物的释放总量,并对计算结果进行了分析,可为工程治理提供有用的参考数据。     

Miniature Pipe Bundle Heat Exchanger for Thermophoretic Deposition of Ultrafine Soot Aerosol Particles at High Flow Velocities

The deposition of submicrometer soot aerosol particles in a miniature pipe bundle heat exchanger system has been investigated under conditions characteristic for combustion exhaust from diesel engines and oil or biomass burning processes. The system has been characterized for a wide range of aerosol inlet temperatures (390–510 K) and flow velocities (1–4 m s^?1), and particle deposition efficiencies up to 45% have been achieved over an effective deposition length of 27 cm. Thermophoresis was the dominant deposition mechanism, and its decoupling from isothermal deposition was consistent with the assumption of independently acting processes. The measured deposition efficiencies can be described by simple linear parameterizations based on an approximation formula for thermophoretic plate precipitators. The results of this study support the development of modified heat exchanger systems with enhanced capability for filterless removal of combustion aerosol particles.     

Sintering Effect on Material Properties of Electrochemical Reactors Used for Removal of Nitrogen Oxides and Soot Particles Emitted from Diesel Engines

In the present work, 12‐layered electrochemical reactors (comprising five cells) with a novel configuration including supporting layer lanthanum strontium manganate (LSM)‐yttria stabilised zirconia (YSZ), electrode layer LSM‐gadolinia‐doped cerium oxide (CGO) and electrolyte layer CGO were fabricated via the processes of slurry preparation, tape casting and lamination and sintering. The parameters of porosity, pore size, pore size distribution, shrinkage, flow rate of the sintered reactors and the electrical conductivities of the supporting layer and the electrode in the sintered reactors were characterised. The effect of sintering temperature on microstructures and properties of the sintered samples was discussed, and 1,250 °C was determined as the appropriate sintering temperature for reactor production based on the performance requirements for applications. Using the present ceramic processing route, porous, flat and crack‐free electrochemical reactors were successfully achieved. The produced electrochemical reactors have the potential application in the removal of NO_x and soot particles emitted from the diesel engines.     

超微粒子的合成及其应用

本文综述了超微粒子的合成方法和应用。着重叙述了超微粒子在催化、生物、医学、记录材料、传感材料等方面的应用。     

气溶胶用石墨/白碳黑超细复合粒子的制备及表征

通过对石墨/白碳黑复合粒子的制备及性能的分析测试研究,表明石墨复合粒子较纯石墨粉具有更好的分散性、更大的比表面积及孔容,更高的悬浮稳定性及红外吸收特性。     

Quantitative measurement of interdiffusion at polymer–polymer interfaces with TEM/EDS and EELS

Transmission electron microscopy and energy dispersive spectroscopy (TEM/EDS) were used to map the concentration profile at the interface of a poly(vinyl chloride) and poly(methyl methacrylate) bilayer. Thin sections in the order of 800 Å were cut using an ultramicrotome, examined with TEM, and the concentration profile was mapped with EDS. The intensity of fluorescene X-rays was adjusted for sample thickness variation by measuring the relative thickness across the interface with electron energy-loss spectroscopy (EELS). The interfacial thickness of the bilayer after 6 h at 120°C was 1.5 μm, whereas the interdiffusion coefficient was determined as 8.0 × 10^?14 cm²/s. © 1995 John Wiley & Sons, Inc.     

超细分级技术的现状与发展

对超继分级技术的现状与发展进行了综述，着重介绍了近几年发展起来的各种超细分级机构，工作原理及部分工作参数，并对超细粉分级的热点问题进行了展望。     

超微粒子的特性、制备和应用

对超微粒子的特性、制备和应用作了简明的介绍。特别对超微粒子制备工艺的选择作了比较细致的阐述。     

纳米复合Fe-SiO2粉体的制备和结构

采用非醇盐溶胶-凝胶工艺可获得Fe与Si摩尔比达4.5/1的均匀凝胶,发现可以通过控制SiO2的含量和热处理条件来控制相结构和晶粒尺寸,热处理过程中α-Fe相是由Fe3O4相还原而来,材料中有大量氧参与反应是工艺中采用了沉淀胶溶步骤的结果,最终制备了纳米复合Fe-SiO2粉体.     

