On the Determination of Continuous Submicrometer Liquid Aerosol-Size Distributions with Low Pressure Impactors

The aspects associated with the determination of continuous submicrometer aerosol-size distributions using multijet low pressure impactors have been studied. Multiple sets of error-free and noisy, simulated data sets have been inverted, and impactors have been compared with the differential mobility particle-size analysis (DMA) method by using well-defined, laboratory-generated liquid oleic acid aerosols tagged with ammonium fluorescein. Impactors included in this study were a Berner-type impactor HAUKE 25/0.015 (BLPI), a modified University of Washington Mark 5 impactor (KLPI), and the impactor designed at the University of Florida (LLPI). The inversion of simulated error-free impactor data (i.e., the data with perfect kernel functions) for unimodal submicrometer aerosols with a small (2.5%) stage mass error estimate yields results very close to input distributions, when the method based on constrained regularization is used in the inversion. When the error estimate is increased, inverted spectra are flattened. However, they remain clearly unimodal. When normally distributed random error is added to the data and the error estimate for each data point equals the standard deviation of the random error, the fraction of bimodal and trimodal inverted spectra increases with a rise in the random error level and with the asymmetricity of the kernel functions. When the random error level and data error estimates are equal to or smaller than 10%, inverted spectra are mainly unimodal close to input distribution for both error-free and noisy data. The inversion of impactor data from the detailed laboratory experiments (i.e., the data with real kernel functions) indicates that only BLPI kernel functions are accurate enough to yield unimodal distributions close to those measured with the DMA. When the stage mass error estimate is increased beyond the stage mass determination error, unimodal spectra also for the KLPI and LLPI are found. The decrease of the BLPI stage mass error estimate below the experimental error increases the agreement with DMA results. In most cases the error estimate for BLPI stage masses can be decreased to 2.5%, indicating the validity of both BLPI submicrometer kernel functions and the fluorometric method used to determine stage mass concentrations.The aspects associated with the determination of continuous submicrometer aerosol-size distributions using multijet low pressure impactors have been studied. Multiple sets of error-free and noisy, simulated data sets have been inverted, and impactors have been compared with the differential mobility particle-size analysis (DMA) method by using well-defined, laboratory-generated liquid oleic acid aerosols tagged with ammonium fluorescein. Impactors included in this study were a Berner-type impactor HAUKE 25/0.015 (BLPI), a modified University of Washington Mark 5 impactor (KLPI), and the impactor designed at the University of Florida (LLPI). The inversion of simulated error-free impactor data (i.e., the data with perfect kernel functions) for unimodal submicrometer aerosols with a small (2.5%) stage mass error estimate yields results very close to input distributions, when the method based on constrained regularization is used in the inversion. When the error estimate is increased, inverted spectra are flattened. However, they remain clearly unimodal. When normally distributed random error is added to the data and the error estimate for each data point equals the standard deviation of the random error, the fraction of bimodal and trimodal inverted spectra increases with a rise in the random error level and with the asymmetricity of the kernel functions. When the random error level and data error estimates are equal to or smaller than 10%, inverted spectra are mainly unimodal close to input distribution for both error-free and noisy data. The inversion of impactor data from the detailed laboratory experiments (i.e., the data with real kernel functions) indicates that only BLPI kernel functions are accurate enough to yield unimodal distributions close to those measured with the DMA. When the stage mass error estimate is increased beyond the stage mass determination error, unimodal spectra also for the KLPI and LLPI are found. The decrease of the BLPI stage mass error estimate below the experimental error increases the agreement with DMA results. In most cases the error estimate for BLPI stage masses can be decreased to 2.5%, indicating the validity of both BLPI submicrometer kernel functions and the fluorometric method used to determine stage mass concentrations.The aspects associated with the determination of continuous submicrometer aerosol-size distributions using multijet low pressure impactors have been studied. Multiple sets of error-free and noisy, simulated data sets have been inverted, and impactors have been compared with the differential mobility particle-size analysis (DMA) method by using well-defined, laboratory-generated liquid oleic acid aerosols tagged with ammonium fluorescein. Impactors included in this study were a Berner-type impactor HAUKE 25/0.015 (BLPI), a modified University of Washington Mark 5 impactor (KLPI), and the impactor designed at the University of Florida (LLPI). The inversion of simulated error-free impactor data (i.e., the data with perfect kernel functions) for unimodal submicrometer aerosols with a small (2.5%) stage mass error estimate yields results very close to input distributions, when the method based on constrained regularization is used in the inversion. When the error estimate is increased, inverted spectra are flattened. However, they remain clearly unimodal. When normally distributed random error is added to the data and the error estimate for each data point equals the standard deviation of the random error, the fraction of bimodal and trimodal inverted spectra increases with a rise in the random error level and with the asymmetricity of the kernel functions. When the random error level and data error estimates are equal to or smaller than 10%, inverted spectra are mainly unimodal close to input distribution for both error-free and noisy data. The inversion of impactor data from the detailed laboratory experiments (i.e., the data with real kernel functions) indicates that only BLPI kernel functions are accurate enough to yield unimodal distributions close to those measured with the DMA. When the stage mass error estimate is increased beyond the stage mass determination error, unimodal spectra also for the KLPI and LLPI are found. The decrease of the BLPI stage mass error estimate below the experimental error increases the agreement with DMA results. In most cases the error estimate for BLPI stage masses can be decreased to 2.5%, indicating the validity of both BLPI submicrometer kernel functions and the fluorometric method used to determine stage mass concentrations.The aspects associated with the determination of continuous submicrometer aerosol-size distributions using multijet low pressure impactors have been studied. Multiple sets of error-free and noisy, simulated data sets have been inverted, and impactors have been compared with the differential mobility particle-size analysis (DMA) method by using well-defined, laboratory-generated liquid oleic acid aerosols tagged with ammonium fluorescein. Impactors included in this study were a Berner-type impactor HAUKE 25/0.015 (BLPI), a modified University of Washington Mark 5 impactor (KLPI), and the impactor designed at the University of Florida (LLPI). The inversion of simulated error-free impactor data (i.e., the data with perfect kernel functions) for unimodal submicrometer aerosols with a small (2.5%) stage mass error estimate yields results very close to input distributions, when the method based on constrained regularization is used in the inversion. When the error estimate is increased, inverted spectra are flattened. However, they remain clearly unimodal. When normally distributed random error is added to the data and the error estimate for each data point equals the standard deviation of the random error, the fraction of bimodal and trimodal inverted spectra increases with a rise in the random error level and with the asymmetricity of the kernel functions. When the random error level and data error estimates are equal to or smaller than 10%, inverted spectra are mainly unimodal close to input distribution for both error-free and noisy data. The inversion of impactor data from the detailed laboratory experiments (i.e., the data with real kernel functions) indicates that only BLPI kernel functions are accurate enough to yield unimodal distributions close to those measured with the DMA. When the stage mass error estimate is increased beyond the stage mass determination error, unimodal spectra also for the KLPI and LLPI are found. The decrease of the BLPI stage mass error estimate below the experimental error increases the agreement with DMA results. In most cases the error estimate for BLPI stage masses can be decreased to 2.5%, indicating the validity of both BLPI submicrometer kernel functions and the fluorometric method used to determine stage mass concentrations.     

