Evaporation of methyl- and dimethyl-substituted malonic, succinic, glutaric and adipic acid particles at ambient temperatures

Vapor pressures of five methyl-substituted dicarboxylic acids are inferred from measurements of evaporation rates of sub-micron particles using the TDMA technique at ambient temperatures. Vapor pressures obtained are: , , , , , , . These vapor pressures are compared with available literature data and with vapor pressures of the un-substituted acids. Our results demonstrate that molecular structure is important for solid state vapor pressures of secondary organic aerosol components at ambient conditions.     

About randomness of aerosol size distributions

All aerosol formation and evolution processes, such as nucleation, condensation, fragmentation, etc., are understood and rationalized via fundamental probabilistic concepts such as probabilities of collision, coagulation, dispersion, etc. Therefore all theoretical size distribution functions (lognormal, modified gamma distribution, self-preserving particle size distribution for Brownian coagulation, etc.) are in fact size probability density functions pdf(r). Any (e.g., measured) size distribution f(r) of an aerosol system is some random realization of its pertinent size probability density function pdf(r). When pdf(r) is viewed as a continuous function, the corresponding size distribution vanishes almost everywhere excluding some randomly set of sizes where f(r)=1. We investigate proximity between f(r) and pdf(r) in finite size intervals and derive expressions for estimation of the standard deviations of several aerosol size-dependent properties arising from randomness of f(r).     

Anion impurities in porous alumina membranes: Existence and functionality

We have carried out a detailed investigation on anion impurities in self-organized porous alumina membranes (PAMs) prepared by a two-step electrochemical anodization process in oxalic acid solutions. The employment of the energy dispersive spectroscopy, high resolution transmission electron microscope and infrared absorption spectra has demonstrated the existence and nonuniform distribution of the anions in the PAM sidewalls. The variation of the COO⁻ stretching vibration and CO₂ absorption bands indicates that annealing can lead to the decrease of the concentration in the PAMs due to the decomposition of impurity groups related to . We have further presented clear functionality that the anions have played key roles in the refractive index and absorption coefficient of the PAMs, and the surface morphology and crystallization of the deposited ZnO nanopore arrays.     

Cl electrosorption on Ag(1 0 0): Lateral interactions and electrosorption valency from comparison of Monte Carlo simulations with chronocoulometry experiments

We present Monte Carlo simulations using an equilibrium lattice-gas model for the electrosorption of Cl on Ag(1 0 0) single-crystal surfaces. Fitting the simulated isotherms to chronocoulometry experiments, we extract parameters such as the electrosorption valency γ and the next-nearest-neighbor lateral interaction energy ϕ_nnn. Both coverage-dependent and coverage-independent γ were previously studied, assuming a constant ϕ_nnn [I. Abou Hamad, Th. Wandlowski, G. Brown, P.A. Rikvold, J. Electroanal. Chem. 554–555 (2003) 211]. Here, a self-consistent, entirely electrostatic picture of the lateral interactions with a coverage-dependent ϕ_nnn is developed, and a relationship between ϕ_nnn and γ is investigated for Cl on Ag(1 0 0).     

Spin design of iron complexes on Fe-ZSM-5 zeolites

The spin state of iron ions in Fe-ZSM-5 zeolites can be purposefully varied by adsorption of gaseous probe molecules. The resulting Fe complexes with half-integer spin (, and ) can be reliably identified by electron paramagnetic resonance (EPR). A good correlation has been found between the concentration of surface sites active in low-temperature nitrous oxide decomposition and the concentration of low-spin () nitrosyl complexes of Fe formed after adsorption of NO molecules. Based on the analysis of the formation of such complexes under varying conditions, we conclude that these active sites contain a binuclear iron complex with S = 0 and three adsorbed NO molecules. An approach to investigate various Fe-containing sites in oxidation catalysts is discussed.     

