Spatiotemporal Evolution and Geographic Detection of Driving Factors for PM_2.5-O₃ Composite Pollution in Shandong Province

Based on air quality data,meteorological data,and urban construction data from 2016 to 2024,the spatiotemporal evolution and driving mechanisms of PM_2.5-O₃ composite pollution in Shandong Province were explored by using Pearson correlation coefficient and geographic detector.The results showed that: ①The monthly mean concentrations of PM_2.5 and O₃ showed a "wave-shaped" change characteristic with alternating peaks and troughs,and the amplitude of PM_2.5 fluctuations decreased year by year,alongside a general trend of declining concentration values.O₃ exhibits a "bimodal" pattern,with peaks mostly occurring in June and September.Spatially,PM_2.5 concentrations increased progressively from east to west,while O₃ showed a pattern of higher in the east than in the west and higher in the south than in the north.② From 2016 to 2024,the number of days of compound pollution decreased from 14.2 days to 3.5 days,with April and October being the high-incidence periods.The O₃/PM_2.5 ratio increased from 0.41 to 1.77,and the pollution period shortened from 8 months to 2 months.③Correlation analysis showed that PM_2.5 was significantly positively correlated with CO,NO₂ and SO₂,whereas O₃ was significantly negatively correlated with these three pollutants.The correlation between the two pollutants in compound pollution showed a "positive in summer,negative in winter" pattern,with a gradual shift towards positive correlation in winter over the years.Geographic detectors analysis identified relative humidity as the dominant natural driving factor affecting compound pollution,while particulate matter emissions and the total number of motor vehicles were the core anthropogenic influencing factors.