Function Of Downwind Distance Research Articles

Analytical solution of diffusion equation under chemical reaction and wet deposition from line Source

The pollutants from the environment are absorbed by wet deposition which increases the pollutants transport. To create and produce different substances, the constituent atoms of the reactants should be rearranged by the chemical reaction. The introduced theoretical model demonstrate the dispersal of pollutants inherited from point and line source without and with both wet deposition and chemical reaction, respectively. The advection-diffusion equation is solved. Taking the wind speed is a function of downwind distance, lateral eddy diffusivity is a function of wind speed and vertical eddy diffusivity is a function of both wind speed and vertical height of power “z”. In this paper the variable separable method and Hankel transform are used to get the concentration from point and line source. Predicted concentration of pollutants in unstable condition is done. Variation concentrations of both observed and predicted of radioactive Iodine135 (I-135), inside Research Reactor at Inshas Egyptian Atomic Energy Authority, in unstable condition is shown without chemical reaction and wet deposition. It is discovered that the proposed model is a good harmony with observed concentrations data and the proposed data inside a factor of two. Also, studying the effect of wet deposition and chemical reaction on concentration of air contaminants of line source is analysed.

Rapid evolution of aerosol particles and their optical properties downwind of wildfires in the western US

Abstract. During the first phase of the Biomass Burn Operational Project (BBOP) field campaign, conducted in the Pacific Northwest, the DOE G-1 aircraft was used to follow the time evolution of wildfire smoke from near the point of emission to locations 2–3.5 h downwind. In nine flights we made repeated transects of wildfire plumes at varying downwind distances and could thereby follow the plume's time evolution. On average there was little change in dilution-normalized aerosol mass concentration as a function of downwind distance. This consistency hides a dynamic system in which primary aerosol particles are evaporating and secondary ones condensing. Organic aerosol is oxidized as a result. On all transects more than 90 % of aerosol is organic. In freshly emitted smoke aerosol, NH4+ is approximately equivalent to NO3. After 2 h of daytime aging, NH4+ increased and is approximately equivalent to the sum of Cl, SO42, and NO3. Particle size increased with downwind distance, causing particles to be more efficient scatters. Averaged over nine flights, mass scattering efficiency (MSE) increased in ∼ 2 h by 56 % and doubled in one flight. Mechanisms for redistributing mass from small to large particles are discussed. Coagulation is effective at moving aerosol from the Aitken to accumulation modes but yields only a minor increase in MSE. As absorption remained nearly constant with age, the time evolution of single scatter albedo was controlled by age-dependent scattering. Near-fire aerosol had a single scatter albedo (SSA) of 0.8–0.9. After 1 to 2 h of aging SSAs were typically 0.9 and greater. Assuming global-average surface and atmospheric conditions, the observed age dependence in SSA would change the direct radiative effect of a wildfire plume from near zero near the fire to a cooling effect downwind.

Experimental determination of the dispersion of ions from a point source in the environment

ABSTRACTThe dispersion of ions from a point source has been extensively modelled but there have been very few attempts to experimentally verify the theoretical findings. The main reason for this has been the difficulty of discriminating between cluster ion and charged particle concentrations in the air. In this paper, we describe a novel technique for the experimental determination of the dispersion of ions from a point source in air. Laboratory experiments showed that the lifetime of cluster ions in an aerosol cloud was of the order of minutes. However, once they attached to aerosols, the particles retained the charge for at least 30 min, suggesting that they may be carried long distances in natural winds. A negative air ionizer was used to produce ions and charged particles in an open field in the presence of a steady horizontal wind. A neutral cluster and air ion spectrometer was used to measure cluster ion and charged particle concentrations as a function of downwind distance from the source. The results are broadly consistent with the Gaussian dispersion model for a continuous point source. We estimate that cluster ions can be carried up to a distance of several hundred metres before they fully attach to particles which can then be carried as far as 3–4 km. Therefore, these observations have important bearing on exposure to cluster ions and charged particles downwind of ion sources such as high voltage power lines and busy roads.

