Article pubs.acs.org/est
Coal Fly Ash as a Source of Iron in Atmospheric Dust Haihan Chen,† Alexander Laskin,‡ Jonas Baltrusaitis,§ Christopher A. Gorski,⊥ Michelle M. Scherer,# and Vicki H. Grassian*,†,§ †
Departments of Chemical and Biochemical Engineering, §Chemistry, and #Civil and Environmental Engineering, University of Iowa, Iowa City, Iowa 52242, United States ‡ W. R. Wiley Environmental Molecular Science Laboratory, Pacific Northwest National Laboratories, Richland, Washington 99352, United States ⊥ Environmental Chemistry, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, 8600 Duebendorf, Switzerland S Supporting Information *
ABSTRACT: Anthropogenic coal fly ash (FA) aerosol may represent a significant source of bioavailable iron in the open ocean. Few measurements have been made that compare the solubility of atmospheric iron from anthropogenic aerosols and other sources. We report here an investigation of iron dissolution for three FA samples in acidic aqueous solutions and compare the solubilities with that of Arizona test dust (AZTD), a reference material for mineral dust. The effects of pH, simulated cloud processing, and solar radiation on iron solubility have been explored. Similar to previously reported results on mineral dust, iron in aluminosilicate phases provides the predominant component of dissolved iron. Iron solubility of FA is substantially higher than of the crystalline minerals comprising AZTD. Simulated atmospheric processing elevates iron solubility due to significant changes in the morphology of aluminosilicate glass, a dominant material in FA particles. Iron is continuously released into the aqueous solution as FA particles break up into smaller fragments. These results suggest that the assessment of dissolved atmospheric iron deposition fluxes and their effect on the biogeochemistry at the ocean surface should be constrained by the source, environmental pH, iron speciation, and solar radiation.
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INTRODUCTION Iron is an essential nutrient for marine organisms since it is required in various metabolic processes.1−3 Biological productivity is limited by iron bioavailability in extensive regions of the ocean referred to as high nutrient low chlorophyll (HNLC) regions.4−6 It has been generally thought that soluble iron is mainly derived from the transport and deposition of mineral dust.7−11 While soils have relatively low iron solubility, the high solubility of atmospheric iron observed in field studies has been explained by the atmospheric chemical processing of dust particles during long-range transport.9,12−20 The solubility of aerosol iron is also influenced by the iron speciation in the aerosol source material.21−26 Recent evidence from field, modeling, and laboratory studies suggests that fly ash produced from fossil fuel combustion and biomass burning may also represent an important source of bioavailable iron.10,23,24,27−33 Although the source of bioavailable iron from combustion is not important globally ( mineral dust. Aerosol iron solubility is strongly influenced by the source material. Anticipated increases in energy production from fossil fuel and coal combustion have the potential to exert significant effects on the magnitude and spatial distribution of soluble iron deposition to the open ocean. Compared to the increased flux of windblown mineral dust caused by the global expansion of arid and semiarid regions, increased industrialization, coal combustion, and biomass burning in developing countries (such as China and India) would play a more significant role in increasing soluble iron species to regions of the ocean. While the emission of FA coincides with the emission of trace acidic gases, such as SO2 and NOx, the interaction of FA with acidic gases would further enhance their iron solubility. Current global-biogeochemical models have generally assumed that the fractional solubility of aerosol iron is constant at 1−2% because of the limitation of data available on iron solubility.65−69 As indicated in the current study, this assumption was insufficient to capture the iron distribution on a global scale. Given the potential disintegration of FA particles during long-range transport, the treatment of atmospheric processing of anthropogenic iron-containing aerosols such as FA will be very different from mineral dust aerosol. The assessment of dissolved atmospheric iron deposition fluxes and their effect on surface ocean biogeochemistry should be constrained by taking into account the source, pH, Fe speciation, and solar radiation in future modeling efforts.
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Article
AUTHOR INFORMATION
Corresponding Author
*Phone: (319)335-1392. Fax: (319)353-1115. E-mail:
[email protected].
