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Measurements of Trace Metal (Fe, Cu, Mn, Cr) Oxidation States in Fog and Stratus Clouds

Siefert, Ronald L. and Johansen, Anne M. and Hoffmann, Michael R. and Pehkonen, Simo O. (1998) Measurements of Trace Metal (Fe, Cu, Mn, Cr) Oxidation States in Fog and Stratus Clouds. Journal of the Air & Waste Management Association, 48 (2). pp. 128-143. ISSN 1096-2247. doi:10.1080/10473289.1998.10463659.

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The oxidation state of four transition metals (Fe, Mn, Cu, and Cr) in cloudwater has been investigated during several cloud events at Whiteface Mountain (NY), one cloud event at San Pedro Hill (CA), and one fog event at Bakersfield (CA). Samples were collected and immediately analyzed for the oxidation states of four transition metals: Fe(II) [44 measurements], Cu(I) [30 measurements], Mn(IV) [27 measurements], and Cr(III) [3 measurements]. Extreme care was taken to minimize contamination and interferences when measuring these oxidation states. Particulate and dissolved concentrations of these metals were also determined. Other measurements performed—relevant to the redox chemistry of these metals—included pH, total elemental concentrations (Fe, Cu, Mn, Cr, Al, K, Ca, Na, and Mg), organic anions (formate, acetate, glycolate, oxalate), inorganic anions (chloride, sulfate, nitrate, sulfite), cations (sodium, calcium, magnesium, potassium), peroxides, and formaldehyde. These measurements were then used in thermodynamic-speciation models to understand the speciation of ambient fog and cloudwater. From this analysis, two different cases were found for Fe(III)soluble speciation. Fe(III) was found to exist either as Fe(OH)_2 ^+ or Fe(Oxalate)_2. However, an unidentified strong chelating ligand with Fe(III) was also suggested by the data. Cu(I) and Cu(II) were calculated to be predominantly Cu^+ and Cu^(2+) (with less than 10% as Cu(II)-oxalate complexes). A chemical kinetic model was also used to investigate the transition-metal chemistry. The model results indicate that Fe(II) should be the predominant chemical form of Fe during daylight conditions. This prediction is in agreement with the field measurements in which the highest ratios of Fe(II)/Fe total were found in samples collected during the day. The model results also indicated that Fe(III) should be the predominant form of Fe during nighttime conditions, which is also in agreement with the field measurements. In the model, Cu(II) and Mn(II) were the predominant oxidation states during daylight and nighttime conditions with Cu(I) and Mn(III) increasing during daylight conditions. Mn(III) concentrations were never high enough to influence the redox chemistry of Cr. Overall, Cr(VI) in cloudwater is predicted to be reduced to Cr(III) if free S(IV) is present.

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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1998 Taylor & Francis. Published online: 27 Dec 2011. Special thanks are extended to Dr. K.L. Demerjian at the Atmospheric Sciences Research Center at WM, to Prof. Ted Murphy at BK, and to the Federal Aviation Administration staff at SP. We also thank Prof. J.J. Morgan of Caltech for helpful discussions. Support for this research has been provided by a grant from the National Science Foundation, Division of Atmospheric Sciences, Atmospheric Chemistry Section (ATM 9015775; ATM 9303024). This research was also sponsored by the U.S. Department of Energy, Office of Energy Research, Environmental Sciences Division, Office of Health and Environmental Research, under appointment to the Graduate Fellowships for Global Change administered by Oak Ridge Institute for Science and Education.
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NSFATM 9015775
NSFATM 9303024
Department of Energy (DOE)UNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20150812-143043894
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Official Citation:Ronald L. Siefert , Anne M. Johansen , Michael R. Hoffmann & Simo O. Pehkonen (1998) Measurements of Trace Metal (Fe, Cu, Mn, Cr) Oxidation States in Fog and Stratus Clouds, Journal of the Air & Waste Management Association, 48:2, 128-143, DOI: 10.1080/10473289.1998.10463659
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59457
Deposited By: Ruth Sustaita
Deposited On:13 Aug 2015 15:08
Last Modified:10 Nov 2021 22:20

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