The relative reduction in duration fraction Dpeak/Dtrough at
z/h = 1.5 as a function of the threshold value juwj is depicted in
Fig. 15 for 16 and 17 July. Dtrough is the minimum duration
fraction during the sampling period of minimum pollen
concentration (i.e. 1000–1100 EDT, see Fig. 14b) while Dpeak
is the maximum duration fraction in the pollen sampling
period prior to that (0900–1000 EDT, ‘‘decrease’’) or just after it
(‘‘increase’’, 1100–1200 EDT, see Fig. 14b). Fig. 15 shows that at
the lowest threshold value, Dpeak/Dtrough 1.1 for 16 July and
1.3 for 17 July. As the threshold is increased, Dpeak/Dtrough
increases for both days, the fastest for 17 July as Dtrough is
strongly reduced and becomes near zero at the higher