PRIME2: Development and evaluation of improved building downwash algorithms for rectangular and streamlined structures

Theoretical flaws in PRIME (the building downwash formulation in AERMOD) have recently been documented. To improve PRIME, an industry funded research study was initiated with the following overall objectives: 1) correct the known problems in the theory; 2) incorporate and advance the current state of science; 3) expand the types of structures that can be accurately handled (e.g., streamlined, long, wide); 4) properly document and verify the model formulation and code for the updated PRIME (PRIME2); and 5) collaborate with EPA to work toward implementing the improved model. This paper presents the results from the wind tunnel study used to develop a database of wind speed and turbulence intensity measurements downwind of various rectangular and streamlined structures for three different approach turbulence conditions. Based on those measurements, new equations were developed to estimate the velocity deficit and turbulence intensity increase in the building wake as a function of downwind distance, height, building shape, and approach turbulence intensity. Comparisons of the new equations versus wind tunnel observations showed good agreement; whereas, the equations in PRIME do not agree well above the height of the building and show mixed agreement below the top of the building.

Screening procedure for airborne pollutants emitted from a high-tech industrial complex in Taiwan

Despite the modernization of computational techniques, atmospheric dispersion modeling remains a complicated task as it involves the use of large amounts of interrelated data with wide variability. The continuously growing list of regulated air pollutants also increases the difficulty of this task. To address these challenges, this study aimed to develop a screening procedure for a long-term exposure scenario by generating a site-specific lookup table of hourly averaged dispersion factors (χ/Q), which could be evaluated by downwind distance, direction, and effective plume height only. To allow for such simplification, the average plume rise was weighted with the frequency distribution of meteorological data so that the prediction of χ/Q could be decoupled from the meteorological data. To illustrate this procedure, 20 receptors around a high-tech complex in Taiwan were selected. Five consecutive years of hourly meteorological data were acquired to generate a lookup table of χ/Q, as well as two regression formulas of plume rise as functions of downwind distance, buoyancy flux, and stack height. To calculate the concentrations for the selected receptors, a six-step Excel algorithm was programmed with four years of emission records and 10 most critical toxics were screened out. A validation check using Industrial Source Complex (ISC3) model with the same meteorological and emission data showed an acceptable overestimate of 6.7% in the average concentration of 10 nearby receptors. The procedure proposed in this study allows practical and focused emission management for a large industrial complex and can therefore be integrated into an air quality decision-making system.

Observation of ions and particles near busy roads using a neutral cluster and air ion spectrometer (NAIS)

Motor vehicles emit large quantities of ions in the form of both charged particles and molecular cluster ions. While, the health effects of inhalation of charged particles is largely unexplored, the concentrations near busy roads and the distance to which these particles and ions are carried have important implications for the exposure of the large percentage of the population that lives close to such roadways. We measured ion concentrations using a neutral cluster and air ion spectrometer (NAIS) near seven busy roads carrying on the average approximately 7000 vehicles h−1 including about 15% heavy duty diesel vehicles. In this study, charged particle concentrations were measured as a function of downwind distance from the road for the first time. We show that, at a moderate wind speed of 2.0 m s−1, mean charged particle concentrations at the kerb were of the order of 2 × 104 cm−3 and, more importantly, decreased as d−0.6 where d is the distance from the road. While cluster ions were rapidly depleted by attachment to particles and were not carried to more than about 20 m from the road, elevated concentrations of charged particle were detected up to at least 400 m from the road. Most of the charge on the downwind side was carried on the larger particles, with no excess charge on particles smaller than about 10 nm. At 30 nm, particles carried more than double the charge they would normally carry in equilibrium. There are very few measurements of ions near road traffic and this is the first study of the spatial dispersion of charged particles from a road.

