Comparison Analysis of Two Continuous Heavy Pollution Episodes in Beijing,China

The both heavy pollution episodes which lasted several days occurred from October 6 to 10 and November 29 to December 3 in the year of 2004 in Beijing area. Particulate matter is primary pollutant during the both air pollution events. It made atmospheric transparency bad, low visibility and unfavorable effect to human health, traffic and transportation, ecological environment and so on. In this paper, the temporal and spatial distribution of air pollutants concentration and effect of meteorology are analyzed.

The results indicated that some similar characteristics in the both pollution episodes. They are showed as below:

(1) Particle concentration maintains high level in each episode. The high concentrations for over 300ìg/m3 of 6-hour averaged lasted 4 days and 3 days in the first event(Oct. 6 to 10) and second pollution event(Nov. 29 to Dec. 3), respectively. In these two pollution events, the maximum concentration of PM10 is over 700ìg/m3 and 600ìg/m3 ,respectively. The fine particle matter PM2.5's concentration is also very high in these two episodes.

(2) During the both air pollution events, the synoptic system is very weak. Atmospheric diffusion ability is low in local and regional area. There are stable boundary atmospheric layer, low wind speed, weak turbulent diffusion, continuous inversion and high relative humidity.

However, the air pollution distribution and its formation have some differences for these two heavy air pollution episodes. We concluded as follow,

(1) The former event is a typical local air pollution event which took place in the urban or near suburb in Beijing. The pollution concentration is much higher in Beijing urban than in distant suburb and surrounding cities of North China. But the second event has regional pollution feature. The former process's PM10 and PM2.5 concentration are higher and lasts longer in the first event than in second event.

(2) The other pollution gases also exhibit different variation in the two pollution episodes. In the first pollution episode, the NO2 concentration is a little higher and SO2 concentration is a bit lower than that in the second event. The higher NO2 concentration in Beijing city showed the contribution of local traffic emission is also important, and the SO2 high concentration in second event is due to the increasing coal consume for winter heating.

(3) The weather phenomenon during the first pollution event mostly recorded soot and haze ,while fog and heavy fog occurred in the second event. The low visibility less than 1km maintains longer in first event than in second one. During the first event, there is a clear wind field convergence in urban area. The vertical structure of water vapor or relative humidity's is more complex in the second event.

From the above analysis, it showed that the first continuous long time pollution is mainly caused by emission of local pollution source, weak synoptic system and Beijing ‘s special topographic character, the second continuous pollution is mainly made by regional heavy fog weather and stable boundary layer and is a regional air pollution event.