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Chemical characterization of ambient aerosol collected during the southwest monsoon and intermonsoon seasons over the Arabian Sea: Labile-Fe(II) and other trace metals

Siefert, Ronald L. and Johansen, Anne M. and Hoffmann, Michael R. (1999) Chemical characterization of ambient aerosol collected during the southwest monsoon and intermonsoon seasons over the Arabian Sea: Labile-Fe(II) and other trace metals. Journal of Geophysical Research D, 104 (D3). pp. 3511-3526. ISSN 0148-0227. doi:10.1029/1998JD100067.

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Atmospheric deposition of iron (Fe) to certain regions of the oceans is an important nutrient source of Fe to the biota, and the ability of the biota to uptake Fe is dependent on the speciation of the Fe. Therefore understanding the speciation of Fe in the atmosphere is critical to understanding the role of Fe as a nutrient source in surface ocean waters. Labile ferrous iron (Fe(II)) concentrations as well as total concentrations for Fe and other important trace metals, cations, and anions were determined over the Arabian Sea for two nonconsecutive months during 1995. Ambient aerosol samples were collected during the Indian Ocean intermonsoon and southwest monsoon seasons over the Arabian Sea. Sampling took place aboard the German research vessel Meteor in the months of May (leg M32/3; intermonsoon) and July/August (leg M32/5; southwest monsoon). Both cruise tracks followed the 65th east meridian, traveling for 30 days each (from north to south during leg M32/3 and from south to north during leg M32/5). A high-volume dichotomous virtual impactor with an aerodynamic cutoff size of 3 μm was used to collect the fine and coarse aerosol fractions for metal analysis. A low volume collector was used to collect aerosol samples for anion and cation analysis. The analysis for labile-Fe(II) was done immediately after sample collection to minimize any possible Fe redox reactions which might occur during sample storage. The analytical procedure involved filter extraction in a formate/formic acid buffered solution at pH 4.2 followed by colorimetric quantification of soluble Fe(II). Metals, anions, and cations were analyzed after the cruise. Total atmospheric aqueous-labile-Fe(II) concentrations during the intermonsoon were between 4.75 and <0.4 ng m−3, of which most (>80%) was present in the fine fraction (<3.0 μm). During the southwest monsoon, atmospheric aqueous-labile-Fe(II) concentrations were consistently below the detection limit (<0.34 to <0.089 ng m^(−3), depending on the volume of air sampled). Air mass back trajectories (5 day, three dimensional) showed that air masses sampled during the southwest monsoon had advected over the open Indian Ocean, while air masses sampled during the intermonsoon had advected over northeast Africa, the Saudi Arabian peninsula, and southern Asia. These calculations were consistent with the results of the statistical analysis performed on the data set which showed that the variance due to crustal species during the intermonsoon samples was greater than the variance due to crustal species during the southwest monsoon. The factor scores for the crustal components were also greater when the back trajectories had advected over the nearby continental masses. Principal component analysis was also performed with the intermonsoon samples where aqueous labile Fe(II) was above the detection limit. Aqueous labile Fe(II) did not correlate well with other species indicating possible atmospheric processing of the iron during advection.

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Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1999 American Geophysical Union. Article first published online: 21 Sep 2012. Received July 2, 1998; revised October 20, 1998; accepted October 26, 1998. Special thanks are extended to the crew of the FS Meteor for their help. We also thank J. J. Morgan (Caltech) and M. O. Andreae (Max Planck Institute for Chemistry, Mainz, Germany) 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
Global Change Graduate FellowshipUNSPECIFIED
Issue or Number:D3
Record Number:CaltechAUTHORS:20150807-112623546
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Official Citation:Siefert, R. L., A. M. Johansen, and M. R. Hoffmann (1999), Chemical characterization of ambient aerosol collected during the southwest monsoon and intermonsoon seasons over the Arabian Sea: Labile-Fe(II) and other trace metals, J. Geophys. Res., 104(D3), 3511–3526, doi:10.1029/1998JD100067.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59314
Deposited By: Ruth Sustaita
Deposited On:10 Aug 2015 16:05
Last Modified:10 Nov 2021 22:18

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