is the rod’s effective area (1.52mm 22 mm), f is the rotation
rate of the Rotorod sampler and ts is the sampling time. Each
sampler’s rotation rate was carefully calibrated using a digital
strobe light. The sampled air volume was about 1 m3/h. The
measured pollen concentrations are normalized by the pollen
concentration measured at canopy height, c(z/h = 1) ch, used
as a surrogate for the pollen production (the source strength)
which was not measured directly.