## 4 Experiment  
The conceptual schematic of this study is explained in Figure 1a. Uncharged 100 nm particles at a concentration of \(10^{7}\) particles per cm\({}^{3}\) air (selected as an example of submicron-sized particles) and 1 \(\upmu\)m particles at a concentration of \(10^{4}\) particles per cm\({}^{3}\) air (selected as  
Figure 1: (**a**) Conceptual schematic of aerodynamically assisted electric agglomeration, (**b**) 3D geometry of the vortex generator. an example of micron-sized particles) with air flow were injected into the wire (electrode) to rod (ground) type charger. Half of this particle mixture was positively charged (red) while the other half was negatively charged (blue) before entering the agglomerator. In the agglomerator, larger particles oscillated at higher amplitudes due to their higher charge number acquired when passing through the charger, sweeping smaller particles and leading them to attach to the larger particles. Additionally, the vortex generated by the vortex generator installed in the agglomerator increased the collision probability of particles, enhancing the agglomeration efficiency and reducing the number concentration of smaller particles. Smaller particles are more likely to collide with larger ones because their relative velocity is greater compared to particles of similar size ([PERSON] et al. [23]). The vortex generator consisted of thin plates arranged repeatedly in an isosceles triangle shape (see Figure 1b). Figure 2 shows the experimental setup, mainly composed of (a) the test particle generation part, (b) the particle charging/agglomeration part, and (c) the measuring part. In Figure 2a, compressed air, used as a carrier gas, was purified by passing through a clean-air supply system designed to remove oil droplets, moisture, and contaminants. This clean-air supply system included an oil trap, a diffusion dryer, and a high-efficiency particulate air (HEPA) filter. The purified air entered the particle generation device through a mass flow controller (MFC). Nano-sized NaCl particles were generated using the evaporation-condensation method with a tube furnace. Arizona test dust 4 (A4; micro-sized) particles were generated using a solid aerosol generator (SAG410, TOPAS, Dresden, Germany). In the SAG, a moving toothed belt continuously supplied test dust particles dispersed from the belt by compressed air. Figure 2: Experimental setup: (**a**) test particle generation part, (**b**) particle charging/agglomeration part, and (**c**) measuring part. In Figure 2b, the air flow containing both the NaCl particles and A4 particles passed through the charger with a face velocity of 0.1 m/s. Two corona chargers were located in the charging part in parallel, with DC voltages of +6 kV and \(-\)6 kV applied to the chargers, respectively. Each charger consisted of a wire (diameter: 0.1 mm) and two grounded rods (diameter: 2 mm). The distance between the wire and the grounded rod was 7.95 mm. An AC high-voltage power supply with a peak-to-peak voltage of \(\pm\)20 kV was used, resulting in a field strength of 3.5 kV/cm (rms). The frequency of the AC power supply was 60 Hz. The agglomerator comprised two parallel metal plates placed 4 cm apart and a vortex generator (made of acrylic, length: 60 cm, cross-sectional area: 4 \(\times\) 4 cm\({}^{2}\)). The vortex generator comprised thin plates (width: 4.8 \(\times\) 2 cm\({}^{2}\); thickness: 1.6 mm) arranged repeatedly in an isosceles triangle shape of 55\({}^{\circ}\) (see Figure 1b). Between two triangle shapes of 55\({}^{\circ}\) and 70\({}^{\circ}\), the shape of 55\({}^{\circ}\) was chosen since this shape could cause a lower pressure drop. Details are presented in Section S1 of the Supplementary Materials. After the agglomeration, a portion of the particle flow was delivered to the measuring part (see Figure 2c). The particle size distribution was determined using both a scanning mobility particle size (SMPS) and an aerodynamic particle size (APS, 3321, TSI, Shoreview MN, USA).