Abstract
Abstract. Wind tunnel experiments of dust emissions from different soil surfaces are carried out to better understand dust emission mechanisms. The effects of surface renewal on aerodynamic entrainment and saltation bombardment are analyzed in detail. It is found that flow conditions, surface particle motions (saltation and creep), soil dust content and ground obstacles all strongly affect dust emission, causing its rate to vary over orders of magnitude. Aerodynamic entrainment is highly effective, if dust supply is unlimited, as in the first 2–3 min of our wind tunnel runs. While aerodynamic entrainment is suppressed by dust supply limits, surface renewal through the motion of surface particles appears to be an effective pathway to remove the supply limit. Surface renewal is also found to be important to the efficiency of saltation bombardment. We demonstrate that surface renewal is a significant mechanism affecting dust emission and recommend that this mechanism be included in future dust models.
Highlights
Three dust emission mechanisms have been identified, including (1) aerodynamic entrainment, (2) saltation bombardment and (3) aggregates disintegration (Shao, 2008; Kok et al, 2012; Újvári et al, 2016)
Dust emission is usually “supply limited” (Shao, 2008; Macpherson et al, 2008; Újvári et al, 2016); i.e., the emission is limited by the availability of free particles on the soil surface, rather than by the shear stress that wind exerts
The fraction of particles in the size range of 10– 200 μm increases due to grinding, while for the natural soil and sieved soil the increased fractions are relevant to the size ranges of 1–10 and 30–60 μm
Summary
Three dust emission mechanisms have been identified, including (1) aerodynamic entrainment, (2) saltation bombardment and (3) aggregates disintegration (Shao, 2008; Kok et al, 2012; Újvári et al, 2016). In most existing dust emission schemes, aerodynamic entrainment is assumed to be small and negligible It is questionable, to what extent and under what conditions this assumption is justified because there are hardly any data that enable a rigorous comparison of aerodynamic entrainment from natural soil surfaces with the other dust emission mechanisms. It has been suggested that the dust flux arising from aerodynamic entrainment is insignificant because aerodynamic lift force for small particles is in general small compared to interparticle adhesion. Based on their wind tunnel experiments, Loosmore and Hunt (2000; LS2000 hereafter) suggested that
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