Oxide Aerosols Research Articles

Simulation of nitrate aerosol concentrations over East Asia with the model system RAMS-CMAQ

The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to analyse the geographical and the seasonal characteristics of nitrate aerosol (ANO3) concentration distributions over East Asia. Three-dimensional concentrations in January,March, April, July and October of 2001 are simulated, and for the evaluation of model performances, the simulated values of wind direction, wind speed, temperature, specific humidity, nitric oxide (NO), nitrogen oxide (NO2), ANO3 and ammonium aerosol (ANH4) are compared with the observational data obtained onboard the P-3B aircraft during its four consecutive flights over the South China Sea, the East China Sea, the Yellow Sea and the water areas to the east of Japan conducted on 13, 17, 18 and 21 March 2001. The observed data are 5-min averaged and the model results with a 1-hour temporal resolution are interpolated to the aircraft location and time using trilinear interpolation. Comparison shows that the observed values exhibit strong temporo-spatial variations, and the model reproduces these variations reasonably well. The simulated values of wind direction, wind speed, temperature and specific humidity are generally in good agreement with the observed ones, their correlation coefficients reach 0.66, 0.94, 0.99 and 0.96, respectively. Comparison also shows that the average mixing ratios of modelled and observed NO, NO2, ANO3 and ANH4 agree reasonably well with each other, the correlation coefficient for ANO3 and ANH4 are larger than 0.8, but the simulated standard deviations are smaller than the observed one, and the correlation coefficient for NO and NO2 are 0.48 and 0.44.Analysis of horizontal distributions of monthly averaged ANO3 concentrations in the boundary layer indicates that the ANO3 mixing ratios have noticeable differences among the four seasons. Generally the concentrations are high in the winter, spring and fall and low in the summer, and seasonal variations are typically strongest over China and Japan. Highest concentrations are found over eastern China where emissions of nitrogen oxides and ammonia are high and long-range transport may cause elevated concentrations in remote areas under favourable meteorological conditions, but the seasonal variation in the ANO3 concentrations is heavily influenced by the changes in precipitation and temperature.

Evaluation of cerium oxide and cerium oxide based fuel additive safety on organotypic cultures of lung slices

Among the various technological proposals under consideration to limit diesel exhaust particles (DEP) emissions, the use of a particulate filter in conjunction with a fuel-borne catalyst is currently the primary focus and likely to be introduced over the coming years. One specific catalyst is a cerium-based compound Envirox™ developed by Oxonica (Kidlington, UK) and used as a fuel additive to reduce particulate matter (PM) emissions from diesel engines. Prior to any commercialization it is necessary to undertake an assessment of any potential adverse health effects resulting from exposure to cerium oxide particles especially via the inhalation route, i.e., on the lung. Since the composition of engine exhaust emissions from additized fuel might be different to those emissions from un-additized diesel fuel, the second phase of the current investigation compared the potential biological impact of engine emissions from cerium oxide additized fuel to that of a reference fuel. An experimental procedure developed in our laboratory using an organotypic culture of lung slices was used. Biological endpoints were chosen in order to evaluate cell viability (ATP, intracellular GSH), pro-inflammatory reaction (TNF alpha) and anti-oxidant enzyme activity (total GPx, Mn SOD, catalase). No impact of nanoparticulate cerium oxide aerosol on lung tissue biological parameters was observed with one exception, an increased catalase activity which was not associated with a concomitant loss in cell viability. It is therefore concluded, on the basis of this study and from the prospective potential exposure to cerium oxide, that a very low prospective risk is associated with the expected dissemination of cerium oxide in the atmosphere. Concerning the biological impact of Envirox™ additized-diesel fuel, the observed effects are of very limited incidence in that the observed trend on organotypic culture viability and TNF alpha is beneficial, while a limited oxidant activity is observed through catalase induction. Emissions from diesel fuel additized with the tested cerium oxide catalyst do not induce any increase in the known adverse biological effects caused by diesel fuel engine emissions alone in our experimental set-up.

