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Large seasonal variations in fine aerosol precipitation rates revealed using cosmogenic 7Be as a tracer

Chae, Jung-Seok, Kim, Guebuem
The Science of the total environment 2019 v.673 pp. 1-6
aerosols, air, data collection, dry season, models, monsoon season, particulates, seasonal variation, spring, summer, tropopause, Korean Peninsula
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.