Experimental and Numerical Study of Aerosol Coagulation by Gravitation

The behaviors of aerosols having particle diameters of 1–5 μm were studied experimentally and the results were compared with numerical calculations. For the experimental study, a specially designed coagulation cylinder was developed and the moment method was used in the numerical predictions. The experimental results were characterized by the size parameters including the geometric mean diameter (GMD), the geometric standard deviation (GSD) and the particle number concentration (N). Particle distributions in the cylinder were measured at certain time intervals. In a closed cylinder, the mechanism governing aerosol behavior appeared to be gravitational coagulation. Separately, the numerical calculations were carried out using the moment method. The experimental results and the numerical predictions were in reasonable agreement. It is believed that the present work represents the first experimental study on gravitational coagulation.     

激光在不同类型气溶胶中传输特性研究

激光在大气中的传输衰减特性是激光工程应用中需要考虑的一个重要问题.本文针对常用的1.06 μm和10.6μm激光,基于Mie散射理论计算了气溶胶粒子的单次散射参量;对于激光在气溶胶中多次散射传输衰减,建立了蒙特卡罗模拟计算模型,利用Matlab语言编制了相应的计算程序,计算分析了两种波长的激光分别在沙尘性、水溶性、海洋性和煤烟性四种不同类型气溶胶中透过率与传播距离、能见度的关系,并将蒙特卡罗方法和单次散射的计算结果进行了比较.结果表明,当能见度较低、气溶胶粒子反照率较高时,单次散射计算存在很大的误差,用蒙特卡罗方法更能揭示多重散射现象;煤烟性气溶胶对1.06 μm激光的传输衰减影响最大,沙尘性气溶胶对10.6 μm激光的传输衰减影响最大.     

Size distribution of sulfur species in fine and ultrafine aerosol particles using sulfur K-edge XANES

The sulfur species existing in different size aerosol particles were determined based on the `white line' energy shift and the features of post edge structure of sulfur K-edge XANES (X-ray Absorption Near Edge Structure). The results indicated that sulfates were dominant sulfur species in aerosol particles. However, small amount of reductive sulfur species were also found in the ultrafine aerosol particles(<0.1 μm). Sulfates in aerosols mostly exhibited as (NH₄)₂SO₄ and gypsum. Most (NH₄)₂SO₄ distributed in aerosol particles finer than 0.952 μm, while gypsum was the dominant sulfate in coarse aerosols.

     

Small angle X-ray scattering by spherical particles of Polystyrene and Polyvinyltoluene

The high intensity, high resolution multiple reflection diffractometer has been applied to make accurate measurements of the small angle X-ray scattering of eight different Dow Chemical latexes with stated diameters 2.051, 1.305, 0.814, 0.557, 0.365, 0.264, 0.126, and 0.088 μm. Using thin dry samples, the measured intensities of diffraction extrema with orders higher than the third were found to agree well with the simple Rayleigh-Gans theory which neglects multiple scattering as well as interparticle interference. Orders below the fourth showed a distinct effect of interparticle interference. This effect could be demonstrated to vanish when a liquid solution sample was used instead of a dry one. Scattering curves of thick dry samples had strongly decreased contrast between maxima and minima, an effect which is known to be due to multiple scattering. The following particle diameters were determined from the measured scattering curves: 2.102±0.013 μm, 1.313±0.008 μm, 0.823±0.004 μm, 0.552±0.002 μm, 0.352±0.002 μm, 0.254±0.002 μm, 0.119±0.001 μm and 0.078±0.001 μm. The discrepancies between these and the stated sizes are larger for the smaller particles. It is believed that the X-ray measurements are more accurate than the stated sizes which are based on measurements in the electron microscope. Therefore, as secondary standards, the diameter obtained from the X-ray measurements should be used.     

Optimization of highly nonlinear dispersion-flattened photonic crystal fiber for supercontinuum generation

A simple type of photonic crystal fiber (PCF) for supercontinuum generation is proposed for the first time. The proposed PCF is composed of a solid silica core and a cladding with square lattice uniform elliptical air holes, which offers not only a large nonlinear coefficient but also a high birefringence and low leakage losses. The PCF with nonlinear coefficient as large as 46 W 1 · km-1 at the wavelength of 1.55 μm and a total dispersion as low as ±2.5 ps · nm-1 · km-1 over an ultra-broad waveband range of the S-C-L band (wavelength from 1.46 μm to 1.625 μm) is optimized by adjusting its structure parameter, such as the lattice constant Λ , the air-filling fraction f , and the air-hole ellipticity η. The novel PCF with ultra-flattened dispersion, highly nonlinear coefficient, and nearly zero negative dispersion slope will offer a possibility of efficient super-continuum generation in telecommunication windows using a few ps pulses.     

