Particle Charge Distribution Measurement for Commonly Generated Laboratory Aerosols

ABSTRACT

An improved particle charge analyzer system has been developed to measure the absolute charge distribution of common generated laboratory aerosols. The charge analyzer system consists of an integral cylindrical mobility analyzer used in conjunction with an optical aerosol spectrometer, with computer assisted operation and data reduction. The charge analyzer collects aerosol particles over an absolute electrical mobility range from 4.2*10^?4 to 400 cm²/(stat · Volt second) and flow rates that can vary from 0.3 to 30 liters per minute. The charge analyzer has been used to investigate the nature of spray and contact electrification during aerosol generation by measuring the residual charge distribution on the liquid and solid generated particles. In addition, the neutralization of charged particles by bipolar ions also was studied using conventional neutralizers that use ionizing radiation from alpha and beta sources. Charge distribution measurements were performed on alumina dust (Al), Arizona road dust (ARD), potassium chloride (KCl), sodium chloride (NaCl) and di-octyl sebacate (DOS) liquid particles. Aerosol generation devices include a Collison atomizer, a condensation aerosol generator and a fluidized bed dust generator. Our work provides experimental charge distribution data for comparison with simple models of electrification theory. Experimental results showed that charge levels of atomized KCl and NaCl particles were high and decreased as the dissolved ion concentration increased. DOS particles generated by evaporation-condensation were both neutral and moderately charged. These conclusions support the existence of a dipole layer at the liquid-gas interface that interacts with dissolved particles and changes their charge state. Alumina and ARD generated by the fluidized bed disperser are highly charged due to strong contact electrification during dispersion. In most cases, the charge on generated aerosols could be reduced to Boltzmann charge equilibrium conditions by commonly used radioactive neutralizers.     

Influence of Air Pollutants in the 7Be Size Distribution of Atmospheric Aerosols

ABSTRACT

The atmospheric behavior of ⁷Be aerosols was studied by using 1-ACFM cascade impactors. The activity distribution of Be measured by gamma spectrometry (E _γ=477 keV), was largely associated with submicron aerosols in the accumulation mode (0.4–2.0 μm). The activity median aerodynamic diameter, AM AD ranged from 0.62 to 1.00 yam (average 0.80 μm). The geometric standard deviation, σ_g ranged from 1.87 to 2.50 (average 2.22). Low AMADs of ⁷Be aerosols have been observed at locations characterized with relatively low pollution. Some dependency of AMADs on height has been also observed. In near marine environment the ⁷Be activity size distribution was observed in higher size range of aerosol particles (AMAD 0.82 μm).     

An Intensive Study of the Size and Composition of Submicron Atmospheric Aerosols at a Rural Site in Ontario,Canada

Atmospheric sampling was conducted at a rural site near Egbert, about 70 km north of Toronto, Ontario, Canada from March 27 to May 8, 2003 to characterize the physical and chemical properties of the ambient aerosol in near real-time. The instrumentation included a tapered element oscillating microbalance (TEOM), an ultrafine condensation particle counter (UCPC), a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), an aerosol mass spectrometer (AMS), and a particulate nitrate monitor (R&P 8400N) for aerosol measurements. Gas-phase non-methane hydrocarbon compounds (NMHCs) were measured by gas chromatograph-flame ionization detection (GC-FID). Filter samples were also collected for analysis of inorganic ions by ion chromatography (IC). Aerosol properties varied considerably depending upon meteorological conditions and airmass histories. For example, urban and industrial emissions advected from the south strongly influenced the site occasionally, resulting in higher particulate mass with the higher fractions of nitrate and organics. Cleaner northwesterly winds carried aerosols with relatively higher fractions of organics and sulfate. The AMS derived mass size distributions showed that the inorganic species in the particles with vacuum aerodynamic diameters between about 60 nm and 600 nm had mass modal vacuum aerodynamic diameters around 400–500 nm. The particulate organics often exhibited two modes at about 100 nm and 425 nm, more noticeable during fresh pollution events. The small organic mode was well correlated with gas-phase nonmethane hydrocarbons such as ethylbenzene, toluene, and propene, suggesting that the likely sources of small organic particles were combustion related emissions. The particulate nitrate exhibited a diurnal variation with higher concentrations during dark hours and minima in the afternoon. Particulate sulfate and organics showed evidence of photochemical processing with higher levels of sulfate and oxygenated organics in the afternoon. Reasonable agreement among all of the co-located measurements is found, provided the upper size limit of the AMS is considered.     

