Persistent cold air pools and associated sustained haze pollution in Taiyuan Basin

Persistent cold air pools (PCAPs) frequently occur in mountain basins during winter and are critical meteorological phenomena leading to sustained haze pollution. However, the mechanisms linking PCAPs' evolution to air quality remain insufficiently understood, particularly in topographically complex regions such as Taiyuan Basin, China. This study investigated the meteorological features, relationships between haze and PCAPs, as well as the physical mechanism driving the PCAPs' evolution within Taiyuan Basin from 2018 to 2022. A refined identification method was developed based on multi-station meteorological and sounding observations, and the WRF model was validated to simulate PCAP-related meteorological conditions. A total of 56 PCAP events were identified, primarily occurring from September to March, with winter events commonly lasting over 48 h. These events were associated with enhanced surface-based inversions, increased valley heat deficit, and suppressed boundary layer ventilation capacity. A notable 12-h lag was found between valley heat deficit intensification and peak PM_2.5 concentrations (R = 0.55, p < 0.01), highlighting a delayed pollutant response to atmospheric stagnation. Case analysis revealed that warm advection aloft was the dominant mechanism maintaining PCAPs, while terrain-induced lee-side slope subsidence warming further reinforced their persistence. PCAPs' dissipation typically occurred following strong cold advection and boundary layer recovery. Overall, the life cycle of PCAPs in Taiyuan Basin is jointly modulated by synoptic-scale thermal advection and local terrain effects. These findings improve the understanding of haze formation in basin environments and offer valuable insights for air quality forecasting and mitigation in complex terrain.