ZIMORA – An Atmospheric Dispersion Model

This paper presents a development and validation of a 3D numerical model for the advection-diffusion equation. Atmospheric flow field generated by mesoscale circulation model is used as input for the wind speed. As the mesoscale model gives information at scale higher than the necessary for description of a plume trajectory a weighted linear average proper interpolation was developed for intermediate these distances. Diffusion coefficients are variables in time and space and are different for lateral and vertical directions. This assumption is important and considers that the turbulence is not isotropic. Numerical scheme is explicit and conservative and has small implicit diffusion in the advection part of the model. Boundary conditions are open at lateral domain and normal in the bottom and at the top of the Planetary Boundary Layer (PBL) height. Output of the model can be viewed at any time step as well as the concentration distributions are showed at horizontal or vertical surfaces. For validation of the model two experiments were carried out near a thermoelectric power plant located in the south of Brazil. Each experiment was forty days longer. Hourly SO2 concentrations were collected in four receptors around the power plant. During the experiments micrometeorological measurements and tethered balloons were also used in order to describe properly the local atmospheric circulation and PBL characteristics. Various static indices indicate that the model works very well at least for the source and the terrain were it is located, i.e. continuous emission and homogeneous topography.

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