Dispersion Of Ultrafine Particles Research Articles

Interaction between two car models with application to pollutant dispersion

Nowadays, air quality monitoring is a major concern. Among pollutants, exhaust UltraFine Particles (UFP) have a harmful effect on health due to their small size and to their ability to penetrate the bloodstream, the respiratory system, the brain as well as the placental barrier. Out of the industrial emissions, road traffic is a major source of air pollution. UFP emitted from the cars can infiltrate the car cabin through leakages and ventilation system leading to poor air quality in the passenger compartment. Improving the knowledge regarding the dispersion of exhaust UFP in the wake of a car considering road traffic is then mandatory. In this paper, the dispersion of UFP is studied in the wake of a leading vehicle (LV) followed by a second one. Two rear slant angles (φ) for LV and 6 inter-vehicle distances are considered. Velocities and UFP concentrations are collected in a wind tunnel. The influence of the rear slant angle of the leading vehicle is discussed on both wake dynamics and concentration fields. The results indicate that a critical inter-vehicle distance can be identified above which the recirculation region remains unchanged. Considering the concentration fields, for a leading vehicle with φ=0°, the large recirculation region tends to entrap the particles and to homogenize the particle mixing. For φ=25°, the attachment of the flow in the rear slant angle has a strong impact on the particle dispersion. It leads to a small recirculation region, which entraps particles leading to a non-homogeneous mixing. The Particle Concentration fields in Number (PNC) reveal high levels in the exhaust tailpipe plane that can contribute to lower PNC levels in the car cabin. Comparisons with previous studies are discussed and possible recommendations are suggested.

Coagulation patterns and the impacts on traffic-related ultrafine particle dispersion in road tunnels employing dynamic mesh algorithms.

.In this study, we continue to analyze the diffusion mechanism of ultrafine particles and the particle coagulation phenomenon with a size range of 26-287 nm exhausted from vehicles during the process of passing through a 100-m-long tunnel using the realizable k-ε model and dynamic grid technique. A three-dimensional model consisting of a 100-m highway tunnel and four side-by-side gasoline vehicles (L × W × H = 4.5 m × 1.8 m × 1.5 m) was established in the STAR-CCM+ computational fluid dynamics software. The gasoline vehicles traveled simultaneously under different situations of three driving speeds of 60 km h-1, 40 km h-1, and 20 km h-1 during the simulation. Through data analysis and research, it was found that the coagulation process of particles is very complicated, especially at low speeds. When the vehicle speed is 20 km h-1, the variation in particle concentration at the vehicle wake near the tailpipe (at the vertical plane located 0.1 m behind the exhaust pipe) causes a large error if the coagulation action is not considered. The relative error of the average particle concentration at 0.5 s of the vertical section 0.1 m away from the exhaust pipe is as high as 193.51%. The relative error in the entire tunnel is only 2.82%, which is less than 5%. Thus, it is recommended that particle coagulation should be considered when analyzing particle dispersion in the near-wake region behind the vehicle and the breathing areas, especially when the vehicle travels slowly inside the tunnel. However, when evaluating the particle concentration and exposure levels for the entire tunnel, coagulation can be ignored without significant errors, especially at a high vehicle speeds. This study clarified the importance of coagulation in different areas and its influence on the diffusion of particulate matter. This is conducive to further analysis of the diffusion characteristics of particulate matter and can appreciably reduce the pollution degree in a tunnel by changing the coagulation efficiency of particulate matter in the future.

Ultrafine particle dispersion in the metropolitan area of Guadalajara, Mexico

Objectives: Dust, soil and leaf samples of Ficus benjamina were collected in the metropolitan area of Guadalajara (GMA) (Peña-García et al., 2017), allowing to identify the type of metallic particles, size, shape and spatial distribution. With the results obtained, the possible effects of metallic particles on human and plant health were discussed (Peña-García et al., 2019). Methodology: The sampling was in six municipalities of the GMA; Atomic absorption spectrophotometry analyses were carried out on leaves, which identified the presence of various elements that mostly exceeded the reference values. Through X-ray fluorescence, 23 elements were identified in soil, including Th and Ac in at least 14 sites. Using the scanning electron microscopy technique and elemental mapping analysis, coarse, fine and ultrafine metallic particles were identified in human bronchus and lung tissue, as well as fragments of cement, plastic, yeast and bacteria. The similarity between the metallic particles in the collected samples and those observed in lung tissue, warns of latent risks to the health of the GMA population. Contribution: The results obtained with the methodology used in this work allow us to glimpse the polluting potential in urban areas.

