Chemical and optical properties of atmospheric aerosol iron sources: coal fly ash and Icelandic dust


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Baldo, Clarissa (2022). Chemical and optical properties of atmospheric aerosol iron sources: coal fly ash and Icelandic dust. University of Birmingham. Ph.D.

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This thesis describes laboratory measurements of the chemical and physical properties of coal fly ash (CFA) and volcanic dust from Iceland which are important sources of atmospheric aerosol iron (Fe). These measurements are needed to determine the impacts of Fe-containing aerosols on the radiative balance and marine biogeochemistry and to reduce the uncertainty in model predictions. The spectral optical properties and size distribution of Icelandic dust were measured using the multi-instrument atmospheric simulation chamber CESAM (based at LISA CNRS, France). The Fe dissolution kinetics of CFA samples were determined by time-dependent leaching experiments that simulated atmospheric processing. A wide range of analytical techniques including X-ray diffraction (XRD) analysis, X-ray fluorescence (XRF) analysis, X-ray absorption near edge structure (XANES) analysis, and sequential extractions were used to determine the chemical and mineralogical composition in the samples with particular focus on the Fe mineralogy/speciation.

Our laboratory measurements indicate that the high ionic strength in the atmospheric aerosol water can strongly influence the Fe dissolution rates of CFA during the atmospheric transport. Our results also suggest that the Fe speciation is a key factor in determining the Fe solubility of CFA which varied considerably in different types of CFA. We also showed that CFA dissolves faster (up to 7 times) than mineral dust at similar experimental conditions. Based on these results, we developed a new Fe release scheme for coal combustion sources which has been implemented into the global atmospheric chemical transport model IMPACT to estimate the deposition flux of aerosol dissolved Fe to the ocean.
In addition, we built a new dataset on chemical composition, mineralogy, Fe solubility, size distribution, and optical properties of Icelandic dust and quantified the differences from typical low-latitude dust (e.g., from northern African and eastern Asian). Our results indicate that Icelandic dust could make a substantial contribution to dissolved Fe to the subpolar North Atlantic Ocean in particular in the Iceland Basin. Our results also suggest that in Icelandic dust magnetite is a major contribution to light absorption particularly between 660 and 950 nm, which can be 2-8 times higher than in low-latitude dust. This new dataset of chemical and physical parameters can be used in global models to estimate the deposition fluxes of aerosol dissolved Fe to the North Atlantic Ocean and to determine the radiative impact of Icelandic dust in the Arctic.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Life & Environmental Sciences
School or Department: School of Geography, Earth and Environmental Sciences, Department of Earth and Environmental Sciences
Funders: Natural Environment Research Council
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences


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