Structure and thermal stability of mesostructured zirconium oxophosphates

Highly ordered mesoporous zirconium oxophosphates (designated as ZOP) with hexagonal P6₃/mmc and cubic symmetries were firstly prepared by using gemini cationic surfactants as templates. It has been found that the thermal stability was elevated with the structure curvature order: cubic , hexagonal P6₃/mmc and cubic . The ZOP mesoporous materials with cubic and hexagonal P6₃/mmc structures were stable up to 800 °C, which provides a new insight into the structural factors governing self-assembly of thermally stable mesoporous materials and would open up new possibilities of porous materials for advanced applications.     

Synthesis of ceria nanoparticles by flame electrospray pyrolysis

A flame electrospray pyrolysis is presented for synthesizing CeO₂ nanoparticles with a dense morphology, high crystallinity and nanometer size. Hydrated cerium nitrate precursor dissolved in an ethanol/diethylene glycol butyl ether mixture was injected into a CH₄/air premixed flame using an electrospray method. The number size distributions of the as-prepared particles were trimodal. It is suggested that the particles for the fine mode were formed by a Rayleigh disintegration of the charged precursor droplets during the droplet evaporation. The particles for the coarse and middle modes are surmised to come from primary and secondary droplets, respectively, which were formed simultaneously during the atomization processes. The CeO₂ nanoparticles for the coarse mode were nonspherical and composed of few crystallites. The nanoparticles for the fine and middle modes were nearly spherical and nonagglomerated. The as-prepared CeO₂ nanoparticles showed highly crystallinity.     

Counting and particle transmission efficiency of the aerodynamic particle sizer

The aerodynamic particle sizer (APS) measures the size distributions of particles with aerodynamic diameter between 0.5 and in real time. To provide accurate size distributions, the APS must measure both particle size and concentration correctly. The objective of this study was to characterize the counting efficiency of the APS as a function of particle size (0.8–), particle type (liquid or solid), and APS model number (3310 vs. 3321). For solid particles, counting efficiencies ranged between 85% and 99%. For liquid droplets, counting efficiencies progressively declined from 75% at 0.8-μm drops to 25% for 10-μm drops. Fluorometric wash tests indicated that transmission losses occur when larger droplets impact on the instrument's inner nozzle. However, transmission losses did not account entirely for the reduced droplet counting efficiencies, indicating that additional losses may have occurred downstream of the inner nozzle. Between instrument comparisons revealed that although multiple APSs report similar number concentrations, small deviations in particle sizing can produce substantial errors when number concentrations are converted to mass concentrations.     

Effect of spacers on the electrostatic charge properties of metered dose inhaler aerosols

The electrostatic charge properties of commercial metered dose inhaler (MDI) aerosols, including Ventolin^®, Flixotide^®, Tilade^® and QVAR^®, sampled through new and detergent-coated AeroChamber^® Plus spacers were studied using a modified 13-stage electrical low pressure impactor (ELPI) with aerodynamic cutoff diameters ranging from 0.028 to . Aerosol particles deposited on the impactor stages according to their aerodynamic diameters and their charges were simultaneously measured by the electrometers. The deposited drug mass was assayed chemically using HPLC. The surface potential on the inner spacer wall was measured with an electrostatic probe before and after aerosol actuation. High surface potentials were found on the new spacers whereas the detergent-coated spacers had minimal charges due to the conductive coating. MDI aerosol charges were decreased when spacers were used but the charge profiles of the aerosols were not altered qualitatively. New spacers had the lowest throat deposition, fine particle dose, and net aerosol and fine particle charges as a result of high spacer retention. These trends were partially reversed by the detergent-coated spacers. In general, the charge per mass of drug (charge-to-mass ratio) for particles from detergent-coated spacers was higher than those from new spacers. This was thought to be due to the reduction of electrostatic deposition inside the spacer thus leading to particles carrying higher charges being sampled. The calculated number of elementary charges per drug particle ranged from zero to several hundred, which is sufficiently high to potentially affect lung deposition. The ELPI provided high resolution charge profiles on MDI aerosols delivered through spacers.     

