Abstract
The compounding effects of urban thermal environment (TE) degradation and air pollution pose severe threats to public health. However, the complex modulating mechanisms of urban morphology on these synergistic risks remain insufficiently decoded. Focusing on Beijing (2014–2024), this study integrates long-term multi-source data, the Local Climate Zone (LCZ) framework, and machine learning to systematically investigate the spatiotemporal synergies between Land Surface Temperature (LST) and air quality (PM2.5 and O3). Results reveal divergent evolutionary rhythms between the two compound risks, demonstrating that extreme meteorological events (e.g., heatwaves and dust storms) can exceed the physical buffering thresholds of urban climates, thereby disrupting established environmental steady states. Mechanistically, specific spatial configurations bifurcate localized aerodynamic and thermodynamic outcomes: fragmented built environments with massive emissions (LCZ 1–8) are strongly associated with stagnation zones, whereas highly homogeneous flatlands (LCZ D/9) degenerate into passive settling sinks. Crucially, we uncover a pollutant-specific divergence regarding three-dimensional urban forests (LCZ A and B). While dense high-canopy vegetation effectively mitigates PM2.5, it paradoxically exacerbates O3 risks under severe thermal stress, a phenomenon highly likely linked to heat-induced biogenic emissions and subsequent photochemical catalysis. Furthermore, inappropriate dense greening within highly compact overheated cores can severely obstruct aerodynamic connectivity. This obstruction contributes to a dual paradox of chemical catalysis and aerodynamic stagnation. These findings challenge conventional “one-size-fits-all” greening strategies, advocating for a paradigm shift towards targeted morphological interventions—such as aerodynamic unlocking and windward interception—to build climate-resilient cities.
Keywords: Urban compound risk; Local Climate Zone (LCZ); spatiotemporal synergy; thermal environment; air quality; climate-resilient planning.