Potential contribution of distant sources to airborne Betula pollen levels in NE Iberian Peninsula

What is it about?

Betula (birch) pollen is one of the most important causes of respiratory allergy in Northern and Central Europe. While birch trees are abundant in Central, Northern, and Eastern Europe, they are scarce in the Mediterranean territories, especially in the Iberian Peninsula (IP), where they grow only in the northern regions and as ornamental trees in urban areas. However, the airborne birch pollen patterns in Catalonia (Northeastern IP) show abrupt high concentrations in areas with usually low local influence. The intensity of the derived health problems can be increased by outbreaks due to long-range pollen transport. The present work evaluates the different potential contributions to Catalonia from the main source regions.

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Photo by Kalineri on Unsplash

Photo by Kalineri on Unsplash

Why is it important?

This is the first study to quantify the contributions of the different distant source regions to the Betula pollen registered in Catalonia. Nearly 40% of the monitored pollen corresponded to long-range transport, which occurred every year in several episodes. Based on the residence time of the air-masses, we estimate that 37% of this Betula pollen came from the Pyrenees and Northern Iberian Peninsula, while 63% came from the French Central Massif (44%) and Black Forest / Vosges Massif (19%). Most of the peak days corresponded to situations of northerly advection favoured by the presence of a high pressure centre over Northwestern Europe. In a certain way, the Pyrenees act as a barrier, which the air masses bypass as they are channelled through two entry routes to Catalonia: the Alberes passage at the eastern end of the Pyrenees, and the Ebro Valley, with the characteristic northwest wind of this region called the Cierzo.