Identification of anthropogenic Fe originated from East Asia using Fe stable isotope ratios of aerosols collected on Fukue Island

Atmospheric aerosol is an important source of iron (Fe) to the ocean surface. However, contributions of natural and anthropogenic sources remain poorly constrained. Although the iron stable isotope ratio (δ 56 Fe) is a useful tracer of Fe sources, the endmember values for anthropogenic Fe are still uncertain. In this study, aerosols were collected on Fukue Island, a location suitable for observing aerosol transport from East Asia to the North Pacific, to estimate the representative δ 56 Fe of anthropogenic Fe and to investigate its controlling factors. Total and soluble Fe concentrations in fine particles (< 2.5 μm) increased from winter to spring, with δ 56 Fe ranging from –2.21‰ to –0.07‰. Enrichment factors and trace element concentrations indicated a shift from an anthropogenic to a mineral dust regime. A good correlation between the δ 56 Fe and the inverse of total Fe concentration indicated a mixing of natural and anthropogenic Fe with particular δ 56 Fe values. The anthropogenic δ 56 Fe endmember was estimated to be –3.3±1.2‰, which likely reflects a constant mixing of evaporated (negative δ 56 Fe) and non-evaporated (positive δ 56 Fe) anthropogenic Fe. The contributions of anthropogenic Fe to total and soluble Fe concentrations were estimated to be 25±15% and 53±21%, respectively, highlighting its significant contribution to the soluble phase, especially in winter. Atmospheric chemical transport model suggests the majority of Fe in anthropogenic Fe originated from coal and steel industry in East Asia. As the model suggests, contributions of different anthropogenic Fe sources vary globally. Therefore, further observations in diverse regions are necessary in future. • Isotope ratio (δ 56 Fe) of anthropogenic Fe in East Asia was estimated as –3.3±1.2‰. • Mixing of evaporated and non-evaporated Fe sources determines anthropogenic δ 56 Fe. • Anthropogenic Fe concentrations remained stable from winter to spring. • Anthropogenic contributions to total and soluble Fe in PM 2.5 were 25±15% and 53±21%. • Model shows anthropogenic Fe mainly from coal and steel industry in East Asia.