| 14 Jul 2026
Isotopic composition of aerosol iron from anthropogenic sources: implications for source apportionment of aerosol iron
Abstract. Aerosol iron (Fe) significantly impacts human health, atmospheric chemistry and marine biogeochemistry. The stable isotope ratio of Fe, typically reported as δ56Fe, has emerged as a promising method for source apportionment of total and soluble aerosol Fe. However, the δ56Fe endmember values remain poorly constrained for aerosol Fe from various non-dust sources, impeding the application of Fe isotopes in atmospheric research. This work measured isotopic compositions for aerosol Fe from desert dust and several anthropogenic sources. The average δ56Fe was determined to be +0.14 ± 0.10 ‰ for the seven dust samples we examined, in good agreement with previous work. We found that different anthropogenic aerosols exhibit a wide range of Fe isotopic composition. Compared to desert dust, the average δ56Fe was found to be higher for power plant coal fly ash (+0.26 ± 0.18 ‰, n = 28), slightly lower for steelwork fly ash (−0.07 ± 0.41 ‰, n = 18), and considerably lower for biofuel burning aerosol (−0.28 ± 0.39 ‰, n = 11). In addition, the average δ56Fe was determined to be +0.20 ± 0.12 ‰ (n = 2) for municipal incineration fly ash, +0.38 ± 0.13 ‰ (n = 1) for heavy oil bottom ash, and +0.08 ± 0.13 ‰ for certificated urban particulate matter sample (n = 1). We suggest that not all the anthropogenic aerosol Fe is isotopically lighter than natural dust Fe, in contrast to what is conventionally assumed. Our findings also imply that Fe isotope-based source apportionment must account for the δ56Fe endmember variability both among and within different anthropogenic aerosols. Overall, our work substantially improves our ability to constrain δ56Fe endmember values from various anthropogenic sources.
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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General comments:
The submitted MS egusphere-2026-3780 highlights new iron isotopes measurements in anthropogenic aerosol samples. This research work highlights “Isotopic composition of aerosol iron from anthropogenic source”. This study has high scientific significance, improving our current understanding of iron isotopic source signatures. There are very few studies discussing Fe isotope signature in anthropogenic aerosol, which makes this MS special. This manuscript perfectly fits with journal criteria. The scientific quality and presentation quality of the paper are excellent and need minimal improvement. The new Fe isotope data on anthropogenic aerosol will improve source apportionment capability by enhancing end member criteria. Before the publication of this manuscript, the author should address few minor corrections, which will improve the manuscript quality. Those corrections are listed below
Specific comments:
Line 106-108: “In contrast to what is conventionally assumed, we found….” this is the result/ conclusion of the paper, it will be ideal if you include in the conclusion section not in the introduction section.
Line-188-189: Author conducted sequential protocol at 120 oC, using 1) HNO3-HF, 2) H2O2-HNO3, 3) Aqua Regia, and 4) HCl, respectively. Is it necessary to conduct step-2, in general H2O2-HNO3 used for removing organic matter and volatiles as a predigestion step. Authors were also followed the same for their fly ash samples (line-193-195). If they followed two different methods, it should be justified with proper descriptions as well as references.
Section-2.2.2 (line-199-209) references for the purification steps should be included.