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ACKNOWLEDGMENTS This material is based on upon work supported by the National Science foundation under Grant CHE1012037. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not reflect the views of the National Science Foundation. A. Laskin acknowledges support by Laboratory Directed Research and Development funds of Pacific Northwest National Laboratory (PNNL). The CCSEM/EDX analysis was performed at the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at PNNL. Pacific Northwest National Laboratory is operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract No. DE-AC06-76RLO 1830.
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REFERENCES
(1) Martin, J. H.; Gordon, R. M.; Fitzwater, S. E. The case for iron. Limnol. Oceanogr. 1991, 36 (8), 1793−1802. (2) Falkowski, P. G.; Barber, R. T.; Smetacek, V. Biogeochemical controls and feedbacks on ocean primary production. Science 1998, 281 (5374), 200−206. (3) Morel, F. M. M.; Price, N. M. The biogeochemical cycles of trace metals in the oceans. Science 2003, 300 (5621), 944−947. (4) Martin, J. H. Glacial-interglacial CO2 change: The iron hypothesis. Paleoceanography 1990, 5 (1), 1−13. (5) Martin, J. H.; Coale, K. H.; Johnson, K. S.; Fitzwater, S. E.; Gordon, R. M.; Tanner, S. J.; Hunter, C. N.; Elrod, V. A.; Nowicki, J. L.; Coley, T. L.; Barber, R. T.; Lindley, S.; Watson, A. J.; Vanscoy, K.; Law, C. S.; Liddicoat, M. I.; Ling, R.; Stanton, T.; Stockel, J.; Collins, C.; Anderson, A.; Bidigare, R.; Ondrusek, M.; Latasa, M.; Millero, F. J.; Lee, K.; Yao, W.; Zhang, J. Z.; Friederich, G.; Sakamoto, C.; Chavez, F.; Buck, K.; Kolber, Z.; Greene, R.; Falkowski, P.; Chisholm, S. W.; Hoge, F.; Swift, R.; Yungel, J.; Turner, S.; Nightingale, P.; Hatton, A.; Liss, P.; Tindale, N. W. Testing the iron hypothesis in ecosystems of the equatorial pacific-ocean. Nature 1994, 371 (6493), 123−129. (6) Moore, J. K.; Doney, S. C.; Glover, D. M.; Fung, I. Y. Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean. Deep-Sea Res., Part II 2002, 49 (1−3), 463−507. (7) Duce, R. A.; Tindale, N. W. Atmospheric transport of iron and its deposition in the ocean. Limnol. Oceanogr. 1991, 36 (8), 1715−1726. (8) Fung, I. Y.; Meyn, S. K.; Tegen, I.; Doney, S. C.; John, J. G.; Bishop, J. K. B. Iron supply and demand in the upper ocean. Global Biogeochem. Cycles 2000, 14 (1), 281−295. (9) Mahowald, N. M.; Baker, A. R.; Bergametti, G.; Brooks, N.; Duce, R. A.; Jickells, T. D.; Kubilay, N.; Prospero, J. M.; Tegen, I. Atmospheric global dust cycle and iron inputs to the ocean. Global Biogeochem. Cycles 2005, 19 (4), GB4025, DOI: 10.1029/ 2004GB002402. (10) Mahowald, N. M.; Engelstaedter, S.; Luo, C.; Sealy, A.; Artaxo, P.; Benitez-Nelson, C.; Bonnet, S.; Chen, Y.; Chuang, P. Y.; Cohen, D. D.; Dulac, F.; Herut, B.; Johansen, A. M.; Kubilay, N.; Losno, R.; Maenhaut, W.; Paytan, A.; Prospero, J. A.; Shank, L. M.; Siefert, R. L. Atmospheric iron deposition: Global distribution, variability, and human perturbations. Annu. Rev. Mar. Sci. 2009, 1, 245−278. (11) Jickells, T. D.; An, Z. S.; Andersen, K. K.; Baker, A. R.; Bergametti, G.; Brooks, N.; Cao, J. J.; Boyd, P. W.; Duce, R. A.; Hunter, K. A.; Kawahata, H.; Kubilay, N.; laRoche, J.; Liss, P. S.; Mahowald, N.; Prospero, J. M.; Ridgwell, A. J.; Tegen, I.; Torres, R. Global iron connections between desert dust, ocean biogeochemistry, and climate. Science 2005, 308 (5718), 67−71.
