Application of field portable X-ray fluorescence to the analysis of desert varnish samples in areas affected by coal-fired power plants

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doi:10.1071/EN11139

Environmental problems - Chemical approaches

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Application of field portable X-ray fluorescence to the analysis of desert varnish samples in areas affected by coal-fired power plants

Piotr Nowinski ^A ^D, Vernon F. Hodge ^B and Shawn Gerstenberger ^C

^A Clark Counry Department of Air Quality, 4701 W Russell Road., Suite 200, Las Vegas, NV 89118, USA.
^B Department of Chemistry, University of Nevada, Las Vegas, 4505 S Maryland Parkway, Box 454009, Las Vegas, NV 89145-4009, USA.
^C Department of Environmental and Occupational Health, University of Nevada, Las Vegas, 4505 S Maryland Parkway, Box 453064, Las Vegas, NV 89145-3064, USA.
^D Corresponding author. Email: nowinski@clarkcountynv.gov

Environmental Chemistry 9(4) 379-388 http://dx.doi.org/10.1071/EN11139
Submitted: 4 November 2011 Accepted: 14 May 2012 Published: 30 July 2012





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Environmental context. Rock surfaces are often covered with a dark coating called desert varnish that can capture and retain air pollutants. A field portable X-ray fluorescence spectrometer was used for direct non-destructive analysis of varnished rocks in the fallout zones of two coal-fired power plants. At one power plant where tracer studies had been carried out, the highest concentration of elements including Cr, As, Pb and Zn in the rock varnish samples, coincides with the peak tracer concentration locations.

Abstract. Desert varnish samples were collected near two coal-fired power plants to determine if the varnish contained a record of recent air pollution. Samples were collected: (1) in the fallout patterns of the shuttered Mohave Power Plant (MPP), located in Laughlin, NV; and (2) near the operating Reid-Gardner Power Plant (RGPP), just east of Las Vegas, NV. Small pieces of varnished rocks were analysed by field portable X-ray fluorescence spectroscopy (FPXRF). Results were obtained for 15 elements: Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Zr, Mo, Hg and Pb. The FPXRF data indicate that the elements commonly found in fly ash from coal-fired power plants (e.g. Cr, Zn, As and Pb) had significantly higher concentrations in the rock coatings in relation to the unvarnished substrate rock. For one of the power plants, where tracer plume studies had been carried out, the highest concentrations in the desert varnish coincided with the peak tracer concentration locations. Thus, these elements in desert varnish hold promise for identifying those geographical regions affected by nearby power plants. However, additional samples are required to demonstrate unequivocally that the power plants are indeed the sources of these elements. Overall, it is apparent that desert varnish can be utilised as a passive environmental monitor to investigate recent air pollution (past 20–30 years) and that FPXRF can be used as a surveying tool to obtain multi-element data from a large number of samples.

Additional keywords: air pollution, environmental monitoring, pollution sources, trace metals, XRF.

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