Aerosol Charge Neutralization by a Radioactive Alpha Source

The performance of a Po-210 radioactive ionizer for aerosol charge neutralization and bipolar charging has been evaluated. Monodisperse neutral and singly charged aerosols have been passed through the ionizer and their approach to the steady-state Boltzmann charge measured by measuring the fraction of particles that are electrically charged. The result shows that an Nt of approximately 2.5 × 10⁵ cm^?3 s is needed for the development of a steady-state charge fraction equal to that given by the Boltzmann' s law where N is the ion concentration and t is the residence time of the aerosol in the neutralizer. In addition, the performance of the ionizer for particle charge neutralization in a vibrating-orifice aerosol generator has been evaluated and the result shows that the source is less effective for this application and the residual charge on the particles is considerably higher than that given by the Boltzmann's law.     

Regression approach to analyzing the informativity and interpretation of aerosol optical measurements

A regression approach is proposed for planning aerosol optical experiments and for estimating the potential accuracy of the derived microphysical parameters of atmospheric aerosols taking the features of the apparatus and the available a priori information into account. This method is used to evaluate the informativity of polarization spectronephelometer measurements with respect to the microphysical parameters of continental aerosols. The problem of choosing the most informative aerosol optical characteristics with respect to the mass concentrations of the PM _2.5 and PM ₁₀ respirable fractions is examined and regression equations are derived for determining these concentrations from lidar probe data at wavelengths of 0.355 and 1.064 μm, as well as from reference measurements at 0.37 and 0.98 μm. The theoretical results obtained here are compared with AERONET data.     

A sampler designed for nanoparticles and respirable particles with direct analysis feature

A sampler has been designed to collect particles in the nanometer and respirable sizes directly onto a membrane filter and transmission electron microscopy (TEM) grid. The novel design aspects of this sampler include the selection of the diameter of the inlet probe, geometry of the sampler, and the resulting air flow to the sampler. Together, they control the cutoff diameter, which was determined experimentally to be a mass median aerodynamic diameter (MMAD) of 3.8 μm. The maximum aerodynamic diameter entering the sampler is designed to be approximately 8 μm. Nanometer-sized particles are collected on both the filter and grid through diffusion, as confirmed by testing with aluminum oxide engineered nanoparticles collected on the filter which measured a count median diameter (CMD) of 500 nm and a geometric standard deviation (GSD) of 1.97. The primary particles and small agglomerates collected on the grid have a CMD of 100 nm and GSD of 2.3. This diffusion sampler collected close to, if not 100%, of the particles entering the sampler. The sampler is easily wearable for personal exposure and environmental sampling, operates at 0.3 L/min, and can collect particles in various settings at indoor and outdoor environments. Particles are analyzed directly by transmission electron microscope on the grid and by scanning electron microscope on the filter to assess the exposure through particle counts and elemental composition analysis.     

Aerosol generation and measurement of multi-wall carbon nanotubes

Mass production of some kinds of carbon nanotubes (CNT) is now imminent, but little is known about the risk associated with their exposure. It is important to assess the propensity of the CNT to release particles into air for its risk assessment. In this study, we conducted aerosolization of a multi-walled CNT (MWCNT) to assess several aerosol measuring instruments. A Palas RBG-1000 aerosol generator applied mechanical stress to the MWCNT by a rotating brush at feed rates ranging from 2 to 20 mm/h, which the MWCNT was fed to a two-component fluidized bed. The fluidized bed aerosol generator was used to disperse the MWCNT aerosol once more. We monitored the generated MWCNT aerosol concentrations based on number, area, and mass using a condensation particle counter and nanoparticle surface area monitor. Also we quantified carbon mass in MWCNT aerosol samples by a carbon monitor. The shape of aerosolized MWCNT fibers was observed by a scanning electron microscope (SEM). The MWCNT was well dispersed by our system. We found isolated MWCNT fibers in the aerosols by SEM and the count median lengths of MWCNT fibers were 4–6 μm. The MWCNT was quantified by the carbon monitor with a modified condition based on the NIOSH analytical manual. The MWCNT aerosol concentration (EC mass base) was 4 mg/m³ at 2 mm/h in this study.     

Determination of the X-pinch-based X-ray source size

It is shown that an X-ray source 0.5–2 μm in size for the spectral region above 3 keV can be implemented based on a compact pulse generator with an impedance of 0.13Ω using an X-pinch made of four molybdenum wires. The technique for determining the source sizes and the results of the experimental determination of the X-pinch emitting region sizes are presented. The parameters of the X-pinch consisting of wires of different diameters are optimized for this generator to fabricate an X-ray source of minimum sizes.     