ASSOCIATED CONTENT
* Supporting Information S
A summary table of the physical and chemical properties of all three FA samples (Table S1); correlation coefficients calculated for Fe dissolution and Fe speciation in all three FA samples (Table S2); SEM images and elemental maps of FA 2690 and 2691(Figure S1); Mössbauer spectral fitting results (Figure S2); elemental maps of processed FA particles (Figure S3); Fe dissolution measurements as a function of time under simulated cloud processing (Figure S4); Fe dissolution under irradiation conditions as a function of time (Figure S5). This material is available free of charge via the Internet at http://pubs.acs.org. 2118
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Article
(30) Sholkovitz, E. R.; Sedwick, P. N.; Church, T. M. Influence of anthropogenic combustion emissions on the deposition of soluble aerosol iron to the ocean: Empirical estimates for island sites in the North Atlantic. Geochim. Cosmochim. Acta 2009, 73 (14), 3981−4003. (31) Kumar, A.; Sarin, M. M.; Srinivas, B. Aerosol iron solubility over Bay of Bengal: Role of anthropogenic sources and chemical processing. Mar. Chem. 2010, 121 (1−4), 167−175. (32) Upadhyay, N.; Majestic, B. J.; Herckes, P. Solubility and speciation of atmospheric iron in buffer systems simulating cloud conditions. Atmos. Environ. 2011, 45 (10), 1858−1866. (33) Furutani, H.; Jung, J.; Miura, K.; Takami, A.; Kato, S.; Kajii, Y.; Uematsu, M. Single-particle chemical characterization and source apportionment of iron-containing atmospheric aerosols in Asian outflow. J. Geophys. Res. 2011, 116 (D18), D18204, DOI: 10.1029/ 2011JD015867. (34) Li, W.; Shao, L. Transmission electron microscopy study of aerosol particles from the brown hazes in northern China. J. Geophys. Res. 2009, 114 (D9), D09302, DOI: 10.1029/2008JD011285. (35) Vlasenko, A.; Sjögren, S.; Weingartner, E.; Gäggeler, H. W.; Ammann, M. Generation of submicron Arizona test dust aerosol: Chemical and hygroscopic properties. Aerosol Sci. Technol. 2005, 39, 452−460. (36) Laskin, A.; Cowin, J. P.; Iedema, M. J. Analysis of individual environmental particles using modern methods of electron microscopy and X-ray microanalysis. J. Electron Spectrosc. Relat. Phenom. 2006, 150 (2−3), 260−274. (37) Baltrusaitis, J.; Usher, C. R.; Grassian, V. H. Reactions of sulfur dioxide on calcium carbonate single crystal and particle surfaces at the adsorbed water carbonate interface. Phys. Chem. Chem. Phys. 2007, 9 (23), 3011−3024. (38) Cwiertny, D. M.; Baltrusaitis, J.; Hunter, G. J.; Laskin, A.; Scherer, M. M.; Grassian, V. H. Characterization and acid-mobilization study of iron-containing mineral dust source materials. J. Geophys. Res. 2008, 113 (D5), D05202, DOI: 10.1029/2007JD009332. (39) Rancourt, D. G.; Ping, J. Y. Voigt-based methods for arbitraryshape static hyperfine parameter distributions in Mössbauer spectroscopy. Nucl. Instrum. Methods Phys. Res., Sect. B 1991, 58 (1), 85−97. (40) Fu, H.; Cwiertny, D. M.; Carmichael, G. R.; Scherer, M. M.; Grassian, V. H. Photoreductive dissolution of Fe-containing mineral dust particles in acidic media. J. Geophys. Res. 2010, 115 (D11), D11304, DOI: 10.1029/2009JD012702. (41) Pruppacher, H. R.; Jaenicke, R. The processing of water vapor and aerosols by atmospheric clouds, a global estimate. Atmos. Res. 1995, 38 (1−4), 283−295. (42) Spokes, L. J.; Jickells, T. D. Factors controlling the solubility of aerosol trace metals in the atmosphere and on mixing into seawater. Aquat. Geochem. 