Multi-isotope constraints on PM2.5 source fingerprints across contrasting urban environments in South Korea under the East Asian monsoon

초록

In monsoon-influenced East Asia, PM2.5 reflects the interplay of emission mixtures, seasonal meteorology, and atmospheric processing, yet these controls differ among urban environments. We analyzed 14C fraction modern (F14C) and δ13C of total carbon (TC), and δ15N of total nitrogen (TN) in 237 PM2.5 samples collected from January 2021 to June 2022 across six contrasting urban environments in South Korea. Using a regime-based seasonal framework, we evaluate how seasonal changes in meteorology and chemistry alter aerosol composition, the fossil versus non-fossil split of carbon, and the separability of urban-specific source fingerprints. δ15N declined during nitrate-rich winter high-PM2.5 episodes, providing a clear isotopic marker of episodic nitrate enhancement. Radiocarbon apportionment showed that fossil carbon increased from cold to warm season at the coastal port city Busan, whereas non-fossil carbon increased at the megacity Seoul, highlighting season-specific and urban-specific control priorities. δ13C converged near −25‰ in the cold season, but northern cities remained relatively 13C-enriched, consistent with stronger regional transport and heating-related influence. In the warm season, Busan showed the lowest F14C (0.5 ± 0.1) and δ13C values consistent with liquid fossil-fuel influence, whereas the inland basin city Chuncheon showed high F14C (0.7 ± 0.1) and more C3-plant-like signatures. Together, these results show that winter observations are well suited for capturing high-PM2.5 regional episodes but often compress local source contrasts through synoptic mixing, whereas warm-season observations more effectively resolve place-specific source signatures. The findings provide a regime-based framework for season- and location-targeted PM2.5 mitigation in monsoon-affected East Asian cities. © 2026 The Authors

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