Comparison between pollen counts at ground and at roof level in Basel (Switzerland)

Measurements of pollen frequency were made using two identical pollen traps, one situated at ground level and one at the height of about 30 m. There was no special difference between the results for the two traps in 1995, apart from an excess of pollen in the ground level trap originatinig from trees growing near the trap. In 1996 there was also a greater amount of birch pollen, this time at the roof level. There was also a great difference in the time at which the pollen first appeared between the two years, especially in the early spring.