In recent years, satellite remote sensing has been increasingly used in the long-term observation of ozone (O.sub.3) precursors and its formation regime. In this work, formaldehyde (HCHO) data from Ozone Monitoring Instrument (OMI) were used to analyze the temporal and spatial distribution of HCHO vertical column densities (VCDs) in Shanghai from 2010 to 2019. HCHO VCDs exhibited the highest value in summer and the lowest in winter, the high VCD being concentrated in western Shanghai. Temperature largely influences HCHO by affecting the biogenic emissions and photochemical reactions, and industry was the major anthropogenic source. The satellite-observed formaldehyde-to-nitrogen dioxide ratio (FNR.sub.SAT) reflects that the O.sub.3 formation regime had significant seasonal characteristics and gradually manifested as a transitional ozone formation regime dominating in Shanghai. The uneven distribution in space was mainly reflected in the higher FNR.sub.SAT and surface O.sub.3 concentration in suburban areas. To compensate for the shortcoming of FNR.sub.SAT that it can only characterize O.sub.3 formation around satellite overpass time, correction of FNR.sub.SAT was implemented with hourly surface FNR and O.sub.3 data. After correction, the O.sub.3 formation regime showed the trend moving towards being VOC-limited in both time and space, and the regime indicated by FNR.sub.SAT can better reflect O.sub.3 formation for a day. This study can help us better understand HCHO characteristics and O.sub.3 formation regimes in Shanghai and also provide a method to improve FNR.sub.SAT for characterizing O.sub.3 formation in a day, which will be significant for developing O.sub.3 prevention and control strategies.