Formation of metal oxide nanoparticles in combustion of titanium and aluminum droplets

A study was performed of the formation of metal oxide nanoparticles during combustion of aluminum and titanium drops which moved in air at a velocity of up to 3 m/sec. The source of the burning particles was a pyrotechnic mixture which contained an oxidizer, a binder, and metal particles of size 4–350 µm. Transmission electron microscopic studies showed that the combustion products were 1–10 µm aggregates of fractal structure consisting of primary particles (spherules) of Al2O3/TiO2 5–150 nm in diameter. The Brownian diffusion of the aggregates and their motion in electric and gravitational fields were observed using videomicroscopic recording. The charge distribution of TiO2 aggregates and the equivalent radius of Brownian mobility were determined. In Al combustion, the zone of nanoparticle formation is separated from the particle surface by a distance approximately equal to the particle radius, and in Ti combustion, this zone is located directly near the surface. Coagulation of the oxide aerosol in the track of a burning particle leads to aerogelation with the formation of huge aggregates. Analytical expressions for approximate calculation of the parameters of the oxide particles and zones of their formation are proposed.

Fractal growth modelling of [formula omitted] nanoparticles

The kinetics of iodine oxide aerosol production and growth was studied in an aerosol flow reactor by the photolysis of I 2 in an excess of O 3 , 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 I 2 O 5 [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.

A numerical study of radiation heat transfer in sodium pool combustion and response surface modeling of luminous flame emissivity

A response surface model of the luminous flame emissivity of sodium pool fire has been proposed for use in safety analysis computer codes of a liquid metal fast reactor. The liquid sodium burns in air resulting in not only heat generation but also release of sodium oxide aerosols of sub-micron diameters. Aerosols levitating in air are radiative and they influence the allocation of combustion heat from the flame to atmospheric gas or sodium pool. The emissivity of the flame needs to be quantified, as it is one of user-specified parameters of the computer codes for the sodium fire analysis. The response surface model of the flame emissivity is developed based on numerical experiments on the physics of mass and heat transfer and behavior of the aerosol. Thermal-hydraulic equations have been solved coupled with aerosol dynamics and chemical reaction. Three influential variables on the emissivity are identified as pool temperature, gas temperature and oxygen molar fraction in the air. It has been found that the emissivity is calculated reasonably as a function of the three variables. The proposed response surface model can be easily employed in the sodium fire analysis codes because it is a simple quadratic expression. For the safety evaluation of the sodium fire, combined use is recommended of the proposed model and the lumped-mass zone model code.

Generation of metal oxide aerosol particles by a pulsed spark discharge technique

A pulsed spark discharge generated copper oxide aerosol particles has been characterized. Experiments were conducted for spark electrode gap distance from 10 to 30 mm and air flow rates from 3 to 15 l/min. The results show that the average diameter of generated particles can be controlled from 0.2–4.0 μm and the density of particle also can be controlled by changing discharge electrode gap distance and gas flow rates.

The Speciation and Morphology of Chromium Oxide Nanoparticles in a Diffusion Flame

The impact of combustion conditions on the formation of chromium oxide aerosol has been studied in a hydrogen diffusion flame seeded with Cr(CO)6 vapor. Specifically, the effects of the precursor concentration, the flame temperature and the flame residence time on properties of the postflame chromium oxide aerosol were investigated. Each of these flame parameters was found to affect the particle size distribution and/or particle morphology. These effects were partially associated with the fact that the chromium speciation in the final flame products was sensitive to the precursor concentration and the flame temperature. The flame residence time was found to affect the crystallinity of the Cr(III) particles in the postflame chromium oxide aerosol. Conversion of Cr(III) particles to Cr(VI) in the high temperature zone of the flame was proposed to explain changes in the particle size distribution, composition, and morphology. The proposed mechanism was able to explain the experimental findings satisfactorily.

