## 2 Materials and Methods
### Experimental Wind Tunnel Design  
To analyze the ability of crops to reduce fine dust, a small wind tunnel was designed and constructed. In field experiments, environmental conditions continuously change, making it very challenging to conduct stable experiments to determine dust reduction coefficients. To analyze the fine dust reduction effect of crops, the concentration of fine dust must be measured before and after it passes through the crops. Since the wind tunnel has a constant and stable wind speed, and the space where the air moves is confined, it is possible to stably measure the concentration of fine dust before and after passing through the crops.  
The wind tunnel was manufactured with a height of 1 m, width of 0.5 m, and length of 10 m, and two variable fans with a maximum air volume of 4740 m\({}^{3}\)/h were installed to enable negative pressure ventilation (Figure 3). To prevent fine dust from sticking to the wind tunnel surface, the interior walls made of particle board were coated with Teflon film. To facilitate the installation of crops for the experiment and cleaning before and after the experiment, each component of the wind tunnel was designed as a detachable modular type with wheels attached. The fine dust injection device was installed by combining a  
Figure 2: Experimental site for field monitoring with cultivation of **(a)** barley and **(b)** trtictale in the **(c)** crop cultivation test areas located in the Saemangeum reclaimed land in Korea.  
pump so that air mixed with fine dust in a Tedlar bag could be introduced and mixed into the wind tunnel at a constant flow rate. The temperature, humidity, and flow rate inside the wind tunnel were analyzed using an indoor environment measuring instrument (AMI 310, KIMO, Saint-Priest, France).  
Barley and tritticale were sampled just before harvest in the experimental area and used for the wind tunnel test. The harvested crops were carefully washed using triple distilled water to clean the fine dust adsorbed on the crop surface without damaging the crops; and after washing, they were naturally dried in preparation for the experiment. The prepared crops were installed in the crop zone of the wind tunnel, and the arrangement of the crops was performed at 5 cm intervals according to the sowing standards provided by the Rural Development Administration in Korea. The density of sowing was categorized as densely, moderately, and sparsely sowing, each placed at intervals of 20, 25, and 35 cm, respectively (Figure 4).  
Figure 4: Arrangement according to crop density for calculating dust reduction coefficient through the wind tunnel experiment. (**a**) Densely crop sowing, (**b**) Moderately crop sowing, (**c**) Sparsely crop sowing.  
Figure 3: Design of a small wind tunnel to analyze the fine dust reduction coefficiency according to crops and its densities.  
The size distribution of particulate matter at the reclaimed land site was monitored by using OPCs (Optical Particle Counter, 11-D, Grimm Inc., Freising, Germany), which can measure aerosol concentrations divided into 31 sizes ranging from 0.253 \(\upmu\)m to 35.15 \(\upmu\)m at 6-s intervals. Capturing the fine dust from the site and reproducing it in the experimental chamber was very challenging. Therefore, using the measured size distribution, the experimental fine dust was combined by two standard dusts to achieve a particle size distribution as similar to the results measured on-site (Figure 5). The standard dusts used were nominal 0-3 micron Arizona test dust (Powder Technology Inc., Arden Hills, MN, USA) and A1 test dust (ISO 12103-1 [33], Powder Technology Inc., Arden Hills, MN, USA). The size distribution of fine dust measured in the field showed the highest proportion at 5.5-11 \(\upmu\)m range, and mixing the two types of standard fine dusts at various ratios showed the most similar size distribution at a 5:5 ratio (Figure 5).