1995, 1 (4), 355−374. (43) Mackie, D. S.; Boyd, P. W.; Hunter, K. A.; McTainsh, G. H. Simulating the cloud processing of iron in Australian dust: pH and dust concentration. Geophys. Res. Lett. 2005, 32 (6), L06809, DOI: 10.1029/2004GL022122. (44) Norton, G. A.; Markuszewski, R.; Shanks, H. R. Morphological and chemical characterization of iron-rich fly ash fractions. Environ. Sci. Technol. 1986, 20 (4), 409−413. (45) Kutchko, B. G.; Kim, A. G. Fly ash characterization by SEMEDS. Fuel 2006, 85 (17−18), 2537−2544. (46) Hansen, L. D.; Silberman, D.; Fisher, G. L.; Eatough, D. J. Chemical speciation of elements in stack-collected, respirable-size, coal fly ash. Environ. Sci. Technol. 1984, 18 (3), 181−186. (47) Dyar, M. D. A review of Mössbauer data on trioctahedral micas Evidence fortetrahedral Fe3+ and cation ordering. Am. Mineral. 1987, 72 (1−2), 102−112. (48) Dyar, M. D.; Agresti, D. G.; Schaefer, M. W.; Grant, C. A.; Sklute, E. C. Mössbauer spectroscopy of Earth and planetary materials. Annu. Rev. Earth Planet. Sci. 2006, 34 (1), 83−125. (49) Winburn, R. S.; Grier, D. G.; McCarthy, G. J.; Peterson, R. B. Rietveld quantitative X-ray diffraction analysis of NIST fly ash standard reference materials. Powder Diffr. 2000, 15 (3), 163−172.
(12) Zhuang, G. S.; Yi, Z.; Duce, R. A.; Brown, P. R. Link between iron and sulfur cycles suggested by detection of Fe(II) in remoate marine aerosols. Nature 1992, 355 (6360), 537−539. (13) Pehkonen, S. O.; Siefert, R.; Erel, Y.; Webb, S.; Hoffmann, M. R. Photoreduction of iron oxyhydroxides in the presenc of important atmospheric organic-compounds. Environ. Sci. Technol. 1993, 27 (10), 2056−2062. (14) Zhu, X.; Prospero, J. M.; Savoie, D. L.; Millero, F. J.; Zika, R. G.; Saltzman, E. S. Photoreduction of iron(III) in marine mineral aerosol solutions. J. Geophys. Res. 1993, 98 (D5), 9039−9046. (15) Spokes, L. J.; Jickells, T. D.; Lim, B. Solubilization of aerosol trace-metals by cloud processing - A laboratory study. Geochim. Cosmochim. Acta 1994, 58 (15), 3281−3287. (16) Zhu, X. R.; Prospero, J. M.; Millero, F. J. Diel variability of soluble Fe(II) and soluble total Fe in North African dust in the trade winds at Barbados. J. Geophys. Res. 1997, 102 (D17), 21297−21305. (17) Johansen, A. M.; Siefert, R. L.; Hoffmann, M. R. Chemical composition of aerosols collected over the tropical North Atlantic Ocean. J. Geophys. Res. 2000, 105 (D12), 15277−15312. (18) Meskhidze, N.; Chameides, W. L.; Nenes, A.; Chen, G. Iron mobilization in mineral dust: Can anthropogenic SO2 emissions affect ocean productivity. Geophys. Res. Lett. 2003, 30 (21), 2085, DOI: 10.1029/2003GL018035. (19) Solmon, F.; Chuang, P. Y.; Meskhidze, N.; Chen, Y. Acidic processing of mineral dust iron by anthropogenic compounds over the north Pacific Ocean. J. Geophys. Res. 2009, 114, D02305, DOI: 10.1029/2008JD010417. (20) Shi, Z.; Krom, M. D.; Bonneville, S.; Baker, A. R.; Jickells, T. D.; Benning, L. G. Formation of iron nanoparticles and increase in iron reactivity in mineral dust during simulated cloud processing. Environ. Sci. Technol. 