Effect of precipitation on reducing atmospheric pollutant over Beijing

Precipitation is one of the major mechanisms for removing aerosol particles in the atmosphere. In this study, the effect of precipitation on reducing particulate matter (PM) is analyzed by using the concentration data of PM2.5 (diameters less than 2.5 mu m) during 2008-2017 and PM10 (diameters less than 10 mu m) during 2014-2017 and meteorological data in the same period in Beijing, China. The results show that there are obvious differences in the removal of PM by different intensity precipitation processes. Drizzle shows a negative removal effect on PM2.5 with an efficiency between - 16.5% and -36.5%, while a positive removal effect is found for PMcourse (diameters between 2.5 and 10 mu m), and the efficiency varies from 31.7% to 38.4%.The removal effects of other precipitation events (intensity >= light rain) are positive for both PM2.5 and PM(course )and the efficiency is 19.1-68.5% and 31.7-86.3%, respectively. Generally, the effective removal durations for PM2.5 and PMcourse are 2-9 and 2-10 h, respectively, and the removal effect becomes better as the PM diameters increase. Moreover, the strongest removal effect of precipitation on PM2.5 occurs in autumn while that for PMcourse occurs in spring, and nighttime precipitation has higher removal efficiency and longer removal duration than daytime precipitation. Additionally, a longer duration of precipitation results in a higher removal efficiency for PM with large diameters and a longer duration for effective removal.