## Materials and Methods
### Sample Processing  
On each test day, collection of the spray drift was carried out during the daytime, and the PTFE lines collected were moved to the laboratory in the shortest possible time. Analysis of the fluorescence characteristics of the spray liquid containing Rhodamine-B was performed on an F-380 fluorescence spectrophotometer (Tianjin Gangdong Technology Co., Ltd., Tianjin, China). The excitation wavelength of 542 nm and emission wavelength of 579 nm was selected by scanning the spray liquid. Because there is a linear relationship between the concentration of the Rhodamine-B aqueous solution and the fluorescence intensity only at low concentrations, the volume of ultrapure water for elution should be determined according to the deposition amount at each sampling line. 40 mL of ultrapure water was injected into the zip-lock bags with a pipette to wash off the tracer on the PTFE line, which was collected when the UAV rotors were rotating. According to the test observation, the droplets sprayed from the nozzle may drift seriously if the UAV rotors did not rotate. Therefore, the volume of ultrapure water depended on the actual situation when processing the sampling lines obtained from the rotor non-rotating treatments. For full extraction, the bags were shaken and rubbed for almost 30 s. A 3 mL fraction of each extract was poured into a cuvette for analysis.  
Five calibrated working solutions at the concentrations of 0.01, 0.1, 0.2, 0.5, and 1 mg/L were prepared by thinning a stock solution with ultrapure water. After a large number of comparative studies between solutions of known concentration and the linear response relationship (Y = 0.002158x \(-\) 0.541634, R\({}^{2}\) = 0.9998), the maximum and minimum detection limits for Rhodamine-B were 1 mg/L and 0.01 mg/L, respectively. Taking into account factors of the volume of the dilution solution, the concentration of Rhodamine-B in the spray solution, the spray time, the flow rate, the background (collector and dilution liquid), and the calibration line, the reading of the test solution on the fluorometer can be converted to the droplet deposition amount per unit length (\(\mu\)L/m) (Equation (1)).  
\[\beta_{dep}=\frac{\left(\rho_{smpl}-\rho_{blk}\right)\times F_{cal}\times V_{ dill}}{\rho_{spray}\times A_{col}}, \tag{1}\]  
where \(\beta_{dep}\) is the drift deposition, \(\mu\)L; \(\rho_{smpl}\) is the fluorimeter reading of each sampling line; \(\rho_{blk}\) is the fluorimeter reading of the blanks (collector and dilution water); \(F_{cal}\) is the calibration factor, \(\mu\)g/L; \(V_{dill}\) is the volume of dilution used to solute tracer from collector, L; \(\rho_{spray}\) is the spray concentration, g/L; \(A_{col}\) is the collection area of the collector for capturing the spray drift. In this paper, \(A_{col}\) is regarded as 1, because the deposition of the entire sampling line is needed.  
[PERSON]'s research on the exposure of pesticide applicators showed that the recovery rates of different concentrations of dyes were diverse [6]. For the recovery of Rhodamine-B from sampling lines to be studied, clean PTFE lines were spiked with four appropriate volumes of Rhodamine-B solution in order to reach the concentrations of 0.05, 0.15, 0.35, and 0.75 mg/L when 40 mL of ultrapure water was injected into bags. The extraction and fluorescence analysis methods followed those described for the drift test. For the four concentration levels, the recovery rates and relative standard deviations (supplied in parentheses) were 87.38% (7.53%), 95.26% (3.91%), 100.12% (3.09%), and 83.69% (5.27%), respectively. The fluorimeter readings were corrected based on the recovery rates of the calibration solution interval.