Scavenging Effect of Rime and East Wind on PM2.5 Under Air Heavy Pollution in Beijing

: In order to study the scavenging effect of rime and east wind on the concentrations of PM2.5 in Beijing during the air heavy pollution, PM2.5 concentration data of some mountains and plains stations was used, together with meteorological data, wind profile data, aerosol extinction coefficient radar data collected during December 19 to 27, 2015, to analyze the clearance mechanisms of rime and east wind on PM2.5.The results showed that ①the removal of PM2.5 by rime was a different mechanism from that by the north wind and rainy weather, in the cooling conditions, the droplets touched the branches, wire for solid condensation, leading to formation of rime, and the concentration of PM2.5 decreased;②the east wind is a special kind of wind in Beijing area, when easterly wind decreased with height, a strong upward motion could be formed, and the PM2.5 was uplifted from the surface layer to the top, while with larger westerly wind in top, it was removed into downstream and cleaned; when east wind increased with height, a weak downward movement was easy to form, and when this sinking motion could not reach the ground, the surface layer of PM2.5 capacity became small, which was beneficial to increase the concentration of PM2.5;③the PM2.5scavenging ability of east wind depended on two points, one was the strength and development of upward movement of the height formed by the east wind, and the second was the initial height of uplifted motion formed by east wind, the lower the origin of the ascending motion height, the more obvious the removal of PM2.5;④after occurrence of east wind, along with the ascending motion to m·s-1 magnitude, the mixed layer height increased to 1200-1800 meters, and PM2.5 was uplifted to top layer and cleaned.