The fluctuations of the allergenic pollen content of the air in Brussels (1982 to 1997)

The pollen content of the air was studied from1982 to 1997 in Brussels. Fluctuations weremainly observed in the tree pollen content whilethe amount of pollen originating from herbaceousplants remained more stable during theinvestigation period.The number of allergenic tree pollen grains didnot rise steadily during this period. We noted,however, the existence of years with high pollenproduction following the physiological biorhythmof the trees. Years with high annual sums for agiven tree pollen type did not coincide withyears with high annual sums for another treepollen type. Variations in annual sums of allergenicherbaceous pollen types were less important thanthose of tree pollen types. No rise, nor cyclicpatterns were observed. The most important allergenic pollen types(Betulaceae, Fagaceae, Gramineae and Artemisia) have been presented in histograms.