Spatial and temporal variations in the distribution of birch trees and airborne Betula pollen in Ireland

International audienceIn an Irish context, and indeed in Northern Europe, one of the most important allergenic pollen types is birch (Betula spp.). Thus, forecasts of such atmospheric pollen are important tools for helping patients suffering from allergenic rhinitis and/or atopic asthma to avoid high ambient concentrations and manage their symptoms. This work aims to improve knowledge about the spatial and temporal variations in the distribution of birch trees and airborne Betula pollen in Ireland, which is an important step towards producing such forecasts. The footprint of airborne Betula pollen recorded in Ireland was determined by using HYSPLIT backward Lagrangian dispersion modelling methodology and mapped using Geographic Information System (GIS) software during the Main Pollen Season (MPS) and for days with airborne concentrations > 80 pollen grains/m3 in Dublin and Carlow (72 km apart) for 2018 and 2019. An inventory of birch trees within broadleaved forests was constructed using statistical data from different vegetation inventories for Ireland with a resolution of 100 m x 100 m. Historical datasets of airborne Betula pollen recorded in Dublin during 1978-1980 and 2010-2011 were also related to changes in land cover and climatic conditions over the same period. Dispersion modelling showed that air masses arriving in Ireland on days with Betula pollen concentrations >80 pollen grains/m3 resided for a longer time over Great Britain. The birch tree inventory for Ireland will enhance the performance of forecast models. Airborne Betula pollen concentrations in Ireland have increased over the last 40 years, which is related to concomitant increases in the fraction of birch trees in forest areas as well as the ornamental use of birch trees in urban areas and their reaching maturity. Climate change did not seem to influence birch pollination