To determine the seasonal variations in the removal efficiency of fine aerosols (PM2.5) in the Northeast Asia, we analyzed 7Be data collected for the surface air and precipitation over 20 years in Korea. The 7Be activity concentrations in the surface air were relatively higher in spring owing to tropopause folding but lower in summer owing to efficient removal by precipitation. The monthly 7Be concentrations decreased as the precipitation amounts increased showing a negative correlation (r2 = 0.34) against the precipitation amount. These results indicate that the concentrations of 7Be and fine aerosols are mainly controlled by the same washout effect, although the sources are different. The mean depositional velocities of fine aerosols, based on the 7Be mass balance model, showed a large seasonal variation, with its maximum value (1.9 cm s−1) in July and minimum value (0.22 cm s−1) in March. The 7Be depositional velocity reflects the net deposition of fine aerosols excluding moisture effects. Thus, the concentrations of fine aerosols can occur as high as five-fold in the dry season, if the input terms of fine aerosols remain the same. Our results imply that precipitation plays a critical role in the seasonal changes in the concentrations of fine aerosols, providing much clean air in the summer monsoon season in the Northeast Asia. Display omitted •The highest 7Be activities were observed in spring due to large stratospheric air inputs.•The lowest 7Be activities were observed in summer due to larger removal by precipitation.•The deposition velocity of fine aerosols was maximum in summer due to large precipitations.•The residence time of fine aerosols in winter is 5-fold longer than that in summer.