Development Method to Estimate the Complex Index of Refraction of Dielectric Aerosols

A method to estimate the complex refractive indices of dielectric aerosols is developed. The three-dimensional radiative transfer problem in an absorbing-scattering medium is solved by the Monte Carlo method. Mie scattering theory is used to handle particle scattering and absorption. Magnesium oxide aerosol, with its well-known complex index of refraction, is selected as an example of a dielectric aerosol. Magnesium is burnt to produce MgO aerosol and the transmission of the radiation from a black body furnace through the aerosol layer is measured. The analytical results of the transmitted energy profiles along the wall facing the emission source, a black body furnace, were obtained for a wide range of complex indices of refraction

Surface Area of Respirable Beryllium Metal, Oxide, and Copper Alloy Aerosols and Implications for Assessment of Exposure Risk of Chronic Beryllium Disease

Surface Area of Respirable Beryllium Metal, Oxide, and Copper Alloy Aerosols and Implications for Assessment of Exposure Risk of Chronic Beryllium Disease

Surface area of respirable beryllium metal, oxide, and copper alloy aerosols and implications for assessment of exposure risk of chronic beryllium disease.

The continued occurrence of chronic beryllium disease (CBD) suggests the current occupational exposure limit of 2 microg beryllium per cubic meter of air does not adequately protect workers. This study examined the morphology and measured the particle surface area of aerodynamically size-separated powders and process-sampled particles of beryllium metal, beryllium oxide, and copper-beryllium alloy. The beryllium metal powder consisted of compact particles, whereas the beryllium oxide powder and particles were clusters of smaller primary particles. Specific surface area (SSA) results for all samples (N=30) varied by a factor of 37, from 0.56 +/- 0.07 m(2)/g (for the 0.4-0.7 microm size fraction of the process-sampled reduction furnace particles) to 20.8 +/- 0.4 m(2)/g (for the </=0.4 microm size fraction of the metal powder). Large relative differences in SSA were observed as a function of particle size for the powder of beryllium metal, from 4.0 +/- 0.01 m(2)/g (for the particle size fraction >6 microm) to 20.8 +/- 0.44 m(2)/g (for the particle size fraction </=0.4 microm). In contrast, little relative difference in SSA (<25%) was observed as a function of particle size for the beryllium oxide powder and particles collected from the screening operation. The SSA of beryllium metal powder decreases with increasing particle size, as expected for compact particles, and the SSA of the beryllium oxide powders and particles remains constant as a function of particle size, which might be expected for clustered particles. These associations illustrate how process-related factors can influence the morphology and SSA of beryllium materials. To avoid errors in predicting bioavailability of beryllium and the associated risks for CBD, the mechanisms of particle formation should be understood and the SSA of beryllium particles should be measured directly.

Short-Term Inhalation of Particulate Transition Metals Has Little Effect on the Electrocardiograms of Dogs Having Preexisting Cardiac Abnormalities

There is growing epidemiological evidence for statistical associations between increases in air pollution, especially particulate matter, and increases in cardiovascular morbidity and mortality. Laboratory studies have shown that transition metals contribute strongly to the effects of high lung doses of model particles on changes in the electrocardiograms of animals. The present study evaluated the effects of short-term inhalation exposure to respirable particles of specific oxide and sulfate forms of transition metals on heart rate and the electrocardiogram of old dogs having preexisting cardiac abnormalities. Conscious beagle dogs were exposed by oral inhalation for 3 h on each of 3 successive days to aerosols of manganese, nickel, vanadium, iron, and copper oxides, and nickel and vanadium sulfates as single compounds at concentrations of 0.05 mg/m 3. Electrocardiograms were recorded and evaluated for exposure-related changes in heart rate, heart rate variability, and abnormalities of waveforms. Although the electrocardiograms of this population of dogs having potential age and cardiovascular susceptibility factors reflected their underlying clinical abnormalities, no significant effect of exposure to the transition metal aerosols was observed.

Numerical investigation of multi-dimensional characteristics in sodium combustion

Multi-dimensional sodium combustion behavior has been numerically investigated in the present paper. A new computer code AQUA-SF has been developed for this purpose. The code includes two sodium combustion models (so called ‘spray combustion’ and ‘pool combustion’), a mass and heat transfer model considering a six-flux gas radiation and a coagulation and sedimentation model of sodium oxide and hydroxide aerosols. The sodium spray combustion rate is evaluated by a summation of the combustion rate of each sodium droplet with an individual diameter. A flame sheet model is applied to situations where sodium spreads out on the floor and a pool combustion takes place. The model assumes an infinitely thin flame above the pool surface and is based on a mass and energy balance in the flame. As the results of numerical analyses of a sodium spray combustion test, a location of high-temperature core region and a maximum temperature agrees with the experiment. Good agreements of an overall transient behavior are obtained in a large-scale sodium combustion test analysis. The numerical analyses also demonstrate that the distributions of temperature and chemical species concentration vary with sodium combustion modes. If sodium scatters and the spray combustion is dominant, the distributions vary in space. When a large amount of sodium exists on a floor and the pool area is enlarged, the distributions are more uniform in space.

