In a turbulent flow field, we can associate the force for
keeping pollen suspended into the atmosphere with wallnormal
turbulent velocity fluctuations. Simplistically, i.e. if
particle inertia is neglected, upward directed turbulent
fluctuating velocities in excess of the particle’s settling
velocity would lift the particle upwards provided their
strength exceeds aminimum threshold imposed by the pollen
settling velocity. Since the mean settling velocity of corn
pollen in turbulent flows was not measured, the quiescent air
value is used as a reference, wt
s ¼ 0:27ms1