2009, 43 (17), 6592−6596. (21) Veranth, J. M.; Smith, K. R.; Huggins, F.; Hu, A. A.; Lighty, J. S.; Aust, A. E. Mössbauer spectroscopy indicates that iron in an aluminosilicate glass phase is the source of the bioavailable iron from coal fly ash. Chem. Res. Toxicol. 2000, 13 (3), 161−164. (22) Journet, E.; Desboeufs, K. V.; Caquineau, S.; Colin, J. L. Mineralogy as a critical factor of dust iron solubility. Geophys. Res. Lett. 2008, 35 (7), L07805, DOI: 10.1029/2007GL031589. (23) Schroth, A. W.; Crusius, J.; Sholkovitz, E. R.; Bostick, B. C. Iron solubility driven by speciation in dust sources to the ocean. Nat. Geosci. 2009, 2 (5), 337−340. (24) Trapp, J. M.; Millero, F. J.; Prospero, J. M. Trends in the solubility of iron in dust-dominated aerosols in the equatorial Atlantic trade winds: Importance of iron speciation and sources. Geochem. Geophys. Geosyst. 2010, 11 (3), Q03014, DOI: 10.1029/ 2009GC002651. (25) Shi, Z.; Bonneville, S.; Krom, M. D.; Carslaw, K. S.; Jickells, T. D.; Baker, A. R.; Benning, L. G. Iron dissolution kinetics of mineral dust at low pH during simulated atmospheric processing. Atmos. Chem. Phys. 2011, 11 (3), 995−1007. (26) Shi, Z. B.; Krom, M. D.; Bonneville, S.; Baker, A. R.; Bristow, C.; Drake, N.; Mann, G.; Carslaw, K.; McQuaid, J. B.; Jickells, T.; Benning, L. G. Influence of chemical weathering and aging of iron oxides on the potential iron solubility of Saharan dust during simulated atmospheric processing. Global Biogeochem. Cycles 2011, 25, GB2010, DOI: 10.1029/2010GB003837. (27) Chuang, P. Y.; Duvall, R. M.; Shafer, M. M.; Schauer, J. J. The origin of water soluble particulate iron in the Asian atmospheric outflow. Geophys. Res. Lett. 2005, 32 (7), L07813, DOI: 10.1029/ 2004GL021946. (28) Sedwick, P. N.; Sholkovitz, E. R.; Church, T. M. Impact of anthropogenic combustion emissions on the fractional solubility of aerosol iron: Evidence from the Sargasso Sea. Geochem. Geophys. Geosyst. 2007, 8, Q10Q06, DOI: 10.1029/2007GC001586. (29) Luo, C.; Mahowald, N.; Bond, T.; Chuang, P. Y.; Artaxo, P.; Siefert, R.; Chen, Y.; Schauer, J. Combustion iron distribution and deposition. Global Biogeochem. Cycles 2008, 22 (1), GB1012, DOI: 10.1029/2007GB002964. 2119
dx.doi.org/10.1021/es204102f | Environ. Sci. Technol. 2012, 46, 2112−2120
Environmental Science & Technology
Article
(50) McBride, M. B. Environmental Chemistry of Soils; Oxford University Press: New York, 1994. (51) Gieré, R.; Carleton, L. E.; Lumpkin, G. R. Micro- and nanochemistry of fly ash from a coal-fired power plant. Am. Mineral. 2003, 88 (11−12), 1853−1865. (52) Gieré, R.; Blackford, M.; Smith, K. TEM study of PM2.5 emitted from coal and tire combustion in a thermal power station. Environ. Sci. Technol. 