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Geology and hydrology of the Hartford Research Center CANEL site Middletown, Connecticut (1965)

Baker, J. A. ; Lang, S. M. ; Thomas, M. P.

Washington, DC : United States Gov. Print. Off.

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Call number: SR 90.0001(1133-G)

In: U.S. Geological Survey bulletin

Type of Medium: Series available for loan

Pages: IV, G-42 S. + 2 pl.

Series Statement: U.S. Geological Survey bulletin 1133-G

Language: English

Location: Lower compact magazine

Branch Library: GFZ Library

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Minor effect of physical size sorting on iron solubility of transported mineral dust (2011)

Shi, Z. ; Woodhouse, M. ; Carslaw, K. ; [et al.]

In: Atmospheric Chemistry and Physics

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Publication Date: 2020-02-12

Description: Observations show that the fractional solubility of Fe (FS-Fe, percentage of dissolved to total Fe) in dust aerosol increases considerably from 0.1% in regions of high dust mass concentration to 80% in remote regions where concentrations are low. Here, we combined laboratory geochemical measurements with global aerosol model simulations to test the hypothesis that the increase in FS-Fe is due to physical size sorting during transport. We determined the FS-Fe and fractional solubility of Al (FS-Al) in size-fractionated dust generated from two representative soil samples collected from known Saharan dust source regions using a customized dust re-suspension and collection system. The results show that the FS-Fe is size-dependent and ranges from 0.1-0.3% in the coarse size fractions (〉 1 mu m) to similar to 0.2-0.8% in the fine size fractions (〈 1 mu m). The FS-Al shows a similar size distribution to that of the FS-Fe. The size-resolved FS-Fe data were then combined with simulated dust mass concentration and size distribution data from a global aerosol model, GLOMAP, to calculate the FS-Fe of dust aerosol over the tropical and subtropical North Atlantic Ocean. We find that the calculated FS-Fe in the dust aerosol increases systematically from similar to 0.1% at high dust mass concentrations (e. g., 〉 100 mu gm(-3)) to similar to 0.2% at low concentrations (〈 100 mu gm(-3)) due to physical size sorting (i.e., particle gravitational settling). These values are one to two orders of magnitude smaller than those observed on cruises across the tropical and sub-tropical North Atlantic Ocean under an important pathway of Saharan dust plumes for similar dust mass concentrations. Even when the FS-Fe of sub-micrometer size fractions (0.18-0.32 mu m, 0.32-0.56 mu m, and 0.56-1.0 mu m) in the model is increased by a factor of 10 over the measured values, the calculated FS-Fe of the dust is still more than an order of magnitude lower than that measured in the field. Therefore, the physical sorting of dust particles alone is unlikely to be an important factor in the observed inverse relationship between the FS-Fe and FS-Al and the atmospheric mineral dust mass concentrations. The results suggest that processes such as chemical reactions and/or mixing with combustion particles are the main mechanisms to cause the increased FS-Fe in long-range transported dust aerosols.

Language: English

Type: info:eu-repo/semantics/article

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Influence of chemical weathering and aging of iron oxides on the potential iron solubility of Saharan dust during simulated atmospheric processing (2011)

Shi, Z. ; Krom, M. ; Bonneville, S. ; [et al.]

In: Global Biogeochemical Cycles

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Publication Date: 2020-02-12

Description: The flux of bioavailable Fe from mineral dust to the surface ocean is controlled not only by the processes in the atmosphere but also by the nature and source of the dust. In this study, we investigated how the nature of Fe minerals in the dust affects its potential Fe solubility (Fe-psol) employing traditional and modern geochemical, mineralogical, and microscopic techniques. The chemical and mineralogical compositions, particularly Fe mineralogy, in soil samples as dust precursors collected from North African dust source regions were determined. The Fe-psol was measured after 3 days of contact with sulfuric acid at pH 2 to simulate acid processes in the atmosphere. Fe-psol of the soil dust samples were compared with calculated predictions of Fe-psol based on the amount of individual Fe-bearing minerals present in the samples and Fe solubilities of corresponding standard minerals. The calculated Fe-psol deviated significantly from the measured Fe-psol of the soil dust samples. We attributed this to the variability in properties of Fe minerals (e. g., size of Fe oxides and heterogeneity of chemical compositions of clay minerals) in soil dusts in comparison to the standard minerals. There were, however, clear relationships between the degree of chemical weathering of North African soils and Fe-psol. The Parker index and ratio of ascorbate plus dithionite Fe to total Fe ((FeA+FeD)/FeT) are positively and negatively correlated with Fe-psol, respectively. In addition, the ratio of FeA/(FeA+FeD), which decreases with aging of the Fe oxides, was found to be positively correlated with Fe-psol in the soil dusts. Overall, our results indicate that there is a significant regional variability in the chemical and Fe mineralogical compositions of dusts across North African sources, as a result of the differences in chemical weathering and aging of Fe oxides. Furthermore, the indices for these weathering processes can provide an estimate of the fraction of Fe which can be solubilized if acid processed in the atmosphere.

