The
scaling of c(z/h = 2)/ch with sw is shown in Fig. 13. Only data
points on 16, 17 and 19 July when ch exceeded 10 grainsm3 are
plotted. Although there is significant scatter, the data indicate
that the ratio c(z/h = 2)/ch increases as sw increases. Furthermore,
a least square linear fit to the data indicates that nopollen
is transported upwards at a threshold value of sw = 0.22ms1
which is of the same order as the pollen settling velocity in
quiescent air, wt
s ¼ 0:27ms1, Eq. (5).