Differences in ozone formation among urban, suburban, and rural areas: A case study in a typical industrial city in the North China plain.

In recent years, surface ozone (O3) pollution has become increasingly prominent in China. However, studies comparing O3 formation mechanisms across different zones remain limited. Clarifying O3 formation mechanisms across urban, suburban, and rural areas is crucial for formulating effective control strategies. In this study, comprehensive field observations of O3 and its precursors was conducted in August 2021 in Zibo, a typical industrial city in the North China Plain, at three representative sites: urban (Fangzhen, FZ), suburban (Tianzhen, TZ), and rural (Chengdong, CD). An observation-based model was employed to analyze the in-situ O3 formation process, radical budget, radical chain length, O3 formation sensitivity, and synergistic reduction strategies at the three sites. Results indicated that the urban-FZ site had the highest concentrations of nitrogen oxides (NOx) and reactive volatile organic compounds (VOCs), which promoted efficient O3 production through intense radical cycling. In contrast, the suburban-TZ site exhibited the lowest radical cycling efficiency, attributed to relatively lower VOC reactivity, lower NOx mixing ratios, and less favorable photochemical conditions. Despite having the lowest precursor concentrations, the rural-CD site showed the highest O3 concentrations, which were attributed to O3 transport processes. Additionally, analysis of the OH chain length indicated more efficient O3 production in polluted environments. Sensitivity analysis revealed that O3 formation at all three sites occurred under a VOC-limited regime. Based on simulations of synergistic reduction scenarios, to meet O3 attainment, the VOCs at CD and FZ should be at least 30%, with NOx reductions specified as 0-14% and > 6%, respectively. At TZ, the minimum reductions ratio of VOCs and NOx should be 10% and 0-7%. These findings deepen our understanding of O3 formation mechanisms and provide a scientific basis for urban-scale O3 prevention and control measures.