Dispersion of ultrafine particles in the wake of car models: A wind tunnel study

Worldwide around 7 million annual deaths are due to air pollution. Among all pollutants, Ultrafine Particles (UFP) cause strong adverse effects. In this paper, the dispersion of UFP is studied in the wake of car models characterized by different rear slant angles (ϕ). Velocities and UFP concentrations are collected in a wind tunnel. The influence of the flow topology on the dispersion of these UFP is discussed. The results indicate that its structure strongly influences their dispersion. Whatever the rear slant angle is, the size of the recirculation region is a key parameter governing the dispersion of these UFP. For ϕ ​= ​0°, the flow is almost symmetric and concentration levels are higher and homogeneous in the close wake. The recirculation region is the largest one. The dispersion is enhanced in both horizontal and spanwise directions. For ϕ ​= ​25°, the flow is attached on the rear slant leading to a strong downwash effect. The volume of the recirculation region is the smallest. Longitudinal vortices develop from the edges of car model entrapping particles. Particle Number Concentration field is no more symmetric. For ϕ ​= ​35°, results are almost similar to those obtained for ϕ ​= ​0°. Comparisons with previous studies are discussed and possible applications are suggested.

Car Wake Flows and Ultrafine Particle Dispersion: From Experiments to Modelling

Improving air quality in urban environments and transportation systems is crucial. Concerns are related to health and environmental issues associated with huge costs. Car cabin is a microenvironment where pollutants can accumulate with possible risks for occupants. In automotive engineering, it has then become mandatory to study the path and dispersion of such pollutants emitted from the tailpipe of a car. In the present paper, the relation between the flow topology and the dispersion of ultrafine particles (UFP) in the wake of a vehicle is discussed. Experiments were undertaken at a reduced scale using simplified car models. Experimental conditions were defined to be representative of a vehicle in an urban environment. Based on experimental data, a simplified analytical model is developed, which aims at describing the concentration fields of UFP in the wake of a single vehicle for different rear slant angles. The strengths and limits of the present model are discussed and ways of improvements are suggested. Additional experiments are presented to assess the influence of the inter-vehicle distance on this recirculation region. Critical inter-vehicle distances were determined based on defined criteria for different rear slant angles of the leading vehicle and compared to safety clearances.

Experimental Evaluation of Three Local Exhaust Ventilation Systems Designed to Reduce Ultrafine Dust Emission During a Polishing Process

Aerosol transport is a fundamental phenomenon in many environmental and industrial applications. The study of the dispersion of aerosols, such as contaminants, in the workplace and the search for solutions to capture them are the biggest challenges currently faced in the field of occupational safety and health. In addition, laws and regulations that limit the level of worker exposure to contaminants in workplaces are becoming stricter. The aim of this study was to help reduce exposure to dust, including crystalline silica dust, emitted during the granite polishing process. During this process, the ultrafine particles generated are more difficult to capture than the fine ones, especially in rotational polishing, which causes the worst cases of dust exposure. An experimental test bench was set up to simulate ultrafine particle dispersion and assess three solutions for reducing worker exposure during the rotational polishing process. The use of the test bench allowed experiments to be performed while avoiding human exposure. Results showed that the test bench efficiently simulated the dispersion of ultrafine particle dust. Three solutions designed to reduce dust emissions, based on local exhaust ventilation, were evaluated on the test bench: a push–pull system, a dust shroud and a tool with integrated suction slots. They proved to be more than 95% effective. The results of this work highlight that the performance of local exhaust ventilation systems is very sensitive to the suction flowrate and the speed of the rotating disc, thus illustrating the complexity of dust removal associated with polishing processes in industrial environments.

