## 2 Materials and Methods  
The experiments conducted on a typical loess soil of the northern Negev, Israel. The semi-arid region of the northern Negev is characterized by annual average rainfall of \(\sim\)200 mm. Most of the loess soils in northern Negev are a secondary material that reworked under pedogenic and geomorphological processes after investment of aeolian and/or pluvial materials [17]. Currently, the northern Negev loess is subjected to intense human activities and related soil erosion and dust emission, e.g., [6; 18]. The texture of the soil is silt-loam with a relatively high content of silt and clay particles. Particle size distribution was obtained by the ANALYSETTE 22 MicroTec Plus (Fritsch, Idar-Oberstein, Germany) laser diffraction, which measures particles in the size range of 0.08-2000 \(\upmu\)m [19; 20]. Replicas (100 mg) were dispersed in Na-hexamvetaphosphate solution (0.5%) by sonication (38 kHz). The data was calculated using the Fraunhofer diffraction model with a size resolution of 1 \(\upmu\)m using MasControl software (Figure 1a). Mineralogical analysis, which was obtained by the X-ray power diffraction (XRPD) method, shows typical loess composition with high content of quartz, clays (illite, kaolinite), as well as Ca-based components that are found in arid loess (Figure 1b). For the dust control experiment, the soil was placed in trays that fit the wind tunnel dimensions (0.5 \(\times\) 1.0 m, with height of 0.02 m). Three trays (replicas) were prepared for each soil treatment/product. Table 1 presents the products used for the laboratory experiment and their application on the soil. The composition of the solution of each substance and the concentration of the solution to be applied by spraying on the soil surface were provided by the suppliers of the products and are typical in dust control. The soil samples were left outside for a drying process of several days before the experiment to avoid the impact of the amount of the solution (water content) on wind erosion and dust emission. The geopolymer for the dust control experiment was composed of metakaolin (MK) with an activation solution containing NaOH and sodium silicate in a constant ratio. The activation solution was added to the soil mixture in over-saturated until reaching a shed state of the mixture. The MK amount added to the soil sample was 30% of the soil sample weight. The geopolymer was mixed in the soil sample and tested after a drying process of 28 days. The soils were tested in a wind tunnel for dust emission--overall 30 runs were performed by the wind tunnel (5 samples, 3 replicates, 2 wind velocities). These experiments were performed in the portable boundary-layer wind tunnel of the Aeolian Simulation Laboratory at BGU [8]. Boundary-layer wind tunnels enable simulations under standardized quasi-natural wind conditions and provide quantitative information on dust emission rates from the soils. The wind tunnel has a cross sectional area in the order of 0.5 \(\times\) 0.5 m with open-floored working sections of up to 10 m length. Air push or air suction flow in the tunnel is generated by an axial fan up to a maximum velocity of 18 m s\({}^{-1}\)Instruments installed in the test section of the tunnel enable quantification of wind characteristics and dust (PM) concentrations. The tunnel was operated under two wind velocities, 6.5, and 9.5 m s\({}^{-1}\), which represent medium and strong natural winds that are associated with dust emission in semi-arid loess soils [13]. Each run of specific wind velocity lasted 30 s to record the trend of dust emission. Dust concentrations (\(\mu\)g m\({}^{-3}\)) PM10 were recorded by a light-scattering device, DustTrak DRX 8534 (TSI, Shoreview, MN, USA), in the range of 0.001-150 \(\mu\)g m\({}^{-3}\) (\(\pm\)0.1% of reading) at 1-s intervals, which was placed at 25 cm above the tunnel bed. The recorded PM10 concentrations were converted into mass flux emitted from the soil surface (mg m\({}^{-2}\) s\({}^{-1}\)) based on the wind tunnel dimensions, the area of the soil bed, and the wind