BECAPEX科学试验城市建筑群落边界层大气环境特征及其影响

CHARACTERISTICS OF ATMOSPHERIC ENVINRONMENT OF BOUNDARY LAYER STRUCTURE OF CITY COMMUNITY IN BECAPEX AND INTEGRATE INFLUENCE

20 0 1～ 2 0 0 3年在北京实施了大气边界层动力、热力、化学综合观测试验 (BECAPEX ,BeijingCityAtmosphericPollutionObservationFieldExperiment) ,获取了北京城市大气动力和大气化学三维结构图像。综合观测试验分析研究发现 ,城市区域呈非均匀次生尺度热岛分布 ,并伴随着城市次生尺度环流 ,影响了局地空气污染物分布特征。MODIS卫星遥感 地面观测资料经过变分分析 ,可发现北京城市空气污染与周边区域影响源有密切关系 ,并影响城市群落环境气候特征 ,导致该区域日照、雾日、低云量和能见度呈显著年代际变化趋势。

The Beijing City Atmospheric Pollution Observation Field Experiment (BECAPEX) was deployed during 2001—2003 to obtain the 3-dimensions structure integrate images of Beijing atmospheric dynamic and chemical process. Research on the integrated observations show the thermal-dynamic structure of city area is a non-uniform secondary heat island with a secondary circulation, which affects the distribution of the local pollutants. The data revealed the existence of an air dome (a dome-shape boundary layer) around urban Beijing and provided a comprehensive set of parameters that defined the characteristics of the air dome. Important findings of this study include the synchronous characteristics of the life cycle of pollutants within the urban atmospheric boundary layer and obvious diurnal variation of pollutants in the boundary layer or under the air dome. In fact, the data reveal that the air dome acts like a large canopy covering the city of Beijing. This phenomenon is closely associated with the temperature inversion and the vertical structure of the boundary layer. Moreover, the diffusion and distribution of air pollutants are related to the multiscale interaction among large-scale circulation, mountain and valley wind, and urban heat island circulation. As a result, air pollution in Beijing usually come from local sources, but the sources in the vicinity also have prominent influence. Features of the urban heavy pollution processes of Beijing are significantly correlated with the impact of the emission sources of southern peripheral cities, and the pollutants transferred northwards from distant upstream sources are retarded by the U-shape “valley” topography in Beijing's periphery. The two factors are responsible for the formation of the S-N zonal influencing domain of pollutants from the southern peripheral areas to Beijing. The variational correction analysis of MODIS RS-surface observations indicate that Beijing air pollution has close relationship with its surrounding regional influencing sources, and affects the environment-climate of city community. It might cause the obvious interdecadal changes of sunshine duration, fog day, low cloud cover and visibility. BECAPEX has been assessed as the pilot project by WMO, and publicized on column of WMO website.