Abstract: Urban clusters, characterized by the most polluted areas, are key hotspots for air pollution research. The Lanzhou urban cluster, a typical region with high emissions and strict regulatory intervention, provides an ideal case study for studying pollution dynamics. This study analyzes the spatiotemporal variations, abrupt changes, and extreme events of aerosol optical depth (AOD) in the Lanzhou urban cluster during 2000-2023, integrating an analysis of the associated circulation drivers. The results show that: (1) AOD exhibits a distinct spatial distribution (0.26-0.38), with lower AOD values in the northern and western regions and higher levels in the main urban area, exhibiting the more pronounced changes in the urban periphery than in the stable urban center. These patterns are intrinsically linked to emission sources, inter-city pollutant transport, and management measures. (2) Dust dominates AOD compositions (80%-95%), followed by sulfate, while organic carbon, black carbon and sea salt contribute the least. Spatially, sulfate, organic carbon, black carbon, and sea salt shows a pattern of high concentrations in the southeast and low concentration in the northwest, whereas dust shows the opposite trend, with high concentrations in the north and west, and low concentrations in the southeast. Temporally, the relative contributions of these components remained consistent throughout the study period. (3) After 2018, a marked AOD decrease coincided with the positive geopotential height anomalies and negative planetary boundary layer height anomalies which theoretically hinder pollutant dispersion, contradicting expectations. This apparent paradox underscores the overriding role of emission reductions and sustained environmental governance in driving air quality improvements. The extreme heavy pollution events in the Lanzhou cluster and heavy pollution events in the southern region are associated with positive geopotential height anomalies and normal planetary boundary layer height anomalies, which theoretically favor dispersion. These episodes highlight the persistent challenges of high emissions and inadequate regulatory enforcement. In contrast, the heavy pollution in the northern regional is due to the synergistic effects of topographic confinement and negative anomalies in local planetary boundary layer height, which exacerbates pollution accumulation. Conversely, extreme clean events characterized by negative anomalies in geopotential height and planetary boundary layer height benefited from enhanced dispersion. This study shows that air pollution in the Lanzhou urban cluster is mainly influenced by emission policy interventions and modulated by regional circulation drivers.