Abstract: Synchronous online observations of multiple sites and species are significant for in-depth analysis of the causes and evolution mechanism of air pollution. In this study, the authors analyzed a typical air pollution event that occurred during 3-11 October 2010, on the basis of NO_x, SO₂, O₃, PM2.5, and PM10 levels recorded at four monitoring sites in Beijing. Variations of the pollutants were determined to be inconsistent, with concentrations of NO_x, SO₂, and O₃ appearing as obvious diurnal variations and PM showing slight daily changes while maintaining high levels of concentration. Calculation of the correlation coefficient and coefficient of variation of concentration for these pollutants revealed the following results: The coefficients of variation for the primary pollutants of NO and SO₂, with correlation coefficients of less than 0.44, were 77% and 70%, respectively, exhibiting distinct spatial distribution. Those for the secondary pollutants NO₂, PM2.5, and O₃, with correlation coefficients above 0.54, were 34%, 36%, and 29%, respectively, exhibiting consistent spatial distribution. These findings were applied to the Fifth-Generation Penn State/National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5), which revealed that advection inversions caused by continued southeast warm air flows at 825 hPa and radiation inversions near the ground induced the mixed layer at a height lower than 1200 m, which respectively hindered the atmospheric vertical and horizontal diffusions to result in the synchronous accumulation of air pollutants.