Spatiotemporal Variability Analysis of PM_2.5 and O₃ Pollution Characteristics in the Fenwei Plain

The Fenwei Plain (FWP) is a typical basin-type region in northern China characterized by complex PM_2.5 and O₃ composite pollution. Based on hourly monitoring data from 11 cities (2015-2024), this study integrated the Mann-Kendall test, standard deviation ellipse (SDE), spatio-temporal cross-correlation function (STCCF), and spatio-temporal geographically weighted regression (GTWR) to systematically analyze decadal pollution patterns and coupling mechanisms. Results revealed a profound transition from particulate-dominated to photochemical-regime pollution: PM_2.5 concentrations decreased significantly by 32%, whereas MDA8 O₃ rose by 47%. Spring emerged as the critical compound pollution window, accounting for 66.7% of simultaneous exceedances. Spatially, both pollutants maintained a consistent Northeast-Southwest orientation, with PM_2.5 hotspots concentrated along the Weihe River Valley. Cluster analysis categorized the 11 cities into O₃-dominant, compound-high-risk, and PM_2.5-dominant clusters. Furthermore, a dominant positive synergy was observed on an annual scale, although a localized "see-saw" effect occurred at a 150-200 km distance with a 3-year lag. The GTWR model demonstrated high robustness (R²: 0.75-0.86), underscoring the influence of localized driving forces. These findings provide a scientific basis for synergistic governance and precision air quality management in northern basin-type regions.