People
| Post Doctoral Fellow | René van Hout |
| Project Supervisors | Prof. Joseph Katz |
Outline
The measurement of the pollen density is based on the measurement of the settling velocities of pollens in two different fluids. The settling velocities of individual corn pollens were measured using an In-line Digital Holography system. The system consisted of a HeNe laser (632.8 nm), optics, a settling chamber and a Kodak ES4 CCD camera (2kx2k) with a maximum frame rate of 15 fps. A neutral density filter was used to attenuate the laser beam intensity after which the beam was expanded and spatially filtered. The spatially filtered beam was then collimated and sent through the volume of interest (VOI) in the settling chamber. The interference between the reference and the object beam created a diffraction pattern that was recorded by the CCD camera without a lens. The settling chamber consisted of a square Acrylic chamber with a height of 45 cm and an inside channel width of 5 cm.
Facility
The recorded holograms were reconstructed in two different ways. First in order to speed up the data analysis time, a recorded hologram was reconstructed digitally by collapsing all the different planes into one one image (collapsed reconstruction). Second, in order to know the shape of the particle, in-focus reconstruction was performed. In this case multiple planes are reconstructed and the in-focus plane is found.
Background
Results – Pollen Size Distributions
The mean size of pollen grains, based on the projected area, were measured using an Optical Microscope (Leica). The results are shown below for different pollen species.
In the case of corn pollen, size measurements were carried out under the Optical Microscope, Scanning Electron Microscope and directly from the reconstructed in-focus holograms. Measurements were made when the pollen was dry as well in fully wetted state. Some examples of pollen shapes in different “settings” are shown below.
The pdf’s of corn pollen sizes are very similar in shape under different conditions. However, the mean value is different.
Particle Settling Velocities and Pollen Density
The settling velocities of corn pollen grains were measured in two different fluids. The pdf’s of the settling velocities are shown below. The corn pollen density can then be calculated using the fluid properties and the measured settling velocities.
Corn pollen submerged in water changes its shape and becomes almost spherical. However after some time the pollen protoplasm starts to leak out of the pollen which reduces its effective density (see image below).
Pollen Images
Click Here – Pollen Images
Publications
van Hout, R., Katz, J. (2004). A method for measuring the density of irregularly shaped biological aerosols such as pollen. Journal of Aerosol Science. 35(11). 1369-1384. doi:10.1016/j.jaerosci.2004.05.008
van Hout, R., Katz, J., 2003. A method for measuring the density of irregularly shaped particles such as pollen. AGU 2003 Fall meeting, 8-12 December, Moscone Center West, San Francisco. PDF