This paper presents a framework to simulate pollen dispersal by the wind based on the large eddy simulation(LES) technique. Important phenomena such as the pollen emission by the plants and the ground deposition are parameterized by the lower boundary condition. The numerical model is validated against previously published experiments of point source releases of glass beads and pollen grains in the atmospheric boundary layer. The numerical model is used together with experimental data of pollen emission and down wind deposition from a natural field obtained near Washington,DC, in the summer of 2006. The combined analysis of experimental and numerical data allows to elucidate the emission/transport/deposition process inconsiderable detail. In particular, the relative fractions of pollen deposited inside the source field and airborne at the edge of the field can be quantified. The use of LES allows quantification of important intermittent deposition events far from the source field.