2006, 40 (20), 6235−6240. (53) Davison, R. L.; Natusch, D. F. S.; Wallace, J. R.; Evans, C. A. Trace elements in fly ash. Dependence of concentration on particle size. Environ. Sci. Technol. 1974, 8 (13), 1107−1113. (54) Zhu, X. R.; Prospero, J. M.; Millero, F. J.; Savoie, D. L.; Brass, G. W. The solubility of ferric iron in marine mineral aerosol solutions at ambient relative humidities. Mar. Chem. 1992, 38 (1−2), 91−107. (55) Desboeufs, K. V.; Losno, R.; Vimeux, F.; Cholbi, S. The pHdependent dissolution of wind-transported Saharan dust. J. Geophys. Res. 1999, 104 (D17), 21287−21299. (56) Stumm, W.; Morgan, J. J. Aquatic chemistry: chemical equilibria and rates in natural waters, 3rd ed.; John Wiley & Sons: New York, 1996. (57) Vassilev, S. V.; Menendez, R.; Borrego, A. G.; Diaz-Somoano, M.; Rosa Martinez-Tarazona, M. Phase-mineral and chemical composition of coal fly ashes as a basis for their multicomponent utilization. 3. Characterization of magnetic and char concentrates. Fuel 2004, 83 (11−12), 1563−1583. (58) Bacci, P.; Del Monte, M.; Longhetto, A.; Piano, A.; Prodi, F.; Redaelli, P.; Sabbioni, C.; Ventura, A. Characterization of the particulate emission by a large oil fuel fired power plant. J. Aerosol. Sci. 1983, 14 (4), 557−572. (59) Stumm, W.; Lee, G. F. Oxygenation of ferrous iron. Ind. Eng. Chem. 1961, 53 (2), 143−146. (60) Millero, F. J.; Sotolongo, S.; Izaguirre, M. The oxidation-kinetics of Fe(II) in seawater. Geochim. Cosmochim. Acta 1987, 51 (4), 793− 801. (61) Desboeufs, K. V.; Losno, R.; Colin, J. L. Factors influencing aerosol solubility during cloud processes. Atmos. Environ. 2001, 35 (20), 3529−3537. (62) Baker, A. R.; Jickells, T. D. Mineral particle size as a control on aerosol iron solubility. Geophys. Res. Lett. 2006, 33 (17), L17608, DOI: 10.1029/2006GL026557. (63) Miller, W. L.; King, D. W.; Lin, J.; Kester, D. R. Photochemical redox cycling o iron in coastal seawater. Mar. Chem. 1995, 50 (1−4), 63−77. (64) Cunningham, K. M.; Goldberg, M. C.; Weiner, E. R. Mechanisms for aqueous photolysis of adsorbed benzoate, oxalate, and succinate on iron oxyhydroxide (goethite) surfaces. Environ. Sci. Technol. 1988, 22 (9), 1090−1097. (65) Archer, D. E.; Johnson, K. A model of the iron cycle in the ocean. Global Biogeochem. Cycles 2000, 14 (1), 269−279. (66) Aumont, O.; Maier-Reimer, E.; Blain, S.; Monfray, P. An ecosystem model of the global ocean including Fe, Si, P colimitations. Global Biogeochem. Cycles 2003, 17 (2), 1060, DOI: 10.1029/ 2001GB001745. (67) Gregg, W. W.; Ginoux, P.; Schopf, P. S.; Casey, N. W. Phytoplankton and iron: validation of a global three-dimensional ocean biogeochemical model. Deep-Sea Res., Part II 2003, 50 (22−26), 3143−3169. (68) Moore, J. K.; Doney, S. C.; Lindsay, K. Upper ocean ecosystem dynamics and iron cycling in a global three-dimensional model. Global Biogeochem. Cycles 2004, 18 (4), GB4028, DOI: 10.1029/ 2004GB002220. (69) Moore, J. K.; Doney, S. C. Iron availability limits the ocean nitrogen inventory stabilizing feedbacks between marine denitrification and nitrogen fixation. Global Biogeochem. Cycles 2007, 21 (2), GB2001, DOI: 10.1029/2006GB002762.
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