Synthesis of ultramarine analogs from erionite

Colored products have been obtained by thermal treatment of erionite mixed with elemental sulfur and alkalis (Na₂CO₃ or K₂CO₃). Synthesis at lower temperature (500 °C) resulted in forming colored materials with preserved ERI structure (particularly with potassium cations), whereas the treatment of highly alkaline mixtures at high temperature (800 °C) caused re-crystallization to SOD (when Na was used) or to unknown structures (with K). The ESR spectra of the products with preserved original ERI structure recorded at room temperature show two signals, one with g = 2.030 and another with g tensor value either 2.045 (for sodium containing samples) or 2.005 (for the potassium bearing products). The latter signal could be considered as a reflection of radicals immobilized in small ε-cages, but it is more likely that it presents anisotropic component of the radical spectrum. The spectra measured at 77 K show anisotropy indicating three values of orthorhombic g-tensor, which is typical of radical, although the values vary for particular samples.     

Development of a large sonochemical reactor at a high frequency

The large sonochemical reactor was developed by using 12 PZT transducers. The frequency was 500 kHz and the total effective electric power applied to transducers was 620 W. The sample and volume were aqueous solution of potassium iodide and 112 dm³, respectively. The ultrasonic power dissipated into solutions was measured by a calorimetric method.

The energy conversion efficiency from electricity to ultrasound was 70%. When the liquid height was from 400 to 435 mm, the production rate has a maximum value. The production rate increased with increasing ultrasonic power. In the case of high ultrasonic power, the production rate for transducers located at the side wall was higher than that at the bottom wall. The sonochemical efficiency for a large sonochemical reactor operated at 500 kHz was close in value to those for laboratory scale reactors at 500 kHz.     

Fractal growth modelling of nanoparticles

The kinetics of iodine oxide aerosol production and growth was studied in an aerosol flow reactor by the photolysis of I₂ in an excess of O₃, at a temperature of 295 K and a total pressure of 1 atm. The time-resolved evolution of the particle size distribution was fitted using a model which assumes that the initial period of particle growth (in the free molecular flow regime) is dominated by collision-coalescence, maintaining spherical shape and compact structure. This leads to the formation of primary particles of about 3 nm radius, which trigger fractal (agglomerative) growth in the transition regime resulting in particle aggregates characterised by lower mass fractal dimensions (D_f) in the range 2.2–2.5. Enhancement of the particle pair collision kernels due to competing van der Waals and hydrodynamic forces is treated within the model. The densities of the fractal aggregates are lower than that of the bulk material, recently identified as I₂O₅ [Saunders, R. W., & Plane, J. M. C. (2005). Formation pathways and composition of iodine oxide ultrafine particles. Environmental Chemistry, 2, 299], as a result of internal void space within the aggregate structures.     

Basic viscoelastic fluid flow problems using the Jeffreys model

Using Laplace transformation technique, semi-analytical solutions are obtained for three basic viscoelastic fluid flow problems under the effect of the Jeffreys model. These semi-analytical solutions are not available in the literature. The present work investigates the effect of two types of driving forces on the flow behavior. These two types are the velocity-type and shear-type driving forces. The effect of the relaxation and retardation times on the flow behavior for these two types of driving forces may be viewed well using the obtained semi-analytical solutions. The three fundamental problems are transient Couette flow, transient wind-driven flow over finite domains and the transient Poiseuille flow in parallel-plates channels. It is shown that as the dimensionless relaxation time (λ₁) increases, the flow response to the imposed driving force becomes slower. This implies that the flow needs more time to feel the presence of the driving force and hence needs more time to attain steady-state behavior. On the other hand, the effect of the dimensionless retardation time (λ₂) depends on the type of the driving force imposed on the system. For a velocity-type driving force, the flow response becomes faster as the dimensionless retardation time (λ₂) increases and for a shear-type driving force the flow response becomes slower as the dimensionless retardation time (λ₂) increases.     

