A method for measuring the settling velocity distribution of large biotic particles

Abstract

A simple method for measuring the settling velocity (V s) distribution of pollen and spores 30–100 μm in diameter is detailed and evaluated. The method is called the ‘settling tower' and consists in taking sequential pictures of particles falling under gravity in calm air. The scene is illuminated by a cold light source, while a camera takes 15 pictures per second. Between 20,000 and 100,000 images are analysed to obtain the distribution of V s for a given set of particles. The method was validated using two standard particles with mean diameters of 68 and 108 μm, respectively, as well as Lycopodium spores, with a mean diameter of 35 μm. For each set of particles, the theoretical V s distribution was estimated from the particle diameter distribution and the volumetric mass using a non-Stokian law, as the Reynolds numbers of the particles were large. The mean V s was measured with the ‘settling tower' with less than 12% error, while the standard deviation of the V s distribution was estimated with less than 51% error. The maximum error on the mean V s was 12% for the Lycopodium spores and less than 2% for the two larger particles. The mean V s of Lycopodium spores was 4.2 cm s−1, and its standard deviation was 0.7 cm s−1. The reason for the small overestimation of V s for Lycopodium spores by the ‘settling tower' method is discussed. Preliminary measurements shows that, the ‘settling tower' could be of great practical interest for measuring the distribution of V s of maize pollen as well as other types of pollen or spores

Modelling and inference of maize pollen emission rate with a Lagrangian dispersal model using Monte Carlo method

“…3); therefore, lower meanW S leads to less deposition. The settling velocity, as well as many of the biophysical characteristics of pollen, is mainly determined by pollen water content (Di-Giovanni et al, 1995;Aylor, 2003;Loubet et al, 2007;Marceau et al, 2012). Indeed, pollen water content affects pollen mass, diameter and density which determine pollen settling velocity as formulated by Di-Giovanni et al (1995).…”

“…These variables describe pollen and canopy characteristics as well as pollen interactions with its environment. There are four continuous variables: two variables of the Gaussian distribution of pollen settling velocity (mean, meanW s , ranged from 0.15 m/s, which corresponds to dry pollen to 0.35 m/s, which corresponds to fresh pollen and standard deviation, StdW S , ranged from 0.01 to 0.06 m/s) (Aylor, 2002; Loubet et al ., 2007; Marceau et al ., 2012); horizontal and vertical projections of the leaf area density LAD x and LAD z , respectively ( LAD x ranged from 0 to 0.55 m 2 /m 3 and LAD z ranged from 0 to 0.65 m 2 /m 3 , Drouet (2003)). More specifically, LAD x influences deposition due to the gravitational settling, and for example, LAD x = 0 m 2 /m 3 means that no deposition occurs within the canopy due to the gravitational settling.…”

Does pollen aerodynamics correlate with pollination vector? Pollen settling velocity as a test for wind versus insect pollination among cycads (Gymnospermae: Cycadaceae: Zamiaceae)

“…Hence, although the values in Figure 5 represent direct measurements of settling velocity as measured in the POLLEN AERODYNAMICS AND POLLINATION VECTOR 79 laboratory, we have presented these values as a 'settling velocity index', rather than velocities in cm s -1 , so as to minimize any confusion between our relative comparison of settling velocities and the more accurate values for the settling velocity of hydrated pollen grains, as reported by previous authors (e.g. Di-Giovanni et al, 1995;Aylor, 2002;Loubet et al, 2007;Sosnoskie et al, 2009).…”

“…Di-Giovanni et al, 1995;Aylor, 2002;Loubet et al, 2007;Sosnoskie et al, 2009). However, as all our samples experienced the same storage and laboratory environment, we assume our values represent a valid relative comparison of pollen behaviour under a consistent set of laboratory conditions.…”

“…the rate of falling in still air (e.g. Di-Giovanni et al, 1995;Aylor, 2002;Loubet et al, 2007;Sosnoskie et al, 2009). Wind-borne pollen is also expected to disperse as dry, non-adhesive isolated grains, and to have a smooth rather than sculpted exine (Faegri & Van der Pijl, 1979;Whitehead, 1983;Dafni, 1992;Proctor et al, 1996;Ackerman, 2000;Culley et al, 2002;Friedman & Barrett, 2009).…”