Large eddy simulation is a powerful technique that can be used together with experimental data to improve our understanding of complex phenomena in atmospheric sciences. In this seminar a combination of numerical and experimental data to study pollen dispersion in the atmospheric boundary layer will be presented. This is an important subject in fields such as ecology and atmospheric sciences and has gained renewed interest in the context of genetically modified crops. The focus here is on the development and validation of a numerical model based on the large eddy simulation technique to simulate pollen transport. Important phenomena such as the pollen emission by the plants and the ground deposition are parameterized by the lower boundary condition. A theoretical profile that incorporates effects of particle settling and atmospheric stability to the log-law obtained for passive scalars is derived and used to impose the lower boundary condition. An approach for the numerical discretization that combines the (energy-conserving) pseudospectral method for the velocity field and a physically bounded finite-volume discretization for the pollen concentration equation is developed and implemented. A new interpolation scheme is designed to couple the two discretization techniques and enforce a divergence-free velocity field on the finite-volume faces. The numerical model is validated against previously published experiments of point-source releases of heavy particles and pollen grains in the atmospheric boundary layer. The numerical model is used together with experimental data of pollen emission and downwind deposition from a natural field obtained near Washington DC in the summer of 2006. The combination of experimental and numerical data provides a good understanding of whole emission/transport/deposition process. The potential applicability of the numerical model developed to other problems will be discussed.