Jonas C. Carvalho

Application of a model system for the study of transport and diffusion in complex terrain to the TRACT experiment

Abstract The transport and diffusion processes of a tracer gas released near the ground in the Rhine valley region, in Central Europe, during the 1992 TRACT field experiment, are simulated by a computational model system for complex terrain. This system (RMS) is composed of the prognostic mesoscale model RAMS, the Lagrangian stochastic dispersion model SPRAY and the interface code MIRS, which links RAMS to SPRAY. Three flow simulations were performed, with different initialisations and the one showing the best agreement with the measured flow was selected for the simulation of the TRACT tracer experiment. Tracer concentrations measured by an array of samplers at ground level and by an airplane aloft, are used to evaluate the 3-D concentration field simulated by the model system. The analysis of the simulation results generated by RMS shows that our model system very well reproduces the general behaviour of the contaminant plume, the temporal and spatial distribution of the concentration and the location of the concentration maxima.

An iterative Langevin solution for contaminant dispersion simulation using the Gram–Charlier PDF

Abstract An alternative numerical method to solve the three-dimensional stochastic Langevin equation applied to the air pollution dispersion is proposed and tested. We obtain a first-order differential equation whose solution is known and determined by an integrating factor. A Langevin model for inhomogeneous turbulence is obtained, considering the Gram–Charlier Probability Density Function (PDF) of turbulent velocity. The calculus process is based on an iterative scheme through the Picard Iterative Method. Numerical simulations and comparisons with measured data from two different tracer experiments are realized, showing a good agreement between predicted and observed values. Furthermore, the results obtained with the new approach are compared with the ones obtained by three different models.

Lagrangian stochastic dispersion modelling for the simulation of the release of contaminants from tall and low sources

A Lagrangian particle model is used to study the dispersion of pollutants released in two different tracer experiments: Prairie Grass and Copenhagen. The model is based on a generalized form of the Langevin equation. Turbulence inputs are parameterized according to a scheme able to generate continuous values in all stability conditions and in all heights in the planetary boundary layer. Predicted values of ground-level concentration agree quite well with observed ones. The major progress of this paper is as follows: For air quality modeling it is highly necessary to include a parameterization that allows a correct description of the turbulent transport of contaminants released simultaneously from low and tall sources.

Analytical solution of the Eulerian dispersion equation for nonstationary conditions: development and evaluation

An analytical technique to solve the Eulerian advection-diffusion equation for nonstationary conditions and passive contaminant within the Planetary Boundary Layer is analysed in this paper. The approach produces comparable results when considering the most important quantity in air-pollution application, that is the ground level concentration distribution. This is a promising result as this computer-based technique may be used for quantitative and qualitative estimations of contaminant distribution.

Short Communication: Semi-analytical solution of the asymptotic Langevin Equation by the Picard Iterative Method

In this work, a semi-analytical solution for the asymptotic Langevin Equation (Random Displacement Equation) applied to the pollutant dispersion in the Planetary Boundary Layer (PBL) is developed and tested. The solution considers as starting point the first-order differential equation for the random displacement, on which is applied the Picard Iterative Method. The new model is parameterized by a turbulent eddy diffusivity derived from the Taylor Statistical Diffusion Theory and a model for the turbulence spectrum, assuming the hypothesis of linear superposition of the mechanical and thermal turbulence mechanisms. We report numerical simulations and comparisons with experimental data and other diffusion models. The main motivation for this work comes from the fact that the round-off error influence and computational time can be reduced in the new method.

Short Communication: Analytical solution of the advection-diffusion equation with nonlocal closure of the turbulent diffusion

In this work we consider the nonlocal closure of the turbulent diffusion in the advection-diffusion equation. Accounting for the current knowledge on the Convective Boundary Layer structure and characteristics, we obtain an expression for the advection-diffusion equation depending on eddy diffusivity, skewness, Lagrangian time scale and vertical turbulent velocity. This expression is solved analytically using the Laplace transform technique. The present study shows that the inclusion of the countergradient term modifies the maximum concentration which is one of the most important parameters in air-quality applicative context.

Employing a Lagrangian stochastic dispersion model and classical diffusion experiments to evaluate two turbulence parameterization schemes

Considering a Lagrangian stochastic particle dispersion model and diffusion experiments, two turbulence parameterizations have been tested. The parameters obtained from the Taylor turbulence parameterization are derived from observed spectral properties and characteristics of energy containing eddies. Taylor turbulence scheme provides continuous values for the turbulent parameters in the planetary boundary layer. Hanna turbulence parameterization is obtained from theoretical considerations and second–order closure models and it does not provide continuous vertical profiles for the turbulent parameters. The predicted values by a Lagrangian diffusion model utilizing Taylor turbulence parameterization and the Hanna turbulence scheme are compared with observed concentration data from diffusion experiments. The use of Taylor turbulence scheme resulted in better results.

Tritium dispersion simulation in the atmosphere from ANGRA I Nuclear Power Plant

In this work, we check the ability of an air pollution model to simulate the concentration of radioactive material emitted from the Nuclear Power Plant of Angra dos Reis, Brazil. To achieve this goal, we solve the time-dependent two-dimensional equation by the Generalised Integral Laplace Transform Technique (GILTT) method. The wind field was reconstructed by the MM5 mesoscale model and the analysis of the results shows a good agreement between the values computed by the model against the experimental ones.

Derivation of third-order vertical velocity turbulence moment in the convective boundary layer from large eddy simulation data: an application to the dispersion modeling

A new formulation for the vertical turbulent velocity third statistical moment in a convective boundary layer is proposed. The parameterization is based directly on the definition of this higher order moment, with velocity skewness and variance being calculated from large eddy simulation data. The formulation, included in a Lagrangian stochastic dispersion model, has been tested and compared with expressions for the third moment obtained from experimental data and reported in the literature, using concentration data from field experiments. The application of a statistical evaluation shows that the proposed parameterization has one of the best overall adjustments to the data.

A ventilação e a fumaça ambiental de cigarros

A fumaca ambiental de cigarros (FAC) e uma das principais contribuintes para o aumento da concentracao e da exposicao a particulas em ambientes fechados. E comprovado que muitos de seus compostos quimicos sao toxicos ou cancerigenos e que sua inalacao pode causar varios danos a saude. Embora, salvo em areas especificadas, proibido por lei, o fumo em recintos coletivos e comum no Brasil e, na maioria dos casos, as areas destinadas a ele, quando existentes, nao sao devidamente isoladas, prejudicando os nao-fumantes. A industria do tabaco e a da hospitalidade vendem a ventilacao como a solucao desse problema, mas estudos indicam que ela nao o e. Este artigo aborda a problematica da exposicao a FAC por seus aspectos ligados a saude e a poluicao.