Quantitative trends in annual totals of five common airborne pollen types (Betula, Quercus, Poaceae, Urtica, and Artemisia), at five pollen-monitoring stations in western Europe

The existence of long-term (20-33 years) trends in the annual totals of daily airborne pollen concentrations of five common and/or allergenic wind pollinating taxa was evaluated at five pollen-monitoring stations in western Europe: Delmenhorst (D), Helmond (NL), Brussels (B), Leiden (NL), and Derby (UK). At all stations, identical or comparable volumetric traps were used to sample pollen from the air. For grass pollen no increasing or decreasing trends were found at any station. Trends for birch pollen and oak pollen are increasing, but not significant at the stations with the higher annual totals (Delmenhorst and Helmond), probably due to strong year-to-year fluctuations. At all five stations significant increasing trends for stinging nettle pollen were observed. Trends for mugwort pollen are significant at all stations, but in different directions. Longer periods of observations are needed to arrive to more definitive conclusions about trends in airborne pollen concentrations.