Calculations are presented of the charge distribution on spherical particles that are large compared with the mean free path of air molecules, resulting from long-term exposure to low concentrations of ions. A system ...
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Calculations are presented of the charge distribution on spherical particles that are large compared with the mean free path of air molecules, resulting from long-term exposure to low concentrations of ions. A system of sparse linear simultaneous equations is developed, relating the probability of ultimate capture by the particle of ions at every radial position in the ionized gas to that of ions at adjacent points. The coefficients in the equations are derived from a consideration of the microscopic motion of the ions under diffusion and drift in the electric field of the particle. Image forces, for the case of conducting particles, can be easily included in the model;and the steady state charge distribution resulting is close to the Boltzmann distribution.
The co-located optical (argon-ion lidar) and acoustic (Doppler sodar) radar systems at the Indian institute of Tropical Meteorology (IITM), Pune (18 degrees 32'N, 73 degrees 51'E, 559 m AMSL), India, have been...
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The co-located optical (argon-ion lidar) and acoustic (Doppler sodar) radar systems at the Indian institute of Tropical Meteorology (IITM), Pune (18 degrees 32'N, 73 degrees 51'E, 559 m AMSL), India, have been employed to study the nocturnal aerosol pollution dynamics or air quality. Both the systems have been operated simultaneously in order to sample the common atmospheric volume. The results of the experiments thus conducted on same typical nights are presented in this paper. The time-height cross section of the mean, horizontal and vertical components of the wind field derived from the sodar observations indicate that the wind is either easterly or northerly with its vertical component negative (downdraft) for most of the observational period, The interesting feature is that the winds are either calm or relatively weaker in the night-time boundary layer compared with those in the region aloft. This is more evident in the north-south direction in which the lidar and sodar equipment are located, Furthermore, the regions where stable/elevated layer formation is active are found to be associated with the smallest wind gradients, leading to accumulation of aerosol particles or larger temperature structure parameters. The time evolution of the mixed-layer heights and the associated ventilation coefficients, determined from the combined lidar-aerosol and sodar-wind observations, are found to be useful to explain the transport and diffusion of pollutants across the elevated temperature inversions over the experimental station. The details of the experimental techniques are presented and their value for application in the study of regional air quality and pollution potential is discussed.
Two types of numerical models for homogeneous nucleation and particle growth are compared: models in which the time rate of change in the stable aerosol population is given by an analytical expression for the nucleati...
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Two types of numerical models for homogeneous nucleation and particle growth are compared: models in which the time rate of change in the stable aerosol population is given by an analytical expression for the nucleation rate, and discrete models, in which an expression for the nucleation rate is not required nor explicitly calculated. The classical expression for the homogeneous nucleation rate, coupled to a moment model, is found to produce poor agreement with a discrete-sectional model except for very low values of dimensionless surface tension. A new expression for the homogeneous nucleation rate is proposed, which when coupled to a moment model produces excellent agreement with a discrete-sectional model over a wide range of dimensionless surface tensions. The new expression is also consistent with experimental data on homogeneous nucleation of dibutylphthalate.
Deposition of ash on heat transfer surfaces is a major factor in determining boiler performance. Deposits so formed consist of tightly bound ``inside" deposits close to the heat transfer surface and loosely bound...
