Measurement of Size,Number Concentration and Velocity of Aerosol Particles using an optical particle counter

An aerosol measurement instrument is presented which allows for the simultaneous measurement of the size distribution, number concentration and velocities of particles. A commercial optical particle counter (OPC) was modified in terms of optics and signal evaluation to provide the required measurement information. The design of this instrument allows the definition of a cubic measuring volume by purely optical means. This is achieved by an aperture/lens system which projects a sharply defined light beam into a stream of aerosol flow. Light scattered from single particles at average angles of 90° is collected by two opposite receiver units, each projecting light on to a separate photomultiplier. The intensity of the scattered light with this instrument is found to be an unambiguous function of the particle size. The total number of particles detected per unit time results in the particle flux. The particle velocity can be calculated, in principle, through the correlation of the signal length and the optical length of the measuring volume, provided that the particles have a straight trajectory through the measuring volume and the measuring volume length in the mean flow direction is well defined. The absence of sharpness in real optical projections effects a border zone of definite length, in which the illumination declines to zero. This leads, together with the low-pass filtering of the particle signals, to an increase in the length of the signal slopes, causing some difficulties in the determination of the signal length. A digital signal evaluation technique was developed that renders possible the clear differentiation between the slope and the kernel region of the signal. The latter represents the motion of particles through the completely illuminated region, which can be a more accurate parameter to define the signal length. In addition to the signal length determination, a cross-correlation technique was tested for its potential to obtain particle velocity. the instrument has two interlaced measuring volumes of nearly the same size, which are shifted for this special application in the main flow direction by 20 μm. The phase difference between the signals from the two photomultipliers, together with the optical distance, yields the particle velocity.     

沙尘气溶胶粒子群的散射和偏振特性

根据Mie散射理论,以对数正态分布函数描述沙尘气溶胶粒子群的粒径尺度分布,计算了沙尘气溶胶粒子群在0.2～40μm波段间对太阳短波辐射和地球大气长波辐射的单次散射反照率、散射相矩阵函数,揭示了不同相对湿度时,沙尘粒子群对入射辐射的散射和偏振的特征。结果表明,沙尘粒子群的单次散射反照率随着入射波长的增加有较大起伏,不同相对湿度条件下,变化趋势基本一致;在可见光、近红外波段单次散射反照率随湿度增加而变大,湿度95%时非常接近于1;大于10μm的热红外波段单次散射反照率随相对湿度增加而减小,具有较强的吸收辐射能力。散射辐射强度受湿度影响较小,随散射角的增加呈现先减小后增大的趋势,且增大的趋势随着波长的增加而减弱;不同波段上,线偏振和圆偏振随散射角和相对湿度变化存在差异;在前向和后向仅对入射辐射为圆偏振辐射产生圆偏振散射;散射光的偏振特性及其湿度差异主要表现在后向散射区,多以拱形形式体现。拱顶峰值散射角位置存在差异,且峰值散射角随相对湿度的降低向后向漂移。     

Size Controlled Synthesis of Gold Nanoparticles using Photochemically Prepared Seed Particles

Gold nanoparticles having prechosen size ranging from 5 to 110 nm have been prepared in two steps. Firstly, small spherical particles (seed) of average diameters between 5 and 20 nm were prepared by varying the ratio of gold ion concentration to stabilizer/reductant, TX-100 concentration and using UV irradiation. Secondly, 20–110 nm particles were formed by a non-iterative seed-mediated growth where small particles produced by the above irradiation technique were exploited as seeds and fresh Au(III) ions were reduced onto the surface on the seed particles by ascorbic acid. The kinetics of particle formation has also been reported. These methods were fast and showed improved monodispersity sphericity and excellent reproducibility.     

