A three-dimensional plume rise model for dry and wet plumes

We present a plume rise model which can be applied to situations with arbitrary wind fields and source exit directions and to both dry and wet plumes. The model is an integral model which considers plume properties averaged over the plume cross section. It is validated by means of water tank, wind tunnel, and field experiments (stacks and cooling towers).     

Plume rise from multiple sources: A new model

In 1974 and 1975, Briggs presented two semiempirical models for computing plume rise from multiple sources for stacks with the same height and emission. Since in our country there are many power plants with more than one stack and generally of different heights and emissions, we developed a new model based on “virtual” stack concept, able to provide estimates of maximum plume height for this problem. Firstly we compared a simplified expression, derived from our model for the case of chimneys of equal heights and emissions, with the above mentioned Briggs' models and with a series of data quoted by Briggs in his 1974 paper. Then we tested our model with a few experimental data relative to stacks of different heights and obtained during the La Spezia field experiments. All the comparisons made showed a satisfactory agreement. Finally a comparison among an empirical expression due to Montgomery et al. giving the correction factor for ground level concentrations in the multiple sources case and the analogue ones derived from our and Briggs' models is presented.     

A fluctuating plume dispersion model for the prediction of odour-impact frequencies from continuous stationary sources

A fluctuating plume dispersion model has been developed to facilitate the prediction of odour-impact frequencies in the communities surrounding elevated point sources. The model was used to predict the frequencies of occurrence of odours of various magnitudes for 1 h periods. In addition, the model predicted the maximum odour level. The model was tested with an extensive set of data collected in the residential areas surrounding the paint shop of an automotive assembly plant. Most of the perceived odours in the vicinity of the 64, 46 m high stacks ranged between 2 and 7 odour units and generally persisted for less than 30 s. Ninety-eight different field determinations of odour impact frequencies within 1 km of the plant were conducted during the course of the study. To simplify evaluation, the frequencies of occurrence of different odour levels were summed to give the total frequency of occurrence of all readily detectable (>2 OU) odours. The model provided excellent simulation of the total frequencies of occurrence where the odour was frequent (i.e. readily detectable more than 30% of the time). At lower frequencies of occurrence the model prediction was poor. The stability class did not seem to affect the model's ability to predict field frequency values. However, the model provided excellent predictions of the maximum odour levels without being sensitive to either stability class or distance from the source. Ninety-five percent of the predicted maximum values were within a factor of two of the measured field maximum values.     

A puff pollutant dispersion model with wind shear and dynamic plume rise

A puff diffusion model, which includes wind shear and dynamic plume rise, is developed for numerical prediction of pollutant concentrations under unsteady and non-uniform flow conditions. The plume from a continuous source is treated as a series of puffs emitted successively from the source. Each puff is represented by a set of six tracer particles, which define the size, shape and location of the puff. Initially these particles are located at the surface of the source, on arbitrarily chosen orthogonal axes. The location of the particles is computed at each time step by taking into account advection, eddy diffusion, wind shear and entrainment of ambient air during plume rise. The concentration distribution of each puff is determined by fitting an ellipsoid to the cluster of the six particles and assuming a three-dimensional Gaussian distribution, with standard deviation equal to the half-lengths of the principal axes of the ellipsoid. The concentration at a point of interest is obtained by summing the contributions from nearby puffs. The effect of wind shear on the pollutant concentration is investigated by use of a typical wind shear encountered in the atmosphere. The results show that, at 600 m downstream from the source, the present model gives concentrations a factor of 2 higher and lower at one standard deviation below and above the plume center, respectively, than that of conventional models in which no wind shear is considered. The plume-rise formulation is calibrated against the observations compiled by Briggs and the model is used to predict the trajectory of a plume observed by Slawson and Csanady. Excellent agreement between the prediction and the observation can be achieved if an appropriate eddy diffusivity is chosen.     

An inverse Gaussian plume approach for estimating atmospheric pollutant emissions from multiple point sources

A method is developed for estimating the emission rates of contaminants into the atmosphere from multiple point sources using measurements of particulate material deposited at ground level. The approach is based on a Gaussian plume type solution for the advection–diffusion equation with ground-level deposition and given emission sources. This solution to the forward problem is incorporated into an inverse algorithm for estimating the emission rates by means of a linear least squares approach. The results are validated using measured deposition and meteorological data from a large lead–zinc smelting operation in Trail, British Columbia. The algorithm is demonstrated to be robust and capable of generating reasonably accurate estimates of total contaminant emissions over the relatively short distances of interest in this study.     

