In order to better understand long-range dispersal of maize pollen we have developed an approach aimed at simulating the trajectories and dehydration of pollen grains in the atmosphere at regional scale. To this purpose we have modified the non-hydrostatic mesoscale Meso-NH model so as to introduce source terms for pollen emission, conservation equations for pollen concentration and moisture as well as a deposition velocity. Several simulations are performed over the Aquitaine region in South-West France, on several days during the maize pollination period. MesoNH is run in a two-way nested configuration including three nested computational domains down to a 2-km horizontal resolution. All the maize fields of the region have been previously identified from remotely sensed data.
Considering several days during which airborne measurements were performed at several times, observed and simulated concentration profiles are found to agree well throughout the atmospheric boundary layer. The simulations allow the pollen plume to be characterized through each day and maps of pollen deposition to be produced. The deposition rates at remote distances from the maize fields are in the same range as those measured in situ. Test simulations are also performed using specific landuse patterns. For example, on a typical convective day a single 12-km square maize source plot is shown to generate a plume that extends over about 100 km in the mean wind direction, and the accumulated deposition downwind from the source exhibits a long tail spanning over five orders of magnitude.