In this study, an online monitoring platform for vertical measurement of air pollutants was established atop a tall building (623 m), namely, the Shanghai Tower. Moreover, air pollutants such as CO, NO2, O3 and particles with an aerodynamic diameter of 2.5 μm or smaller (PM2.5) were measured vertically at nine different heights. Based on continuous measurement data from June to November 2019, the seasonal and daily variation characteristics of the vertical profiles of these air pollutants in Shanghai were analyzed. The results indicated that CO, NO2 and PM2.5 generally showed a decreasing trend from the near ground to a height of 105 m, and the NO2 concentration continued to decrease to less than 20 μg m−3 above 600 m. The PM2.5 concentration fluctuated with height. However, the O3 concentration increased with height in general and the increase was more significant at higher altitudes in summer, with an increase rate of 1.28 μg m−3/10 m above 415 m. CO and PM2.5 tended to be impacted by regional transport in higher altitudes in autumn. Besides, a typical air pollution event in summer was analyzed to elucidate the detailed evolution process of the vertical concentration distribution. The obtained vertical observation data clearly revealed the impact of planetary boundary layer (PBL) structure that the sudden decline of planet boundary layer height (PBLH) by nearly 2/3 in an hour led to the explosive growth of O3 at all heights, especially at 105–255 m. Our study demonstrates that the established vertical online monitoring platform plays an important role in comprehensively capturing the vertical structure of urban air quality and explaining the air pollution evolution processes.