Continuous dry dispersion of multi-walled carbon nanotubes to aerosols with high concentrations of individual fibers

The assessment of the toxicity of airborne nanofibers is an important task. It relies on toxicological inhalation studies and validated exposure measurement techniques. Both require nanofiber-containing aerosols of known morphological composition and controlled fraction of individual fibers. Here, a dry powder dispersion method is presented that operates with mixtures of nanofibers and microscale beads. Aerosolization experiments of mixtures of multi-walled carbon nanotubes (MWCNTs) and glass beads that were continuously fed into a Venturi nozzle enabled high generation rates of aerosols composed of individual and agglomerate nanofiber structures. The aerosol process achieved good stability over more than 2 h with respect to concentration and aerodynamic size distribution. Its operation duration is limited only by the reservoir volume of the cyclone used to separate the beads from the aerosol. The aerosol concentration can be controlled by changing the mass ratio of MWCNTs and glass beads or by adapting the mass feed rate to the nozzle. For two agglomerated MWCNT materials, aerosol concentrations ranged from 1700 to 64,000 nano-objects per cm³. Comprehensive scanning electron microscope analysis of filter samples was performed to categorize and determine the morphological composition of the aerosol, its fiber content as well as fiber length and diameter distributions. High fractions of individual fibers of up to 34% were obtained, which shows the setup to be capable of dispersing also highly tangled MWCNT agglomerates effectively.     

Instrumentation for Simultaneous Gas and Particle Velocity Measurements at Mach 5

This study deals with re‐entry vehicles passing through high‐altitude clouds of ice particles. The particles disturb the flow field and are erosive, thereby increasing the turbulent heat flux considerably. Measurements were performed in a blow‐down wind tunnel to analyze the effects of a particle field on the flow. The wind tunnel flow was seeded by two aerosols. The first was used for LDV flow velocity measurements. Its size was checked by the analysis of its passage through a plane shock wave. The second aerosol was made of uniform micro‐spheres of 200 μm diameter, used to simulated the water droplets. The velocity, feeding and scattering of the latter aerosol need to be accurately measured. The velocities of the flow field and of the micro‐spheres were measured simultaneously by laser velocimetry. This paper describes the instruments used to seed, ascertain and measure this flow with two aerosols.     

Frequency of the methane-stabilized He-Ne laser at 3.39 μm measured relative to the 10.17 μm R(32) transition of the CO2 laser

The frequency difference between the methane-stabilized 3.39 μm He-Ne laser and the third harmonic of the 10.17 μm R(32) transition of the CO₂ laser was measured by harmonic generation and mixing in a tungsten-nickel diode. The difference is 55 200 952 ± 16 kHz. This result corroborates the findings of other workers and is special interest in current discussions to redefine the international metre.     

整体毛细管X光透镜在大气颗粒物单颗粒分析中的应用

对大气颗粒物进行单颗粒X射线荧光(XRF)分析,是一种识别大气颗粒物来源的有力手段.为了利用实验室X射线光源对大气颗粒物进行单颗粒XRF分析,建立了基于整体毛细管X光透镜和实验室X射线光源的微束X射线谱仪.透镜焦斑处的功率密度增益在103数量级,焦斑直径为30 μm左右.该微束X射线谱仪对Fe-Kα线的最小探测极限为0.7 Pg.在Mo靶光源电压和电流分别为30 kV和50 mA的条件下,利用该谱仪对直径为9 μm的大气颗粒物单颗粒进行XRF分析时,测谱时间在180 s左右.实验表明,基于毛细管X光透镜和实验室X射线光源的微束X射线分析技术在大气颗粒物单颗粒分析中有着潜在的应用价值.     

Comparison of indigenously developed micro pulse polarization lidar with EZ lidar profiles

A Micro Pulse Polarization LIDAR (MPPL) has been designed and developed for aerosol and cloud studies at National Physical Laboratory, New Delhi, India (28° 35′ N, 77° 12′E) using a low-energy pico-second pulsed Nd:YAG laser at 532 nm and single PMT detector. This has been used for detecting depolarization characteristics with back-scatter coefficient of atmospheric aerosols and clouds. The back-scattered signals are detected at the emitted wavelength with co-polarization and cross-polarization discrimination with a mirror on stepper motor for aerosols and cloud. Data are obtained by MPPL and are inter-compared with a well-established commercial Leosphere made EZ LIDAR, industry standard at the same site and time, and the results are found to be in good agreement. In the present communication the back-scattered coefficient, aerosols optical depth, depolarization ratio etc. obtained using MPPL & EZ LIDAR are discussed in detail.     

