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This work presents a strategy for three-dimensional finite element simulation of pollu tion evolution in highly complex terrains. The strategy is useful for the impact assess ment of punctual emissions in the near field, up to few tens of kilometres. This scale is appropriate to be linked with the standard meshes used in most advanced air quality pho tochemical models, where the minimum grid size is about 2 to 4 km. These mesoscale models are specially designed for simulations up to hundreds of kilometres and are prop erly linked to meteorological prognostic models. Remarkably, most advanced mesoscale models include in-grid parcel evolution (puff) models for the near field impact of punc tual emissions. The proposal of this work is to show that the finite element simulation is an appropriated alternative to this hybrid approach. The simulation of the pollution evolution is driven by the wind field, which is computed with a mass consistent model for wind field adjustment [1,2]. The transport and reaction model is given by a convection, diffusion, reaction system of equations. The reaction term includes the photochemical modelling of pollutants. Two simple reaction models are considered here: First, a linear reaction model between two components, and second, the RIVAD acid rain model, which involves four components and a highly nonlinear coupled relationship [3]. Finite element problems involving highly complex terrains and detailed discretization of punctual emission sources can easily involve hundreds of thousands of tetrahedral ele ments and tens of thousands of grid nodes. Remarkably, they include element sizes rang ing to four orders of magnitude (from a few meters close to the source to few kilometers faraway). Meshes are appropriate from the point of view of wind simulation. However, corresponding transport reaction problems present strong numerical requirements due to different scales involved. The linear case (constant rate transformation between species) is solved using a Least Square approach with the Crank-Nicolson scheme for time inte gration [4]. The discretized problems are a sequence of symmetric linear systems with

Finite Element Simulation of Chimney Emissions: A Proposal for Near Field Impact Assessment in Highly Complex Terrains