Quantitative trends in annual totals of five common airborne pollen types (Betula, Quercus, Poaceae, Urtica and , Spieksma, F.Th.M., Cordon J.M., Detandt M., Millington W.M., Nikkels H., and Nolard N. , Aerobiol., 0/0/2003, Volume 19, Number 184, p.171 - 184, (2003)