| 08 Jul 2026
Size-resolved characterizations of Fe in aerosols in East Asian outflow in winter and spring: Source apportionment and bioaccessibility
Abstract. Trace metals in aerosol particles affect the Earth's radiative budget, human health, and ocean biogeochemistry. Semi-continuous measurements of the elemental composition of fine-mode (PM2.5) and total (PM10) aerosols and high-volume air sampling (5-d)/offline chemical analyses were conducted on a remote island of Japan in winter–spring 2023–2024 to characterize the source apportionment and water-soluble (i.e., bioaccessible) concentrations/fractions of trace elements such as Fe in the East Asian outflow region. Temporal variations in PM2.5 and PM10 Fe concentrations were classified into dust and non-dust contributions based on multilinear regression using concentrations of tracer species. Size-segregated water-soluble Fe fraction (fFe,sol) was investigated using dust Fe contributions and aging processes (e.g., transport time). Source apportionment (dust vs. non-dust) was essential to account for fFe,sol variations for PM2.5 aerosols, whereas those for coarse-mode aerosols were largely affected by aging processes. Temporal variations in total water-soluble Fe (Fesol) concentrations were strongly correlated with black carbon (BC) concentrations, indicating the role of continental combustion sources in enhancing Fesol concentrations in the outflow regions. The enhancement ratios of Fesol to BC concentrations were 53.8 (±11) ng µg−1 on average during the observation period and increased from ~40 ng µg−1 in winter to ~90 ng µg−1 in spring. This may reflect increased dust contributions to Fesol and reduced BC emissions from residential sector, as indicated by model analyses. These offer useful constraints for developing, validating, and refining numerical models of aerosol Fe behavior in the East Asian outflow.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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