Atmospheric dispersion of accidental release of radioactive gases from high enriched and low enriched fuel of Miniature Neutron Source Reactors (MNSR)

Abstract Analysis has been done for accidental release of radioactive gases from high and low enriched fuel of miniature neutron source reactors (MNSR). Calculations have been performed for existing high enriched uranium (HEU) fuelled core and prospected low enriched uranium (LEU) fuelled core. Composition of existing HEU fuel is UAl4-Al while prospected LEU fuel is UO2. The ORIGEN2 code has been used for burn up and source term calculations. The “Hotspot” version 2.06 has been employed for radiological dispersion analysis to model the release of radioactivity in case of accident. Site specific meteorological data has been employed to determine the dose values for different stability classes as a function of downwind distance. In case of a radiological accident releasing radioactive gases at ground level, the maximum Total Effective Dose Equivalent (TEDE) is about 0.26 Sv for the most prevailing meteorological conditions at the site. There were no appreciable differences found in doses for HEU and LEU fuel.

Ions in motor vehicle exhaust and their dispersion near busy roads

Measurements in the exhaust plume of a petrol-driven motor car showed that molecular cluster ions of both signs were present in approximately equal amounts. The emission rate increased sharply with engine speed while the charge symmetry remained unchanged. Measurements at the kerbside of nine motorways and five city roads showed that the mean total cluster ion concentration near city roads (603 cm −3) was about one-half of that near motorways (1211 cm −3) and about twice as high as that in the urban background (269 cm −3). Both positive and negative ion concentrations near a motorway showed a significant linear increase with traffic density ( R 2 = 0.3 at p < 0.05) and correlated well with each other in real time ( R 2 = 0.87 at p < 0.01). Heavy duty diesel vehicles comprised the main source of ions near busy roads. Measurements were conducted as a function of downwind distance from two motorways carrying around 120–150 vehicles per minute. Total traffic-related cluster ion concentrations decreased rapidly with distance, falling by one-half from the closest approach of 2 m to 5 m of the kerb. Measured concentrations decreased to background at about 15 m from the kerb when the wind speed was 1.3 m s −1, this distance being greater at higher wind speed. The number and net charge concentrations of aerosol particles were also measured. Unlike particles that were carried downwind to distances of a few hundred metres, cluster ions emitted by motor vehicles were not present at more than a few tens of metres from the road.

Mathematical model for hermitized atmospheric dispersion in low winds with eddy diffusivities as linear functions of down wind distance

In the present paper, an attempt is made for generalized the atmospheric diffusion operator. This can be accomplished by employing the realizability procedure, to identify a surface operator, that ensures self-adjointness’ of the atmospheric diffusion operator. The dispersion modeling in low wind speeds assumes importance because of the high frequency of occurrence and episodic nature of these poor diffusion conditions. A steady-state mathematical model for hermitized model has been calculated for the dispersion of air pollutants in low winds by taking into account the diffusion in the three coordinate directions and advection along the mean wind. The eddy diffusivities have been parameterized in terms of downwind distance for near source dispersion (Arya, 1995). The constants involved in this parameterization are the squares of intensities of turbulence. An analytical solution for resulting advection-diffusion equation with the physically relevant boundary conditions has been obtained. The solution has been used to simulate the field tracer data collected at IIT Delhi in low wind convective conditions.

A 3D Lagrangian particle model for the atmospheric dispersion of toxic pollutants

A 3D Lagrangian particle model has been presented for the atmospheric dispersion of the toxic pollutants released from industrial stacks. As the mean wind speed and direction is changed with height in a real atmosphere, the height of the exhaust stack may have a strong impact on the pollutant dispersion and ground concentrations. An elevated continuous release of non-buoyant gas in a neutrally stratified atmosphere has been simulated, for various stack heights. The turbulent atmospheric parameters like vertical profiles of fluctuat ing wind velocity components and eddy lifetime were calculated using a semi-empirical mathematical model. The numerically calculated horizontal and vertical dispersion coefficients (σy and σz) are compared with the Pasquill's empirical σ's. The ground concentration as a function of downwind distance has been compared with the Green glow data. The ground concentrations for various release heights were compared with the Gaussian plume model. The comparison indicated a need for using either a modified Gaussian model or a 3D numerical mathematical model for pollutant dispersion and ground concentration calculations. Copyright © 2002 John Wiley & Sons, Ltd.

