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The vehicle-based particle measuring system, software and observing data of urban air pollution in Beijing in Jun. and Dec. 2000 are introduced. The observing results show that there are big differences in the concentration of particles in near ground air in summer and in winter, in urban area and in suburb area and the concentration of particles in near ground air has an obvious change from day to night even in the same area, the same season. The experiment of monitoring urban air pollution indicates that the vehicle-based measuring system can record the size and concentration characteristics of particles in near groundair, the traveling track and the velocity of the vehicle.