Table 1.

Pollen genera considered in this study and their physical properties.

Genus	Pollen Species Included	Density ρP (kg·m−3)	Diameter DP (μm)	Settling (Velocity Vdp (m·s−1)	CalculatedaVdp (m·s−1)	Canopy Height Hs (m)	Threshold Friction Velocitybu*te (m·s−1)
Betula (birch trees)	Betula pedula	800c	24c	0.013d	0.014	6c	0.37
Bromus (grass)	B. diandrus and B. mollis	900d	24c	N.A.	0.0158	0.1	0.37
Juglans (walnut trees)	J. regia and J. californica	940d	35	0.029–0.044d	0.035	9.2	0.31
Morus (mulberry trees)	M. alba, M. rubra, and unspciated Morus trees	1140e	19	N.A.	0.0126	7.6	0.41
Olea (olive trees)	O. europaea	1000	25	N.A.	0.019	7.2	0.36
Platanus (plane trees)	P. acerifolia	920d	19	0.0104d.	0.0096	6.8	0.42
Quercus (oak trees)	Early-blooming oak species: Q. agrifolia, Q. douglasii, Q. dumosa, Q. engelmannii,Q. laurifolia, Q. lobata, Q. turblinella, Q. velutina, Q. virginiana, Q. wislizeni Late-blooming oak species: Q. alba, Q. chrysolepis, Q. coccinea, Q. gambelii, Q. garryana,Q.grisea, Q. Ilex, Q. kelloggii, Q. macrocarpa, Q. palustris, Q. rubra, and misc. Quercus species	1058f	31	0.029d	0.0309	9.6f	0.33

^aCalculated using Equation (6) and the listed density and diameter.

^bAssume air density ρ of 1.161 kg/m³, 10-m wind speed U₁₀ of 3 m s⁻¹ and empirical threshold wind speed U_10e of 2.9 m s⁻¹ in Eq. (5).

^cEfstathiou et al. (2010).

^dJackson & Lyford (1999).

^eMartonen and O'Rourke (1993);

^fSchuler and Schlunzen (2006).