Two-dimensional analytical model for estimating crosswind integrated concentration in a capping inversion: eddy diffusivity as a function of downwind distance from the source

A mathematical model has been proposed for computing crosswind-integrated concentration in a capping inversion layer by considering the eddy diffusivity as a function of down wind distance from the source. An analytical solution of the resulting partial differential equation with the physically relevant boundary conditions has been obtained for the general functional form of eddy diffusivity using the method of eigen-function expansion. The model with eddy diffusivity as a linear function of downwind distance is validated with the available data in the literature from Copenhagen in Denmark and plume validation experiment conducted by Electric Power Research Institute at Kincaid in USA. The agreement is found to be good between the computed and the observed concentrations in both the experiments. In fact, majority of the concentrations predicted from the model are with in a factor of two to observations.

A 3-D Lagrangian stochastic model for the meso-scale atmospheric dispersion applications

A fully 3-D Lagrangian stochastic particle trajectory model is presented and applied to the meso-scale atmospheric dispersion and ground concentration calculations. The use of Gaussian plume model (GPM) with Pasquill–Gifford σ's for downwind distances exceeding 10 km is critically viewed. Further, the effect of variation in release height on the ground concentration and dispersion parameters ( σ y , σ z ) is studied for continuous releases. A continuous release of a non-buoyant gas in a neutral stratified atmosphere is simulated for various stack heights. The turbulent atmospheric parameters like vertical profiles of the fluctuating wind component and the eddy lifetimes for the horizontal and vertical directions, etc. were calculated using a semi-empirical mathematical model and compared with a E– ϵ model. The numerically calculated horizontal and vertical dispersion coefficients ( σ y , σ z ) are compared with the Pasquill–Gifford empirical σ's and with the Pasquill-modified σ y . The ground concentration values as a function of downwind distance, have been compared with the Green Glow data and with a GPM for various release heights. The comparison of the results demonstrate a need of using a 3-D model over the simple GPM for meso-scale atmospheric dispersion applications. The GPM overpredicts the ground concentration because it cannot take into account the vertical wind shear, which is observed in the atmosphere under all stability conditions. A weak dependence on the release height in the numerically calculated dispersion coefficients σ's, is also observed.

Effect of chemical reaction on the dispersion of a solute in a porous medium

A mathematical model is presented in this paper which describes the dispersion of a chemically active solute in the laminar flow in a sparsely packed porous medium. The validity of time-dependent dispersion coefficient is widened by using a generalized dispersion coefficient. The effect of porous parameter and chemical reaction on the dispersion coefficient is studied. The exact solution for the mean concentration distribution of a chemically active solute is obtained as a function of downwind distance and time. Results are also obtained for pure convection.

Instantaneous Spread of Plumes in the Surface Layer

Abstract Data are presented from two recent tracer campaigns regarding relative diffusion of surface-level plumes. One study consists of tests performed amid flat, rural terrain near Galen, Montana, while other experiments were conducted above a poplar forest with uniform canopy density and height near Boardman, Oregon. In both cases, sulfur hexafluoride was released near the surface at a constant rate, and fast-response analyzers were used to measure plume concentrations along crosswind traverses and at fixed locations within 1 km of the source. This paper characterizes horizontal plume spread on near-instantaneous time frames during 29 tests, and the field data are used to test seven empirical and theoretical approaches for estimating relative diffusion coefficients using on-site wind data. Five of the equations utilize simple turbulence statistics to predict plume spread as a function of downwind distance; one method utilizes stability-based power-law formulas; and the last technique invokes second-ord...

The depth of the stably stratified internal boundary layer over the sea

As an air mass is advected from a heated land surface over a cooler sea, it is extensively modified by the underlying surface with the subsequent formation of a stably stratified internal boundary layer (SIBL). Due to weak turbulence, changes in surface forcing are communicated very slowly across the depth of the SIBL and its growth rate cannot be described in terms of local parameters. Therefore, it has been proposed that the growth of the SIBL is controlled by the fetch integrated value of surface heat flux. This approach is adopted in the present paper in order to develop a simple equation capable to describe the development of the SIBL as a function of downwind distance and external forcings, such as pressure gradient force, surface roughness and potential temperature difference between sea and land surface. The derived relationship is tested against a limited data set from the Öresund experiment.

