Upon completing the experiments, the collected pollen
grains on each rod were counted manually using an optical
microscope (Leica, model DML B) in the laboratory, in order to
avoid contamination. A comparison between the pollen
counts, Np, of the two simultaneously sampled collector rods
1 and 2 is shown in Fig. 3 for all sampling periods. A least
square linear fit is displayed with a slope of 0.98 and R2 = 0.94.
Differences in pollen counts between the two rods in terms of
themaximumdaily pollen count for each day ranged from 10%
to 30%. In the following discussion, the average count of the
two collector rods for each sampling period is used in the data
analysis. Pollen concentration is defined as the number of
collected pollen grains divided by the corresponding air
volume sampled by the rotating collector rod, c = Np/Vr. The
sampled air volume of one rod is given by Vr = 2prAfts where
r = 4.3 cm, is the radius about which the collector rod rotates,A