Comparison and Combination of Aerosol Size Distributions Measured with a Low Pressure Impactor,Differential Mobility Particle Sizer,Electrical Aerosol Analyzer,and Aerodynamic Particle Sizer

Data from a different mobility particle sizer (DMPS) or an electrical aerosol analyzer (EAA) has been combined with data from an aerodynamic particle sizer (APS) and converted to obtain aerosol mass distribution parameters on a near real-time basis. A low pressure impactor (LPI), a direct and independent measure of this mass distribution, provided information for comparison.

The number distribution of particles within the electrical measurement range was obtained with the DMPS and EAA. Data from the APS for particles greater than that size were used to complete the number distribution. Two methods of obtaining mass distribution parameters from this number data were attempted. The first was to convert the number data, channel by channel, to mass data and then fit a log-normal function to this new mass distribution. The second method was to fit a log-normal function to the combined number distribution and then use the Hatch-Choate equations to obtain mass parameters.

Both the DMPS / APS and the EAA / APS systems were shown to successfully measure aerosol mass distribution as a function of aerodynamic diameter. Careful operation of the measurement equipment and proper data manipulation are necessary to achieve reliable results. A channel-by-channel conversion from number to mass distribution provided the best comparison to the LPI measurement. The DMPS / APS combination furnishes higher-size resolution and accuracy than the EAA / APS system. A small gap was observed in the EAA / APS combined data; however, this did not seem to adversely affect the determination of mass distribution parameters.     