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Deposition of ash on heat transfer surfaces is a major factor in determining boiler performance. Deposits so formed consist of tightly bound ``inside" deposits close to the heat transfer surface and loosely bound ``outer" deposits that are easily dislodged. This paper describes research focusing on both the composition of inner and outer deposits, and also on the rate of deposition of the inner deposit layer. Presented are selected results from a wide ranging study concerned with mechanisms governing the formation of fouling deposits during air and oxy-coal combustion in a 100 kW test rig. The primary focus is on establishing a relationship between the size segregated composition of the coal ash aerosol, and the spatially resolved composition of the deposit layer, and this is accomplished by experimentation that addresses the impacts of conversion from air-firing to oxy-firing. Experiments involved three different coals ( Powder River Basin or PRB, Illinois and a 60/40 Blend of Illinois and PRB), each burned under air-and oxy-coal combustion conditions. Data for the PRB coal suggested that changes in the composition of the inner deposit layer were caused by variations in sub-micron aerosol compositions, but that these occurred only when there were significant changes in flame temperature. An increase of the latter also led to increasing submicron particle concentrations and deposition rates. Although both aerosol and deposit compositions depended greatly on coal compositions, rates of deposition of the inner deposit layer correlate linearly with the concentration of the submicron aerosol in the flue gas, for all three coals, and under all air- and oxy-firing conditions for which data are available. This result suggests the amount rather than the ( variable) composition of the submicron aerosol is important. There was no correlation between deposition rates and total ash concentrations. (C) 2016 Elsevier Ltd. All rights reserved.
aerosols are generated in many normal or accident situations associated with the nuclear enterprise. For a good understanding and modeling of the nuclear source term, for example, good experimental data and computatio...
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aerosols are generated in many normal or accident situations associated with the nuclear enterprise. For a good understanding and modeling of the nuclear source term, for example, good experimental data and computational programs relating to aerosol evolution are needed. In the past several years there has been an effort to explore use of the Direct Simulation Monte Carlo (DSMC) approach for such estimations to improve fidelity of computations to the actual physics and chemistry of the accidents. An integral part of these efforts has been verification and validation of the DSMC technique against other available results wherever possible. This paper explores verification of DSMC against one existing and two new benchmark problems covering condensation, coagulation, deposition and two-component aerosols. The simulations compare well with the exact results, providing further confidence in the use of DSMC. (C) 2018 Published by Elsevier Ltd.
A large-particle sampler was tested in an environmental wind tunnel to characterize the efficiency as a function of particle size and type (solid or liquid). The sampler, which had been developed by another organizati...
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A large-particle sampler was tested in an environmental wind tunnel to characterize the efficiency as a function of particle size and type (solid or liquid). The sampler, which had been developed by another organization, has two slotted-cylinder collection elements which are rotated through air at a tangential speed of 39 m/s. Data from wind tunnel tests show the efficiency of liquid droplet collection to increase with particle size to approximately 50% at 25 μm and then decrease with a further increase in particle size. It is suggested that the air flow patterns created by the sampler produce this anomalous behavior. Results of tests with solid particles show higher efficiencies than are obtained with liquid droplets of the same size. It appears that solid particles, which rebound from collection sites other than a slot, can subsequently enter the slots. Supporting data were obtained on the performance of a single slotted cylinder that was fixed in the discharge region of a small free-jet tunnel. Those results show the impaction efficiency of all sizes of liquid droplets in the slotted cylinder follow the type of trend expected for a circular cylinder, i.e., a curve in which efficiency monotonically increases with size. However, 41-μ m diameter solid particles are re-entrained in the air stream and show reduced efficiency in comparison with liquid aerosol particles.
We present a preliminary study of some optical properties of atmospheric aerosols over the area of Valencia, Spain, a coastal Mediterranean city. Measurements of spectral direct irradiance in the 300-1100 mn range wer...
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We present a preliminary study of some optical properties of atmospheric aerosols over the area of Valencia, Spain, a coastal Mediterranean city. Measurements of spectral direct irradiance in the 300-1100 mn range were taken simultaneously at three sites: rural-continental, rural-coastal, and urban-costal, all located within a 50 km radius of the city of Valencia. The irradiance measurements were obtained using three Li-cor 1800 spectroradiometers provided with radiance limiting tubes with field of views (FOVs) of 4.7 degrees. The measurements were made under clear sky conditions during a field campaign carried out in the summer of 1998. In order to avoid the uncertainties associated with the determination of the water vapor content and the other atmospheric constituents, the analysis of the spectral aerosol optical thickness (AOT) values was limited to the 400-670 nm spectral band. From the values of the spectral AOT, both the Angstrom coefficients and the aerosol size distributions were obtained. The results show the great dependence of the optical aerosol characteristic on the direction of the prevailing winds (maritime or continental) in this area.
