Aerobiological study of airborne pollen in Tétouan (NW of Morocco): diversity, intensity and calendar

Pollen grains of the anemophilous plants are the most important source of allergens in the atmosphere, triggering allergic diseases such as rhinitis and asthma in atopic individuals. Pollen grains in the atmosphere of Tétouan (NW of Morocco) were recorded during a 10 years/period (2008–2017) using a 7 day recording volumetric pollen trap by Burkard. Daily mean pollen concentrations of 10-day periods were summed and averaged over the study period to construct the pollen calendar. The average annual pollen integral (APIn) recorded during this period was 37,955 p*day/m3, belonging to 52 higher plant taxa (30 trees and/or shrubs and 22 herbaceous species). The maximum APIn (62,848 p*day/m3) was recorded in 2009 and the minimum (18,423 p*day/m3) in 2017. During the study period, the main pollen was registered from February to June (89%), with the highest daily mean pollen concentrations recorded in March (26.38%) and February (21.13%). The timing, intensity and length of the pollen seasons varied according to the taxa. The pollen calendar of Tétouan atmosphere reflects a great pollen diversity (37 pollen types), Pollen omnipresence throughout the year, long pollination periods and typically Mediterranean taxa: Cupressaceae, Olea, Platanus and Quercus. Some trees and herbaceous plants perform their anthesis in winter: Cupressaceae, Fraxinus, Populus, Pinus, Mercurialis and Parietaria. Some of them extend their pollen season until spring at the same time as other types of pollen appear typical of spring. Morus and Pistacia have a short pollen season, while Cannabis sativa, Amaranthaceae, Olea, Parietaria, Plantago, Poaceae, Quercus, Rumex and U. membranacea are characterized by prolonged pollen season. The pollen spectrum of Tétouan is differentiated by Cannabis pollen, and a longer and more intense pollination period than that detected in other Mediterranean regions. Based on these results, pollen calendar of Tétouan provides interesting and useful information to aerobiologists as well as professionals working in fields such as allergy and public health.