Development and implementation of the PEMM model for pollen emission and dispersion in the central Iberian Peninsula

Airborne pollen concentrations have increased steadily in recent decades together with shifts in their phenological cycles, leading to higher population exposure and growing public health concerns. Reliable tools for estimating pollen emissions and their atmospheric dispersion are therefore required to adequately characterise these changes. This study presents the development and evaluation of the Pollen Emission Mesoscale Model (PEMM), based on the STaMPS and PECM approaches, applied to the main allergenic pollen taxa in central Iberian Peninsula (Olea, Platanus, Cupressaceae, Poaceae and Quercus), and its coupling with the WRF-CMAQ modelling system. The model coupling was successfully implemented, and simulated emissions showed strong spatial consistency with vegetation cover fraction maps. The estimation of the main pollen season revealed systematic delays in onset dates at higher altitudes, indicating a clear altitudinal dependence of pollen release. Model performance was assessed through comparison with observational pollen data from stations belonging to the Spanish Aerobiology Network for the 2020-2021 study period, focusing on the representation of the main pollen season and simulated concentration levels. Olea, Platanus and Quercus exhibited the best agreement in reproducing the timing of the main pollen season, whereas daily pollen concentration simulations performed better for Poaceae and Platanus, with correlation coefficients of 0.72 and 0.62, respectively. Overall, PEMM provides a consistent framework for regional-scale pollen emission modelling within a chemistry-transport system. Remaining discrepancies highlight the sensitivity of pollen season timing to meteorological uncertainties and the need for improved representation of local-scale processes in future developments.