Environmental Sciences & Urban Planning

Air pollution control in Fujian Province showed a clear upward trend from 2016 to 2024, though improvement rates were uneven. Initially, all cities had composite indices below 0.6 in 2016, with over half below 0.5. A rapid surge occurred between 2019 and 2020, followed by a moderation into high-level refinement. By 2024, Longyan and Nanping stabilized above 0.85, most cities clustered in the 0.7-0.8 range, and interannual fluctuations narrowed. Regional disparities persisted, with Zhangzhou remaining the lowest-ranking city, not surpassing the 0.7 median. Spatially, air pollution control exhibits a pronounced gradient and clear regional clustering (Figure 2). High-composite zones (≥ 0.8) are concentrated in Nanping and Longyan, forming a stable 'inland dual-core.' Transition zones (0.7-0.8) include Fuzhou, Xiamen, Ningde, and sometimes Quanzhou and Putian, showing strong spatial continuity. Low-composite areas (below 0.6) are exemplified by Zhangzhou, remaining relatively isolated. The spatial pattern is characterized by 'dual-core leadership, gradient distribution, and localized lag,' with strong inter-regional differences yet close spatial linkages.

Sports venue construction is fundamental for addressing fitness facility gaps and promoting mass sports. From 2016 to 2024, Fujian Province saw overall growth with significant regional imbalance (Figure 3). Fuzhou, Xiamen, and Quanzhou acted as core engines, far outpacing other cities. The initial phase (2016-2020) involved volatile growth, including a universal dip in 2020, followed by rapid growth from 2021 onwards. The leading trio entered a mature stage with indices sustained above 0.75. However, initially lagging cities like Putian and Zhangzhou showed only modest growth, highlighting persistent regional disparity challenges. Spatially (Figure 4), Quanzhou, Xiamen, and Fuzhou dominate with a pronounced and stable coastal agglomeration. Zhangzhou and Putian, initially behind, showed accelerated growth, forming secondary zones around the high-value cores. Zhangzhou surpassed 0.2 in 2021 and rose above 0.4 by 2024, while Putian exited the low-value range in 2024. Ningde and Nanping remained below 0.2 for extended periods, forming a crescent-shaped low-value zone across northwestern inland Fujian, reflecting clear development lags. Overall, sports venue construction exhibits a pronounced three-tier gradient, robust and stable over the long term.

The coupling coordination degree model was applied to analyze the coordinated development between sports venue construction and air quality levels across the nine prefecture-level cities from 2016 to 2024 (Figure 5). During 2016-2020, Xiamen, Fuzhou, and Quanzhou consistently ranked highest in coupling coordination, with Xiamen showing particularly stable development (0.800 by 2020). Most other cities were below 0.500, indicating disordered or barely coordinated stages and significant regional imbalances. From 2021-2024, the province's coordinated development level significantly improved, with all cities transitioning out of the disordered recession state. Zhangzhou and Putian steadily ascended into the Coordinated development stage, while other cities showed slower but continuous improvement. Spatially (Figure 6), coordination exhibits clear gradient differentiation and clustered agglomeration. High coordination areas (Xiamen, Fuzhou, Quanzhou) exceed 0.9, forming a continuous high-value coastal corridor. Zhangzhou and Putian, as secondary zones, improved their coordination, reflecting partial spatial transmission. Ningde, Nanping, Sanming, and Longyan largely fall within the over-harmonization range (0.4-0.6), forming low-value plates that contrast with the coastal high-value corridor, showing significant regional disparities and strong inertia in the spatial structure. Typological differentiation (Figure 7) reveals distinct patterns: Fuzhou and Xiamen (balanced and mature), Quanzhou (improvement-oriented), Zhangzhou and Putian (latecomer catch-up), Sanming and Nanping (environmental advantage with weak coordination improvement), and Longyan and Ningde (intermediate stage). These paths reflect city-specific resource endowments, functional positioning, and governance strategies, highlighting multi-path synergy. In conclusion, air pollution control showed steady improvement, while sports venue construction rapidly expanded later. Coordination strengthened, but disparities persist. High-level regions exhibit spillover effects, but a significant gap remains with backward regions, risking solidification without targeted measures. The study notes limitations, including potential time lags in data and limited scope to six pollutants in one region, suggesting future dynamic analysis and expanded coverage.