Computational and Experimental Analysis of Ultrafine Particle Dispersion During Granite Polishing

The granite manufacturing industry is an environment in which workers are exposed to high levels of ultrafine particles (UFPs) and crystalline silica dust. Overexposure to crystalline silica can cause health problems, in particular silicosis. This fatal lung disease persists worldwide despite knowledge of methods to control it. One way to partially overcome the problem of subjectivity and try to achieve objective experimental results is to run field crystalline silica dust surveys with trained human assessors (panelists). Such field inspections allow the determination of ambient air concentrations and are now seen as being a more convenient method for UFP impact assessment in the field. One drawback of field inspections is that they can get rather expensive, especially if the survey is conducted for an extended period of time involving a high number of panelists. This paper reviews the techniques that can be adopted to measure UFPs in the field and discusses how such techniques can be used as an alternative to, or in combination with, gas tracer dispersion methods for UFP impact assessment purposes, and how the results of field UFP measurements and model outputs can be related and compared to each other. Two simulation methods were used to study crystalline silica dust exposure during the granite polishing process (experimental and numerical). This study presents a method to measure UFP dispersion during granite manufacturing processes. A computational model was constructed to simulate the physical problem. The numerical study was carried out, on a simplified configuration (bench), modeling particle distribution near a rotating tool. CFD simulation results were compared to the experimental data using NaCl particles, a tracer gas (CO2), and UFP dispersion from granite polishing. The results showed good agreement between the two methods.

Numerical study of ultrafine particles dispersion in the wake of a cylinder

The dynamics of ultrafine particles are strongly dependent to the air flow topology. In this study, the dispersion of carbon nanoparticles in the wake of a cylinder placed in an air flow at Reynolds number of 9300 is numerically investigated. An Eulerian/Lagrangian approach is used to compute the two-phase flow; the carrier phase is predicted through a RANS (Reynolds Averaged Navier-Stokes) model while a particle Lagrangian tracking method provides the trajectory of each nanoparticle. The present numerical investigation allows studying the influence of Brownian and turbulence effects on the nanoparticles dispersion. The main results reveal that: (1) The Brownian diffusion tends to concentrate the carbon nanoparticles in the form of a filament at the periphery of the vortices that are generated in the cylinder wake. (2) The turbulence increases the lateral dispersion of the nanoparticles. It disperses them from the edge to the core of the vortices. (3) The highest concentration levels decrease from the near wake of the cylinder to the far wake region while the lateral dispersion increases.

Sensitivity analyses of ultrafine particle dispersion inside an isolated street canyon

Ultrafine particles originating from vehicle exhausts may deteriorate the air quality inside the street canyon, so it is of importance for the air quality control to clarify the formation and dispersion characteristics of ultrafine particles. In this study, the population balance model considering the nucleation, condensation and evaporation, as well as the species transport and RNG k-ε turbulent models were employed, and the sensitivities of the dispersion of ultrafine particles to the wind direction, emission rates of H2SO4 vapor and organic compounds, traffic flow and ambient temperature inside an isolated street canyon were analyzed. The results show that the wind direction is a key issue to the particle number concentration. The emission rates of H2SO4 vapor and organic compounds play dominant roles in the formation and growth of particles, so should be strictly controlled to reduce the air pollution. Restricting the use of private vehicles based on the even-and-odd number licensed trip can conspicuously lower the ultrafine particle concentrations by more than one order of magnitude. More powerful nucleation among the vehicle exhausts will be triggered in a cold environment, therefore the haze pollution may break out in winter more easily.

