Spatial–Temporal Variability of PM2.5 and Ozone Pollution in the Huaihai Economic Zone of China

Fine particulate matter (PM2.5)and ozone (O3) compound pollution poses an important air-quality challenge in rapidly industrializing regions, and their relationships are affected by complex emission, chemical, and meteorological processes. This study investigates the long-term variations in PM2.5 and O3 and their relationships with anthropogenic emissions in the Huaihai Economic Zone of eastern China. Using Multi-resolution Emission Inventory for China (MEIC) emission data (2000–2020) and PM2.5 and O3 concentration data (2000–2023), emission trends, emission–concentration relationships, sectoral emission contributions, and sensitivity to meteorological and temporal variability were analyzed. PM2.5 emissions and concentrations declined markedly after approximately 2013, whereas volatile organic compound (VOC) emissions increased until approximately 2015 before declining; O3 concentrations generally increased after an earlier declining phase. The original monthly analysis revealed a strong negative relationship between PM2.5 emissions and O3 concentrations (r = −0.773), while further adjustment for meteorological variability, seasonality, and long-term trends substantially modified this relationship (r = 0.137 after strict adjustment). The associations between precursor emissions and O3 concentrations also varied under different adjustment scenarios, reflecting the complexity of emission–O3 relationships in the Huaihai Economic Zone. Sector-resolved MEIC analysis showed that Xuzhou had larger contributions from power generation to PM2.5 and nitrogen oxides (NOx) emissions and from solvent use to VOC emissions compared with the broader Huaihai Economic Zone. Overall, this study provides a long-term characterization of PM2.5–O3 pollution evolution in the Huaihai Economic Zone and demonstrates the importance of considering emission structure, meteorological variability, and temporal trends when analyzing emission–concentration relationships.