Surface ozone (O₃) is influenced by regional background and local photochemical formation under favorable meteorological conditions. Understanding the contribution of these factors to changes in O₃ is crucial to address the issue of O₃ pollution. In this study, we propose a novel integrated method that combines random forest, principal component analysis, and Shapley additive explanations to distinguish observed O₃ into meteorologically affected ozone (O_{3_MET}), chemically formed from local emissions (O_{3_LC}), and regional background ozone (O_{3_RBG}). Applied to three typical stations in Shanghai during the warm season from 2013 to 2021, the results indicate that O_{3_RBG} in Shanghai was 48.8 ± 0.3 ppb, accounting for 79.6%–89.4% at different sites, with an overall declining trend of 0.018 ppb/yr. O_{3_LC} at urban and regional sites ranged from 5.9–9.0 ppb and 8.9–14.6 ppb, respectively, which were significantly higher than the contributions of 2.5–7.4 ppb at an upwind background site. O_{3_MET} can be categorized into those affecting O₃ photochemical generation and those changing O₃ dispersion conditions, with absolute contributions to O₃ ranging from 13.4–19.0 ppb and 13.1–13.7 ppb, respectively. We found that the O₃ rebound in 2017, compared to 2013, was primarily influenced by unfavorable O₃ dispersion conditions and unbalanced emission reductions; while the O₃ decline in 2021, compared to 2017, was primarily influenced by overall favorable meteorological conditions and further emissions reduction. These findings highlight the challenge of understanding O₃ change due to meteorology and regional background, emphasizing the need for systematic interpretation of the different components of O₃.