Comparison of Particle Size Distributions at Urban and Agricultural Sites in California's San Joaquin Valley

As part of the California Regional PM _2.5 and PM ₁₀ Air Quality Study (CRPAQS) particle size distributions were measured simultaneously at two sites; the city of Fresno and the agricultural site of Angiola. Reported here are data obtained by scanning mobility analysis over the size range from 10 nm to 400 nm for the intensive study period from December 1, 2000 through February 6, 2001. These high time resolution data show variability in the character of the distributions, as well as the in the total number concentrations. The most pronounced feature of the data set is a consistent, nighttime maxima in particle number concentrations with a modal diameter near 80 nm during the evening hours at the urban Fresno site. Although these maxima are correlated with CO, NO, and black carbon, the particle size is larger than the 30–40 nm modal diameters observed for traffic aerosols during the commute hours, and is attributed to a non-vehicle source. At the agricultural site, the morning maxima particle number concentration coincides with the maxima in NO concentration, but often precedes the morning maxima in black carbon. Values for the geometric mean particle diameter varied from day to day, but are correlated between the two sites, with somewhat larger particle sizes at Angiola during periods of stagnation.     

Comparison of Vehicle Exhaust Particle Size Distributions Measured by SMPS and EEPS During Steady-State Conditions

Fast-sizing spectrometers, such as the TSI Engine Exhaust Particle Sizer (EEPS), have been widely used to measure transient particle size distributions of vehicle exhaust. Recently, size distributions measured during different test cycles have begun to be used for calculating suspended particulate mass; however, several recent evaluations have shown some deficiencies in this approach and discrepancies relative to the gravimetric reference method. The EEPS converts electrical charge carried by particles into size distributions based on mobility classification and a specific calibration, and TSI recently released a matrix optimized for vehicle emissions as described by Wang et al. (Submitteda). This study evaluates the performance of the new matrix (soot matrix) relative to the original matrix (default matrix) and reference size distributions measured by a scanning mobility particle sizer (SMPS). Steady-state particle size distributions were generated from the following five sources to evaluate exhaust particulates with various morphologies estimated by mass-mobility scaling exponent: (1) A diesel generator operating on ultralow sulfur diesel, (2) a diesel generator operating on biodiesel, (3) a gasoline direct-injection vehicle operating at two speeds, (4) a conventional port-fuel injection gasoline vehicle, and (4) a light-duty diesel (LDD) vehicle equipped with a diesel particulate filter. Generally, the new soot matrix achieved much better agreement with the SMPS reference for particles smaller than 30 nm and larger than 100 nm, and also broadened the accumulation mode distribution that was previously too narrow using the default matrix. However, EEPS distributions still did not agree with SMPS reference measurements when challenged by a strong nucleation mode during high-load operation of the LDD vehicle. This work quantifies the range of accuracy that can be expected when measuring particle size distribution, number concentration, and integrated particle mass of vehicle emissions when using the new static calibration derived based on the properties of classical diesel soot.

Copyright 2015 American Association for Aerosol Research     

Particle Chromatographic Separation of Coal Fly Ash

Abstract

Attempts were made to totally separate the 13 types of particles in a coal fly ash. While a considerable separation was obtained, it was far from complete even with optimal operating conditions. The best results were obtained with camphor as the host material in the tilt rotating zone melting technique with a tube rotation rate of 25 rpm and a tube tilt angle of 30° to the horizontal. Additional zone passes improved the separation only slightly. The zone travel rate at which each particle type was trapped, and the length over which each type was trapped, both increased as the tube rotation rate was increased and as the tilt angle was decreased. If a bubble contacted the interface during horizontal operation, the trapping occurred at significantly lower freezing rates and the separation was considerably worse. The smaller particles were trapped at lower freezing rates than larger particles. Naphthalene and biphenyl proved to be poor hosts because of extensive bubble formation at the interface during zoning. Particles were trapped at impractically low freezing rates with Salol.     

Fitting Size Distributions to Optical Particle Counter Data

The theoretical considerations of fitting distributions to aerosol-size spectra derived from optical particle counters are discussed. Based on this, a simple procedure is proposed for fitting the density functions of the commonly used Junge and lognormal distributions, and a special case of the modified gamma distribution. The method uses a generalized linear model to allow for the count statistics of particle sampling.     