Inverting cascade impactor data for size-resolved characterization of fine particulate source emissions

In this paper, the inversion processing of cascade impactor data to construe continuous size distributions within fine particulate matter (PM_2.5) is examined for residential oil furnace and fireplace appliance emissions. Impactor data from tests with these emissions sources are selected for the challenges they pose to comprehending the size distributions of aerosol mass and chemical species. In specific, the oil furnace aerosol offers an opportunity to apply data inversion to study a bimodal lognormal distribution in which much of the aerosol mass is impactor-penetrating nanoparticles . The fireplace emissions on the other hand cover the issue of a chemical size distribution, which is subject to particle loss and characterized by a single lognormal, accumulation mode peak. Computational steps relevant to the application of the data inversion are illustrated in detail. Evaluation of correlation coefficients (0.992) indicates that the inversion model predictions fit the impactor data well. Simulations of systematic measurement error (±10%) at each impactor stage are shown to have a negligible impact on the inversion results for test data. It is concluded that data inversion can be effective when (i) source emissions contain a portion of particles that falls outside the measurement range of cascade impactors, (ii) a mass size distribution of an individual species is determined without the knowledge of the total mass concentration for that species, or when (iii) losses in the particle charger system are significant.     

Characterization of composite nanofiltration membrane using two-parameters model of Extended Nernst–Planck Equation

The characteristics of polyamide membranes with respect to interfacial polymerization of diamine mixtures with trimesoyl chloride (TMC) are studied using two-parameter model of Extended Nernst–Planck Equation. The investigation provided the information about the effect of TMC content and reaction time on the diffusive and convective flow of ions through the membrane. These indirectly reflected structural properties such as effective skin thickness, pore size and structural integrity of membrane. Membrane flux and rejection are related to the TMC content and reaction time, when NaCl and CuSO₄ are used as testing solutes. The diffusive transport, and convective transport, J_vC_1,0(1−R^′₁) contributions are successfully determined by fitting the model to the experimental data to get f^′₁ and R^′₁ parameters. It was found that at high TMC content the contribution of convective transport over diffusion transport is increased due to the increase of effective thickness. However, for smaller size and higher diffusive solute like Na⁺, the ratio of diffusive flow over convective flow is increased at high TMC and high reaction time. This indicated that numbers of tightened pores membrane are increased. An optimum membrane with high flux and high copper ion rejection could be obtained by incorporating 0.1% (w/v) of TMC in the polymerization reaction mixture under reaction time period of 5 s.     

The morphology of MoS2, WS2, Co–Mo–S, Ni–Mo–S and Ni–W–S nanoclusters in hydrodesulfurization catalysts revealed by HAADF-STEM

HAADF-STEM studies have provided detailed morphological insight regarding MoS₂, WS₂, Co–Mo–S, Ni–Mo–S and Ni–W–S nanostructures in graphite-supported catalysts. It is found that the technique allows the catalytically active edges to be imaged even for single layer metal sulfide structures. Unpromoted MoS₂ and WS₂ are predominantly present as slightly truncated triangular clusters containing only a single S–M–S layer (M = Mo, W). The addition of promoter atoms results in more heavy truncations consistent with the expected tendency for the Co–Mo–S structures to expose promoted S-type edges at the expense of unpromoted Mo-type edges. However, the HAADF-STEM (High-Angle Annular Dark-field Scanning Transmission Electron Microscopy) results show for the first time that Co–Mo–S and Ni–W–S may also expose extended high index truncations.     