Theoretical Study of Equilibrium Bipolar Charge Distribution on Nonuniform Primary Straight Chain Aggregate Aerosols

A general theory describing the equilibrium bipolar charge distribution for straight chain aggregate aerosols consisting of primary spheres of different diameters was derived from a theory previously developed for linear chain aggregate of uniform spheres. The present theory is based on the assumptions that (1) the individual primary particles of a straight chain aggregate are charged independently, (2) the probability that a particular primary particle has acquired q elementary charges is governed by the Gaussian distribution predicted by Boltzmann's law, based on particle size; and (3) the resultant charge of a straight chain aggregate is the algebraic sum of the charges carried by the constituent primary spheres. The present theory can be stated as follows: The equilibrium bipolar charge distribution of straight chain aggregate aerosols with nonuniform primary spheres can be expressed by Boltzmann's law with an equivalent diameter such that d_eL = Σ ⁿ _i=1 d_i . The limitations imposed by the assumptions are also discussed.     

快速钻井条件下提高岩屑录井准确性的措施

PDC钻头结合扭力冲击器的复合钻井技术大大提高了机械钻速,但也造成岩屑细小、破碎的问题,给录井岩屑识别、剖面归位等带来了困难。为了提高岩屑录井准确性,分析了快速钻井条件下岩屑录井面临的难题,并针对录井技术特点,提出了相应的对策。     

广州大气颗粒物与酸沉降的关系研究

本文研究了大气颗粒物的酸度和酸缓冲能力,实验证实广州大气颗粒物中存在着游离的硫酸,其水溶性离子中SO4^2-及NO3^-占很大的比例。颗粒物中的碱性成分含量大于酸性成分,对酸性降水有一定的缓冲能力。气溶胶中细颗粒物的酸性大于粗颗粒物,且酸缓冲能力远低于粗颗粒物。     

Formation of Metal Oxide Aerosols for Conditions of High Supersaturation

High concentrations of submicron particles of inorganic materials are found in the off-gases of various high-temperature processing units such as smelters and coal combustion systems. Metal oxide aerosols can form in combustion systems when hot gases that contain metal vapor species mix with oxygen-bearing gases and when these mixed gases are cooled. Experiments were conducted in an evaporation-oxidation furnace simulating the geometric configuration of a diffusion flame and using zinc as the test substance. The average metal oxide particle size and particle size distribution were measured for various experimental conditions. It can be shown that the conditions under which most metal oxides are formed in combustion gases correspond to extremely high degrees of supersaturation, with respect to the stable solid or liquid oxide phase. For these conditions, the homogeneous nucleation mechanism, utilizing the Becker-Doring theory, does not apply. An alternative approach is the “chemical nucleation” process, starting with an essentially irreversible chemical reaction in the gas phase to form a monomer of the oxide molecule and proceeding through steps of condensation and coalescence that are controlled by the diffusion rate and collision frequencies of the reacting species and the growing oxide particles. The fluid dynamics of the gases in the system are important in the kinetics of the process because they influence the concentrations of precursor species and particles and the lengths of diffusion paths. A chemical nucleation model is proposed to describe quantitatively the formation of zinc oxide particles as a function of process parameters such as partial pressure of metal vapor, oxidation temperature, and characteristic parameters of the gas flow system.     

炸药装药在不同应变率响应条件下的安全性研究进展

综述了不同应变率响应条件下炸药装药安全性最新研究进展。通过对炸药装药应用中常用的应变率范围为1~106 s-1的大型落锤实验技术、分离式霍普金森压杆(SHPB)实验技术、一级轻气炮实验技术等进行了评述。分析了不同应变率响应条件下炸药装药安全性实验中存在的问题。根据炸药装药安全性研究的趋势,认为应加强中高应变率响应实验技术的发展,重点完善落锤-霍普金森压杆实验系统的理论及试验体系,提高一级轻气炮实验技术的可控性及重复性。附参考文献61篇。     

不同射击工况下膛内模块装药的热安全性预测

为研究火炮多发连续射击情况下模块装药滞留膛内的热安全性问题,建立了膛内模块装药二维非稳态烤燃模型,采用FLUENT软件对模块装药在膛内的烤燃过程进行了数值模拟,分析了3种射击工况下多发连续射击后继续装填模块装药留膛时的烤燃特性。结果表明,常温下不同射击工况对膛内模块装药的烤燃响应时间影响较大,对烤燃起始响应位置影响较小,对烤燃响应温度几乎无影响;采用5发/min射速射击32发后模块装药的烤燃响应时间为399.2s,采用1发/min射速射击43发和采用混合射速射击41发后模块装药的烤燃响应时间分别为176.4s和179.6s。3种射击工况下均是靠近模块盒右侧端面处的单基药最先着火,并形成环形烤燃响应区,单基药的烤燃响应温度分别为459.2、462.7和460.0K。     

