Filtration of Chain Aggregate Aerosols by Model Screen Filter

A screen type diffusion battery was used as a model screen filter for studying the filtration of chain aggregate aerosols. The aerosols, with well-defined diameter and length, were generated with a system that included a flame aerosol generator and a differential mobility analyzer. Particle sizes were characterized using transmission electron microscopy and a digital image processing technique. The penetration efficiency of the aerosols through even stages of the diffusion battery at certain flow velocities were measured using a condensation nucleus counter (CNC). Quantitative data were obtained by operating the CNC in count mode simultaneously with a laser aerosol spectrometer. Results indicated that penetration efficiency decreased exponentially with the number of screens and increased with flow velocity. In addition, theoretical analysis of filtration mechanisms based on the fan model theory has been made and compared with the measurements of penetration efficiency. Results showed that the collection of chain aggregates on model screen niters was in the regime dominated by an interception mechanism. Average orientation angles of the aerosols with respect to the flow field were also estimated.     

Generation of Radiolabeled Soot-Like Ultrafine Aerosols Suitable for Use in Human Inhalation Studies

We have developed a method for radiolabeling ultrafine carbon particle aggregates with technetium-99m. The carbon aggregate aerosol was chosen to mimic the physical properties of urban combustion or ''soot-like'' particulate. The radioisotope is a short lived (t_1/2 = 6.02 h) gamma emitter commonly used in human studies where scintigraphic methods are employed. Primary carbon parti cles, the aggregation of which is controlled by concentration and time, were produced by arcing between graphite electrodes under an argon atmosphere. Radiolabeling of particles was accomplished by applying a pertechnetate solution onto the tips of electrodes prior to arcing. The activity median diameter of experimental aerosols could be varied from 50 to 150 nm. The specific activity of aerosols increased with the amount of activity applied to the electrodes and decreased with time of generator operation. In-vitro leaching of the radioisotope from particles into solution was also measured. Leaching appeared to increase with the specific activity of the aerosol but was not affected by particle size.     

In Situ Dynamic Measurement of Polydisperse Chain Aggregate Aerosols Using Photocorrelation Spectroscopy Technique

An experimental technique was developed to perform in situ photo correlation spectroscopy measurements on length distribution of dynamic polydisperse iron oxide aerosols with diameters ranging from 0.01 to 0.05 μm. The cumulant analytical method is used to determine the average length of the chain aggregate. The experimental results show that the average length of the iron oxide aerosols obtained by the photo correlation spectroscopy technique is basically consistent with the results obtained by TEM. Results indicate that the length of the iron oxide samples increases as the liquid carbonyl temperature increases and the gas flow dilution ratio decrease.     

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.     

Drag Force and Slip Correction of Aggregate Aerosols

The drag force on aggregate particles of uniform spheres was measured in a Millikan apparatus as a function of Knudsen number. Our experiment was designed to study the effect of particle orientation on the slip correction factor of nonspherical particles. The velocities of charged particles in a gravitational field with and without an applied electrical field were measured. An electrical field strength of 2000 V/cm was used to align doublet and triplet particles. Results showed that an aggregate particle moved in random orientation while in the gravitational field. The same particle moved with its polar axis parallel to the electric field (doublets) or with its plane of centers parallel to the electrical field (triangular triplets). Using a nonlinear regression method, both the dynamic shape factor and slip correction factor could be determined separately from the data. The dynamic shape factors at different orientations were in good agreement with those obtained previously in a sedimentation tank. The slip correction factor of singlet particles agreed with results previously obtained by Allen and Raabe for latex particles. Slip correction factors of doublets and triangular triplets can also be expressed in the Knudsen-Weber form: 1 + 2λ/d _a [1.142 + 0.558 exp(?0.999 d _a/2λ)]. The adjusted sphere diameter d _a was 1.21 d ₁ (primary diameter) for doublets moving parallel to the flow and 1.31 d ₁ for doublets randomly oriented. These results show that the slip correction factor of a nonspherical particle depends on the orientation and confirm the theory proposed by Dahneke.     

