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.

General comments

The stable isotope ratio of Fe has been used for source apportionment of total and soluble aerosol Fe. However, there are still large uncertainties in the δ56Fe endmember values for aerosol Fe from various sources. The authors collected and measured δ56Fe for fly and bottom ash samples. The measurements conducted in this study might contribute to a better understanding of the mechanisms of isotopic fractionation. However, the misuse of the heavy δ56Fe endmember values for fly ash samples would contradict observational facts. Moreover, the caveats in recommendations for future work and conclusion should be carefully considered for the interpretation in the main text. Major revisions are needed before this manuscript can be considered for publication in ACP.

Major comment

1. Please clarify that the heavy δ56Fe samples are captured as large particles before the emission into the ambient atmosphere. Additionally, please measure δ56Fe for the raw materials (except biofuel burning) and for actual aerosols in the ambient atmosphere to suggest the use of δ56Fe endmember values for the ambient aerosols, and discuss the mechanisms of isotopic fractionation. Since these isotopically heavy Fe aerosols (except biofuel burning) are captured or retained before being emitted to the atmosphere, the actual aerosols in the ambient atmosphere could be lighter, as the volume mean diameters of fly ash samples are mostly a few tens of μm, which are considerably larger than those for submicron aerosols with light δ56Fe. Please reconsider the interpretation throughout the manuscript.
2. Please separate the discussion of δ56Fe between biofuel burning and open biomass burning, as aerosol Fe during open biomass burning is mainly derived from soil-suspended particles.

Specific comments

l.122, l.128, and l.168: Please explain the size and collection method of the particles.

l.334: Even though domestic biofuel burning may not be representative of wildfires, why did you compare it with open biomass burning? Please reconsider the interpretation to explain the meaning of the comparison throughout the manuscript.

l.385: Please separate the discussion between biofuel burning and open biomass burning.

l.404: Previous studies used δ56Fe for the aerosols in the ambient atmosphere, not assumed δ56Fe captured before being emitted into the atmosphere. Since these isotopically heavy Fe aerosols as large particles cannot be emitted to the atmosphere owing to the emission control devices, the actual aerosols in the ambient atmosphere can be lighter. Please discuss the mechanisms of isotopic fractionation.

l.433: The earlier study does not contradict the mechanisms of isotopic fractionation during the evaporation-condensation process in combustion. Industrial particles (< 50 µm) were collected prior to emission, so that the actual aerosols emitted into the ambient atmosphere can be smaller particles with lighter δ56Fe. The aerosol particles collected on impaction plates can include mineral dust aerosols, so that the average δ56Fe of total Fe is similar to that for desert dust Fe. Please provide more precise information and reconsider the interpretation.

Technical comments

l.238: Please correct this to Figure 2.