Measurement of thermal conductivity of fluids using 3-<Emphasis Type="Italic">ω</Emphasis> method in a suspended micro wire

A thermally controlled, compact device employing the 3-ω technique, used to measure the thermal conductivity of fluids, is designed, developed, and presented in this paper. The 3-ω method, which analyzes temperature oscillations data in the frequency domain, requires a microscopic sample and extremely low heating power. The functionality is derived from the approximate solutions of temperature oscillations of a line heater based on the infinite line-heater model over an empirically and analytically chosen range of frequencies. The method is devoid of errors related to transient measurements, fluid thermal stratification and mobility errors, which pose difficulties in other methods. A platinum (99.99% pure) wire of 50 μm diameter and a length of 30 mm, suspended in a sample volume of 25 μl of the test fluid, serves simultaneously as the heater and thermometer. Structure-wise, the device is designed to support measurements over a range of temperatures and fluid pressures providing modularity and flexibility to the instrument. The device is successfully employed to measure the thermal conductivity of de-ionized water for temperatures between 15 and 35°C with an accuracy of ±1.2% inmeasurement.     

The nonlinear optical coefficient,phasematching, and optical damage in the chalcopyrite AgGaSe2

We have made a direct measurement of the absolute nonlinear coefficient for AgGaSe₂ by phasematched second harmonic generation. The measured value is d₃₆ = (3.24 ± 0.50) × 10^?11 m/V. For CO and Co₂ lasers the observed phasematching angles for second harmonic generation and frequency mixing are within one degree of the values calculated by fitting the reported index of refraction data to Sellmeier equations. At 1.06 μm the optical damage threshold depends on the number of incident laser pulses. For 1000 pulses damage occurs at 11 MW/cm². The samples were cut from crack-free single crystal boules with absorption coefficient smaller than 0.1 cm^? at 10.6 μm.     

Tunable infrared generation in KTA and applications

Noncollinear difference frequency mixing of dye laser and Nd:YAG second harmonic (fundamental) radiation from a commercial laser system is employed for the generation of 2.7–5.3 μm (1.6–1.7 μm) radiations in a flux-grown KTiOAsO₁ crystal. The generated radiation is used to scan the methane absorption in the fundamental (v ₃) and its first overtone (2v ₃) band at pressure 90 torr in a laboratory made single pass gas cell of length 33 cm.     

基于反射太阳光反演气溶胶光学厚度和有效半径

根据太阳光的极化特性,提出了一种利用单波长太阳光遥感反演球形水凝物气溶胶光学厚度和有效半径的方法.根据矢量辐射传输理论,利用累加法,计算了λ=0.75μm(可见光)和3.3μm(近红外)两种波长太阳光入射时气溶胶的反射矩阵.气溶胶的有效半径为0.01—1.5μm,光学厚度为0.05—1.利用计算机模拟了反演过程,结果表明,当粒子的有效半径小于0.4μm时可以利用可见光波段进行反演;当粒子有效半径大于1.0μm时可以利用近红外波段反演;在0.4—1.0μm之间,利用这两个波段均可以得到精确性很 关键词： 光学厚度 有效半径 极化 反演     

Die Anlagerung von radioaktiven Atomen und Ionen an Aerosolteilchen

The attachment of radioactive atoms and ions to spherical aerosol particles has been studied theoretically. For uncharged atoms the deposition is considered to be solely governed by thermal diffusion. With calculations based on the “limiting-sphere”-method ofArendt-Kallman it is found, that the attached activity is proportional toΦ ² for aerosol particle diametersΦ smaller than 0.1 μm, and proportional toΦ forΦ greater than 1 μm. For charged ions the diffusion process is modified by the influence of electrostatic forces between the diffusing ions and the aerosol particles. In the frequently occurring case of a symmetrically bipolar charged aerosol this influence can be expressed by a functionG _p(Φ), which depends on the diameterΦ and the effective numberp of elementary charges on the aerosol particle. For an aerosol particle diameterΦ greater than 0.1 μm the attached activity is proportional toΦ ^1.1, and forΦ smaller than 0.01 μm it is proportional toΦ ^1.55. The effects of neglecting various terms in the calculation are considered. The distribution of natural radioactivity on atmospheric aerosols has been calculated for various particle size distributions according toJunge. The calculation shows that about 90% of the total natural activity should be attached to particles smaller thanΦ=0.5 μm, and about 35% to particles smaller thanΦ=0.1 μm. The time T_1/2, in which the concentration of the radioactive particles decreases to half the initial value, depends on the concentration of the aerosol particles and on their size distribution. For 10⁴ aerosol particles per cm³ and the size distributions mentioned,T _1/2 varies between 15 and 30 seconds for radioactive ions. For radioactive atomsT _1/2 is greater than it is for ions in the range of aerosol particle diameters belowΦ=0.25 μm, and smaller ifΦ greater than 0.25 μm.