## 3 Results and Discussion
### Development of Optimal Dust Suppressant Formula
#### 3.1.3 Optimization Experiment of Dust Suppressant Formula  
A certain amount of hygroscopic and moisturizing enhancer can increase its photosynthesis, so the concentration of this enhancer has been determined to be lower than 0.5%. ecologically. With reference to the Standard of China Environmental Protection Industry Association-Water-Soluble Road Dust Suppressant Industry Standard (T/CAEPI 7-2017), the concentration of Cl\({}^{-}\) should not exceed 0.1%. Four groups of optimized formulas were obtained by adding different concentrations of hygroscopic and moisturizing enhancers into the preliminary formula. According to Table 5, one preliminary formula and four groups of optimized formulas for dust suppressant solutions and dust samples were prepared. The five groups of samples were placed in the natural environment. According to the requirements of this experiment, the mass of samples was weighed at 9:00 am and 14:00 pm each day so as to calculate their water loss rates and evaluate their water retention effects. The changes in water loss rate over time are shown in Figure 5a.  
According to Figure 5a, the moisture retention for all dust suppressant samples is better than that of pure water samples; the addition of hygroscopic and moisturizing enhancer can improve the water retention effect of dust suppressant appropriately, and the water loss rate decrements range from 0.47% to 6.47%. Within 60 h, the hygroscopic and moisturizing enhancer can obviously reduce the water loss rate of samples, whose maximum decrement can reach 6.47%. However, the moisture enhancing performance of the enhancer exhibits a decrease with time. According to the measured data, within 60 h, dust suppressants with an extra 0.25% and 0.50% of hygroscopic and moisturizing enhancers demonstrate better moisture enhancing performance. In combination with the requirements of industry standard (T/CAEPI 7-2017) on Cl\({}^{-}\) concentration, the concentration of hygroscopic and moisturizing enhancer was preliminarily determined to be 0.25%.  
Under the moisture conditions of 30%, 40%, 50%, 60%, and 70%, the changes in hygroscopicity of above five groups of samples were calculated and are shown in Figure 5b. According to Figure 5b, the moisture retention rates for all dust suppressant samples are higher than that of pure water samples when the moisture is above 40%; the addition of hygroscopic and moisturizing enhancer can effectively improve the hygroscopicity of the dust suppressant. The hygroscopicity of the dust suppressant sample prepared  
Figure 5: (**a**) Variation curves of water loss rate of samples; (**b**) variation curves of the hygroscopicity rate of samples with moisture.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Formula Names** & **Main Components** & **Optimized Components** \\ \hline
1\# (Preliminary formula) & 6\%BS, 6\%XS, 0.12\%NB and 0.06\%BZ & – \\
2\# (Optimized formula) & 6\%BS, 6\%XS, 0.12\%NB and 0.06\%BZ & 0.25\%A \\
3\# (Optimized formula) & 6\%BS, 6\%XS, 0.12\%NB and 0.06\%BZ & 0.50\%A \\
4\# (Optimized formula) & 6\%BS, 6\%XS, 0.12\%NB and 0.06\%BZ & 0.75\%A \\
5\# (Optimized formula) & 6\%BS, 6\%XS, 0.12\%NB and 0.06\%BZ & 1.00\%A \\ \hline \hline \end{tabular}
\end{table}
Table 5: Optimization design table for preliminary formula.  
with the preliminary formula is poorer than that of the pure water sample when the moisture content is lower than 42%. The hygroscopicity of that sample is higher than that of the pure water sample at low moisture conditions after the addition of hygroscopic and moisturizing enhancer. At this point, the higher the concentration of hygroscopic and moisturizing enhancer, the more effective the enhanced hygroscopicity will be. In combination with the results of moisture retention tests under natural conditions, the concentration of hygroscopic and moisturizing enhancer has finally been determined as 0.25%; that is, the optimal formula is the preliminary formula with the addition of 0.25% of hygroscopic and moisturizing enhancer.