Global climate change will affect: air, water in California

As we enter the 21st century, it is possible to reach beyond the headlines to describe what is now known about climate change. The Intergovernmental Panel on Climate Change evaluated the scientific aspects of global climate change; the current consensus is described in a recent series of reports. Since the 19th century, concentrations of atmospheric carbon dioxide, methane, nitrous oxide and sulfate aerosol dust have increased significantly. While there is scientific agreement that warming is occurring, the controversy now concerns the extent of subsequent impacts in the future. In California, the impacts of global warming are likely to include reduced water availability and quality, poorer air quality, associated economic consequences, biodiversity shifts and health effects. The changes are expected to continue at an increasing pace well into the next century, perhaps outstripping our scientific, economic and social ability to cope with them.

Nanoparticle Formation by Laser Ablation

The properties of nanoparticle aerosols of size ranging from 4.9 nm to 13 nm, generated by laser ablation of solid surfaces are described. The experimental system consisted of a pulsed excimer laser, which irradiated a rotating target mounted in a cylindrical chamber 4 cm in diameter and 18-cm long. Aerosols of oxides of aluminum, titanium, iron, niobium, tungsten and silicon were generated in an oxygen carrier gas as a result of a reactive laser ablation process. Gold and carbon aerosols were generated in nitrogen by non-reactive laser ablation. The aerosols were produced in the form of aggregates of primary particles in the nanometer size range. The aggregates were characterized using a differential mobility analyzer and electron microscopy. Aggregate mass and number concentration, electrical mobility size distribution, primary particle size distribution and fractal dimension were measured. System operating parameters including laser power (100 mJ/pulse) and frequency (2 Hz), and carrier gas flow rate (1 l/min) were held constant.

F134 ナトリウム燃焼で発生したエアロゾル雰囲気中での 3 次元透過解析

A method to estimate optical properties of sodium oxide aerosol is developed. They are used to solve the radiative heat transfer problems in a system with aerosol generated by sodium fire. For the purpose, three-dimensional radiative transfer in an absorbing-scattering media is solved by the Monte Carlo method. The Mie's scattering theory is used to handle particle scattering during the analysis. By comparing the experimental results of the intensity and the angular distribution of the transmitted energy with the analyzed results obtained by assuming the complex index of refraction, it is shown that the value if the complex refractive index can be estimated.

A model for two-component aerosol coagulation and phase separation: a method for changing the growth rate of nanoparticles

In previous studies of particle growth we have synthesized binary metal oxide aerosols and have observed the evolution of internal phase segregation during growth of molten nanodroplets. We have also generated NaCl/metal aerosols in which the metal nanoparticle is enveloped within a salt droplet. In both systems the nanoparticles were grown in the molten state. In this paper we propose a model which incorporates phase segregation in a binary aerosol. The model assumes that complete phase segregation is the thermodynamically favored state, that no thermodynamic activation energy exists, and that the phase segregation process is kinetically controlled. The results indicate that a steady state behavior can be reached in which the characteristic time for aerosol coagulation and the characteristic time for the growth of the minority phase coincide such that the number of distinct segregated entities within each aerosol droplet is constant. The results suggest what we believe to be an important concept that can be utilized in materials synthesis. This is that the major phase can be used to moderate the growth rate of the minor phase by changing the characteristic encounter frequency and therefore the eventual growth rate of the minority phase. In particular, temperature, which does not play an important role in aerosol coagulation, is seen to be a very sensitive parameter for the growth of the minority phase nanoparticles. We discuss the parameter space necessary for this to occur.

