The diurnal cycle of pollen emission into the atmosphere
was measured for 10 consecutive days as described in Section
2. Fig. 5 presents the diurnal variation of pollen concentration,
c, at all four measurement heights. We show results only for
days with significant pollen concentrations, i.e. from 13 to 17
July and 19 July (Fig. 4). Note that sunrise occurred around 0555
EDT and sunset around 2030 EDT resulting in a difference of
about 75 min between solar time and EDT. On all of these days,
pollen was emitted after sunrise and peak values of airborne
pollen concentration occurred during the morning hours.
During afternoons, pollen concentrations decreased except for
14 July between 1400 EDT and 1600 EDT, just prior to a
thunderstorm. On 2 days (15 and 16 July, Fig. 5c and d) the start
of pollen emission coincided with sunrise while on the other
days pollen emission only started between 0900 and 1000 EDT.
In all cases, pollen concentrations became negligible 2 h
before sunset. Pollen concentrations decreased with increasing
measurement height. Concentrations were highest at
canopy height where the tassels were located and pollen was
emitted, and decreased at higher elevations. Peak pollen
The diurnal cycle of pollen emission into the atmosphere
was measured for 10 consecutive days as described in Section
2. Fig. 5 presents the diurnal variation of pollen concentration,
c, at all four measurement heights. We show results only for
days with significant pollen concentrations, i.e. from 13 to 17
July and 19 July (Fig. 4). Note that sunrise occurred around 0555
EDT and sunset around 2030 EDT resulting in a difference of
about 75 min between solar time and EDT. On all of these days,
pollen was emitted after sunrise and peak values of airborne
pollen concentration occurred during the morning hours.
During afternoons, pollen concentrations decreased except for
14 July between 1400 EDT and 1600 EDT, just prior to a
thunderstorm. On 2 days (15 and 16 July, Fig. 5c and d) the start
of pollen emission coincided with sunrise while on the other
days pollen emission only started between 0900 and 1000 EDT.
In all cases, pollen concentrations became negligible 2 h
before sunset. Pollen concentrations decreased with increasing
measurement height. Concentrations were highest at
canopy height where the tassels were located and pollen was
emitted, and decreased at higher elevations. Peak pollen
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