Dust Generation From Aggregate Comminution During Transport in a Laboratory Wind Tunnel

Particle aggregates blown along the surface of playas have been linked to the disruption of interparticle bonds, comminution, and dust production. This mechanism was investigated in a set of wind tunnel experiments with the purpose of examining the rate of comminution during transport, role of bed roughness, influence of humidity, system dynamics, and proportionate amount of dust production. The playa sediment selected for testing was obtained from Owens Lake in California, USA. Particle aggregates with diameters between 500 and 710 μm (0.5 ϕ-1.0 ϕ) were isolated by sieving. Small 20 g subsamples were then introduced into the wind tunnel via a drop tube, with some particles captured on a downwind array of sticky glass plates. Aggregate diameter was found to decrease linearly by 30-56 μm per meter of transport (<i>r</i> ² = 0.43) over a total distance of 8.3 m. Enhanced geometric roughness of the bed surface increased this rate, but not dust production and suspension. As compared to an equivalent mass of disaggregated parent material representing the dust emission potential, comminution produced only 0.5%-4% as much suspended PM₁₀. Weak longitudinal flow instabilities involving downwelling and upwelling were found to influence the vertically integrated mass transport rate. This affirms the high sensitivity of dust transport to the structure of the wind field and the need for a paradigm shift in wind tunnel simulations of dust emission to extend measurement of the factors governing dispersion beyond one dimension, and specifically, friction velocity.