Development of a Model of Dispersion Parameters for Odour Transmission from Agricultural Sources

A mathematical model of the dispersion parameters in the Gaussian plume model is developed for calculating ground-level odour concentration and for analysing the effect of wind speed on odour concentration. The model has three coefficients. The dispersion parameters are expressed as functions of downwind distance and wind speed, with wind speed being the most important factor to affect downwind concentration of odour from an agricultural source. The model was investigated by using the Pasquill–Gifford data. The range of downwind distances for which the model is applicable is from 100 to 1000 m, the zone of interest for odour dispersion from agricultural sources. The model is shown to fit the Pasquill–Gifford data effectively. The non-linear regression results also show that there is a dominant coefficient that determines the final estimation of the model. The error caused by incorporating the wind speed into the model is random.

Characteristics of worst‐case maximum air concentrations

The properties of the Gaussian plume equation have led many industrial designers to plan their stack system so that ambient pollutant concentrations are reduced to levels considered safe from the standpoint of undesirable effects. This paper demonstrates the characteristics of worst‐case maximum air concentrations due to an elevated point source diffusing over flat terrain. The critical wind speed, critical plume rise and critical downwind distance are obtained from the Gaussian plume model. The analysis is based on the assumption that dispersion parameters σy and σz are functions of downwind distance and atmospheric stability. The proposed methodology should be especially useful in applications in design of stacks, air quality management and air pollution episode control planning.

Mesoscale atmospheric dispersion experiments using tracer and tetroons

In April 1983, March 1984 and March 1985 four mesoscale atmospheric dispersion experiments were performed near the Kernforschungszentrum Karlsruhe. The experiments comprised: tracking of tetroons by radar up to distances of more than 100 km; release of the tracer SF 6 at a height of 100 m or 140 m, respectively, and downwind sampling at more than 50 locations during up to seven successive periods of 30 min duration each up to source distances of 66 km; meteorological measurements at a 200 m high tower and radiosonde ascents up to a height of at least 2000 m. The measured data have been analyzed to obtain dispersion parametersσ y and σ z as a function of downwind distance and sampling time.σ y derived from tracer concentrations and from tetroon trajectories can be well compared, if the duration of the sampling time is taken into account. Vertical wind speeds and turbulence intensities are determined from tetroon trajectories. The turbulence intensities are compared to stability classes derived from meteorological measurements.

Characterization of concentration fluctuations of a surface plume in a neutral boundary layer

We describe a new high-resolution sampling technique which can be used to measure concentration fluctuations simultaneously at several points in space. The technique has been used to measure the probability distribution function as a function of the detector location relative to a continuous and steady source. Results are compared to previous experiments and theoretical predictions. The spectra of the concentration fluctuations are analyzed and their behaviour as a function of downwind distance from the source is described.

Negatively buoyant plume dispersion: a comparison of simple mathematical models, hydraulic simulations and field data

The ground-level concentration distribution for negatively buoyant gases of various densities, emitted from stacks with heights, diameters and exit velocities varying in the typical range of geothermal drilling activities, was studied by means of hydraulic simulations performed in neutral conditions at different flow speeds. These measurements, and a few others taken in the field in nearly neutral and unstable atmosphere during tests of CO2 release from a geothermal well, were compared with the values expected from a Gaussian formula corrected for denser-than-air, tilted plumes. For calculating theoretical concentrations, three couples of horizontal and vertical plume standard deviations as functions of downwind distance from source were employed: those given by Singer-Smith and Briggs and a third one obtained by our group during a previous water channel experiment. Also the maximum ground-level concentration and its distance from the source were measured in each simulation and compared with the prediction of our Gaussian formula, as well as with a best-fit expression given by Meroney. The concentration pattern χ(x, y, 0) given by the corrected Gaussian formula proved to be in good agreement with experimental data, especially in association with Singer-Smith's or our sigmas. When only maximum g.l. concentrations are needed, also the simple formula suggested by Meroney can give a good approximation.