# Dust Emission Thresholds in Loess Soil Under Different Saltation Fluxes
## 3 Results
### Saltation Mass  
The saltation mass measured during the experiment is presented in Figure 4. In most cases of the experiment (total of 120 runs), a vast amount of the material was collected only in the lower traps close to the tunnel bed (<0.05 m). The saltation threshold at all sand samples is at \(\mathrm{u_{s}}=0.31\) m s\({}^{-1}\) as no distinct saltation mass was recorded in the lower shear velocities (0.11-0.24 m s\({}^{-1}\)). The saltation mass in the \"sand dune\" sample resulted in a range of 0.63 g (at the saltation threshold) to a maximum value of 8.14 g at shear velocity of 0.52 m s\({}^{-1}\) during the a 30-s run of the experimental procedure. In the  
Figure 3: Particulate matter (PM) concentrations measured in the wind tunnel as a result of dust emission from the reference samples under various shear velocities. The reference soils are presented by the weight ratio of clay and silt and sand 10%, 25%, and 50%. No dust concentration was recorded for the sand (dune) sample. The average concentration is presented by the solid line inside the minimum-maximum box, and standard deviations are in bar lines. Note that the black dots represent extreme values. \"sand 90%\" sample, the saltation mass run from 0.48 g at 0.31 m s\({}^{-1}\) to a maximum mass of 6.07 g at shear velocity of 0.52 m s\({}^{-1}\). These values are significantly lower than the \"sand dune\" sample at the same shear velocities. Unlike the 100% sand sample, the dust fraction received in the saltation mass was 4-36% (Table 1). The saltation mass of the \"sand 75%\" sample was much lower than the \"sand 90%\" sample, and ranged from 0.17 to 4.79 g. From wind shear velocity of 0.31 to 0.43 m s\({}^{-1}\), the mass increased only 10%, which is at the same level (7%) as in the sample of \"sand 50%\". The maximum value of the dust fraction in the \"sand 75%\" sample was measured at a wind velocity of 0.39 m s\({}^{-1}\). The maximum amount of the dust fraction in the saltation (26%) was measured from wind velocity of 0.39 to 0.52 m s\({}^{-1}\) (Table 1). The calculated saltation flux refers to the mass of all the particles; sand, silt, and clay, that pass a specific distance over the surface (Section 2.2, Equation (2)). With all soil samples, the saltation flux was started at shear velocity 0.31 m s\({}^{-1}\) as shown in the record of the saltation mass (Figure 4). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Shear Velocity (m s\({}^{-1}\))** & **Sand (Dune)** & **Sand (90\%)** & **Sand (75\%)** & **Sand (50\%)** \\  & & **Dust (10\%)** & **Dust (25\%)** & **Dust (50\%)** \\ \hline
0.11 & N/A & N/A & N/A & N/A \\ \hline
0.13 & N/A & N/A & N/A & N/A \\ \hline
0.19 & N/A & N/A & N/A & N/A \\ \hline
0.24 & N/A & N/A & N/A & N/A \\ \hline
0.31 & 0 & 0.04 & 0.12 & 0.18 \\ \hline
0.36 & 0 & 0.36 & 0.19 & 0.22 \\ \hline
0.37 & 0 & 0.08 & 0.19 & 0.17 \\ \hline
0.39 & 0 & 0.11 & 0.34 & 0.26 \\ \hline
0.43 & 0.01 & 0.11 & 0.15 & 0.25 \\ \hline
0.52 & 0 & 0.11 & 0.18 & 0.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The dust fraction received in the saltation mass calculated as the class weight of the dust particles (<63 μm) in the total weight of the saltation: [1 – (dust (g)/sand (g) + dust (g)]. Note that no saltation was recorded in shear velocity below 0.31 m s\({}^{-1}\). Figure 4: Saltation mass from the wind tunnel measurements of the reference samples under various shear velocities. Note that no distinct saltation mass was recorded in shear velocity below 0.31 m s\({}^{-1}\). The calculated PM10 flux refers to transported particles from the surface (Section 2.2, Equation (3)). The results show a linear positive correlation between the saltation flux and the PM10 flux (Figure 5) in all soil samples. As the amount of dust in the sample decreases, both the saltation flux and the PM10 emission decrease. The highest correlation was recorded in the \"sand 90%\" (R\({}^{2}\) = 0.99), while the (relatively) lowest correlation was recorded in the sample of \"sand 50%\" (R\({}^{2}\) = 0.91).