Dynamic impact model of plastic deformation between micro-particles and flat surfaces without adhesion

This article considers the normal elastic–plastic impact of micro-particles against a flat surface without adhesion, and a dynamic model of plastic deformation was developed to describe the rebound behavior of impacting particles. Analytical expression for restitution coefficient was obtained and it was validated by the experimental data in the literature. The effects of material properties and impact velocities on the rebound behavior were also discussed. The relationship of normal force, particle velocity, plastic deformation, and contact duration was derived. The results show that the evolution of the normal force for the elastic–plastic impact is asymmetric, and the contact time for the elastic–plastic impact is obviously longer than the equivalent perfectly elastic impact for a given impact velocity. It is also found that the evolutions of contact time and loading time varying with impact velocities are in good agreement with the experimental observations.

Copyright © 2016 American Association for Aerosol Research     

Evaluation of portable dilution system for aerosol measurement from stationary and mobile combustion sources

This study presents the emission factor of PM_2.5, elemental carbon (EC), organic carbon (OC), and water-soluble ions for biomass-fired-induced downdraft gasifier and light duty diesel vehicle (LDDV). A portable dilution system (PDS) developed for on-field measurement of aerosol and their precursors from combustion sources were used for quenching of aerosol at near-atmospheric condition before collection on filters. PDS consists of a heated duct and particle sampling probe, dilution tunnel, zero air assembly, and a power supply unit. PDS was evaluated under controlled conditions in laboratory for gasifier cookstove and LDDV over wide range of dilution ratios to understand the effect of dilution on mixing, particle formation, and loss. The invariability in CO₂, recorded along the length and at radial distances of cross-section of dilution tunnel, confirmed the rapid and homogenous mixing inside the dilution tunnel. The particle loss and nucleation inside the dilution tunnel accounted for 6–20% at different dilution ratios (30:1–90:1). PM_2.5 emission factors for wood combustion in gasifier cookstove showed mild decrease (13%) with increasing dilution ratio from 75:1 to 108:1. However, a considerable decrease of 37% (221–139 mg km^?1) was observed for LDDV with increase in dilution ratio from 39:1 to 144:1. Similar decrease in particulate organic carbon emission rates were observed indicating scarcity of sorptive organics, and insufficient residence time for condensation limited the particle formation from vapor phase organic compounds at high dilution ratios.

© 2016 American Association for Aerosol Research     

Experimental study on mechanical filtration through tobacco columns: Influence of cut-filler shape and size distribution on filtration efficiencies

Tobacco columns are extreme examples of heterogenous packed beds, which have various cut-filler shapes and a wide range of size distribution. The behavior of mechanical filtration through tobacco columns has been investigated by using polystyrene latex (PSL) standard particles to compare the actual filtration efficiency with the predicted filtration efficiency calculated by theoretical equations for spherical packed beds. The influence of cut-filler shape and the range of cut-filler size distribution on filtration efficiency have been examined. The effect of diffusion in tobacco columns was lower and the effect of interception and inertia were higher than in spherical packed beds. These results show that a partially faster flow could have occurred in tobacco columns. It means that it is difficult to utilize the theoretical equations for spherical packed beds to heterogenous packed beds as proposed. Filtration efficiency through tobacco columns had a relationship with the factor that shows cut-filler shape and size distribution (r = 0.894, p < 0.05) and the factor that shows cut-filler size distribution (r = 0.683, p < 0.15). The factor showing cut-filler shape and size distribution was expected to be an effective factor of filtration efficiency for heterogenous packed beds. From these experiments, empirical equations that can be applied to tobacco columns have been proposed, and the prediction accuracy during burning was validated. It has been found that the prediction accuracy was precise, revealing the importance of taking the influence of cut-filler shape and size distribution into account in the filtration equations.

Copyright © 2016 American Association for Aerosol Research     

Effects of temperature on the formation of secondary organic aerosol from amine precursors

Aerosol formation is directly influenced by meteorological properties such as temperature and relative humidity. This study examines the influence of temperature on the physical properties and chemical composition of the aerosol produced from radical oxidation of aliphatic amines. Aerosol formation for temperatures ranging from 10 to 40°C was investigated in dual 90 m³ indoor atmospheric chambers. Further, chemical and physical responses of aerosol formed at one temperature and then raised/cooled to another were investigated in detail. Around two to three times more aerosol formation occurred at 10°C than at 40°C. This has important implications for locations influenced by amine emissions during the winter months. Significant aerosol formation occurred with the oxidation of amines with nitrate radical (100–600 μg/m³) and consisted largely of amine nitrate salts. These reactions are important contributors to aerosol formation during the nighttime hours, when nitrate radical is the dominant oxidant and temperatures tend to be cooler. Solid/gas partitioning of amine nitrate salt aerosol was consistent with literature results. A novel, temperature dependent, mechanism describing peroxy and hydroperoxy radical reactions was observed in the trimethylamine with hydroxyl radical oxidation experiments.