A simplified benchmark of ultrafine particle dispersion in idealized urban street canyons: A wind tunnel study

The paper proposes a benchmark for computational fluid-dynamic models of ultrafine particle (particles' diameter lower than 100 nm) dispersion in urban street canyons. In particular, an on-scale symmetric street canyon was designed and settled in a wind tunnel considering a perpendicular wind condition. An experimental campaign was carried out to: i) investigate the fluid-dynamic conditions inside the canyon through a Particle Image Velocimetry (PIV), ii) evaluate the uncertainty budget of the PIV measurements, iii) design proper particle injection and sampling systems in the street canyon not influencing the fluid-dynamic conditions of the canyon itself, iv) provide particle number concentration profiles at different sections of the canyon (at different heights on both the canyon facades and at a background level) through ultrafine particle generation (Submicrometer Aerosol Generator 3940, TSI Inc.) and measuring devices (CPC 3775 and SMPS 3936, TSI Inc.).The study can be considered the very first attempt to set a benchmark for ultrafine particle dispersion in street canyons through wind tunnel systems.

The exposure to coarse, fine and ultrafine particle emissions from concrete mixing, drilling and cutting activities

Building activities generate coarse (PM10≤10μm), fine (PM2.5≤2.5μm) and ultrafine particles (<100nm) making it necessary to understand both the exposure levels of operatives on site and the dispersion of ultrafine particles into the surrounding environment. This study investigates the release of particulate matter, including ultrafine particles, during the mixing of fresh concrete (incorporating Portland cement with Ground Granulated Blastfurnace Slag, GGBS or Pulverised Fuel Ash, PFA) and the subsequent drilling and cutting of hardened concrete. Particles were measured in the 5–10,000nm size range using a GRIMM particle spectrometer and a fast response differential mobility spectrometer (DMS50). The mass concentrations of PM2.5–10 fraction contributed ∼52–64% of total mass released. The ultrafine particles dominated the total particle number concentrations (PNCs); being 74, 82, 95 and 97% for mixing with GGBS, mixing with PFA, drilling and cutting, respectively. Peak values measured during the drilling and cutting activities were 4 and 14 times the background. Equivalent emission factors were calculated and the total respiratory deposition dose rates for PNCs for drilling and cutting were 32.97±9.41×108min−1 and 88.25±58.82×108min−1. These are a step towards establishing number and mass emission inventories for particle exposure during construction activities.

Stabilization of Silicon Carbide (SiC) micro- and nanoparticle dispersions in the presence of concentrated electrolyte

Achieving a stable and robust dispersion of ultrafine particles in concentrated electrolytes is challenging due to the shielding of electrostatic repulsion. Stable dispersion of ultrafine particles in concentrated electrolytes is critical for several applications, including electro-codeposition of ceramic particles in protective metal coatings. We achieved the steric stabilization of SiC micro- and nano-particles in highly concentrated electroplating Watts solutions using their controlled coating with linear and branched polyethyleneimines (PEI) as dispersants. Branched polyethyleneimine of 60,000MW effectively disperses both microparticles and nanoparticles at a concentration of 1000ppm. However, lower polymer dosages and smaller polymers fail to disperse, presumably due to insufficient coverage and bridging flocculation. Dispersion stability correlates well with the adsorption density of PEI on microparticles. We discuss the results in the framework of DLVO theory and suggest possible dispersion mechanisms. However, though the dispersion is enhanced with extended adsorption time, the residual PEI in solution adversely affects electroplating. We overcome this drawback by precoating the particles with the polymer and resuspending them in Watts solution. With this novel approach, we obtained robust dispersions. These results offer new possibilities to control dispersion at high electrolyte concentration, as well as bring new insights into the dispersion phenomenon.

Studying passive ultrafine particle dispersion in a room with a heat source

The distribution of particles in a room is of great interest because of the effect of particles on human health. Using computational fluid dynamics, it is possible to study the behaviour of particles in a room. In this study, the commercial software STAR-CCM+ was used to simulate the dispersion of passive particles in a room with displacement ventilation system. In addition, some experiments are performed to verify the accuracy of the simulation results. According to the comparison of the experiment and the simulations in front of supply opening, the k–ε model seems to give better results than the k–ω model. It is shown that, in order to have an accurate result, the simulation of radiation effect is essential. Furthermore, the results of particle simulations show that when the passive particle source is in the height of 1.5 m and the heater is at the height of 0.5 m, the average concentration in the room is the lowest. Depending on the particle source height and heater location, the average particle concentration profile will change. In remote areas, the concentration profile does not show any significant difference between upper zone and lower zone.

