This study investigated the effectiveness of tap water application in reducing nano-sized wear particles at a wheel-rail contact interface and its impact on air quality at different train velocities. Airborne wear particles (AWPs) were simulated using a twin-disk rig at 500, 800, and 1,300 RPM. Mass concentration of nano-sized wear particles was measured using a fast mobility particle sizer (FMPS) at a sampling frequency of 1 Hz. To simulate various vehicle dynamics and contact conditions, the slip rate was incrementally increased from 0 to 3%. During wet conditions, water was applied at a rate of 7 L/min. PM0.1 and PM0.56 under dry and wet conditions were compared to evaluate the method’s effectiveness. The analysis showed that the tap water application method improved the air quality by reducing PM0.56 by at least 74% and PM0.1 by approximately 80%. In conclusion, the water application method can effectively improve air quality by reducing generation of nano-sized wear particles. The train velocity affected the generation of nano-sized wear particles under both conditions.