title: Morphological and chemical characteristics of airborne tungsten particles of Fallon, Nevada.
abstract: Morphological and chemical characteristics were determined for airborne tungsten particles in Fallon, Nevada, a town that is distinguishable environmentally by elevated airborne tungsten and cobalt. From samples of airborne dust collected previously at six different places in Fallon, tungsten-rich dust particles were isolated and analyzed with automated electron microprobe and wavelength-dispersive spectrometry. Representative W particles were further analyzed using transmission electron microscopy. Morphologically, Fallon W particles are angular and small, with minimum and maximum sizes of < or = 1 microm and 5.9 microm in diameter, respectively. The number and size of tungsten-rich particles decrease in Fallon with distance from a hard-metal facility located near the center of town. Chemically, Fallon airborne W particles include mixtures of tungsten with cobalt plus other metals such as chromium, iron, and copper. No W-rich particles were identifiable as CaWO4 (scheelite) or MnWO4 (huebnerite). From d-spacings, Fallon particles are most consistent with identification as tungsten carbide. Based on these multiple lines of evidence, airborne W particles in Fallon are anthropogenic in origin, not natural. The hard-metal facility in Fallon processes finely powdered W and W-Co, and further investigation using tracer particles is recommended to definitively identify the source of Fallon's airborne tungsten.
authors.affiliation: Laboratory of Tree-Ring Research, University of Arizona, Tucson, Arizona 85721, USA. sheppard@ltrr.arizona.edu
authors.forename: Paul R
authors.initials: PR
authors.lastname: Sheppard
authors.forename: Paul
authors.initials: P
authors.lastname: Toepfer
authors.forename: Elaine
authors.initials: E
authors.lastname: Schumacher
authors.forename: Kent
authors.initials: K
authors.lastname: Rhodes
authors.forename: Gary
authors.initials: G
authors.lastname: Ridenour
authors.forename: Mark L
authors.initials: ML
authors.lastname: Witten