A Fast Scanning Mobility Particle Spectrometer for Monitoring Transient Particle Size Distributions

The Scanning Mobility Particle Spectrometer (SMPS) is a key tool for measuring particle size distribution. The application of the instrument to obtain size distributions throughout a wide range of particle sizes for transient systems, such as motor vehicle emissions, has been limited by the time resolution of the SMPS. In this paper, we present a fast-SMPS (f-SMPS) that utilizes a Radial Differential Mobility Analyzer (rDMA) and a Wixing Condensation Particle Counter (mCPC). The combination of these two components allows for the acquisition of particle size distributions on the time scale of several seconds. The Instrument has an operating range of 5–98 nm and can obtain particle size distributions at rates of up to 0.4 Hz. This paper presents the initial construction and calibration of the instrument followed by its application to several sampling scenarios. Samples from the on-road testing of a heavy-duty diesel (HDD) vehicle demonstrate the utility of this instrument for momtor vehicle emissions measurements as size distributions can now be associated with discrete events taking piace during vehicle onroad operation. For instance, these data indicate the presence of a number peak at 15 nm during transient vehicle operation. Previous work indicates that these particles are associated with the loss of engine lubricating oil.     

Evolution of Particle Size Distributions due to Turbulent and Brownian Coagulation

The time evolution of particle size distribution due to Brownian and turbulent coagulation (using the kernel of Kruis and Kusters (1997)) was systematically investigated. Using a new definition of dimensionless size distribution parameters based on the geometric mean values, self-preserving particle size distributions for turbulent coagulation were found to exist. The width of such distributions depends on the initial size distribution as well as the turbulence intensity. When starting with submicron aerosols, however, only the turbulence intensity plays a role in determining the final self-preserving form, whereas the initial conditions have no influence. Typically, broad particle size distributions with σ g in the 1.5-1.9 range are obtained. Because of the importance of scavenging by the largest particles in the size distribution, the possibility of developing a "runaway mass" exists, for which some experimental indications in turbulent systems exist.     

Packing and Sintering of Two-Dimensional Structures Made fro Bimodal Particle Size Distributions

Binary mixtures of spheres were used to prepare a variety of two-dimensional structures ranging from ordered to disordered. The extent of particle order was influenced by the size ratio and the concentration of the bimodal constituents. If either the sizes or the concentrations were very different, the structures became phase separated into ordered regions of small spheres and ordered regions of large spheres. Disordered structures were produced when particles were present in equal concentrations and when sizes differed by about 30%. The sintering behavior of these two-dimensional structures was also examined. The domain boundaries in the ordered samples were found to develop into cracks during sintering if the domain size was large. In contrast the disordered structures sintered homogeneously, without the formation of large processing defects.     

气流床粉煤气化熔渣与其原煤灰特性比较

对气流床粉煤气化熔渣及其原煤灰特性进行了对比研究。采用X射线荧光光谱仪(XRF)、X射线衍射仪(XRD)分析了熔渣及煤灰的化学成分和矿物组成。测试了熔渣及煤灰的熔融及黏温特性,并利用热力学软件Fact Sage模拟计算了二者对应的四元平衡相图和特殊温度下熔体中的矿物质组成及其含量。结果表明,由于熔渣经历了高温气化、激冷过程,原煤灰与熔渣的化学成分和矿物质组成并不存在明显的对应关系;两样品熔融温度差别较小,真液相时黏温特性曲线几乎重合,在临界黏度温度(Tcv)时出现差异,随着温度的降低,熔渣的Tcv出现较早,黏度急剧增大至固相的温度较高。热力学模拟计算结果与实验结果相吻合。对原煤煤灰熔融性及黏温特性的分析,可以为工业气化炉的开车运行提供指导。     

激光粒度仪分级测定水煤浆粒度分布的研究

为确定多种磨矿产品级配制得水煤浆样品的粒度分布,文章提出了分级测定水煤浆粒度的方法,已知各磨矿产品的粒度分布,通过分级拟合的方法得到不同质量比级配样品的粒度分布。结果表明:分级计算方法得到的煤样粒度分布可以准确反映出级配样品的峰型,且粒度测试结果较为准确。     

Ash Vaporization and Condensation During Combustion of a Suspended Coal Particle

The results of a theoretical study of the formation and growth of the submicron flyash aerosol around a single burning coal particle are presented. The vaporization of ash and subsequent aerosol formation near the coal particle are studied because the local combustion environment influences these processes strongly. A mathematical model is developed that describes the transport of ash vapor and and the growth of the aerosol. The ash aerosol calculation is superimposed on an existing solution to the combustion problem. Included in the model are the effects of convective transport and of both homogeneous and heterogeneous condensation of the ash vapor. The results of the calculations show that refractory compounds with low surface tension, like silica, nucleate very near the coal particle's surface and produce a substantial mass loading of aerosol. The presence of the aerosol does not greatly affect the ash vaporization rate, which is primarily a function of combustion conditions. The size and amount of the submicron ash aerosol are determined by both the local combustion conditions and the ash's physical properties.     