PM2.5气溶胶光学特性研究

利用FA-3型Anderson撞击式气溶胶粒度分布采样器采集大气中的可吸入颗粒物。在实验室使用光学测量系统对粒径低于PM2.5的气溶胶颗粒物进行透过率测量。结果表明,透过率随气溶胶粒子粒径的增大具有逐渐增加的趋势。粒径低于PM2.5的气溶胶颗粒与PM10粒径范围内的透过率相比,具有明显的波长选择性。     

Photo- and Thermophoresis of Heated Medium-Size Spherical Aerosol Particles

Technical Physics - A theory of photo- and thermophoresis of a heated medium-size spherical aerosol particle is proposed in the quasi-stationary Stokes approximation at relatively small Reynolds...     

大气气溶胶粒子折射率虚部反演方法研究

提出了反演折射率虚部的方法.以光散射为原理的粒子计数器测量光学等效直径,其结果受折射率虚部的影响较大;以粒子飞行时间为原理的粒子计数器测量空气动力学直径,其结果不受折射率虚部的影响.利用两种仪器的测量结果受折射率影响的差异来反演大气气溶胶的折射率虚部.通过与其它独立的测量结果对比表明,该方法反演气溶胶折射率虚部是合理的.     

大气气溶胶粒子折射率虚部反演方法研究

提出了反演折射率虚部的方法.以光散射为原理的粒子计数器测量光学等效直径,其结果受折射率虚部的影响较大;以粒子飞行时间为原理的粒子计数器测量空气动力学直径,其结果不受折射率虚部的影响.利用两种仪器的测量结果受折射率影响的差异来反演大气气溶胶的折射率虚部.通过与其它独立的测量结果对比表明,该方法反演气溶胶折射率虚部是合理的.     

单分散长椭球形气溶胶粒子的散射相函数研究

选取冰晶、沙尘和碳黑等典型气溶胶粒子为例, 应用T矩阵方法, 探讨了单分散长椭球形气溶胶粒子的散射相函数随纵横比、尺度参数和折射率的变化规律.折射率虚部为0时, 以纵横比为0.4的冰晶粒子和等表面积的球形冰晶粒子为例, 将两者的相函数比值ρ划分为5个数值区域: 1) 0°附近的前向散射ρ≈1, 2) 从5°左右到30°左右ρ>1, 3) 从30°～35°到80°～110°ρ<1, 4) 从80°～110°到150°～160°ρ1, 5) 160°以后ρ<1. 同等条件下, 由于折射率的变化, 沙尘粒子ρ<1对应的范围扩大至更大角度, 而ρ1和ρ<1对应的角度区域均相应减小, 而碳黑粒子的ρ1和ρ<1对应的角度区域则消失, ρ演变为3个数值区域.上述长椭球形粒子散射相函数的结论为气溶胶粒形检测和分析提供了理论依据.     

基于模糊聚类算法的苯系物二次有机气溶胶质谱数据分析

OH自由基启动苯系物光氧化形成的二次有机气溶胶能够影响气候变化,降低大气能见度,危害人类健康。我们实验室自行研制的气溶胶飞行时间质谱仪能够用于二次有机气溶胶的实时检测研究。该仪器在检测过程中产生大量的实验数据,对这些数据快速、自动处理并提取有价值的信息是整机系统的关键之一。本文介绍模糊聚类算法在苯系物二次有机气溶胶单粒子聚类分析中的成功运用。利用该算法对OH自由基启动1,3,5-三甲苯光氧化形成的二次有机气溶胶单粒子质谱数据进行了聚类分析,在得到的五个聚类中包含了芳香醛、酚类化合物、硝基酚和羧酸等重要的光氧化产物,为研究苯系物光氧化机理提供了新的信息。     