The Generation and Characterization of Metallic and Mixed Element Aerosols for Human Challenge Studies

A spark discharge aerosol generator (Palas GFG 1000) has been utilized to generate aerosols of pure metals and of carbonaceous aerosols containing a metal component. This was achieved by fabricating metal electrodes of the desired dimensions and also by repeated instillation of saturated FeCl 2 solution into a machined recess in an existing graphite electrode. Number size distributions of the resultant aerosols were measured, and field emission gun transmission electron microscopy (FEG TEM), coupled with energy dispersive X-ray (EDX) analysis, were performed on the collected samples. Whilst utilizing two identical metallic electrodes, it was found that particle-number concentration and modal diameter generally increased with a greater electrical and thermal resistivity of the electrode material. Utilizing zinc as a single electrode, or pair of electrodes, one observed an effect of enhanced airborn mass concentration of this element upon spark discharge. It is postulated that this phenomenon was due to zinc's inherent low melting and boiling points. Measurements performed with EDX analysis indicated the composition of carbon/metal aerosols to consist primarily of carbon. Aerosols generated using a stainless steel/carbon system show dense regions present, with an observed composition very close to that of stainless steel, indicating little, if any, fractionation of these particular elements during the aerosol formation process. This observation, together with evidence gained from FEG TEM imaging in further systems, suggests that droplet formation directly from the metallic electrode surface constituted an important role in the aerosol formation process.     

Differences in Diffusion Charging of Dielectric and Conducting Ultrafine Aerosols

The effect of the dielectric constant on unipolar and bipolar charging rates is investigated. This effect is manifested through the image potential. Bulk dielectric constants of aerosol materials range from 2.5 to 50. The corresponding image potentials range from about 40% to about 96% of the image potential for a perfect conductor. Charging simulations were carried out for this parameter range and typical results are presented. For dielectric constants greater than 2.5 the charging behavior shows a strong image potential effect, and may be approximated by calculations for a perfect conductor. This suggests that charging models that do not allow for image potential effects are likely to be inaccurate except, perhaps, for larger particles, where the Coulomb potential dominates the image potential. The simulations are compared with unipolar charging data from recent experiments, which tend also to support this conclusion.     

Deposition of Ultrafine Aerosols in a Human Oral Cast

This paper reports experimental measurements of the total deposition of ultrafine aerosols in a human oral airway cast. A clear polyester resin cast of the upper airways of a normal human adult, including the nasal airways, oral cavity, tongue, nasopharynx, and larynx, was made from a postmortem solid cast. Measured pressure drop in the oral airway was slightly lower than in the nasal airway. The measured oral flow resistance was similar to the values reported for human volunteers breathing through the mouth at rest and for spontaneously opening of the mouth. Aerosol deposition data in the cast for monodisperse NaCl aerosols between 0.2 and 0.005 μm in diameter deposited in the cast were obtained for inspiratory and expiratory flow rates of 4, 20, and 40 L/min. Deposition efficiency increased with decreasing particle size and flow rate indicating that turbulent diffusion was the dominant mechanism for deposition. Higher deposition efficiency was observed for inspiratory flow in the oral airway than for expiratory flow. Oral deposition and nasal deposition for inspiratory flow were similar, but oral deposition was lower for expiratory flow. Deposition efficiency can be expressed as a function of the flow rate and diffusion coefficient of the particle.     

Isotopic Characterization of Carbonaceous Aerosols

Carbonaceous aerosol samples were collected during numerous field experiments either in continental or oceanic areas in the two hemispheres. An experimental procedure has been optimized for the collection, concentration analysis, and isotopic composition determination (¹³C / ¹²C) by mass spectrometry of size-segregated samples. Data is presented here on the characteristic isotopic composition and isotopic variability of the main sources of atmospheric particulate carbon. Such an approach allows the differentiation between not only marine and continental material but also between continental natural and anthropogenic matter among these aerosols. Particularly, combustion of the vegetation induces a large isotopic separation between the two isotopes and, consequently, the aerosol which is emitted is characteristically depleted in ¹³C. The isotopic tool is used here for the first time to assess the origin of carbonaceous aerosols whatever the environment. The areal and temporal isotopic variabilities of aerosol samples are shown to be related to the diversity of the sources, and also to the proper temporal variability of the intensity and the isotopic composition of these sources. Far from the source regions, carbonaceous aerosols bear their isotopic characteristics; the isotopic tool appears to be a promising tracer of the bulk atmospheric particulate carbon.     

