Using complex systems theory to comprehend the coordinated control effects of PM_2.5 and O₃ in Yangtze River Delta industrial base in China

Regional air pollution represents a multifaceted and dynamic system, rendering linear statistical approaches insufficient for capturing its inherent variability, particularly the intricate fluctuations of multiple pollution indicators. Therefore, this study investigates the synergistic evolution mechanisms of PM_2.5 and O₃ in four cities within China’s Yangtze River Delta industrial base from 2013 to 2022, employing complex systems theory. Initially, the presence of multifractality and long-term persistence between PM_2.5 and O₃ is confirmed in each city using the multifractal detrended cross-correlation analysis. Quantitative indicators are then established to evaluate the synergistic control effects of PM_2.5 and O₃. Furthermore, factors influencing coordinated control are analyzed using the ensemble empirical mode decomposition. Finally, the self-organized criticality (SOC) theory is introduced to elucidate dynamic pollution patterns. The results indicate the following: (1) Multifractality and long-term persistence exist between PM_2.5 and O₃ in the four cities, with persistence strengthening alongside the implementation of atmospheric pollution prevention and control policies. The application of complex systems theory facilitates the explanation and quantification of the synergistic control effectiveness of PM_2.5 and O₃. (2) Since 2013, with the exception of Nanjing, the coordinated control effects of PM_2.5 and O₃ in Shanghai, Hangzhou, and Suzhou have been unsatisfactory and have shown little improvement. (3) Compared to short-term pollution emissions from human activities, annual atmospheric control measures, periodic meteorological variations, and long-range transport of regional pollutants exert a greater influence on the synergistic regulation effects of PM_2.5 and O₃. (4) SOC may serve as the primary mechanism influencing the effectiveness of the synergistic regulation of PM_2.5 and O₃. Sudden events, such as epidemic control measures, can disrupt the existing balance between PM_2.5 and O₃, thereby diminishing the coordinated control effects.