Modelling of airborne birch pollen over Central Europe - model evaluation and sensitivity analysis

In this study, we applied the EMEP MSC-W chemical transport model, extended to include birch pollen emissions and dispersion, over Central Europe. Simulations were run for five consecutive birch pollen seasons (2015-2019), covering various concentration regimes (high, low or moderate seasons). Model predictions were compared to observational data from 12 stations located across Poland. The model consistently predicted earlier start and end dates for the pollen season compared to observations, and generally underestimated pollen concentrations and seasonal pollen integrals (SPIn), especially during high-concentration seasons. A sensitivity analysis was conducted for two selected years (2018 and 2019), adjusting key parameters such as total pollen amount, season length in degree-days, and the heat-sum threshold for season onset. Results showed that modifying the total pollen amount proportionally increased concentrations, while extending the season length tended to decrease early season concentrations, and increase late season concentrations, simultaneously delaying the end of the season. Adjusting the heat-sum threshold for the season start delayed the season, impacting its overall characteristics. Modifying these parameters improved model accuracy, particularly in predicting season onset, which was critical for accurately simulating the temporal dynamics of the pollen season.