Water effect on the conductivity behavior of NH4PO3-based electrolytes for intermediate temperature fuel cells

The electrical conductivity at intermediate temperature of 150–250 °C and the activation energy for conductivity of composite proton conductors, 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ and 2NH₄PO₃–(NH₄)₂SiP₄O₁₃, were investigated as a function of water vapor pressure, P_H2O. The activation energy decreased linearly with the natural logarithm of P_H2O, indicating that water is chemically adsorbed to the electrolytes. The decrease in activation energy is possibly caused by formation of hydrogen bonds between the adsorbed water and the electrolytes. In addition, the pre-exponential factor of Arrhenius equation, σ₀, increased with P_H2O. This suggests that the adsorbed water may generate additional mobile protons for the composite electrolyte. Therefore, the enhancement in the electrical conductivity of a NH₄PO₃-based electrolyte in a water-vapor rich atmosphere originates possibly from the decrease in activation energy as well as the increase in mobile proton concentration.     

Changes in large particle size distribution due to dry deposition processes

A dry deposition model is described that can simulate variations in the size-resolved mass size distribution of large ( diameter) atmospheric particles due to dry deposition processes. The model is unique because it is based on both gravitational and inertial effects in turbulent flow and includes deposition and suspension velocities for large, airborne particles. The model allows the integration of a large number of variables, covering a wide range of conditions (height of particle injection, meteorological conditions, and removal time). Changes in the size distributions that result from model simulations of deposition show the expected decrease in concentration with size since the deposition is greater for the larger particles. However, the size distribution does not decrease with size in a uniform manner as would be suggested by Stokes settling velocity due to the effect of inertial forces acting on the particles. Application of the model reveals a number of patterns, including the development of two peaks in the large particle mass size distribution, a persistent peak in the 1– size range, and a second peak in the 10– range that is strongly affected by meteorological conditions.     

Particle generation by laser ablation during surface decontamination

Laser ablation allows significant number of particles to be generated from the surfaces of cement, chromium-embedded cement, stainless steel, or alumina. The number concentrations and size distributions of the particles were experimentally investigated with respect to applied laser fluence (mJ cm^-2) and wavelength. Based on the measurements, 266-nm laser ablation generates particles most efficiently. Of the three materials tested, cement was the most favorable for material removal, stainless steel was the next, and alumina was the least. The removal of particles from chromium-embedded cement by 532- and 1064-nm-wavelength lasers was less effective than from stainless steel, but more effective than from alumina. For ablation with a 266-nm laser, chromium enhanced the removal above 20 J cm^-2. Comparisons of other characteristics such as the size and removal rate of these particles are also discussed in this paper.     

The contributions of “minimum primary emissions” and “new particle formation enhancements” to the particle number concentration in urban air

In an urban site affected by fresh vehicle exhaust emissions, the ambient air number concentrations of particles coarser than 3 nm (N) was split into two components, N=N1+N2. This was done using a method based on the high correlation between black-carbon (BC) and number (N) concentrations which is typically observed in ambient air and is the result of vehicle exhaust emissions. The component N1 accounts for “those aerosol components directly emitted in the particle phase” and “those components nucleating immediately after emission”. The component N2 accounts for the new particle formation enhancements during the “dilution and cooling of the vehicle exhaust” and is also influenced by “in situ new particle formation in ambient air”. The contribution of N1 to N exhibits a maximum of 55% during the morning rush hours (07:00–08:00). The contribution of N2 to N exhibits a daily evolution with a broad maximum during daylight (as solar radiation intensity), while for about 7 h (11:00–17:00) the N2 contribution to N is about 70%. During some “afternoon N2 events”, N2 contributions exceeded 90%. Enhancements in the new particle formation processes may increase the N/BC concentrations ratio in one order of magnitude, from 4.82×10⁶ particles/ng BC to 47×10⁶ particles/ng BC and during some events up to 97×10⁶ particles/ng BC. The results show evidence of the high potential of the vehicle exhausts and of the urban atmosphere to trigger new particle formation if the ambient air conditions are favourable. The method used in this study is useful in assessing future changes in the number to BC relationship due to forthcoming regulations in the vehicle exhaust emissions.