## 2 Materials and Methods
### Determination of PM Reduction Coefficient  
To calculate the PM reduction coefficient of the crops, the gravimetric method and real-time concentration analysis method were carried out. The first experiment involved directly measuring the amount of PM adsorbed on the surface of the crops after providing fine dust as similar as possible to field environmental conditions. For the experiment, barley and tritcale surfaces were carefully washed with distilled water and completely dried, then fixed and placed in the test section considering three different planting densities (Figure 6). The manufactured particulate matter was mixed with air and supplied steadily at a flow rate of 1 L/min through a spraying device, with 1 mg/L of fine dust. After sufficient time of the particulate matter supply had concluded, the crops were washed using triple-distilled water to clean the adsorbed particulate matter on the surface. Impurities such as plant hairs or epidermal cells included in the washing water were filtered out using a filter with 100 \(\upmu\)m pore size. Subsequently, a filtering apparatus was fabricated by combining filtering apparatus (LT. SS-47S, Korea Ace Scientific, Ltd., Seoul, Republic of Korea) and a 47 mm glass fiber filter (1.0 \(\upmu\)m pore size, PALL 61631, Pall Corp., Washington, DC, USA), and  
Figure 5: Size distribution of fine dust concentration by measured and manufactured fine dust for the wind tunnel experiment: composition ratio of test dust by particle size according to the composition ratio of standard dust of PM-10 and PM-2.5.  
the particulate matter included in the washing water was separated through the filter and pump. The filtered particulate matter was then dried for 24 h in a desiccator, and the weights of the filters before and after the experiment were accurately measured using Micro Analytical Balances (BM-22, AND Weighing Inc., Tokyo, Japan). All experiments were conducted three times under independent conditions, and blank sample filters that did not capture particulate matter were used for correction.  
For the second experiment to determine the PM reduction coefficient of crops, real-time and size-specific monitoring of dust concentrations were performed before and after passing through crop canopy. When using filters by gravimetric methods, it is possible to measure the amount of particulate matter attached to the crop surface, but it is challenging to analyze the size distribution and the particle characteristics. Therefore, optical particle counters (OPC) were installed at three locations within the chamber: at the inlet, and before and after the crop zone. Monitoring was carried out at 6-s intervals for real-time and 31 different sizes of particulate matter. Figure 7 shows the results of continuous monitoring of PM-10 and PM-2.5 before and after the crop zone for moderately sown triticale for 100 min. The real-time concentrations of particulate matter were measured by size, and the data were corrected using the concentration of particulate matter entering from the outside air. It was assumed that the amount reduced or adsorbed by the crops corresponds to the difference in concentration before and after passing through the crops. The results for the two crops and three planting densities were refined using the same procedure, and the difference in particulate matter concentrations before and after the crop zone was used to calculate the reduction amount over time for PM-10 and PM-2.5 separately. The cumulative reduction amount over time was used to derive the PM reduction coefficient.