A note on the maximum ground level concentration for inversion-limited chimney plumes

A model is proposed for the determination of the maximum ground level concentration for buoyant chimney plumes whose rise is limited by the inversion overlying a convective atmospheric boundary layer. Manins' critical parameter for inversion penetration is shown to be equivalent to a geometric constraint on the solution for maximum plume rise in the author's model for unrestricted plume rise. A proposed solution for maximum surface concentration based on an effective source rate at the inversion modified for inversion entrainment has the same functional form as a previous solution for the unrestricted case. Experimental analysis suggests the existence of the critical value of source buoyancy flux in terms of ambient parameters, and supports the validity of the form and order of magnitude of the maximum surface concentration.     

A multi-layer model for pollutant dispersion with dry deposition to the ground

This paper presents a semi-analytical solution for the steady advection–diffusion equation that allows simulating the vertical turbulent dispersion of air pollution with deposition to the ground. The performances of the solution, with a proper parameterization of the vertical profiles of wind and eddy diffusivity, were evaluated against Hanford diffusion experiment dataset using two tracers (Doran and Horst, 1985): a non-depositing gas (SF₆) and depositing particles (ZnS). Results show that the dispersion model with the K-parameterization included produces a good fitting of the measured ground-level concentration data and there are no big differences between the parameterizations taken from literature. A comparison with other models was shown and discussed.     

A comparison of contaminant plume statistics from a Gaussian puff and urban CFD model for two large cities

This paper quantitatively assesses the spatial extent of modeled contaminated regions resulting from hypothetical airborne agent releases in major urban areas. We compare statistics from a release at several different sites in Washington DC and Chicago using a Gaussian puff model (SCIPUFF, version 1.3, with urban parameter settings) and a building-resolving computational fluid dynamics (CFD) model (FAST3D-CT). For a neutrally buoyant gas source term with urban meteorology, we compare near-surface dosage values within several kilometers of the release during the first half hour, before the gas is dispersed beyond the critical lethal level. In particular, using “fine-grain” point-wise statistics such as fractional bias, spatial correlations and the percentage of points lying within a factor of two, we find that dosage distributions from the Gaussian puff and CFD model share few features in common. Yet the “coarse-grain” statistic that compares areas contained within a given contour level reveals that the differences between the models are less pronounced. Most significant among these distinctions is the rapid lofting, leading to enhanced vertical mixing, and projection downwind of the contaminant by the interaction of the winds with the urban landscape in the CFD model. This model-to-model discrepancy is partially ameliorated by supplying the puff model with more detailed information about the urban boundary layer that evolves on the CFD grid. While improving the correspondence of the models when using the “coarse-grain” statistic, the additional information does not lead to quite as substantial an overall agreement between the models when the “fine-grain” statistics are compared. The taller, denser and more variable building landscape of Chicago created increased sensitivity to release site and led to greater divergence in FAST3D-CT and SCIPUFF results relative to the flatter, sparser and more uniform urban morphology of Washington DC.     

Some characteristics of a plume from a point source based on analytical solution of the two-dimensional advection–diffusion equation

The moments of the concentration distribution obtained using a recent analytical solution of the steady-state two-dimensional advection–diffusion equation are presented. The solving methodology is the Generalized Integral Laplace Transform Technique, which allows obtaining a reliable solution of the advection–diffusion equation without any restrictive assumption about the eddy diffusivity coefficients and wind speed profiles. The first four moments and value and position of maximum ground level concentration are calculated. The concentration standard deviation is compared against the semi-empirical ones used in operative Gaussian models.     

