, Volume 32, Issue 3, pp 385–394 | Cite as

Terminal settling velocity and physical properties of pollen grains in still air

  • Yuuki Hirose
  • Kazuo OsadaEmail author


Numerical simulation of wind pollination requires knowledge of pollen grain physical parameters such as size, shape factor, bulk density, and terminal settling velocity. The pollen grain parameters for Japanese cedar, Japanese cypress, short ragweed, Japanese black pine, and Japanese red pine were assessed for dry condition. Terminal settling velocities of dry pollen grains in still air were measured using image analysis of scattered light tracks in a dark settling tube. The measurement system was validated by comparing results to those obtained for standard microspheres of known size and density. Dry pollen grain shape factors indicate the resemblance of particles to spheres, except for pine pollen. Circularity factors of dry pine pollen grains were 0.90–0.86, suggesting more irregular shape than those of other pollen species. Aerodynamic diameters of dry pollen grains were calculated based on the terminal settling velocity. Aerodynamic diameters of Japanese cedar, Japanese cypress, and short ragweed closely resembled the projected area equivalent diameters, suggesting that aerodynamic behaviors of these pollen grains can be managed simply in numerical simulations. However, aerodynamic diameters of dry pine pollen grains were nearly 30 % smaller than projected area equivalent diameters. Sacci on dry pine pollen can reduce the terminal settling velocity through low density and shape effects attributed to their non-sphericity, engendering aerodynamic diameter smaller by more than 10 µm from area equivalent diameters.


Pollen grain Shape factors Settling velocity Aerodynamic diameter 



This research was supported financially by JSPS KAKENHI Grant Nos. 23310004, 25220101, and 15H02803, and by the Environment Research and Technology Development Fund (5B-1202) of the Ministry of the Environment, Japan. We thank Keyence Corporation for the use of the newest digital microscope: VHX-5000.


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Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  1. 1.Graduate School of Environmental StudiesNagoya UniversityNagoyaJapan
  2. 2.Panasonic CorporationOsakaJapan

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