Field Observations and Wind Tunnel Experiments

Dust aerosols profoundly influence climate systems, ecological stability, air quality and public health, underscoring the scientific imperative to understand their emission mechanisms. Traditionally, it isgenerally recognized that dust cannot be directly entrained but depends on saltation bombardment. However, dust that has been directly entrained has beenobserved in different areas. To determinethe mechanism of dust emission, a series of field observations and wind tunnel experimentswere carried out. The results revealed that direct aerodynamic dust entrainmentoccurred and lastedin the dust emission processes in the observed plots where saltation rarely occurred, whereasin most of the observed plots,the threshold friction velocity(TFVa) for dust entrainment was generally lower than that for saltation particles. Even in the plots where the TFVa for dust entrainment was greaterthan that for saltation particles, direct dust entrainmentstill occurred,and the processes wereenhanced by saltationdisturbance. The results of the wind tunnel experiments further revealedthat the contributions of directly entrained dust accounted forthe vast majority of the total emitted dust, and the increase indust emission rates caused by external saltation disturbance was attributed mainly to the replenishmentof available fine soil particles by surface renewal and the breaking of soil aggregates rather than the kinetic energies of saltation particles breakingthe cohesive forces between finer particles. Therefore, the main mechanism of direct aerodynamic entrainmentshould be highlighted in the parameterization of dust emission, and anysaltation disturbance that causessurface renewal and soil aggregatebreaking should also be reconsidered. Our study providesnew evidence that direct aerodynamic entrainmentis the main mechanism of dust emission, and we also proposea framework of entrainment–saltation–renewal–entrainment for dust emission model building.