Airborne Pollen Concentration in Leiden, The Netherlands, 1977–1981

The results of five years' (1977–1981) continuous monitoring of airborne pollen concentrations with a volumetric trap in Leiden indicate that almost 25% of the total pollen count derives from wild grasses. June is by far the most important month for airborne grass-pollen, generally taking more than 50% of the total seasonal count, July accounting for on average 30%. In spite of the consistency of this general seasonal pattern, the fluctuations from day to day and from hour to hour can be very large and highly irregular, and there is no consistent diurnal pattern in the grass-pollen count. Long-term prediction of the start of the grass-pollen season and of the intensity and course of the grass-pollen concentration is not (yet) possible. However, a short-term and relative prognosis for hay fever, intended for at least 200 000 sufferers in The Netherlands, has reached an accuracy of more than 80%.