Terminal settling velocity and physical properties of pollen grains in still air
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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.
KeywordsPollen 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.
- Gregory, P. H. (1973). The microbiology of the atmosphere (2nd ed.). New York: Wiley.Google Scholar
- Hinds, W. C. (1999). Aerosol technology: Properties, behavior, and measurement of airborne particles. New York: Wiley.Google Scholar
- Ichikura, M., & Iwanami, Y. (1981). Studies of fall-velocity of pollen grains. Japanese Journal of Palynology, 27, 5–13.Google Scholar
- Lewis, W. H., Vinay, P., & Zenger, V. E. (1983). Airborne and allergenic pollen of North America. Baltimore: Johns Hopkins University Press.Google Scholar
- Niklas, K. J. (1992). Plant biomechanics: An engineering approach to plant form and function. Chicago: University of Chicago Press.Google Scholar
- Watrud, L. S., Lee, E. H., Fairbrother, A., Burdick, C., Reichman, J. R., Bollman, M., et al. (2004). Evidence for landscape-level, pollen-mediated gene flow from genetically modified creeping bentgrass with CP4 EPSPS as a marker. Proceedings of the National Academy of Sciences of the United States of America, 101, 14533–14538.CrossRefGoogle Scholar