The Beijing City Air Pollution Observation Experiment (BECAPEX) and some Preliminary Results (Formerly paper number 7.5)

The “Beijing City Air Pollution Observation Experiment” (BECAPEX) conducted in Beijing City and its surrounding region in spring 2001 and summer 2003. A three-dimensional observing network utilizing grand-based observations and space-based satellite remote sensing was setup to monitor the urban environment in and surrounding Beijing. It was the first comprehensive air pollution monitoring attempt around Beijing city utilizing advanced observing instruments including atmospheric profiler, tethersonde, ultra-sonic anemometer sodar and lidar, lower boundary micro meteorology gradient observation system, roof-mounted pollutant observation and collection instrument, 10 level atmospheric chemistry profiler mounted on a 325 m tower, a 3 level aerosol observation system, as well as satellite remote sensing. The focus of the field experiment was on the environmental dynamics of air pollution, a central issue concerning the formation mechanism, control and mitigation of the effect, of air pollution. The purpose of the experiment was to characterize the three-dimensional physical and chemical structure of the atmospheric planetary boundary layer (PBL) surrounding Beijing area, and to obtain a coherent three-dimensional depiction of various scales of boundary layer phenomenon, such as urban heat island, urban lee wind, street circulation, etc. The results from the BECAPEX experiment provided a detailed three-dimensional description of the dynamic and thermal structure of Beijing's urban atmospheric environment, the physical and chemical characteristics of air pollutants, their variation, transportation, diffusion and transformation, and impact on regional climate. The data revealed the existence of an air dome (a dome-shape boundary layer) around the urban area of Beijing and provided a comprehensive set of parameters that define the characteristics of the air dome. The variation of these parameters determines the severity of air pollution in Beijing. Thus, warning signals related to severe pollution events can be detected by monitoring these parameters. Important findings of this study include the synchronous characteristics of the life cycle of pollutant within the urban atmospheric boundary layer, and obvious diurnal variation in the vertical transport of pollutants in the boundary layer or under the air dome. This phenomenon was closely associated with the temperature inversion and the vertical structure of the boundary layer. Moreover, the diffusion and distribution of air pollutants were related to the multi-scale interaction among large-scale circulation, mountain and valley wind, and urban heat island circulation. As a result, while air pollution in Beijing mainly arises from local emission sources, sources in the vicinity also have prominent influence.