A comparative review of mathematical models of aerosol dynamics is presented. Three approaches are considered that are based on continuous, discrete (sectional), and parametrized (lognormal) representations of the aer...
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A comparative review of mathematical models of aerosol dynamics is presented. Three approaches are considered that are based on continuous, discrete (sectional), and parametrized (lognormal) representations of the aerosol size distribution. Simulations of coagulation and diffusion-limited condensation are performed with these modeling approaches for three case studies typical of clear, hazy, and urban atmospheric aerosol concentrations. The relative accuracies and computational costs of models based on these approaches are compared. The models based on a continuous size distribution provide an accurate solution for both coagulation and condensation. Sectional approaches simulate coagulation very well but require a fine size resolution to minimize numerical diffusion in the simulation of condensation. The parametrized model based on log-normal modal size distributions is computationally efficient but tends to overestimate the rate of coagulation and the peak aerosol concentration resulting from condensational growth. The results of this study provide useful information for the selection of an aerosol model, depending on the accuracy requirements and computational constraints associated with a specific application.
Climate change will have serious effects on the planet and on its ecosystems. Currently, mitigation efforts are proving ineffectual in reducing anthropogenic CO2 emissions. Coral reefs are the most sensitive ecosystem...
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Climate change will have serious effects on the planet and on its ecosystems. Currently, mitigation efforts are proving ineffectual in reducing anthropogenic CO2 emissions. Coral reefs are the most sensitive ecosystems on the planet to climate change, and here we review modelling a number of geoengineering options. and their potential influence on coral reefs. There are two categories of geoengineering, short-wave solar radiation management and longwave carbon dioxide removal. The first set of techniques only reduce some, but not all, effects of climate change. while possibly creating other problems. They also do not affect CO2 levels and therefore fail to address the wider effects of rising CO2, including ocean acidification, important for coral reefs. Solar radiation is important to coral growth and survival, and solar radiation management is no in general appropriate for this ecosystem. Longwave carbon dioxide removal techniques address the root cause of climate change, rising CO2 concentrations. they have relatively low uncertainties and risks. They are worthy of further research and potential implementation, particularly carbon capture and storage, biochar, and afforestation methods. alongside increased mitigation of atmospheric CO2 concentrations. (C) 2009 Elsevier Ltd. All rights reserved.
Particulate matter (PM) is an important constituent of atmospheric pollution especially in areas under the influence of industrial emissions. Megalopolis is a small city of 10,000 inhabitants located in central Pelopo...
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Particulate matter (PM) is an important constituent of atmospheric pollution especially in areas under the influence of industrial emissions. Megalopolis is a small city of 10,000 inhabitants located in central Peloponnese in close proximity to three coal opencast mines and two lignite fired power plants. 50 PM10 samples were collected in Megalopolis during the years 2009-11 for elemental and multivariate analysis. For the elemental analysis PIXE was used as one of the most effective techniques in APM analytical characterization. Altogether, the concentrations of 22 elements (Z = 11-33), whereas Black Carbon was also determined for each sample using a reflectometer. Factorization software was used (EPA PMF 3.0) for source apportionment analysis. The analysis revealed that major emission sources were soil dust 33% (7.94 +/- 0.27 mu g/m(3)), biomass burning 19% (4.43 +/- 0.27 mu g/m(3)), road dust 15% (3.63 +/- 0.37 mu g/m(3)), power plant emissions 13% (3.01 +/- 0.44 mu g/m(3)), traffic 12% (2.82 +/- 0.37 mu g/m(3)), and sea spray 8% (1.99 +/- 0.41 mu g/m(3)). Wind trajectories have suggested that metals associated with emission from the power plants came mainly from west and were connected with the locations of the lignite mines located in this area. Soil resuspension, road dust and power plant emissions increased during the warm season of the year, while traffic/secondary, sea spray and biomass burning become dominant during the cold season. (C) 2015 Elsevier B.V. All rights reserved.
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