积雪与气溶胶粒子混合的光谱反照率模拟研究

积雪中的黑碳气溶胶粒子会导致积雪光谱反射率显著下降,进而引起的气候辐射变化会推迟或提前积雪融化时间,严重影响了干旱区地表径流特征、区域水循环过程,由此引起的干旱区生态水文问题也越来越受到关注。2018年1月在新疆北疆地区开展积雪中气溶胶粒子观测实验,借助ASD地物光谱仪、Snow Folk积雪特性仪与HR-1024外场分光辐射度计等仪器获取原始积雪光谱数据与其他积雪参数,应用Snow,Ice,and Aerosol Radiation model(SNICAR)模型模拟了不同雪粒径下、不同太阳天顶角、不同Black Carbon(BC)浓度下的积雪光谱反照率变化状况,讨论了BC、雪粒径在不同光谱范围内敏感性,结果表明:太阳天顶角对雪面光谱反照率的影响在近红外波段比其他波段表现得更明显,在积雪光谱曲线中太阳天顶角从0°变化到80°,可见光波段600 nm处光谱反照率升高了0.045,近红外波段1000,1200和1300 nm处光谱反照率分别升高了0.16,0.225和0.249;在天顶角为60°时,雪粒径从100μm增大到800μm,对应的光谱反照率减少量最大可达到0.15,且100~300μm范围内的雪粒径比400~800μm范围内的引起光谱反照率的下降量明显增大,雪粒径的增大能使吸光性颗粒物的光吸收效应增强;随着BC浓度的增加,积雪反照率会显著下降,且不同浓度的BC对积雪的反照率的差值不同,随着BC浓度的增加,反照率的差值量越来越小。不同的BC浓度在近红外波段对光谱反照率影响较小,影响较大的范围主要集中可见光波段,在光谱800和1100 nm处,5μg·g-1的BC浓度使光谱反照率减小了0.13和0.04,5μg·g-1的BC可使350与550 nm处的光谱反照率减小0.25与0.23;比较不同粒径下,BC浓度对积雪光谱宽波段反照率的减少情况可发现,在BC存在的情况下,雪粒径的增加会增大BC的光吸收效应,且浓度越高,吸收增加的越多;从光谱指数角度表明BC在可见光波段350~740 nm比较敏感,相关系数较高;雪粒径在近红外波段1100~1500 nm比较敏感,尤其在1000与1300 nm左右,BC与雪粒径在积雪光谱曲线中的敏感波段相关性都较高,R 2高达0.9以上;最后将模型模拟的积雪反照率与实测数据进行验证对比,R 2为0.738,模拟效果较好,可为干旱区积雪光谱反照率的研究奠定数据基础。     

Characterization of Agglomerated and Aggregated Aerosol Particles Using Image Analysis

Accurate particle size characterization of aggregated and agglomerated particles is only possible by analysis of photographs. Both the primary particle size and the morphology of the aggregate are important experimental results. Since standard image analysis techniques for particle size analysis usually recognize only single particles, a new programme, called here Sparse Hough Transformation, was developed for the automated recognition of spherical particles within an aggregate. The method is shown to perform well, even for images with many overlapping particles. The structure of the aggregate is analysed using the fractal dimension, determined from the density-density correlation function. Finite size effects, important when dealing with aggregates containing few primary particles, are taken into account by including a cut-off function.     

Size Measurement of Small Magnetic Particles

Many different methods for size measurement are known and since they differ in their physical principles, different results are also obtained. In the recent past, there were rapid developments in new measurement techniques and one can now quickly and routinely determine particle sizes in the very fine range. Smaller particle sizes, on the other hand, tend to increase the probability of agglomeration. The measurement of the particle sizes for magnetic materials is not well understood and this paper reports results regarding the size determination of very fine magnetic materials. Because of their dipole moment, these particles tend to agglomerate even more, which in turn causes certain difficulties during the measurements. Wet and dry laser measurement systems were compared and also magnetic materials with different permeabilities in order to establish the influence of individual factors on the measurement process and on the accuracy of the results obtained.     

