EVS atmospheric scientist Yan Feng is working in collaboration with the beamline scientist Barry Lai of Argonne's Advanced Photon Source (APS) facility and university researchers (e.g., Georgia Tech, Rutgers University, and Cornell University) to unravel the chemical transformation mechanisms of iron in atmospheric dust. This effort is an extension from the three-year research project, entitled “Probing the Chemistry of Atmospheric Dust Particles using X-ray Spectromicroscopy: Implications for Climate Science” and funded by the Laboratory Director's Competitive Grant (2014-2016), strives to address the variations in composition of iron compounds and the dissolution mechanisms involved in the atmospheric transport of dust particles. It combines the synchrotron-based X-ray techniques developed at APS with modeling studies using the high-performance computing capabilities at the Argonne Leadership Computing Facility (ALCF) and the Argonne Laboratory Computing Resource Center (LCRC).
Iron is an essential micronutrient for marine ecosystems. In many ocean regions, it controls the primary production (as organic compounds produced by photosynthetic organisms) and sequestration of carbon dioxide from the atmosphere. Iron in atmospheric dust is a major source of iron (about 95%) for marine ecosystems; therefore, it is critical to understand the factors controlling its solubility and associated bioavailability. Although many hypotheses have been proposed, the chemistry surrounding the dissolution of atmospheric (aerosol) iron is still not well understood. Earth System models conventionally assume a constant rate of iron solubility in dust, which could lead scientists to miscalculate carbon dioxide sequestration, especially in iron-limited oligotrophic waters. Our study addresses the uncertainties in modeled global soluble iron inputs to the ocean ecosystems. Its results will improve the effectiveness of Earth System models, making them more effective tools in understanding ocean biogeochemical cycles and their impact on climate change.
Modern microscopy and microanalysis techniques, such as the X-ray fluorescence (XRF) microspectroscopy developed and advanced at APS, provide scientists the unique capability of probing the mineral composition of individual dust particles. These synchrotron-based techniques have been used mostly in studying interplanetary stardust and have only recently been applied to the study of atmospheric particles. Elements such as iron, silicon, calcium, and aluminum in micron-sized atmospheric dust particles (10-7 to 10-5 meters) can easily be measured using hard X-ray microscopy at the APS beamlines in X-ray fluorescence mode for quantities down to the trace level in the real atmosphere. Using the APS microspectropy beamlines (e.g., 2-ID-D), we can further determine the oxidization states of iron (iron (II) or iron (III)) in dust particles, which is linked to the solubility and bioavailability of iron.
Over the last several years, EVS and collaborators have performed beamline tests on more than a hundred dust samples provided by university collaborators from Rutgers, Georgia Tech, Amity University, University of Hawaii, and University of Paris. These samples were collected from seven locations: the Southern Ocean, the Mediterranean, the Atlantic Ocean, Hawaii, Bermuda, Patagonia, and India. They represent a wide range of dust aerosol characteristics from different source regions and remote oceans. To date, we have analyzed the chemical information for a few hundred individual dust particles.
Strong evidence of reductive iron transformation by acidic pollutants is found in these samples, as well as indicators of the proton-induced reactions that are typically considered in atmospheric models. Because iron reduction reactions occur in different environments from acid processing, our study highlights the importance of modeling the reductive mechanism to capture variations in dust iron dissolution. A few manuscripts have been published on the main findings of this project using the APS synchrotron-based X-ray techniques for climate science applications:
- Longo, A. F., Y. Feng, B. Lai, W. M. Landing, R. U. Shelley, A. Nenes, N. Mihalopoulos, K. Violaki, and E. Ingall, Influence of Atmospheric Processes on the Solubility and Composition of Iron in Saharan Dust, Environ. Sci. Technol., 50 (13), 6912–6920, doi: 10.1021/acs.est.6b02605, 2016.
- Ingall, E., Y. Feng, A. Longo, B. Lai, R. Shelley, W. Landing, P. Morton, A. Nenes, N. Mihalopoulos, K. Violaki, Y. Gao, S. Sahai, and E. Castorina, Enhanced Iron Solubility at Low pH in Global Aerosols, Atmosphere, 9, 201; doi: 10.3390/atmos9050201, 2018.
- McDaniel, M. F.; Ingall, E.; Morton, P.; Castorina, E.; Weber, R.; Shelley, R.; Landing, W.; Longo, A.; Feng, Y.; Lai, B., Relationship between atmospheric aerosol mineral surface area and iron solubility, ACS Earth and Space Chemistry, doi: 10.1021/acsearthspacechem.9b00152, Publication Date (Web): 18 Sep, 2019.
- Meskhidze, N., C. Voelker, H. Al-Abadleh, K. Barbeau, M. Bressac, C. Buck, R. Bundy, P. Croot, Y. Feng, A. Ito, A. M. Johansen, W. Landing, J. Mao, S. Myriokefalitakis, Daniel Ohnemus, Benoît Pasquier, and Y. Ye, 2019: Perspective on Identifying and Characterizing the Processes Controlling Iron Speciation and Residence Time at the Atmosphere-Ocean Interface, Marine Chemistry, Volume 217, 103704, doi: 10.1016/j.marchem.2019.103704, 2019.
The developed data set has been utilized by a broad science community to develop and improve the model representation of dust iron dissolution processes and bioavailable iron cycle in the Earth System models. We have also developed a computational efficient iron dissolution model for the Community Earth System Model (CESM). These modeling studies are documented in the recent high impact journal publications including the Science Advances:
- Ito, S. Myriokefalitakis, M. Kanakidou, N. M. Mahowald, R. A. Scanza, D. S. Hamilton, A. R. Baker, T. Jickells, M. Sarin, S. Bikkina, Y. Gao, R. U. Shelley, C. S. Buck, W. M. Landing, A. R. Bowie, M. M. G. Perron, C. Guieu, N. Meskhidze, M. S. Johnson, Y. Feng, J. F. Kok, A. Nenes, R. A. Duce, Pyrogenic iron: The missing link to high iron solubility in aerosols. Science Advances, 5, eaau7671, doi: 10.1126/sciadv.aau7671, 2019.
- Hamilton, D. S., Scanza, R. A., Feng, Y., Guinness, J., Kok, J. F., Li, L., Liu, X., Rathod, S. D., Wan, J. S., Wu, M., and Mahowald, N. M.: Improved methodologies for Earth system modelling of atmospheric soluble iron and observation comparisons using the Mechanism of Intermediate complexity for Modelling Iron (MIMI v.1.0), Geosci. Model Dev., 12, 3835-3862. doi: 10.5194/gmd-12-3835-2019, 2019.
Our on-going effort is to build on the iron dissolution model developed for CESM and develop a modeling capability of bioavailable iron in the DOE Energy Exascale Earth System model (E3SM). This research work has now been integrated as part of the E3SM project funded by the DOE, Office of Science, Office of Biological and Environmental Research.
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