Ultrafine particles dispersion modeling in a street canyon: Development and evaluation of a composite lattice Boltzmann model

Recently, a branch of particulate matter research concerns on ultrafine particles found in the urban environment, which originate, to a significant extent, from traffic sources. In urban street canyons, dispersion of ultrafine particles affects pedestrian's short term exposure and resident's long term exposure as well. The aim of the present work is the development and the evaluation of a composite lattice Boltzmann model to study the dispersion of ultrafine particles, in urban street canyon microenvironment. The proposed model has the potential to penetrate into the physics of this complex system. In order to evaluate the model performance against suitable experimental data, ultrafine particles levels have been monitored on an hourly basis for a period of 35days, in a street canyon, in Athens area. The results of the comparative analysis are quite satisfactory. Furthermore, our modeled results are in a good agreement with the results of other computational and experimental studies. This work is a first attempt to study the dispersion of an air pollutant by application of the lattice Boltzmann method.

Numerical Simulation of Ultrafine Particle Dispersion in Urban Street Canyons with the Spalart-Allmaras Turbulence Model

The increased traffic emissions and reduced ventilation of urban street canyons lead to the formation of high particle concentrations as a function of the related flow field and geometry. In this context, the use of advanced modelling tools, able to evaluate particle concentration under different traffic and meteorological conditions, may be helpful. In this work, a numerical scheme based on the non-commercial fully explicit AC-CBS algorithm, and the one-equation Spalart-Allmaras turbulence model, was developed to perform numerical simulations of fluid flow and ultrafine particle dispersion in different street canyon configurations and under different wind speed and traffic conditions. The proposed non-commercial numerical tool was validated through a comparison with data drawn from the scientific literature. The results obtained from ultrafine particle concentration simulations show that as the building height increases the dispersion of particles in the canyon becomes weaker, due to the restricted interaction between the flow field in the street canyon and the undisturbed flow. Higher values of approaching wind speed facilitate the dispersion of the particles. The traffic effect has been evaluated by imposing different values of particles emission, depending on the vehicles type, with the lowest concentration values obtained for the Euro 6 vehicles, and the highest for High Duty Vehicles. A parametric analysis was also performed concerning the exposure to particles of pedestrians in different positions at the road level as a function of street canyon geometry, traffic mode, and wind speed. The worst exposure (1.25 × 10 6 part./cm 3 ) was found at the leeward side for an aspect ratio H/W = 1, wind speed of 5 m/s when High Duty Vehicles traffic was considered.

Distribution of Nanoparticles near a Major U.S. and Canada Trade Bridge: Comparison of Simulations with Field Data

Dispersion of ultrafine particles arising from traffic emissions on a major international bridge (the Peace Bridge) between U.S. and Canada was studied during the summer of 2004. A computational model for evaluating the transport and dispersion of vehicular emissions from the Peace Bridge Complex (PBC) into the downwind neighborhood was developed to improve the estimation of ultrafine particle number concentrations in this area of Buffalo, New York. An unstructured computational grid of the Peace Bridge and its vicinity was generated and the mean airflow was simulated using the standard k-ε turbulence model in the FLUENTTM code (ANSYS, Inc, Canonsburg, PA). A Discrete Random Walk (DRW) model was used to simulate the instantaneous turbulence fluctuating velocity. A Lagrangian particle-tracking model was used to simulate the transport and dispersion of particles from the motor vehicles on the bridge and in the Peace Bridge Plaza area. The particle transport model accounts for the drag and Brownian forces acting on the particle, as well as the gravitational sedimentation effects. These results were compared with a series of particle size distribution measurements made over the region of interest. For particulate emissions measured in the size range of 16 to 166 nm, the simulated size-fractionated particle concentrations show agreement with the field measurements with estimated errors of approximately 15%. These results suggest that CFD modeling could provide the basis for reasonable estimates of the exposure from specific major roads in the downwind area.

