Effective air quality management requires a comprehensive understanding of how meteorological variability and emission changes shape multiannual changes in regional PM_2.5 pollution. During the cold seasons of 2015–2017, persistent PM_2.5 pollution occurred in the Pearl River Delta (PRD), South China, despite rapid emission reductions. This study systematically investigated the interconnections between climate variability, meteorology, PM_2.5 levels, source contributions and budgets during these periods, aiming to uncover the detailed impacts of meteorological and emission changes on PM_2.5 pollution. We found that drastic meteorological changes, closely linked to a transition from strong El Niño (2015) to weak/moderate La Niña (2017), were the main drivers of the three-year PM_2.5 changes. Strengthened northerly winds and reduced humidity enhanced cross-regional PM_2.5 transport into the PRD while concurrently suppressing local PM_2.5 production and accumulation. WRF/CMAQ simulations indicate that transport (non-local) contributions to PM_2.5 in the PRD increased from 70 % in 2015 to 74 % in 2016 and 78 % in 2017. While the transport of secondary inorganic PM_2.5 components overall intensified, their responses to meteorological and emission changes varied: Variations in sulfate were more sensitive to emission reductions outside the PRD, whereas those for nitrate were primarily driven by meteorological shifts. Simulated PM_2.5 mass budgets further support the increasing dominance of transport, especially via advections. Our findings underscore the potentially crucial role of meteorological variability in driving multiannual PM_2.5 pollution changes in the PRD and other regions strongly impacted by cross-regional transport, emphasizing the necessity for regionally coordinated emission control strategies to effectively mitigate PM_2.5 pollution.