Influencing domain of peripheral sources in the urban heavy pollution process of Beijing

The effect of city's peripheral pollution sources is one of the key issues urgent to be solved in the decision-making of Beijing's environmental pollution control. This paper comprehensively analyses the surface observations, and the satellite remote sensing data of Moderate Resolution Imaging Spectroradiometer (MODIS) and Total Ozone Mapping Spectrometer (TOMS) during the Beijing City Atmospheric Pollution Experiment (BECAPEX) from January to March, 2001, presents an "upstream" wind field resultant vector method for tracing peripheral pollution sources, and finds that the 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-shaped "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 paper also comprehensively analyses the features of flow field in the heavy pollution process in the Beijing region, and compares the heavy pollution process with samples of good air-quality days from January to March, 2001. The experiment of Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT-4) further reveals the diffusion trajectory of pollutants of the cities in Hebei and Shandong provinces and Tianjin city in the heavy pollution process of Beijing, and the simulations of the Regional Atmosphere Model System (RAMS) confirm the possible contribution of peripheral sources to the exceptionally heavy pollution process of the urban area of Beijing, thus revealing that the input of pollutants from southern peripheral cities is one of the important factors responsible for aggravating urban heavy pollution processes. Copyright by Science in China Press 2005.