atmospheric dispersion Articles
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A Nordic harmonisation effort concerning atmospheric dispersion modelling for real-time accident situations
Neighbouring countries have often chosen different atmospheric dispersion prognosis models for use in emergency situations. This may result in differences in the predictions, which in turn can lead to the authorities adopting different countermeasures. In a Nordic project within the Nordic Nuclear Safety Research Programme (NKS), a Nordic harmonisation and comparison effort was initiated in the ...
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Contrasting methods for validating ADMS using the Indianapolis dataset
This paper shows results of validation of the Atmospheric Dispersion Modelling System (ADMS) against the Indianapolis dataset, comparing arcwise maxima and analysing the results using the BOOT statistical package. There is good agreement between the quality 3 daytime observed and predicted concentrations. At night-time, calculated concentrations depend critically on the value of the surface ...
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Using plume rise schemes to model highly buoyant plumes from large fires
The atmospheric dispersion model Numerical Atmospheric-dispersion Modelling Environment (NAME) is used to simulate the smoke plume from the explosion at the Buncefield oil depot. Simple modelling, in which the plume rise is included through an effective elevated source term, captures the transport and spread of the plume well. More complex modelling, using the NAME plume rise scheme, ...
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The Model Validation Kit - status and outlook
Over the past few years, the so-called Model Validation Kit has been the basis for much work on evaluation of atmospheric point source dispersion models. The kit has recently been enhanced with a supplement which represents urban conditions (experimental data from Indianapolis, USA). A change of methodology is under consideration, based on the concept of near centreline concentrations. The paper ...
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Evaluation of statistical models in atmospheric dispersion modelling
When a gas is released into the atmosphere, there are inevitably random fluctuations in its concentration due to turbulence. Great recent improvements in instrumentation have shown how large these are. This has been acknowledged by CEC (the Commission of the European Communities), for example in that part of its Environment and Climate Programme (Framework IV) dealing with accidents. Likewise, ...
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Development and evaluation of the ADMS building effects module
The structure and algorithms which comprise the ADMS building effects module are summarised and their performance illustrated against ground-level concentration distributions for seven test cases. Overall, this reveals a mean bias up to a factor of 3, being on average a factor of 2 in the near-wake and 0.7 in the main-wake. Some issues that arose from the model development and application are ...
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The 1998 IFDM evaluation with the model validation kit
A modification of the Immission Frequency Distribution Model (IDFM) can reproduce the Kincaid and Indianapolis arc-wise maximum ground-level concentrations (GLCs) and crosswind integrated concentrations (CWICs) fairly well. But we doubt whether these modifications are really an improvement of the description of the natural ambient atmospheric dispersion process, rather than merely fitting a ...
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Modelling of atmospheric flow and dispersion in the wake of a cylindrical obstacle
The computational fluid dynamics code ADREA–HF is used to simulate atmospheric dispersion field experiments around an isolated cylindrical obstacle and two upwind sources of ammonia and propane, with the ammonia source located at different lateral positions. Model calculated concentrations and concentration fluctuations are compared with the experimental results, to investigate the effect of the ...
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A model for simulating atmospheric dispersion in low-wind conditions
A practical model for low-wind conditions was derived by integration of an instantaneous three-dimensional Gaussian puff equation, in which wind speed was assumed to be zero and standard deviations of a smoke (σy and σz) were expressed as a linear function of the dispersion time. When the plume spreads σy and σz were assumed to be linear functions of dispersion time, the ...
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A review of evaluation procedures for atmospheric dispersion models
Evaluation of atmospheric dispersion models is vital to justify their use within the air quality component of environmental assessments. The Model Validation Kit, compiled and distributed by Helge Olesen of NERI, is often used for such evaluations. Whilst the Model Validation Kit has a wide range of functionality, its users often limit their evaluation to a few simplistic calculations. ...
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Simulations of atmospheric dispersion in an urban stable boundary layer
The results of numerical simulations of tracer dispersion in an urban stable boundary layer are presented. Both Gaussian approximation and fourth order closure are considered and a Gram-Charlier probability density function is used in our Lagrangian stochastic model. Different parameterisations for the boundary-layer height and different values of kurtosis are tested. The model is based on the ...
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Validation of the Demokritos dispersion modelling system based on the Indianapolis experiment
To assess the ability of a model to simulate atmospheric dispersion, its performance must be tested using data from real field experiments. This paper presents the results of a validation study of the atmospheric dispersion model Dispersion over Complex Terrain (DIPCOT) against data from the Indianapolis field experiment. Three different modules of the dispersion code are examined a puff model, a ...
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Atmospheric dispersion models for regulatory purposes in the Federal Republic of Germany. Part I: Regulatory modelling
The legal framework for the application of atmospheric dispersion models for air pollution control in Germany is outlined. Atmospheric dispersion models in regulatory procedures are currently essentially based on the Gaussian approach. However, more advanced modelling is already available.Keywords: air pollution control, atmospheric dispersion models, Gaussian model, Germany, regulatory ...
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Towards a new scheme for parametrisation of deep convection in NAME III
This paper describes an updated scheme for parametrisation of atmospheric convection to be used in the Met Office Atmospheric Dispersion Model (NAME III). In this scheme, the vertical transport of particles due to convection is represented in a 1-dimensional model based on a ‘mass-flux’ approach. Empirical formulas are used to obtain the mass fluxes and the convective precipitation is used for ...
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Field tracer experiments over nuclear sites for the validation of a Korean real-time atmospheric dispersion and dose assessment system (FADAS)
A real-time atmospheric dispersion and dose assessment system (FADAS) has been developed. It has been used as a basic tool to monitor the atmospheric dispersion of released radioactive materials and radiological dose assessment to the national emergency preparedness system, CARE, since 1995. Tracer experiments have been conducted for the purpose of validating FADAS and analysing the environmental ...
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Evaluation of new generation atmospheric dispersion models
The paper considers the regulatory view of evaluating dispersion models. There is no proscription for regulatory studies in the UK, so differences between dispersion calculations from different models and versions of models are then as important as their absolute veracity. An example shows variations in calculated concentration due to variations between two different versions of a model and two ...
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Validation of the Gaussian puff models TSTEP and REM-3 using the Kincaid dataset
Two Gaussian short-range atmospheric dispersion models, TSTEP and REM-3, have been validated with the Kincaid dataset of the Model Validation Kit. TSTEP and REM-3 show high scatter compared to the observations. Both models have the tendency to underestimate lower concentratrations and to overestimate higher concentrations, but, within a factor of five, many predictions are in agreement with the ...
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Effect of averaging time on mean concentrations in building influenced dispersion
Tracer gas was released upwind of a cubical model building in the field, under neutral atmospheric conditions, in order to investigate the dependence of mean wake concentrations on averaging time. Two different experimental settings were examined, with the obstacle isolated or embedded within an array of similar obstacles. The averaging periods examined ranged between 10 s and 15 min. A power law ...
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Recent studies to validate and compare atmospheric dispersion models for regulatory purposes in the UK
Some results are presented for recent studies to develop new approaches for (i) validating atmospheric dispersion models using crosswind concentration transects, and (ii) summarising and comparing the predictions of models across a range of efflux and meteorological conditions.Keywords: crosswind concentration, dispersion climate, dispersion modelling, ...
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Effective use of radiation monitoring data and dispersion calculations in an emergency
An essential prerequisite for the proper management of a radiation emergency is that measurement data and calculation prognoses are available and that they are produced in an efficient manner. This paper reviews some of the factors contributing to the practice of performing radiation measurements and atmospheric-dispersion-model calculations effectively and discusses the issues related to the ...
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