Copyright © 2016 American Association for Aerosol Research     

Methodology for quantifying the volatile mixing state of an aerosol

Mixing state refers to the relative proportions of chemical species in an aerosol, and the way these species are combined; either as a population where each particle consists of a single species (‘externally mixed’) or where all particles individually consist of two or more species (‘internally mixed’) or the case where some particles are pure and some particles consist of multiple species. The mixing state affects optical and hygroscopic properties, and quantifying it is therefore important for studying an aerosol's climate impact. In this article, we describe a method to quantify the volatile mixing state of an aerosol using a differential mobility analyzer, centrifugal particle mass analyzer, catalytic denuder, and condensation particle counter by measuring the mass distributions of the volatile and non-volatile components of an aerosol and determining how the material is mixed within and between particles as a function of mobility diameter. The method is demonstrated using two aerosol samples from a miniCAST soot generator, one with a high elemental carbon (EC) content, and one with a high organic carbon (OC) content. The measurements are presented in terms of the mass distribution of the volatile and non-volatile material, as well as measures of diversity and mixing state parameter. It was found that the high-EC soot nearly consisted of only pure particles where 86% of the total mass was non-volatile. The high-OC soot consisted of either pure volatile particles or particles that contained a mixture of volatile and non-volatile material where 8% of the total mass was pure volatile particles and 70% was non-volatile material (with the remaining 22% being volatile material condensed on non-volatile particles).

© 2016 American Association for Aerosol Research     

Improving the signal-to-noise ratio of Faraday cup aerosol electrometer based aerosol instrument calibrations

This study introduces a new bipolar measurement routine for particle number concentration calibrations. In the new routine, singly-charged particles of opposite polarities are measured sequentially with a Faraday cup aerosol electrometer (FCAE). We compared the bipolar routine to the traditional FCAE routine, where particle signal and electrometer offset are measured in turns, by calibrating a single CPC on a wide particle number concentration range (from 1000 to 77,000 cm^?3) with both routines. By increasing the signal-to-noise ratio, the bipolar routine decreases the type A uncertainty of the calibration especially at low particle concentrations. In practice, the new routine enables shortening the measurement times by 80% at the lowest particle concentrations which, in practice, corresponds to hours.

Copyright © 2016 American Association for Aerosol Research     

How well can aerosol instruments measure particulate mass and solid particle number in engine exhaust?

Aerosol instruments provide more informative engine exhaust particulate matter (PM) data than the gravimetric filter and solid particle number methods prescribed by regulations. Yet their lack of conformity to the regulatory methods can limit their acceptance for vehicle development. This article examines the ability of the Dekati Mass Monitor (DMM), Engine Exhaust Particle Sizer (EEPS), and Micro Soot Sensor (MSS) to measure PM_2.5 mass and solid particle number relative to current motor vehicle PM emissions standards. Simultaneous PM measurements are made by these three instruments and the two regulatory methods for 50 tests of six gasoline direct injection and two port fuel injection vehicles over the U.S. Federal Test Procedure. DMM and EEPS determinations of PM mass correlate well to gravimetric values (regression slopes of 1.06 ± 0.04 and 0.98 ± 0.08) down to a few mg/mile, below which filter weighing variability becomes problematic. The MSS exhibits a lower slope of 0.79 ± 0.03 consistent with it measuring the soot fraction, rather than total PM. At emissions rates above ～10¹³ particles/mile, solid particle number determined from DMM and EEPS data correlates respectably with, but overestimates the regulatory method (regression slopes are 1.7 ± 0.1 and 1.4 ± 0.15, respectively). Below this emissions rate, the correlation degrades. EEPS estimates of PM mass are significantly improved with the recent soot optimized inversion algorithm (slope improves from 0.45 to 0.98). While they cannot replace filters and solid particle counting, the present study suggests that these instruments can be used as more informative surrogates during motor vehicle development.

© 2016 Ford Motor Company     

Aqueous film formation on irregularly shaped inorganic nanoparticles before deliquescence,as revealed by a hygroscopic differential mobility analyzer–Aerosol particle mass system

A hygroscopic tandem differential mobility analyzer (H-TDMA) and a hygroscopic coupled DMA and aerosol particle mass (H-DMA-APM) were coupled to examine aqueous film formation and the deliquescence behavior of inorganic nanoparticles. The two systems complement each other because H-DMA-APM measures mass change, while H-TDMA measures mobility diameter (volume) change of nanoparticles upon water uptake. The former mass change was, in particular, more capable to discern minute particle phase changes than the latter size change at moderate RHs. The mass and diameter changes were used to derive the particle effective density for evaluation of aqueous film formation on the nanoparticle surface before and after deliquescence transition. The measurements further showed that approximately 3–5 and 12–20 monolayer equivalents of water molecules formed on the respective surface of 50- and 100-nm inorganic aerosols (ammonium sulfate and sodium chloride) before deliquescence relative humidity (DRH). These findings support the physical basis of the coated-surface model given by Russell and Ming in 2002, and suggest that the phase transition of inorganic nanoparticles near deliquescence is a gradual process instead of an abrupt change. This phenomenon changed the surface energy values, thus confirming the explanation that the DRH of nanoparticles increases as the particle size decreases. This is the first direct observation of nanoparticle deliquescence phase transition using the H-DMA-APM system, and the detailed characterization of aqueous film formation on inorganic nanoparticles is feasible with the presented measurement systems.