A model for kinetically controlled internal phase segregation during aerosol coagulation

In previous studies of particle growth, we have synthesized binary metal oxide aerosols and have observed the evolution of internal phase segregation during growth of molten nanodroplets. We describe a new formulation of the aerosol general dynamic equation (GDE) that incorporates phase segregation in a binary aerosol. The model assumes that complete phase segregation is the thermodynamically favored state, that no thermodynamic activation energy exists, and that the segregation process is kinetically controlled. We develop a GDE formulation that involves the solution of a distribution function N n ( V), where N n ( V) is the number density of aerosols with volume V and n phase domains (which we might think of as enclosures). The GDE is solved using a two-dimensional sectional model, under the assumption that the phase coalescence of the minority phase is controlled by Brownian coagulation. For the purposes of these initial studies, the rate laws governing the enclosures (minority phase) assume a monodisperse particle size distribution. The dynamical behavior of such a system is presented.

ENERGY DISPERSIVE X-RAY SPECTROMETRY IN THE ENTIRE ALVEOLAR MACROPHAGE, A TOOL TO CHARACTERIZE THE CHEMICAL COMPOSITION OF PARTICLES DEPOSITED IN THE DEEP LUNG AFTER INHALATION

The aim of this study was to develop a method to characterize the physico-chemical properties of inhaled particles in alveolar macrophages of rats and primates extracted by pulmonary lavage, by observing the entire cells using electron microscopy. The optimal conditions for identification of phagocytosed particles were dark-field STEM at 200 kV and then energy dispersive X-ray spectrometry was performed. This technique using CdS and mixed (U, Pu) oxide aerosols was applied to rats which were examined a few days after exposure and using U3O8 aerosols on primates which were examined four years after exposure. The method is capable of determining the shape, size, and chemical composition of particles deposited in the deep lung after inhalation. Characterization of the heterogeneity in the chemical composition of particles can be performed in a size of 20–30 nm. Some limitations have been encountered, however, especially for particles containing elements present in the biological matrix such as P.

Particle Size Characterizations of Copper and Zinc Oxide Exposures of Employees Working in a Nonferrous Foundry Using Cascade Impactors

This study characterized exposures to copper and zinc oxide as respirable or nonrespirable using personal impactors and compared the results with previous findings obtained using cyclones. Twenty-five sets of air samples were taken over a 10-month period using single jet cascade impactors. Five to six stages were used to capture and classify aerosols according to their aerodynamic diameter (d(ae)). These ranged from < 0.5 microm to > 10 microm d(ae). Twenty-two air samples were taken on employees casting brass alloys, and three samples were taken in areas in the vicinity where employees routinely worked. Twenty-one air samples were taken during the casting of a single brass alloy (containing 70% copper and 30% zinc), and the remaining samples were obtained from employees casting two different brass alloys: a nearly pure copper alloy and a nickel-copper alloy. The results indicated that 55-96% (by mass) of all copper aerosols collected had a d(ae) > or = 10 microm. More than 85% (by mass) of all copper exposures were estimated as nonrespirable using the current ACGIH-CEN-ISO definition. Zinc oxide aerosols were collected at all stages of the impactors, with significant amounts found to have a d(ae) > or = 10 microm. More than 60% (by mass) of all zinc oxide exposures were estimated to be nonrespirable. A comparison of data collected using impactors and cyclones demonstrated that cyclones could be used to differentiate larger aerosol particles from fumes, rather than requiring the use of impactors. It is recommended that appropriate particle size selective sampling methods be used to classify exposures of metals to dusts and fumes.

Condensation of analyte vapor species in graphite furnace atomic absorption spectrometry

A shadow spectral digital imaging technique (SSDI) with charge coupled device (CCD) camera detection was used to investigate the spatial and temporal distribution of condensation clouds of analyte species generated in a graphite furnace during the atomization of 5–40-μg masses of metals. Complex, non-uniform structures of aerosol species located away from both the graphite tube axis and walls are prevalent. Species giving rise to observed signals are likely clusters of metals in the case of Ag, Au and Pd, and oxide aerosols for elements such as Al, Ca and Mg. Source scatter often arises during the atomization of relatively large masses of analytes (or during the atomization of real samples containing high concentrations of concomitant matrix species) in the graphite furnace due to such aerosol formation. The SSDI technique is an extremely useful aid to the elucidation of this phenomenon and imaging at several wavelengths using both line and continuum sources in combination with (thermal, incandescent) emission from these structures permits a more complete picture to be developed.