团聚对亚微米5A分子筛粒度分析的影响

为了考察小晶粒分子筛团聚对亚微米级5A分子筛粒度分布结果的影响以及适宜的测定条件,实验以水为分散介质,六偏磷酸钠为分散剂,在超声波辅助作用下,用电位/粒度分析仪测定研究了试样浓度、分散剂用量和超声时间对亚微米级5A分子筛分散性的影响。结果表明,当分子筛含量大于5 g/L时,晶粒团聚现象严重,粒度分布呈现单峰(假象),导致粒度测量结果偏大;加入少量(0.005~0.195 g/L)的六偏磷酸钠,有缓解晶粒团聚作用,可将较大团聚粒子(大于2.8μm)分散为较小粒子(1.3μm左右),少量团聚粒子分散成单个晶粒,可测得较小晶粒粒径;超声作用可使较大团聚粒子(0.85~2.80μm)分布峰强度降低,相对较小粒子(0.30~0.85μm)分布峰强度增加。超声时间不宜太长,否则将加剧粒子间团聚,使得测定粒径偏大。当试样中5A分子筛含量为5 g/L,六偏磷酸钠浓度0.195 g/L、超声时间4 min条件下,测得5A分子筛试样粒径分布0.25~0.80μm,峰顶对应粒径为0.473μm,中位径(d50)为0.784μm,与电镜分析结果一致,说明是较为准确的粒度分析方法。     

An Empirical Method for the Determination of the Complex Refractive Index of Size-Fractionated Atmospheric Aerosols for Radiative Transfer Calculations

To adequately assess the effects of atmospheric aerosols on climate, their optical constants (scattering and absorption coefficients) must be known. The absorption and scattering coefficients of the aerosols are derived from the real and imaginary parts of the complex refractive index and are dependent on their size and chemical composition. Because aerosol properties vary significantly with location, it is difficult to assign values for the absorption and scattering of solar radiation by aerosols in models of global climate change. This study reports a new method of collecting size-fractionated atmospheric aerosol samples for the purpose of directly measuring their transmission and reflectance spectra followed by the determination of the complex refractive index across the entire atmospherically relevant spectral range. The samples were collected with a modified Sierra high-volume cascade impactor with the usual filter collection surfaces replaced with Teflon sheets machined to hold quartz (ultraviolet [UV]/visible transparent) and/or silver chloride (infrared transparent) sample collection plates. Reflectance and transmission spectra can be obtained on the aerosol samples directly as a function of wavelength, from 280 nm to 2.5 m, with an integrating sphere coupled to an UV/visible or a Fourier transform infrared (FTIR) spectrophotometer. The effective real and imaginary components of the refractive index of the bulk sample material can then be approximated, as a function of wavelength, from the sample spectra. Preliminary results are presented for carbon soot samples generated in the laboratory and for standard diesel soot samples in the UV/visible spectral range. These are compared to results obtained for size-fractionated atmospheric aerosol samples collected near Pasco, WA, West Mesa, AZ, and Argonne, IL.     

CH_3SH与OH气相反应机理的理论研究

采用密度泛函理论,对CH3SH与OH的反应机理进行了量子化学研究。基于B3LYP/6-311++G(d,p)水平,找到了三条可能的反应通道。结果表明:在需要克服能垒的通道中,巯基上氢抽提在动力学和热力学上最有利,活化能为2.7 k J/mol,低于甲基上的氢抽提通道;而对于不需要克服能垒的通道,产物CH3S(OH)H的能量较高,不如前两种通道产物稳定。     

A Newly Designed and Constructed Instrument for Coupled Infrared Extinction and Size Distribution Measurements of Aerosols

Although atmospheric particles are often non-spherical, Mie theory is commonly used to acquire aerosol optical depth, composition, and transport information from satellite retrievals. In the infrared (IR) region, the radiative effects of aerosols, usually modeled with Mie theory, are subtracted from satellite spectral data to determine key atmospheric and oceanic properties. To gain a better understanding of the infrared radiative effects of aerosols and the methods used to model them, an instrument has been designed to simultaneously measure infrared extinction spectra and particle size distributions obtained from a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS). Infrared extinction spectra are simulated with Mie theory using the measured particle size distributions and available literature optical constants. As a result, the errors associated with using Mie theory to model the infrared extinction of mineral dust aerosol can be quantitatively examined. Initial results for this instrument are presented here. For ammonium sulfate, the Mie theory simulation is in good agreement with our measured extinction spectrum. This is in accordance with the nearly spherical shape of ammonium sulfate particles. However, for illite, an abundant clay mineral, there is poor agreement between the experimental spectrum and the Mie simulation. This result is attributed to particle shape effects.     