超细阿奇霉素的制备及表征

采用超音速气流粉碎技术进行了阿奇霉素微粉化实验，考察了进样速度、压缩空气压力、粉碎次数及分散剂等因素对阿奇霉素微粉颗粒大小和粒径分布的影响，并对微粉化后的粉体进行扫描电镜、粒度、ZETA电位及红外光谱分析。实验结果表明采用超音速气流技术进行超细粉碎，可使阿奇霉素微粉平均粒径达到1．13μm，粒径分布为0.71～1．99μm，且粉碎后并未改变原料的化学成分和结构。     

Total Deposition of Ultrafine Hydrophobic and Hygroscopic Aerosols in the Human Respiratory System

The deposition of ultrafine particles in the human respiratory system was studied under a variety of steady breathing conditions. The monodisperse aerosols tested were hydrophobic kerosene heater, aluminosilicate, and hygroscopic NaCl in the size range of 0.03 to 0.4 μm in diameter. The results for all aerosols show that particle deposition increases with an increase in tidal volume, but with a decrease in breathing frequency. Also, deposition during breath holding increases nearly exponentially with an increase in time. However, particle deposition as a function of particle size is different between hydrophobic and hygroscopic aerosols in the size range tested. The hydrophobic aerosols increase with a decrease in particle size, while hygroscopic aerosols show minimum value in the size range of 0.06 to 0.09 μm. The hydrophobic kerosene heater and aluminosilicate particle deposition confirms the recent theoretical calculations of Yeh and Schum (1980), Yu and Diu (1982), and Yu and Hu (1983). The NaCl particles show a 3.5 to 4.5 fold growth under conditions approximating the respiratory tract.     

Deposition of Inhaled Ultrafine Aerosols in Replicas of Nasal Airways of Infants

Experimentally measured deposition of ultrafine particles, ranging from 13–100 nm in diameter, in nasal airway replicas of ten infants aged 3–18 months is presented. The replicas included the face, nostrils, and nasal airways including the upper trachea. A differential mobility analyzer (DMA) and a condensation particle counter (CPC) were used to quantify the nasal deposition by comparing the number of polydisperse sodium chloride particles, generated by evaporation from a Collison atomizer, at the inlet and outlet of the replicas. Particles were individually classified in size by DMA and subsequently were counted one size bin at a time by CPC upstream and downstream of each replica. Since in vivo data is not available for infants to compare to, we validated our experimental procedure instead by comparing deposition in nasal airway replicas of six adults with in vivo measurements reported in literature. In the infant replicas, tidal inhalation was simulated at two physiologically compatible flow rates and the effect of flow rate on deposition was found to be small. Deposition obtained at constant flow rates is lower than with tidal breathing, indicating the importance of unsteadiness, in contrast to similar data in adults where unsteadiness is known to be unimportant. An empirical equation, containing geometrical features of the nasal airways in the form of related non-dimensional dynamical parameters (Reynolds, Schmidt, and Womersley numbers), was best fitted to the infant data. This equation may be useful for a priori prediction of nasal deposition and intersubject variability during exposure of infants to ultrafine aerosols.     

Fluidized Bed Generation of Stable Silica Nanoparticle Aerosols

A long-lasting generator of continuous silica nanoparticle aerosols based in a fluidized bed of glass beads coated with nanosized silica has been developed. The attrition resulting from the bubbling fluidized bed regime progressively detaches the silica coating from the glass beads, giving rise to a steady production of silica nanosized aerosols with median diameters from 100 to 250 nm depending on the initial size of the coating nanoparticles. Continuous aerosol production could be maintained for more than 12 h, and the nanoparticle concentration can be easily tuned in the range of 2000 to 14,000 #/cm³ by adjusting the fluidization and/or dilution flow rates.

Copyright 2013 American Association for Aerosol Research     

超细二氧化硅的制备和表征

本文以正硅酸乙酯为硅源,通过溶胶-凝胶法制备超细二氧化硅.考察了溶剂、温度、添加剂等因素对制备二氧化硅的影响.通过一系列的实验确定了制备超细二氧化硅较好的工艺条件:以丙酮为溶剂、氨水为催化剂、pH值为9左右、反应温度为40 ℃.并采用XRD、N2等温吸附-脱附、FT-IR、SEM等手段对二氧化硅进行表征.结果表明:所制得的二氧化硅为无定形结构,孔径分布集中在2～25 nm,BET比表面积可达200 m2/g以上.     

不溶性超细蚕丝粉末的制备与表征

用质量分数为98%的浓硫酸催化水解桑蚕茧,当茧丝质量与浓硫酸体积比为1:3时,在100℃条件下反应6h,之后用适量的石灰乳中和酸解液至稍偏酸性,抽滤后将所得滤液用活性炭脱色,之后将所得滤液浓缩,将浓缩液中加入适量的有机溶剂作为沉淀剂,之后静置,待固体完全沉淀之后,过滤,可制得平均粒径为150 nm的丝粉,所得产品可添加于化妆品中,产品产率可达95%。并对所得产品进行了扫描电镜,示差热分析,X-射线衍射等表征分析。     

