• • Hainan's O3 pollution peaks in autumn and winter, while the Pearl River Delta (PRD) shows year-round O3 pollution, establishing PRD as the core control area for O3 in the three provinces.
• • Haikou's O3 and PM2.5 concentrations exhibit strong correlations with Zhanjiang and Maoming throughout the year, with correlations intensifying in winter, indicating significant regional transport linkages.
• • WPSCF analysis reveals that O3 pollution in Haikou is more dependent on stable cross-regional precursor transport and intense photochemical conditions, whereas PM2.5 transport pathways vary seasonally, with autumn driven by stable northeasterly winds and uniform pressure fields.
• • Lag effect analysis confirms that pollution exceedance days are substantially influenced by upwind transport from the previous day, highlighting the dominant role of cross-regional physical transport in driving pollution episodes.