© 2016 American Association for Aerosol Research     

Practical limitations of aerosol separation by a tandem differential mobility analyzer–aerosol particle mass analyzer

A cavity ring-down spectrometer and condensation particle counter were used to investigate the limitations in the separation of singly and multiply charged aerosol particles by a tandem differential mobility analyzer (DMA) and aerosol particle mass analyzer (APM). The impact of particle polydispersity and morphology was investigated using three materials: nearly monodisperse polystyrene latex nanospheres (PSL); polydisperse, nearly spherical ammonium sulfate (AS), and polydisperse lacey fractal soot agglomerates. PSL and AS particles were easily resolved as a function of charge. For soot, the presence of multiply charged particles severely affects the isolation of the singly charged particles. In cases where the DMA–APM was unable to fully resolve the singly charged particles of interest, the peak mass deviated by up to 13% leading to errors in the mass specific extinction cross section of over 100%. For measurements of nonspherical particles, nonsymmetrical distributions of concentration as a function of mass were a sign of the presence of multiply charged particles. Under these conditions, the effects of multiply charged particles can be reduced by using a second charge neutralizer after the DMA and prior to the APM. Dilution of the aerosol stream serves to decrease the total number concentration of particles and does not remove the contributions of multiply charged particles.     

Detection of light-absorbing iron oxide particles using a modified single-particle soot photometer

Copyright © 2016 American Association for Aerosol Research     

A pragmatic approach to the particle sizing of submicrometre emulsions using a laser nephelometer

The use of a commercial laser nephelometer to measure the mean particle size of submicrometre emulsions is described. The instrument is sufficiently sensitive to measure particles smaller than 600 nm. The method is comparative, and two standard materials of known size that are physically and chemically similar to the test emulsion must be used. The method is rapid and inexpensive, and may be used as a routine, in-house quality control procedure for monitoring emulsion production processes such as homogenization. However, it is only suitable if the average particle size of the system is smaller than 600 nm and, probably, with a relatively narrow size distribution.     

A single-particle characterization of a mobile Versatile Aerosol Concentration Enrichment System for exposure studies

Background  

An Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to investigate the size and chemical composition of fine concentrated ambient particles (CAPs) in the size range 0.2–2.6 μm produced by a Versatile Aerosol Concentration Enrichment System (VACES) contained within the Mobile Ambient Particle Concentrator Exposure Laboratory (MAPCEL). The data were collected during a study of human exposure to CAPs, in Edinburgh (UK), in February-March 2004. The air flow prior to, and post, concentration in the VACES was sampled in turn into the ATOFMS, which provides simultaneous size and positive and negative mass spectral data on individual fine particles.     

Synthesis,characterization and ceramization of a novel vinyl-rich liquid precursor for Si(O)C ceramic

Polymethylsilane (PMS) was partially modified with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane ([CH₃(CH₂åCH)SiO]₄, D4Vi) via conventional hydrosilylation. The as-synthesized vinyl-rich liquid precursor (V-PMS) was characterized by the viscosity test, gel-permeation chromatography, Fourier-transform infrared spectroscopy, nuclear magnetic resonances spectroscopy. The results indicate that the obtained precursor is well soluble in common solvents and exhibits a controllable viscosity of 326.9–714.6 mPa s at room temperature. The thermal properties of V-PMS were investigated by differential scanning calorimetry and thermogravimetric analysis. The V-PMS can be cured readily at 150 °C in inert atomosphere. The ceramic yield of V-PMS reaches 81% at 1200 °C, 38% higher than that of PMS. The final pyrolytic residue is hard, dense monolithic up to 1400 °C under Ar atmospheres. The controllable viscosity, excellent thermal curability and high ceramic yield enable the liquid precursor a promising material to shape various Si(O)C ceramic materials for high-temperature application.     

一种新的寡聚酰胺体系的合成及表征

合成了一种新的由2,6-二甲氨基吡啶和2,6-二羧基吡啶单元交替组成的寡聚酰胺化合物,并通过1HNMR、13CNMR和MALDI-TOF质谱对其结构进行了全面的表征。     

新型双偶氮化合物的合成与表征

以三聚氯氰(CNC)和对羟基偶氮苯(p-HAB)为原料,通过亲核取代反应合成了一种新型双偶氮化合物。考察了反应物投料摩尔比,碱的种类和碱的用量,溶剂的种类,反应时间等条件对目标产物收率的影响。结果表明:n(p-HAB)∶n(CNC)=2∶1,碱用NaOH,且n(NaOH)∶n(CNC)=2∶1,以V(丙酮)∶V(水)=1∶1为溶剂,先在冰浴中反应2 h,再加热至30℃反应5 h,双偶氮化合物收率达94.1%。通过红外光谱,元素分析,核磁共振对目标产物结构进行了表征。