Intercomparison of Birch Pollen Source Maps Using Enviro-HIRLAM

Background
Information about distribution of pollen sources, i.e. their presence and abundance in a region of study, plays a crucial role in aerobiological modelling. The recent studies therefore are devoted to developments of inventories allowing to quantify pollen sources. Pollen source inventories are commonly used for exposure studies, atmospheric transport modelling as well as pollen forecasting. The purpose of this study is to evaluate three pollen source maps using an atmospheric transport model.

Methods
Here we evaluate three maps for the birch taxon: (1) a map derived by combining of land use data and forest inventory; (2) a map obtained by using land use data and pollen observations; (3) a statistical map resulted from analysis of forest inventory and forest plot data.
The maps were introduced to the Enviro-HIRLAM (Environment - High Resolution Limited Area Model) as input data to simulate birch pollen concentrations over Europe for the birch pollen season 2006. Six model runs were performed using each of the selected maps in turn with and without calibration with observed pollen data from 2006. The model results were compared with the pollen observation data at 12 measurement sites located in Finland, Denmark and Russia.

Results
It was shown that calibration of the maps using pollen observations significantly improved the model performance for all three maps. The findings also indicate the large sensitivity of the model results to the source maps and agree well with other studies on birch showing that pollen or hybrid based source maps provide the best model performance.

Conclusion
This study highlights the importance of including pollen data in the production of source maps for pollen dispersion modelling and for exposure studies.