Simulating Particle Size Distributions over California and Impact on Lung Deposition Fraction

Reliable simulations of particle mass size distributions by regional photochemical air quality models are needed in regulatory applications because the U.S. EPA's National Ambient Air Quality Standards specify limits on the mass concentration of particles in a specific size range (i.e., aerodynamic diameter <2.5 μm). Considering the associations between adverse health effects and exposure to ultrafine particles, air quality models may need to accurately simulate particle number size distributions in addition to mass size distributions in future applications. In this study, predictions of particle number and mass size distributions by the Community Multiscale Air Quality model with the standard and an updated emission size distribution are evaluated using wintertime observations in California. Differences in modeled lung deposition fraction for simulated and observed particle number size distributions are also evaluated. Simulated mass size distributions are generally broader and shifted to larger diameters than observations, and observed differences in inorganic and carbon (elemental and organic) distributions are not captured by the model. These model limitations can be reasonably accounted for in regulatory modeling applications. Simulated number size distributions are considerably less accurate than mass size distributions and are difficult to represent in air quality models due to large sub-grid-scale concentration gradients. However, modeled number size distributions are responsive to updates of the emission size distribution, and reasonable simulation of background number size distributions might be possible with an improved treatment of emission size distributions. Modeled lung deposition fractions for simulated number size distributions peak in the same lung region as those for number size distributions observed in the background. However, differences in modeled and observed total number concentrations generally suggest large differences in the total number of deposited particles. Future model development on simulating particle mass size distributions should focus on improving predictions of the mass fraction of particles <2.5 μm. Model development for particle number size distributions should focus on reducing differences in modeled lung deposition for modeled and observed distributions.     

Measurement of Atlanta Aerosol Size Distributions: Observations of Ultrafine Particle Events

As part of EPRI's Aerosol Research Inhalation Epidemiology Study (ARIES), measurements of aerosol size distributions in the 3 nm to 2     

The Effect of Particle Size Distributions on the Microstructural Evolution During Sintering

Microstructural evolution and sintering behavior of powder compacts composed of spherical particles with different particle size distributions (PSDs) were simulated using a kinetic Monte Carlo model of solid‐state sintering. Compacts of monosized particles, normal PSDs with fixed mean particle radii and a range of standard deviations, and log‐normal PSDs with fixed mode and a range of skewness values were studied. Densification rate and final relative density were found to be inversely proportional to initial PSD width. Grain growth was faster during the early stages of sintering for broad PSDs, but the final grain sizes were smaller. These behaviors are explained by the smallest grains in the broader PSDs being consumed very quickly by larger neighboring grains. The elimination of the small grains reduces both the total number of necks and the neck area between particles, which in turn reduces the regions where vacancies can be annihilated, leading to slower densification rates. The loss of neck area causes grain growth by surface diffusion to become the dominant microstructural evolution mechanism, leading to poor densification. Finally, pore size was shown to increase with the width of PSDs, which also contributes to the lower densification rates.     

粉煤灰粒度分布及其活性的灰色关联分析

用激光粒度仪测定不同细度粉煤灰的粒度分布,以灰色关联方法分析了粉煤灰粒度分布与其活性之间的相关性.研究表明:粉煤灰粒度分布明显影响其活性;0～19.953 μm范围内的颗粒体积分数与粉煤灰活性指数的关联极性均为正,说明这些颗粒对粉煤灰的活性有积极贡献;其中以5.012～19.953 μm的关联度为最大,说明该粒径范围内...     

机械活化粉煤灰的颗粒分布和活性的研究

主要研究了机械活化粉煤灰的颗粒分布和矿物成分的变化规律,阐述了机械活化粉煤灰火山灰活性提高的原因.     

Effect of Interparticle Potentials and Sedimentation on Particle Packing Density of Bimodal Particle Distributions During Pressure Filtration

Effect of interparticle forces, bimodal particle size distribution, and slurry viscosity on particle packing in alumina bodies consolidated by pressure filtration is presented. The requirements for packing colloidal particles to their highest density are strong repulsive interparticle forces and optimum particle size distribution. Even though these conditions are met, the high packing density in consolidated bodies may be adversely affected by particle segregation resulting from sedimentation. Therefore, the slurry during consolidation must have a sufficiently high viscosity to prevent sedimentation.