The hour at which the first pollen
grains were entrained into the atmosphere varied from dayto-
day, depending strongly on the relative humidity and
related vapor pressure deficit values as well as on the
prevailing wind speeds. Low relative humidity during the
night, i.e. the absence of dew, caused pollen emission
immediately at sunrise consistent with previous measurements
performed by Jarosz et al. (2005). On four consecutive
days, daily pollen concentration patterns were bi-modal
during the morning hours while on other days only a single
peak distribution was observed. Diurnal, bi-modal corn pollen
distributions were previously reported by Flottum et al. (1984)
without providing an explanation for them.