Comparative efficiency of airborne pollen concentration evaluation in two pollen sampler designs related to impaction and changes in internal wind speed

Pollen sampling has been performed using various sampling methods around the world. However, the sampling efficiencies of these methods remain unclear. In this study, we compared the sampling efficiency of a Sigma-2 two-layered aerosol sampling inlet and a Hirst-style wind vane inlet to reveal the relationship between sampling efficiency and samplers’ physical characteristics. The initial results show a higher sampling efficiency for the former. To further explore this finding, we developed a theory based on 1) continuity equations for pollen grain concentrations and 2) impaction theory. Applying our developed theory to the experimental results revealed that impaction is a significant contributor to the relatively higher sampling efficiency of the two-layered sampling inlet, due to the larger cross-sectional area of the two-layered inlet and slower sampled pollen grain speed within the sampler. Additionally, applying a correction based on the theoretical impaction effects improved the experimental results. Our experiment demonstrated the possibility of a pollen sampler showing discrepancies in airborne pollen concentrations and explained the mechanism of this inaccuracy. The application of these results to pollen sampling will aid understanding of actual airborne pollen concentration.