In the Environmental Multi-Phase Flow Laboratory headed by Dr. René van Hout, we study the entrainment, dispersal and capture of aerosols such as pollen. Efficient pollen entrainment and dispersal into the atmosphere is highly influenced by turbulence. Pollen grains released into the atmosphere initially encounter flow structures induced by the plant’s morphology. Questions that we ask are (i) does the peculiar morphology of pollen grains (Fig. 1) help its dispersal over large distances.
Ragweed pollen (diameter ~ 20μm)
(ii) how does the plant morphology affect dispersal and capture of pollen grains. Plant species that are being studied are ragweed (Ambrosia) and pine (Pinus). Both are wind pollinated plants (Fig. 2), the former causing strong allergenic effects (hay fever).
Pine pollen release
In this research two aspects of pollen dispersal mechanisms are studied; first the flow field pattern created by the plant morphology itself and its effect on pollen entrainment; second the effect of homogenous isotropic turbulence on the settling velocity of pollen grains.
The settling behavior of particles was measured in near homogeneous, isotropic turbulence generated in a 40 cm3 transparent chamber (Fig. 3). The flow inside the chamber was generated by 8 woofers mounted on each corner, each of them driven independently at a randomly changing frequency. The generated turbulent flow field was validated using stereoscopic Particle Image Velocimetry (PIV).
Three different pollen types, ragweed (~20μm), pine (50-60 μm) and corn (~80 μm) as well as polystyrene spheres (~80 μm) were tested. The settling trajectories were measured using high-speed, inline digital holographic cinematography. Results indicated increased settling in turbulent conditions.
- Sabban, L., van Hout, R., 2011. Measurements of pollen grain dispersal in still air and stationary, near homogeneous, isotropic turbulence. J. Aeros. Sci. 42, 867-882.
- Sabban, L., Jacobson, N., van Hout, R., 2012. Measurement of pollen clump release and breakup in the vicinity of ragweed (A. confertiflora) staminate flowers. In press to Ecosphere.