Scavenging effect analysis of precipitation on PM_2.5 and PM₁₀ in Sichuan Basin

The Sichuan Basin is one of the most severely air-polluted regions in China. To study the scavenging effect of precipitation on PM_2.5 and PM₁₀ in Sichuan Basin, the PM_2.5 and PM₁₀ mass concentration data from 90 environmental monitoring stations and observation data from 17 ground meteorological stations in Sichuan Basin from 2016 to 2021 were used. First, the effects of precipitation on the spatial distribution of PM_2.5 and PM₁₀ in the Sichuan Basin were analyzed. Then, the influence of precipitation intensity and duration on PM_2.5 and PM₁₀ removal effects was revealed based on the removal rates of aerosol particle mass concentration changes before and after precipitation. Finally, by calculating the removal coefficients using the raindrop spectral distribution, raindrop sizes, and end-of-fall velocities, the removal effects of precipitation on four PM_2.5 and PM₁₀ pollution events in the Sichuan Basin were investigated. The results are as follows: (1) In the Sichuan Basin, precipitation affects the spatial distribution of PM_2.5 and PM₁₀. The greater the precipitation amounts and the longer the duration of precipitation, the greater the removal rates and the more significant the scavenging effect. (2) In cases of heavy rainfall, removal rates are not sensitive to increases in precipitation duration when it exceeds 6 hours. (3) When the raindrop diameter, the total number of raindrops, and the minute rain intensity peak, and the raindrop spectra broaden and intensify, rapid decreases of PM_2.5 and PM₁₀ mass concentrations occur. (4) The removal coefficients are indicative of variations in PM_2.5 and PM₁₀ mass concentrations. When the peak removal coefficients are above 10 h^-1, the scavenging effect of precipitation on PM_2.5 and PM₁₀ is significant.