不溶性超细丝胶粉的制备和表征

用质量分数为98%的浓硫酸催化水解丝胶,当丝胶与浓硫酸在质量体积比为1︰3时,在100℃条件下反应6h,之后用适量的石灰乳中和酸解液至稍偏酸性,抽滤后将所得滤液用活性炭脱色,之后将所得滤液浓缩,将浓缩液中加入适量的有机溶剂作为沉淀剂,之后静置,待固体完全沉淀之后,过滤,可制得平均粒径为160nm的丝胶粉,所得产品可添加于化妆品中,产品产率可达92%。并对所得产品进行了扫描电镜,X-射线粉末衍射,紫外吸收等表征分析。     

Characterization of Multicomponent Aerosols by Raman Spectroscopy

In this work the feasibility of Raman spectroscopy, especially the detection limit of this technique for the chemical characterization of multicomponent aerosols, which appear in technical processes has been investigated. In such kind of aerosols high number concentrations (>10⁶ cm^?3) can be observed whereas the range of the pollutant loading varies from 10–1000 mg/m³. For these purposes different type of aerosols have been investigated. Aerosols in which the pollutant can be found in the dispersed phase as well as in the gas phase (aqueous solutions of NH₃ aerosols), those where the pollutant appears only in the dispersed phase (aqueous solutions containing SO₄ ^2?/ NO₃ ^? salts) and aerosols where there is no Raman shift between the signals of the gas and the dispersed phase (toluene/ dodecane aerosols). Furthermore aerosols generated by the reaction between NH₃ and HCl in nitrogen containing different amounts of vapor are also investigated.

The characterization of the aerosols with Raman spectroscopy with respect to their gas phase is without any difficulty, whereas the analysis in the dispersed phase is partially marginal and in majority of cases almost not possible.

Especially for the reaction aerosols rejection of elastically scattered light is the principle limitation in collecting Raman scattered light from particles in the Mie-scattering regime.     

Deposition of Ultrafine Aerosols and Thoron Progeny in Replicas of Nasal Airways of Young Children

The deposition efficiencies of ultrafine aerosols and thoron progeny were measured in youth nasal replicas. Clear polyester-resin casts of the upper airways of 1.5-yr-old (Cast G), 2.5-yr-old (Cast H), and 4-yr-old (Cast I) children were used. These casts were constructed from series of coronal magnetic resonance images of healthy children. The casts extended from the nostril tip to the junction of the nasopharynx and pharynx. These casts were similar in construction to those used in previous studies (Swift et al. 1992; Cheng et al. 1993). Total deposition was measured for monodisperse NaCl or Ag aerosols between 0.0046 and 0.20 (Jim in diameter at inspiratory and expiratory flow rates of 3, 7, and 16 L min^?1 (covering a near-normal range of breathing rates for children of different ages). Deposition efficiency decreased with increasing particle size and flow rate, indicating that diffusion was the main deposition mechanism. Deposition efficiency also decreased with increasing age at a given flow rate and particle size. At 16 L min^?1, the inspiratory deposition efficiencies in Cast G were 33% and 6% for 0.008- and 0.03-μm particles, respectively. Nasal deposition of thoron progeny with a mean diameter of 0.0013 μm was substantially higher (80%-93%) than those of the ultrafine aerosol particles, but still had a similar flow dependence. Both the aerosol and thoron progeny data were used to establish a theoretical equation relating deposition efficiency to the diffusion coefficient (D in cm² s^?1) and flow rate (Q in L min^?1) based on a turbulent diffusion process. Data from all casts can be expressed in a single equation previously developed from an adult nasal cast: E = 1 - exp(-aD ^0.5 Q ^?0.125). We further demonstrated that the effect of age, including changes to nasal airway size and breathing flow rate, on nasal deposition can be expressed in the parameter “a” of the fitted equation. Based on this information and information on minute volumes for different age groups, we predicted nasal deposition in age groups ranging from 1.5- to 20-yr-old at resting breathing rates. Our results showed that the nasal deposition increases with decreasing age for a given particle size between 0.001 to 0.2 μm. This information will be useful in deriving future population-wide models of respiratory tract dosimetry.     

ZnO超微粉末的制备与表征

以ＺｎＳＯ４·７Ｈ２Ｏ和Ｎａ２ＣＯ３为原料，采用化学法合成了ＺｎＯ超微粉末。应用Ｘ射线粉末衍射法（ＸＲＤ）测定了合成ＺｎＯ的几组晶面的衍射峰形，经数据处理得到ＺｎＯ超微粉末的平均晶粒度和晶格畸变率的定量分析结果。实验结果表明，化学法合成的ＺｎＯ超微粉末的晶粒度范围在２０ｎｍ～３５ｎｍ之间。