Advances in selective flocculation processes for the beneficiation of kaolin

Selective flocculation enables the production of high-brightness kaolin products from kaolin ore once considered too poor in quality for beneficiation into paper-coating pigments. Anatase, Ti(1−X)FeXO2, with X = 0 to 0.05, is a common iron-bearing impurity in sedimentary kaolin that can be unresponsive to kaolin beneficiation processes, such as magnetic separation, due to its extremely fine particle size (<0.3 µm), or chemical bleaching, because of its chemical stability. Described here are selective flocculation technologies that separate anatase by flocculating anatase or flocculating kaolinite from dispersed slurries. Applying the advances in the chemical and mechanical dispersion of ultrafine particles and the selective aggregation of kaolinite or anatase particles have resulted in the selective flocculation processes practiced today that have increased process recoveries from those technologies practiced beginning in the 1960s.

Mechanical Properties of Ultra Fine Particle Dispersion Strengthened Ferritic Steel

The influence of carbides diameter on the mechanical properties of the ferritic steel that was strengthened by the interface precipitated carbides in rows was investigated. Low carbon steel containing titanium as much as carbon in atomic concentration was induction-melt and hot-rolled, followed by the soaking at some temperatures to obtain completely transformed ferrite in which fine carbides precipitated. Lowering holding temperature resulted in fine carbide generation and reduction of the row spacing. Yield strength significantly increased with the decrease in the carbide diameter. The amount of the particle dispersion strengthening was close to the calculation result according to Ashby-Orowan Mechanism. On the other hand, elongation slowly decreased. The decrease in elongation is caused by the reduction of the uniform-elongation. Local elongation did not change by the change of the diameter of the fine carbides in the matrix since voids in the specimen were generated not besides fine carbides but beside large TiN during tensile test.

Dispersion modelling of traffic induced ultrafine particles in a street canyon in Antwerp, Belgium and comparison with observations

The aim of this study is to investigate the dispersion of ultrafine particles and its spatial distribution in a street canyon and its neighbourhood with the 3D CFD model ENVI-met®. The performance of the model at street scale is evaluated and the importance of the boundary conditions like wind field and traffic emissions on the UFP concentration is demonstrated. To support and validate the modelled results, a short-term measurement campaign was conducted in a street canyon in Antwerp, Belgium. The UFP concentration was measured simultaneously with P-TRACK (TSI Model 8525) at four different locations in the canyon. The modelled UFP concentrations compare well with the measured data (correlation coefficient R from 0.44 to 0.93) within the standard deviation of the measurements. Despite the moderate traffic flow in the street canyon, UFP concentrations in the canyon are in general double of the background concentrations, indicating the high local contribution for this particle number concentration. Some of the observed concentration profiles are not resembled by the model simulations. For these specific anomalies, further analysis is performed and plausible explanations are put forward. The role of wind direction and traffic emissions is investigated. The performance evaluation of ENVI-met® shows that in general the model qualitatively and quantitatively describes the dispersion of UFP in the street canyon study.

Modeling fine particle dispersion in an inhomogeneous electric field with a modified drift flux model

Dispersion of ultrafine particles (less than 0.1 μm) and accumulation mode particles (0.1–2.5 μm) remains as an area of major concern to microelectronic and semiconductor industry. A possible means of containing the dispersion of particulate pollutants is to subject them to electrostatic precipitation. The present study is concerned with the dispersion of particles in the presence of an inhomogeneous electric field. The widely accepted drift flux model is used to account for the drift flux induced by the inhomogeneous electric field. The mean turbulent flow field for the present analysis is obtained by solving the re-normalization group (RNG) k– ɛ model with the aid of the open source CFD code – Open∇FOAM version 1.5. In addition to the flow field equations, the Poisson equation for the electric field, the charge continuity equation and the particle concentration equation are solved to obtain a complete solution for the present case. A comparison of the concentration field for a particle size of 0.1 μm with and without electric field reveals the impact of electric field on particle concentration distribution. The simulation results are compared with the available experimental data and numerical results.