Inertial Separation of Ultrafine Particles Using a Condensational Growth/Virtual Impaction System

ABSTRACT

A system for the separation of ultrafine particles (i.e., particles smaller than 0.1 μm) has been developed and evaluated. Ultrafine particles are first grown by means of supersaturation to a size that can be easily separated in a virtual impactor. Thus, inertial separation of ultrafine particles occurs without subjecting them to a high vacuum. The condensational growth/virtual impaction system has been evaluated using monodisperse 0.05 and 0.1 μm fluorescent PSL particles, as well as polydisperse ultrafine ammonium sulfate and potassium nitrate aerosols. The generated aerosols were first drawn over a pool of warm water (50°C) where they became saturated. Subsequently, the saturated aerosol was drawn through a cooling tube (8°C) where particles grew due to supersaturation to sizes in the range 1.0–4.0 μm. By placing a virtual impactor with a theoretical 50% cutpoint of 1.4 μm downstream of the condenser, ultrafine particles were separated from the majority (i.e., 90%) of the surrounding gas. The sampling flow rate of the virtual impactor was 8 L/min and its minor-to-total flow ratio was 0.1. For these operating conditions, the particle collection efficiency of the virtual impactor averaged to about 0.9 for particle concentrations in the range 7 × 10⁴-5 × 10⁵ particles/cm³. Particle losses through the system were found less than 5%. Increasing the particle concentration to levels in the range 106–107 particles/cm³ resulted in a decrease in the collection efficiency of the virtual impactor to about 50–70%, presumably due to the smaller final droplet size to which the ultrafine particles grew for the available supersaturation.     

Real-Time Observation of the Transformation of Ultrafine Atmospheric Particle Modes

An Engine Exhaust Particle Sizer was used on a mobile platform to measure ultrafine particle (5.6–560 nm) concentration profiles in streets and tunnels. Particle size distribution data along the lengths of the tunnels showed that number concentration profiles of < 30 nm particles were highly nonlinear. Conventional point measurement studies inside tunnels to determine, for instance, emission factors of ultrafine particles in this range are therefore location dependent and may not be representative. The particle concentration profiles obtained in this experiment allowed the study of the transformation of 10 nm particles to 50 nm particles. Outside of the tunnels and on heavily traveled highways, particles exhibited a dominant mode at 10 nm and a minor mode at 50 nm. Inside the tunnels, 10 nm particles gradually decreased after an abrupt increase, while 50 nm particles increased from entrance to exit. The 10 nm particles decreased at 2–4 times the rate of increase of the 50 nm particles, therefore, condensational growth of the 10 nm particles alone cannot explain the decrease. The estimated hetero-coagulation rate between 10 nm particles and particles > 30 nm inside the tunnel was substantially higher than that outside due to the increase in the concentration of particles > 30 nm. The hetero-coagulation process is proposed to play a key role in the transformation of particle modes in the tunnel. This study provides new insight on the transformation of ultrafine particle modes in vehicular plumes.     

超细硫酸钡颗粒的絮凝沉降研究

本文研究了影响超细硫酸钡沉降的各种因素 ,并对其进行了絮凝沉降实验。实验表明 ,无机絮凝剂和高分子絮凝剂均能起到加速粒子沉降目的 ;同时发现高分子絮凝剂的絮凝效果较好 ,其适宜用量为 0 3% ,搅拌时间为 8min ,其絮凝沉降速度可达未加絮凝剂的 8～ 9倍。并对其机理进行了初步的探讨     

超细硫酸沙丁胺醇药物颗粒的制备与表征

以沙丁胺醇和硫酸为反应物,在异丙醇溶液中采用反应结晶法制备超细硫酸沙丁胺醇颗粒。对影响产物粒度和产率的因素,如:硫酸浓度、反应温度、搅拌转速、反应时间等进行了系统研究。实验结果表明:当硫酸浓度为1.0mol.L-1、反应温度为15℃、搅拌转速为900r.min-1、反应时间为10min时,可以得到短轴为50~60nm、长径比为20~35且粒度分布较窄的针状硫酸沙丁胺醇颗粒。产品经IR、XRD等验证,符合中国、英国药典的要求,纯度大于98%。