As we noted earlier, the piston effect generated when trains approach the platform can affect PM concentrations. Since the piston wind reaches the rear of the platform first, the largest amount of particulate matter from the tunnel would be pushed to this position. As the train enters the station, decelerates, and stops at the front position, the force of the piston wind continuously decreases and the increase in PM concentrations also weakens. However, the PM2.5 concentration at the front of the platform was also relatively high in Fig. 5.