Modelling Pollen Distribution by Wind through a Forest Canopy(<Special Issue>Environmental Flows)

Pollen released from trees within a forest is transported by the wind through the canopy. Some is trapped by the foliage as it is advected and dispersed while falling under gravity. Taking into account these three mechanical processes, the quantitative model presented here is based on principles of conservation of mass. It is assumed that the pollen particles, being small, quickly reach their terminal velocity with respect to the mean air flow, and are mechanically dispersed by the turbulence generated by the air flow through the foliage. The rate of removal of the pollen from the flow, the so-called "trapping rate", is assumed proportional to the volumetric concentration of the pollen mass in the air. The aim is to obtain analytic solutions to the resulting advection-dispersion-trapping (convection-diffusion-decay) equations. Some examples are presented to illustrate the effects of various parameters.