To better understand the characteristics and processes of ozone formation over the industrial cluster of China, intensive field measurements of atmospheric O₃, volatile organic compounds (VOCs), and related parameters were conducted in a typical industrialized city of China, Zibo, from July 1 to July 31, 2018. Monitoring data and comparison with other observations revealed severe O₃ pollution in Zibo with high frequency (~55%) of the non-attainment O₃ episodes and high average O₃ levels (~42 ppbv). An observation-constrained chemical box model (OBM) was deployed to dissect the O₃ formation mechanism and ozone-precursor relationship during a severe photochemical smog episode. O₃ was produced by NO + HO₂ and NO + RO₂ reaction and destroyed via the NO₂ + RO₂ and NO₂ + OH reaction. The observed O₃ pollution was dominated by intense in-situ O₃ chemical formation with regional transport playing a negative contribution. Sensitivity studies suggested that in situ O₃ production was in a VOC-limited or mixed-control regime with aromatics (mainly 1,3,5-Trimethylbenzene and toluene) being the dominant parent hydrocarbons of O₃. The OBM and positive matrix factorization (PMF) results indicated that the most efficient way to alleviate the O₃ pollution in Zibo is to reduce emissions of aromatics from solvent use, industrial processes and vehicles.