Language: English

Type: info:eu-repo/semantics/article

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Impacts on iron solubility in the mineral dust by processes in the source region and the atmosphere: A review (2012)

Shi, Z. ; Krom, M. ; Jickells, T. ; [et al.]

In: Aeolian Research

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Publication Date: 2020-02-12

Description: Mineral dust is a complex entity containing a range of iron minerals including poorly crystalline to crystalline iron oxides to clay minerals. Important progress has been made to characterize iron mineralogical compositions in the dust recently. These include the quantification of the content of crystalline hematite and goethite, which appear to show a regional variation in North Africa as a result of the differences in the degree of chemical weathering. Fractional Fe solubility (dissolved to total iron, FFS) in the atmospheric aerosols has been reported to range from 0.1% to 80%. However, FFS is usually less than 0.5% in the non-atmospherically-processed dust, suggesting that FFS can be enhanced by atmospheric processes. One of the atmospheric processes, gravitational settling of dust, which has been previously hypothesized to cause the abovementioned enhancement of FFS during dust transport has been shown to be insignificant. Cycling of dust particles in the clouds, in which pH is usually higher than 4, and in the aerosol phase, in which pH is usually substantially lower, can significantly affect iron speciation and FFS. Laboratory experiments showed that a significant amount of iron (〉0.5%) can only be solubilized in the dust when pH is lower than 4. These laboratory data suggest that acid processing rather than cloud processing might be a prime mechanism to cause an increase in FFS in the dust during transport. Further laboratory studies, field measurements, and modelling are needed to increase the ability of models to quantify the atmospheric processing of iron in the dust. (c) 2012 Elsevier B.V. All rights reserved.

Language: English

Type: info:eu-repo/semantics/article

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Iron dissolution kinetics of mineral dust at low pH during simulated atmospheric processing (2011)

Shi, Z. ; Bonneville, S. ; Krom, M. ; [et al.]

In: Atmospheric Chemistry and Physics

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Publication Date: 2020-02-12

Description: We investigated the iron (Fe) dissolution kinetics of African (Tibesti) and Asian (Beijing) dust samples at acidic pH with the aim of reproducing the low pH conditions in atmospheric aerosols. The Beijing dust and three size fractions of the Tibesti dust (〈 20 mu m: PM20; 〈 10 mu m: PM10; and 〈 2.5 mu m: PM2.5) were dissolved at pH 1, 2 and/or 3 for up to 1000 h. In the first 10 min, all dust samples underwent an extremely fast Fe solubilisation. Subsequently, the Fe dissolution proceeded at a much slower rate before reaching a stable dissolution plateau. The time-dependant Fe dissolution datasets were best described by a model comprising three acid-extractable Fe pools each dissolving according to first-order kinetics. The dissolution rate constant k (h(-1)) of each pool was independent of the source (Saharan or Asian) and the size (PM20, PM10 or PM2.5) of the dust but highly dependent on pH. The "fast" Fe pool had a k (25 h(-1) at pH = 1) of a similar magnitude to "dry" ferrihydrite nanoparticles and/or poorly crystalline Fe(III) oxyhydroxide, while the "intermediate" and "slow" Fe pools had k values respectively 50-60 times and 3000-4000 times smaller than the "fast" pool. The "slow" Fe pool was likely to consist of both crystalline Fe oxide phases (i.e., goethite and/or hematite) and Fe contained in the clay minerals. The initial mass of the "fast", "intermediate" and "slow" Fe pools represented respectively about 0.5-2%, 1-3% and 15-40% of the total Fe in the dust samples. Furthermore, we showed that in systems with low dust/liquid ratios, Fe can be dissolved from all three pools, whereas at high dust/liquid ratios (e.g., in aerosols), sufficient Fe may be solubilised from the "fast" phase to dominate the Fe dissolved and to suppress the dissolution of Fe from the other Fe pools. These data demonstrated that dust/liquid ratio and pH are fundamental parameters controlling Fe dissolution kinetics in the dust. In order to reduce errors in atmospheric and climate models, these fundamental controlling factors need to be included.

Language: English

Type: info:eu-repo/semantics/article

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