# Identification of Emission Source Using a Micro Sampler Carried by a Drone
### Instrumentation and Calibration Procedures  
The air compounds collected in the fields were examined by a GC-MS system (6890N and 5973, Agilent, Wilmington, DE, USA). The GC capillary column was HP19091Z-413 HP-1 PDMS (30 m \(\times\) 320 um \(\times\) 0.25 um) (Agilent, Wilmington, DE, USA).  
After VOC sampling, the NTS and Tedlar air bags were analyzed using the GC-MS. The desorption time and temperature at the injection port of GC were 30 s and 250 \({}^{\circ}\)C, respectively. The temperature of the GC oven was increased from 50 \({}^{\circ}\)C in increments of 15 \({}^{\circ}\)C/min to 180 \({}^{\circ}\)C, and was held for 2 min. The carrier gas was helium, and the flow rate was 1.8 mL/min. Notably, based on the earlier works by [PERSON] et al. [21; 22], no carryovers of analytes were available in the packing phase when an NTS was thermally desorbed, as following the above VOC analysis procedures.  
The calibration analysis for VOCs that were collected by NTS carried by a drone was performed using a Tedlar bag with a volume of 1 L. A micro syringe was used to inject 0.05 \(\mu\)L of liquid target chemical into the Tedlar bag, which had been filled with zero air, and the bag was then placed in an oven at 40 \({}^{\circ}\)C. After 1 h, the compound had completely evaporated in the bag, and its concentration was \(C_{1}\). The standard samples for calibration had a concentration range of 0.5-10 ppm. A sampling pump with the same specifications equipped on the drone, was used to connect the NTS to the bag in active sampling mode. As the Tedlar bag was compressible, and its volume gradually decreased with the increasing of exhaustion time of pump, the concentration of the VOCs in the Tedlar bag remained constant. When the exhaustion time of the pump was 1 min, and the NTS analysis area by the GC-MS was \(A_{1}\). The concentration \(C_{2}\) of the target VOC that had been sampled by the NTS at the site is given by  
\[\mathbf{C_{2}}=\left[\left(\frac{\mathbf{A_{2}}}{\mathbf{A_{1}}}\right)\times\frac{\mathbf{1}} {\mathbf{t}}\right]\times\mathbf{C_{1}} \tag{2}\]  
where \(A_{2}\) was the VOC analysis area via the NTS sampling at the site, and \(t\) was the sampling time at the site. An example of the relevant calculation is provided in the Supplementary Materials.  
To conduct a calibration analysis for the air sample that was taken using an NTS in passive mode, the assistant prepared chemicals at specified concentrations in a glass bulb, and used a 1 mL gastight syringe to withdraw a VOC sample from the bulb for analysis by the GC-MS. The integral areas for the specified concentrations of target VOCs were obtained. The VOCs, that were extracted by an NTS, were also determined by a proportional relationship; that is, substituting the data from the calibration analysis into Equation (2). Based on the minimum detected area which were examined by the GC-MS, the method detection limits (MDL) for the VOCs that were sampled by the NTS were for active sampling, benzene and toluene = 0.005 ppm, methanol = 0.18 ppm, and acetone = 0.01 ppm, and for passive sampling, benzene and toluene = 0.008 ppm, methanol = 0.15 ppm, and acetone = 0.022 ppm.