Keywords: air quality modelling, finite element method, adaptive three-dimensional mesh, local scale, Eulerian description, mass-consistent model, wind field simulation.

In this paper, a local scale Eulerian air pollution model is introduced that is related to unsteady propagation problems which may be mathematically described by convection-diffusion-reaction equations. The couple problem is solved by applying a three-dimensional finite element discretization with unstructured and adapted meshes. The tetrahedral mesh is adapted to the topography and the plume rise. The local area of interest is up to tens of kilometres and it includes the stacks. The wind field is crucial for the pollutant transport, especially in complex terrain areas. A mass consistent model is used that is solved with the finite element method taking into account the plume rise effect [1,2,3]. This effect is included by perturbing the vertical component of the resulting wind field along the bent plume trajectory. Wind measurements are used to compute the interpolated wind field. Chemical reactions have been solved using a condensed pseudo-first-order chemical scheme model (RIVAD) involving four species with non-linear chemistry. To solve this problem we apply an Strang splitting and a second order Rosenbrock time integration scheme (ROS2). The linearised numerical solution is obtained using stabilized finite elements with least squares and a Crank-Nicolson time integration. The discretization of the stack geometry permits the definition of the stack pollutant emissions as boundary conditions, and dry deposition is also included as a boundary condition. A previous description of the proposed procedure can be found in [4].

The air pollution that is produced by a stack placed in the Island of La Palma (Canary Island, Spain) is simulated. The results have been simulated within a reasonable computing time.

1

G. Montero, E. Rodríguez, R. Montenegro, J.M. Escobar, J.M. González-Yuste, "Genetic algorithms for an improved parameter estimation with local refinement of tetrahedral meshes in a wind model", Journal of Wind Engineering and Industrial Aerodynamics, 36, 3-10, 2005.

2

J.M. Escobar, E. Rodríguez, R. Montenegro, G. Montero, J.M. González-Yuste, "Velocity field modelling for pollutant plume using 3-D adaptive finite element method", Lecture Notes in Computer Science, 3037, 642-645 Springer-Verlag, 2004.

3

L. Ferragut, R. Montenegro, G. Montero, E. Rodríguez, M.L. Asensio, J.M. Escobar, "Comparison between 2.5-D and 3-D realistic models for wind field adjustment", Journal of wind Engineering and Industrial Aerodynamics, 98, 548-558, 2010. doi:10.1016/j.jweia.2010.04.004

4

A. Oliver, A. Pérez-Foguet, E. Rodríguez, J.M. Escobar, R. Montenegro, G. Montero, "A local scale finite element model for stack pollutant dispersion over complex terrains", 11th EMS Annual Meeting / 10th European Conference on Applications of Meteorology (ECAM), 2011.

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