Particle deposition on and reentrainment from coniferous trees

Conclusions

In the deposition of dust on single leaves of coniferous trees, electrostatic effects were of no significance and did not improve adhesion. The latter finding agrees with that ofPenney (1961, 1962), who refers to the electric field to explain the superior adhesion of electrically precipitated particles. Inertial deposition was the controlling parameter, in agreement with the filtration model for single cylinders. The efficiency of a cedar leaf at 1.30 m/sec for a 2.4-micron-surface-diameter dust was 6 and 0.5% for the edge and broadside positions respectively. Collection on the back of the wires or leaves due to wake turbulence did not take place. The scale of the turbulence was too small (Davies, 1960). Bounce-off upon deposition was not observed. Reentrainment did not take place up to the 2 m/sec velocity in the 1.8 cm-diameter wind tunnel, where boundary layer conditions were much steadier as in the large tunnel. In arrays of leaves a shadowing effect was produced by the forward leaves; i. e., the dust-free streamlines produced by one leaf gave a dust-free area on the leaf behind it. This shadowing was also found with small trees in the large tunnel; i. e., the leaves produced a streamlined flow regime in the confines of the tree.