## 4 Discussion  
The present work tested the atomization and deposition characteristics of surfactant polyethylene glycol 20,000 solution at three concentration levels to compare the effects of the concentration on them. There are few reports about this kind of surfactant, but a lot of experiments on other kinds of surfactants have been done.  
[PERSON] et al. [33] compared and analyzed the droplet size distribution of ST110-01 and ST110-03 nozzles before and after adding different adjuvants and found that most of the adjuvants improved the uniformity of the droplet size and reduced the droplets drift to a certain extent. The results in this paper are similar to this. When adding different  
Figure 6: Drift potential reduction percentage under different spray conditions.  
concentrations of polyethylene glycol 20,000, the amount of drift and deposition of droplets in the horizontal and vertical directions is reduced. [PERSON] et al. [34] added polyethylene glycol 300 (PEG-300) to the pesticide solution and found that the surface tension decreased by 5 N/m on average, and the volume median diameter decreased by 12 m on average. The adhesion of the pesticide solution under indoor conditions without wind was improved nearly 2 times. The results of this study are contrary to this article. Generally speaking, the addition of surfactants can reduce the surface tension of the liquid, enhance the degree of atomization, and the droplet size should become smaller. However, it can be seen from the above research that when the spraying medium is a mixture of PEG-20,000 with different concentrations and clear water, the droplet size increases significantly and is directly proportional to the concentration. The main physical properties that affect the droplet size of the liquid droplet are viscosity and surface tension, both of which hinder the atomization of the liquid [35; 36; 37], among them, some studies have also proposed that the effect of viscosity on the droplet size is greater than that of the surface tension. Therefore, the following research can focus on the viscosity and surface tension of PEG-20,000 solution at different concentrations and explore whether the reason for the increase in the droplet size of PEG-20,000 solution is that the viscosity plays a leading role.  
In general, the results of this article show that as the concentration of polyethylene glycol 20,000 increases, the size of the spray droplets increases and the amount of drift in the vertical and horizontal directions decreases overall. In plant protection spraying operations, minimizing the drift of droplets is the ultimate goal and it is proved in this paper that the addition of polyethylene glycol 20,000 can help reduce drift. For specific diseases, combining the theory of optimal biological particle size and the meteorological conditions during actual spraying can determine the appropriate operating particle size range. After knowing the appropriate particle size range guided by the biological optimal particle size theory, the droplet size range can be appropriately adjusted and reduced according to the actual spraying environment. For example, when the wind speed or the temperature is high, the evaporation and drift of small droplets are serious, the addition amount of polyethylene glycol 20,000 should be appropriately increased.