A model for estimating the effects of fluctuations in long term meteorology on observed maximum acid gas levels

A model is proposed to estimate the effect of long term meteorology on maximum daily acid gas levels for each year of 10 years of data for Newcastle, New South Wales, Australia. The model assumes that (1) the probability density functions of both air pollution data and wind speed are lognormally distributed and (2), on average, an inverse relationship exists between air pollution levels and wind speed. Two acid gas monitoring stations in Newcastle and a nearby wind speed station have data which satisfy both these requirements. The maximum acid levels at both stations vary by a factor of about 3–4 over a ten-year period and the model shows that about half of this variation is directly related to fluctuations in the wind speed distribution, leaving the rest of the variation to be explained either by changes in emissions or more meteorological change. It is clear that, if the two prerequisite conditions hold, a significant proportion of the effect of long-term meteorological fluctions on maximum air pollutant levels may be explained by the model to within a reasonable accuracy.     

A multi-criteria GIS-based model for wind farm site selection with the least impact on environmental pollution using the OWA-ANP method

Environmental Science and Pollution Research - Wind energy is considered one of the most efficient and cost-effective ways to generate electricity, since it has a low environmental impact. So, it...     

An atmospheric dispersion model for the environmental impact assessment of thermal power plants in Japan--a method for evaluating topographical effects

An atmospheric dispersion model was developed for the environmental impact assessment of thermal power plants in Japan, and a method for evaluating topographical effects using this model was proposed. The atmospheric dispersion model consists of an airflow model with a turbulence closure model based on the algebraic Reynolds stress model and a Lagrangian particle dispersion model (LPDM). The evaluation of the maximum concentration of air pollutants such as SO2, NOx, and suspended particulate matter is usually considered of primary importance for environmental impact assessment. Three indices were therefore estimated by the atmospheric dispersion model: the ratios (alpha and beta, respectively) of the maximum concentration and the distance of the point of the maximum concentration from the source over topography to the respective values over a flat plane, and the relative concentration distribution [gamma(x)] along the ground surface projection of the plume axis normalized by the maximum concentration over a flat plane. The atmospheric dispersion model was applied to the topography around a power plant with a maximum elevation of more than 1,000 m. The values of alpha and beta evaluated by the atmospheric dispersion model varied between 1 and 3 and between 1 and 0.4, respectively, depending on the topographical features. These results and the calculated distributions of y(x) were highly similar to the results of the wind tunnel experiment. Therefore, when the slope of a hill or mountain is similar to the topography considered in this study, it is possible to evaluate topographical effects on exhaust gas dispersion with reasonable accuracy using the atmospheric dispersion model as well as wind tunnel experiments.     

A semi-Lagrangian formulation for diffusion from ground-level sources in the neutral boundary layer

Diffusion from ground-level sources in the neutral boundary layer is described using a semi-Lagrangian formulation. The eddy diffusivity is assumed to depend on the standard deviation of the concentration profile at each streamwise location. The approach leads to simple analytical expressions for the variation of concentration in terms of flow parameters as the roughness height and the friction velocity, which are in good agreement with experimental results without requiring the use of a turbulent Schmidt number smaller than unity.     

A comparison of the predictions of a simple gaussian plume dispersion model with measurements of pollutant concentration at ground-level and aloft

The NO_x pollution arising from a nitric acid works has been analysed. Measurements were taken at ground-level using continuous monitors over a 6 month period, and aloft at three heights within the plume using a specially constructed bag sampler. The measured concentrations and σ_z values have been compared with the predictions of a simple Gaussian plume dispersion model using the Turner (1970) values of σ_y and σ_z derived from Pasquill-Gifford stability categories. It was found that ground-level concentrations at 1–2 km distance from the source could be predicted reliably, but that close to the source predicted values of σ_z were greater than those measured experimentally.     

An analytical model for the transport,dispersion and elimination of air pollutants emitted from a point source

The solution of the complete transport diffusion equation with a first order reaction term is obtained for a continuous source. A deposition velocity boundary condition is met at the ground and, optionally, a similar leakage velocity boundary condition can be met at the base of a superjacent layer. The identification of a preliminary transformation of the dependent variable that eliminates the transport and sink terms permits particularly simple analytic solutions to be obtained by means of conventional Laplace transform, Green's function methods. Prior solutions are compared with these results. A linearisation of the solution without an overlying layer provides a simple extension of the conventional Gaussian plume result that permits account to be taken of pollutant settling velocity, of absorption at the ground and of a first order reaction. The accuracy of this linearisation is assessed. Examples of the application of the methods to calculation of the distribution of particulates and of the formation of nitrogen dioxide in a plume are given.