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Desert Varnish As an Indicator of Modern-Day Air Pollution in Southern Nevada

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Desert Varnish As an Indicator of Modern-Day Air Pollution in Southern Nevada UNLV Theses, Dissertations, Professional Papers, and Capstones 2009 Desert varnish as an indicator of modern-day air pollution in southern Nevada Piotr Nowinski University of Nevada Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Analytical Chemistry Commons, Environmental Sciences Commons, and the Geology Commons Repository Citation Nowinski, Piotr, "Desert varnish as an indicator of modern-day air pollution in southern Nevada" (2009). UNLV Theses, Dissertations, Professional Papers, and Capstones. 459. http://dx.doi.org/10.34917/1391234 This Dissertation is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Dissertation in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/or on the work itself. This Dissertation has been accepted for inclusion in UNLV Theses, Dissertations, Professional Papers, and Capstones by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. DESERT VARNISH AS AN INDICATOR OF MODERN-DAY AIR POLLUTION IN SOUTHERN NEVADA by Piotr Nowinski Bachelor of Science, Chemistry University of Nevada, Las Vegas 1988 Master of Science, Chemistry University of Nevada, Las Vegas 1993 A dissertation submitted in partial fulfillment of the requirements for the Doctor of Philosophy in Environmental Science Department of Environmental Studies Greenspun College of Urban Affairs Graduate College University of Nevada, Las Vegas December 2009 Copyright by Piotr Nowinski 2010 All Rights Reserved THE GRADUATE COLLEGE We recommend that the dissertation prepared under our supervision by Piotr Nowinski entitled Desert Varnish as an Indicator of Modern-Day Air Pollution in Southern Nevada be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Environmental Studies Vernon F. Hodge, Committee Chair Krystyna A. Stave, Committee Member Shawn Gerstenberger, Committee Member Moses Karakouzian, Graduate Faculty Representative Ronald Smith, Ph. D., Vice President for Research and Graduate Studies and Dean of the Graduate College December 2009 ii ABSTRACT Desert Varnish as an Indicator of Modern-Day Air Pollution in Southern Nevada by Piotr Nowinski Dr. Vernon Hodge, Examination Committee Chair Professor of Chemistry University of Nevada, Las Vegas Rock varnish, often called desert varnish, is a slow-growing, manganese-rich coating that accumulates on exposed rock surfaces. The mechanism of varnish formation is not fully understood, however, most authors agree that varnishes derive their components from the atmosphere. The main goal of this study was to demonstrate the potential use of desert varnish as a passive environmental monitor of present and past atmospheric pollution. Analysis of varnishes is a new field that can potentially provide records of pre-anthropogenic levels of atmospheric metals and other environmental pollutants. To evaluate the potential of desert varnish as an environmental monitoring tool, the following hypotheses were tested: (1) rock varnish accumulates and preserves a record of airborne heavy elements and can be used as a passive environmental monitor of relatively recent events; (2) anthropogenic pollutants are deposited in the varnish’s outermost layers and can be traced to their sources, such as ore smelters or coal–fired power plants; and (3) heavy metals and radionuclides can be quantified in the varnish coatings using field portable X-ray fluorescence spectroscopy (FPXRF), inductively coupled plasma mass spectroscopy (ICPMS), laser ablation-inductively coupled plasma iii mass spectroscopy (LA-ICPMS), and cold vapor atomic absorption spectrometry (CVAA). Desert varnish samples were collected in the areas surrounding four point sources of air pollution: the Nevada Test Site (NTS), Nye County, NV; the Mohave Power Project (MPP), Laughlin, NV; the Reid Gardner Power Plant (RGPP), Moapa, NV; and the Titanium Metal Corporation (TIMET), Henderson, NV. The chemical composition of rock varnishes was examined with FPXRF, LA-ICPMS, ICPMS, and CVAA. Both FPXRF and LA-ICPMS results show that many trace elements in the analyzed varnishes appear to be enriched relative to the upper continental crust (UCC). Notably, elements that show the highest levels of enrichment relative to the UCC are commonly found in atmospheric emissions from coal-fired power plants. Abundances of these elements plotted against the distance from the power plant show general patterns consistent with the predictions of the Gaussian Plume model for transport and diffusion of the pollutants. The model predicts that lower concentrations of pollutants will be observed at the point of origin followed by a maximum peak concentration and gradual decrease with distance from the source. To confirm correlation of contamination to distance from the power plant, total concentrations of the elements in desert varnish films were determined. Varnishes collected in the downwind locations from MPP and RGPP were stripped from the base rock with concentrated HCl. The resulting solutions were analyzed by quantitative ICPMS for 27 isotopes (9Be, 51 V, 52 Cr, 59 Co, 60 Ni, 63 Cu, 66 Zn, 75 As, 88 Sr, 98 Mo, 102 Ru, 103 Rh, 106 Pd, 111 Cd, 118 Sn, 121 Sb, 133 Cs, 184 W, 187 Re, 195 Pt, 205 Tl, 206 Pb, 207 Pb, 208 Pb, 209 Bi, 232 Th, and 238 U). Additionally, mercury was analyzed by CVAA. The average elemental iv concentrations in the varnish samples were plotted as a function of the distance from each power plant. The ICPMS data confirm that many trace elements have a deposition patterns consistent with the Gaussian Plume model. The results of this study provided basic knowledge of the chemical and radiochemical composition of varnish coatings and, thus, additional evidence to help understand the mechanism of varnish formation. In conclusion, the results of this study will have implications 1) for the mapping of the distribution of some of the components of air contamination, 2) for identifying the sources of air pollution, 3) for deciphering the history of atmospheric pollution, 4) for contributing to our understanding of desert varnish formation, and 5) for use as a prospecting tool. v TABLE OF CONTENTS ABSTRACT ........................................................................................................................ ii LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ............................................................................................................ x ACKNOWLEDGMENTS ............................................................................................... xiv CHAPTER 1 INTRODUCTION AND PROBLEM STATEMENT ............................... 1 Statement of Problem .................................................................................................... 1 Purpose of the Research ................................................................................................ 4 Research Approach ....................................................................................................... 5 CHAPTER 2 ENVIRONMENTAL ARCHIVES ............................................................ 9 Passive Sampling .......................................................................................................... 9 Environmental Archives ............................................................................................. 11 Ice Cores ..................................................................................................................... 12 Marine and Lake Sediments........................................................................................ 13 Soils............................................................................................................................. 15 Peat Bogs .................................................................................................................... 16 Biomonitors................................................................................................................. 17 Lichens ........................................................................................................................ 18 Desert Varnish as an Environmental Monitor ............................................................ 20 CHAPTER 3 DESERT VARNISH LITERATURE REVIEW ..................................... 22 Introduction ................................................................................................................. 22 Chemistry and Mineralogy of Desert Varnish ............................................................ 22 Desert Varnish and Microorganisms .......................................................................... 25 Genesis of Desert Varnish .......................................................................................... 27 Dating Desert Varnish................................................................................................. 31 Desert Varnish Accumulation ..................................................................................... 33 Desert Varnish and Climatic Data .............................................................................
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