[Scavenging Effect of Rime and East Wind on PM Under Air Heavy Pollution in Beijing].

In order to study the scavenging effect of rime and east wind on the concentrations of PM in Beijing during the air heavy pollution, PM 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 PM.The results showed that ①the removal of PM 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 PM 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 PM 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 PM capacity became small, which was beneficial to increase the concentration of PM;③the PMscavenging 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 PM;④after occurrence of east wind, along with the ascending motion to m·s magnitude, the mixed layer height increased to 1200-1800 meters, and PM was uplifted to top layer and cleaned.

[Diurnal Variation of PM Mass Concentration in Beijing and Influence of Meteorological Factors Based on Long Term Date].

Diurnal variation of PM mass concentration is analyzed based on data of BAOLIAN (representing urban area) and SAHNDIANZI BAP-Station (representing rural area) from 2005 to 2014. Furthermore, the influence of meteorological factors was also discussed. The results showed that 10-year-average diurnal variation of PM mass concentration in urban area had a two-peak pattern being coincident with rush-hour.

[A Case Study on the Rapid Cleaned Away of PM₂.₅ Pollution in Beijing Related with BL Jet and Its Mechanism].

The concentration of PM₂.₅ decreased very rapidly from 18:00 to 23:00 on 17th Mar. 2015 in Beijing area.

[Meteorological mechanism for the formation of a serious pollution case in Beijing in the background of northerly flow at upper levels].

There is a kind of serious air pollution case occurring in the situation of northerly flow at the levels above 850 hPa in Beijing area. Meteorological data, NCEP reanalysis data and PM2.5 concentration survey were used to analyze the roles of meteorological mechanism in this kind of air pollution case.

[Comparative analysis on meteorological condition for persistent haze cases in summer and winter in Beijing].

Summer is another peak season for haze besides winter in Beijing area, which is different from that in South China. The data of microwave radiometer, profiler, sounding, AWS, NCEP (NCAR) and air pollution monitors were used in the analysis of two haze cases which occurred in winter and summer, respectively. Both cases lasted for 6 days.