Dry Deposition of Nonspherical Particles on Natural and Surrogate Surfaces

Deposition velocities of prolate and oblate spheroids and dust particles to a smooth surrogate surface, a surface with microroughness and to a sea surface are obtained by a two-layer model, consisting of constant flux layer and deposition layer submodels. The deposition layer model includes the mechanism of interception. Interception depends on particle shape and aspect ratio. Deposition velocities of nonspherical particles and of the equivalent spheres and the ratio between these velocities, the “shape effect ratio,” were calculated for a range of aerodynamical diameters (0.001 to 100 /μm), particle shapes (particle aspect ratio from 3 to 10), particle density (0.1-10 g/cc), wind speed (5-20 μs), and height of microroughness elements (0-22 μm). Interception is most significant for particles with large particle aspect ratios depositing to a smooth surface, under conditions of strong turbulence. Spray droplets from white caps on a sea surface or microroughness on a land surface reduce the effect of interception. The “shape effect ratio” obtains values larger than 1.10 in the range of aerodynamical diameters from 0.080 to 42 μm. For spheroids possessing an aspect ratio equal to 3 (10), the “shape effect ratio” is smaller or equal to 2.2 (9.8). For dust particles possessing an aspect ratio of 3, the “shape effect ratio” is smaller than or equal to 3.6.