the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Apr 2026
Assessment of aerosol iron (Fe) solubility using global dataset, Part I: Mechanisms underlying the inverse relationship between Fe solubility and Fe concentration
Abstract. Atmospheric deposition of aerosol iron (Fe) can stimulate marine primary productivity by supplying dissolved Fe (d-Fe) to the surface ocean, thereby potentially influencing the global climate. Aerosol Fe solubility (Fesol%) is closely linked to its bioavailability, and previous studies have shown that Fesol% generally increases as aerosol Fe concentration decreases. However, the mechanism underlying this widely observed inverse relationship remains unresolved. In this study, aerosol observations from East Asia, the North and South Pacific, and the Atlantic were compiled, and the ratios of total Fe to total Al (T-Fe/T-Al) and dissolved Fe to dissolved Al ([d-Fe]/[d-Al]) were used to estimate the contributions of mineral-derived and anthropogenic Fe to aerosol d-Fe, as well as the Fesol% of each source fraction. Aerosol d-Fe was found to be derived predominantly from mineral dust in many oceanic regions. In addition, both mineral-derived Fe and anthropogenic Fe showed inverse relationships between concentration and solubility. If the inverse relationship between Fe concentration and Fesol% were controlled mainly by simple two-component mixing between low-solubility mineral particles and highly soluble anthropogenic Fe, the Fesol% of each source fraction would not be expected to vary systematically with concentration. Instead, the results suggest that atmospheric chemical processing, together with depositional removal during transport, progressively increases the solubility of Fe remaining in aerosol particles. The ability to estimate the sources and dissolution processes of aerosol Fe from such fundamental concentration data may help improve the parameterization of aerosol Fe dissolution in global climate models.
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CC1: 'Comment on egusphere-2026-1613', Rui Li, 09 Apr 2026
The authors stated that "Limited knowledge of the seasonal variability of Fesol% further contributes to this uncertainty." (Page 3, line 44). I would like to bring to the authors' attention the two following papers which examined seasonal variations of aerosol iron solubility.ÂZhang, H. H., Li, R., Huang, C. P., Li, X. F., Dong, S. W., Wang, F., Li, T. T., Chen, Y. Z., Zhang, G. H., Ren, Y., Chen, Q. C., Huang, R. J., Chen, S. Y., Xue, T., Wang, X. M., and Tang, M. J.: Seasonal variation of aerosol iron solubility in coarse and fine particles at an inland city in northwestern China, Atmos. Chem. Phys., 23, 3543-3559, https://doi.org/3510.5194/acp-3523-3543-2023, 2023.ÂChen, Y. Z., Zhang, T. Y., Wang, Z. Y., Zhu, Z. M., Zhang, Y. F., Liu, M. Y., Wang, F., Ren, Y., Shi, G. L., Zhang, G. H., Wang, X. M., and Tang, M. J.: Sources of total and dissolved aerosol iron at Xi’an, Northwest China: implications for solubility of aerosol iron from different sources, J. Environ. Sci., 165, 29-37, https://doi.org/10.1016/j.jes.2025.06.066, 2026.ÂCitation: https://doi.org/
10.5194/egusphere-2026-1613-CC1 -
RC1: 'Comment on egusphere-2026-1613', Anonymous Referee #1, 12 May 2026
This is a synthesis study on Aerosol Iron fractional solubility, compiling all available soluble Al and Fe data over the Atlantic and Pacific oceans. This study has high scientific significance, improving our current understanding of aerosol iron solubility. This paper improves the understanding of the traditional hyperbolic relation between soluble iron and dust/Aluminum. The scientific quality and presentation quality of the paper are excellent and need minimal improvement. The synthesis of a relationship diagram between the EF T-Fe and [d-Fe]/[d-Al] ratio over a large geographical area has global significance. This study will also motivate atmospheric geochemists to make concordant observations of dissolved iron and aluminum. Before the publication of this manuscript, the author should address the few major corrections, which will improve the manuscript. In general, all axis labels for similar plots should be consistent and align with the text description.
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RC2: 'Comment on egusphere-2026-1613', Clifton Buck, 12 May 2026
The authors have assembled an impressive dataset of aerosol concentration data from previous studies as well as unpublished data of their own. Focusing on total and soluble aerosol iron, along with supporting data that includes total and soluble aluminum, they have attempted to better understand the long recognized inverse relationship between the amount of aerosol iron and its solubility. They explain the data using a previously published framework that associates the calculated enrichment factor of aerosol iron relative to the upper continental crust and the ratio of soluble iron to soluble aluminum. Based on this analysis, they conclude that observed increases in aerosol iron solubility are indicative of atmospheric processing during transport rather than simple mixing of high abundance, low solubility mineral aerosol with low abundance, high solubility anthropogenic aerosol.
The question of what processes and factors control aerosol iron solubility has bedeviled the research community and hampered progress in our ability to model this important input to the surface ocean. The methodology applied in this study shows promise, though its broad applicability is not clear. The soluble aerosol observations utilized in this study are biased toward ‘mild’ leaching techniques which may not be indicative of the ultimate aerosol solubility, and more so, the bioavailability of these aerosol derived trace elements. This comment is not an indictment of the study and certainly does not place it out of step with the current state of the art in the field. The work is an important contribution that could be improved with revision as detailed in the comments to follow.
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