Comment on the Calculation of the Steady-State Charge Distribution on Aerosols < 100 nm by Three Body Trapping Method in a Bipolar Ion Environment

The theory of Fuchs (1963) Fuchs, N. 1963. On the Stationary Charge Distribution on Aerosol Particles in a Bipolar Ionic Atmosphere. Geofis. Pura Appl., 56: 185–192. [Crossref] , [Google Scholar] is widely used for calculation of the steady-state charge distribution on (submicron) aerosol particles in a bipolar ion environment. Hoppel and Frick (1986) Hoppel, W. and Frick, G. 1986. Ion-Aerosol Attachment Coefficients and the Steady-State Charge Distribution on Aerosols in a Bipolar Environment. J. Aerosol Sci., 5: 1–21. [Taylor & Francis Online] , [Google Scholar] and others showed that the Fuchs theory is no longer valid for particle diameters in the order of magnitude of the ionic mean free path. In their 1986 and 1990 papers, Hoppel and Frick published a new calculation method based on the concept of thee-body trapping, which is applicable for small particles down to the size of ions. Some print and procedure mistakes were made in the named publications. Additionally some important calculation information was not given. In this article, the relevant equations are shown, corrected and appended. A recalculation of the charge distributions for small particles based on three-body trapping shows a pronounced difference in comparison to data calculated according to the theory of Fuchs.     

A Differentially Pumped Particle Inlet for Sampling of Atmospheric Aerosols into a Time-of-Flight Mass Spectrometer: Optical Characterization of the Particle Beam

Two methods of characterizing the particle beam generated with a differentially pumped particle inlet are presented. Both methods are based on optical scattering of a laser beam by the particle beam. The first method images a time integrated scatter signal from the entire particle beam onto a charge coupled device (CCD), and an Abel inversion is performed on the image data to arrive at the radial particle density distribution in the beam. The second method, based on counting individual (particle) scatter pulses, yields the radial particle density directly. Initial results of the performance of the particle inlet are reported for particles with diameters between 40 and 800 nm. Under optimal working conditions, particle beams were generated with a full angle divergence on the order of 1-2 mrad. The width, measured 285 mm downstream from the exit of the particle inlet, was 250mu m, half width at half maximum (HWHM).     

A Rapid,Accurate Technique for Determining Densities of High Explosives

An improved gas comparison pycnometer has been developed, based on precise differential pressure measurements coupled with a sample volume compensator. Using helium gas, volumes of solid and powdered explosives can be measured to a precision approaching one part in lo4. Coupled with a precise mass measurement, these volumes allow densities with an uncertainty of ∼± 0.002 g/ml to be inferred. Measurements performed on various explosives have allowed assessment of the purity and homogeneity of individual samples. It is also possible to infer void percentage or porosity in pressed explosive pellets.     

Absorption Enhancement of Coated Absorbing Aerosols: Validation of the Photo-Acoustic Technique for Measuring the Enhancement

A photo-acoustic absorption spectrometer (PAS) and a cavity ring down aerosol extinction spectrometer (CRD-AES) were used, in conjunction with Mie Theory, to measure the refractive index (RI) of absorbing polystyrene spheres (APSS). The PAS and CRD-AES were also used to measure the absorption and extinction enhancement after these APSS were coated in oleic acid. The experimental enhancements were then compared to predictions from coated-sphere Mie Theory. The measured absorption and extinction enhancements both agreed with modeled enhancements to within an average of 5%. A filter-based absorption technique (particle soot absorption photometer, PSAP) was also used to measure the absorption by the APSS and showed a significant size-dependent bias, as evidenced by the filter-based method measuring significantly lower absorption for both uncoated and coated APSS compared to the PAS. These results suggest the validity of applying photo-acoustics to measure the absorption enhancement created by semi-volatile atmospheric species coating absorbing particles.     

Measurements of the Size Distribution of Aerosols Produced by Ultrasonic Humidification

Aerosol number and mass distributions produced by an ultrasonic room humidifier and an ultrasonic medical nebulizer were examined in a limited-scale study. Rapid droplet drying occurred at room humidities and under near saturated conditions. A model was tested describing the diameter of dried particles as a function of the dissolved mineral content of the water and the transducer frequency. Water containing 102 mg/L of dissolved minerals in a humidifier with a 1.6 MHz transducer produced droplets with a mass median diameter of 2.9 μm. The number median diameter of particles after drying was computed to be 0.11 μm. The distribution of particles in a nebulizer tube using a NaCl solution was shown to consist of a mixture of dried salt particles and droplets which included coagulated multiplets.     

Increasing the Efficiency of Coagulation of Submicron Particles under Ultrasonic Action

Theoretical Foundations of Chemical Engineering - The results of studies into the coagulation process of submicron particles (smaller than 1–2.5 μm) under various conditions of...