# Dust Emission Thresholds in Loess Soil Under Different Saltation Fluxes
## 4 Discussion
Nonetheless, [PERSON] and [PERSON] [33] show that in a Pleistocene loess deposits (Nebraska, USA) the dust may emit without saltation with a lower threshold (u, = 0.26 to 0.30 m s\({}^{-1}\)) than the saltation threshold (u, = 0.33 to 0.44 m s\({}^{-1}\)). To further test the relationships between saltation and dust emission, the sandblasting efficiency was examined with comparison to other works (Figure 6). Basically, the sandblasting efficiency increases with the shear velocity as long as there is available dust particle in the soil for emission. The highest values of sandblasting in this study were obtained in the sample of \"sand 50%\", which contains enough amount of dust for emission. When comparing the sandblasting efficiency values with other works conducted in wind tunnel experiment, it revealed that the sandblasting efficiency increases as a function of the amount of dust in the sample and wind velocity. The highest values were recorded at the sample of \"15% sand\" (85% dust), 0.10 to 1.3 m\({}^{-1}\), under velocities of 0.39 and 0.52 m s\({}^{-1}\)respectively [16]. The sandblasting efficiency of the \"sand 90%\" sample of this study is not presented since no dust was recorded from the sample. However, [PERSON] et al. [15] calculated a sandblasting efficiency of \(1.73\times 10^{-7}\) m\({}^{-1}\) from active sand dune at 0.30 m s\({}^{-1}\). Wind tunnels enabled targeted experiments on dust emission processes, in which the empirical data can be used for parametrization of dust models and for validation of model results. Yet, there is little quantitative understanding of how the wide range of particle sizes in realistic dust-emitting soils affects the shear velocity threshold. The dust emission threshold parameterizations used in most models are descriptions of the threshold friction velocity of a dry, bare soil composed of particles of a single grain size. Consequently, dust emissions in models generally increase monotonically with a soil's clay content, and thus do not capture the potentially important mitigating impact of clay particles in raising the threshold friction velocity. [PERSON] and [PERSON] [10] parameterized the threshold as the wind velocity at which the aerodynamic torque on a surface particle exceeds that generated by gravity and the interparticle forces with surrounding sand particles. An improved dust emission scheme incorporates saltation bombardment and aggregates disintegration [34]. The statement of the scheme is that dust emission is proportional to streamwise saltation flux, but the proportionality depends on soil texture. A critical problem in dust research is to estimate size-resolved dust emission rates, which requires reliable dust emission estimates for specific size ranges [35]. Thus, wind tunnel experiments can be used to expand the dust formulation by accounting for the entire particle distribution of the soil (and not just the presence of clay), and accounting for the variability of sand (saltation) particle sizes. This study has some limitations that are discussed as follow. First, we applied four soil samples, which may not represent the entire range of soil texture. However, these samples are common in many soils that are associated with dust emission processes. Second, the use of a wind tunnel to examine the dust emission may not reflect the natural wind in the field where the velocity and direction are constantly changing. However, the controlled wind velocities by the tunnel makes it possible to examine the emission thresholds of various soil samples. Third, the saltation and dust fluxes calculated in this study by the wind tunnel experiment do not necessarily fit the \"real\" values measured in the field, but it does allow to a quantitative comparison of sandblasting efficiency.