Intercity-scale linkage of cold-season PM 2.5 and emissions over South Korea: structural diagnostics from scalable spatial decomposition

Abstract Although national emission control policies have contributed to long-term reductions in PM 2.5 levels, responses across neighboring cities remain heterogeneous, complicating the evaluation of policy effectiveness. This study diagnoses the spatial structure and examines temporal evolution of intercity-scale (tens of kilometers) and neighborhood-scale (a few kilometers) PM 2.5 components, separated from background variation including long-range transport, by applying a recently proposed spatial decomposition framework based on spatial coherence to long-term air quality monitoring network data in South Korea (2016–2023). Within this framework, a hierarchical averaging scheme uses coherence-based neighboring stations to define the intercity-scale variability of background-removed PM 2.5 concentrations. Focusing on the cold season (DJFM), spatial diagnosis reveals dominant intercity-…