微波消解法在气溶胶样品化学分析中的应用

在气溶胶泄漏研究中涉及纤维素滤纸、玻纤滤材、膨润土和砂中铽的含量分析。本工作采用微波密闭消解法作为这些样品分析的前处理 ,并优选了消解试剂及用量、消解压力及消解时间等条件 ,建立了前处理流程。用 ICP-AES分析 Tb的含量 ,结果表明回收率为 65 %— 98% ,待测元素 Tb和内标元素 Lu的回收率比值为 1 .0 0± 0 .0 5     

Photon Doppler Velocimetry and Simulation of Ejection of Particles from the Surface of Shock-Loaded Samples

The results of photon Doppler velocimetry of ejecta from shock-loaded metal samples are reported. The experiments have been performed with tin and lead samples of a given thickness and a given surface roughness. The direct numerical simulation of the process of mass ejection from the surface of shock-loaded samples is performed for conditions close to experimental by the smoothed particle hydrodynamics method. The areal density and initial velocity distribution of the volume density of ejecta are determined. Using these results, we calculate the time dependence of the profile of the volume density at the expansion of the formed dust cloud to air. Applying an approach based on the transport equation for the correlation function of the scattered field, the main parameters of the velocity distribution of ejecta, areal density of ejecta, etc. are reconstructed from spectral photon Doppler velocimetry data. The experimentally observed temporal dynamics of spectra, which is caused by the drag of dust in air, is described at an appropriately chosen size dispersion of dust particles. The masses of ejecta reconstructed from experimental data are in agreement with the smoothed particle hydrodynamics results.     

On-Line Characterization of the Shape and Size of Particles

An image analysis system for extracting on-line quantitative geometric and densitometric information from images of ore samples is described. The apparatus employs a pulsed semiconductor laser as the light source for illuminating of a flowing stream of particles and a non-interlaced solid-state TV camera as size measurement device in a shadowgraph imaging system. The problem of the sampling volume is discussed and several size distributions of solid particulates are presented. The particle size measurement range is 2–400 μm.     

孔隙率对气溶胶凝聚粒子光学特性的影响

采用Monte-Carlo方法,对气溶胶凝聚粒子进行了模拟,讨论了凝聚粒子的孔隙特性,分析了空间结构、原始粒子数目对凝聚粒子孔隙率和等效折射率的影响。结合物质的电结构,将气溶胶凝聚粒子离散为一系列偶极子,利用离散偶极子近似方法,数值计算了不同孔隙率气溶胶凝聚粒子的散射、吸收和消光截面各种取向的统计平均值。结果表明,气溶胶凝聚粒子的孔隙率明显取决于其空间形状和所含原始微粒的数目;气溶胶凝聚粒子的等效折射率、吸收、散射和消光截面则随孔隙率的增加而减小。研究结果可为全面理解气溶胶粒子光学特性提供参考;也可为某些涂层材料光学性能的改变提供参考,通过改变涂层材料中凝聚粒子的孔隙率来改变涂层材料的等效折射率,进而改变涂层材料对光的散射和吸收。     

Size and Shape Prediction of Colloidal Metal Oxide MgBaFeO Particles from Light Scattering Measurements

The size and structure of colloidal metal oxide (MgBaFeO) particles are determined using an Elliptically Polarized Light Scattering (EPLS) technique. The approach is based on a hybrid experimental/theoretical study where the experimental data are compared against predictions obtained using a T-Matrix model that accounts for particle shape irregularities. A power-law distribution function with two parameters is employed to account for the particle size distribution. The refractive index of the particles in ethyl alcohol is calculated based on the Maxwell-Garnet formula. The experiments are conducted using a second-generation nephelometer. It is shown that the current EPLS measurements can effectively be used for identification of both the shape and the size of the colloids.     

单粒子气溶胶的基质辅助激光解吸电离研究

单粒子气溶胶的基质辅助激光解吸/电离飞行时间质谱技术具有快速在线检测环境大气生物气溶胶的潜力．以α-环糊精为分析物,实验研究了吡啶羧酸、2,5-二羟基苯甲酸、芥子酸、阿魏酸四种常用基质材料的效果,考察基质与分析物的摩尔比对分析物单粒子激光质谱信号的影响．实验结果表明阿魏酸做基质时质谱命中率及分析物质谱信号峰检测效率最高,吡啶羧酸做基质时的分析物质谱信号峰激发率最高,信号峰强度最强．吡啶羧酸对分析物摩尔比为100:1时,分析物质谱信号检测效率最高．