Document Type

Thesis - Open Access

Award Date

2016

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Jihong Cole-Dai

Keywords

chlorine, Chilean nitrate, sodium chlorate, CFCs

Abstract

Perchlorate, which derives from both anthropogenic and natural sources in the current environment, constitutes a significant health risk to humans because it competitively inhibits iodine uptake by the thyroid gland. Thus, there has been considerable interest in reducing the human exposure to environmental perchlorate by limiting the release of perchlorate from anthropogenic sources. However, a lack of understanding of the relative contributions from anthropogenic and natural sources has prevented widespread regulation. A 300-year ice core perchlorate record from Summit Station, Greenland (1700-2007 C.E.) that extends beyond the onset of the Industrial Revolution (1850 C.E.) is used to assess the anthropogenic contributions to environmental perchlorate. The perchlorate record shows that the onset of the Industrial Revolution did not impact perchlorate levels in the environment. Despite remarkably consistent concentrations for at least 280 years (1700-1980 C.E.), perchlorate concentrations begin unexpectedly to increase around 1980, its concentration by the early 21st century approximately tripling pre-1980 concentrations. Perchlorate is manufactured primarily for use as an oxidizer and is also produced naturally in the atmosphere. Post-1980 perchlorate concentrations are most likely influenced by changing atmospheric conditions that favor the atmospheric production of perchlorate. Rising stratospheric chlorine concentrations resulting from the emission of chlorine-containing compounds, including chlorofluorocarbons (CFCs), are likely indirectly responsible for approximately two-thirds of the perchlorate present in the current environment. Variations in perchlorate concentrations suggest that natural perchlorate production occurs in the stratosphere and the production rate is dependent on a delicate balance between activated (i.e., radical) chlorine species and ozone concentrations. Furthermore, a link between large, stratospheric volcanic eruptions and brief periods of increased perchlorate concentrations has been discovered. These volcanic eruptions increase stratospheric H2SO4 aerosols, which provides a surface for heterogeneous chlorine activation, resulting in increased perchlorate production. Finally, we suggest that a superbolide event, the Tunguska meteor explosion in 1908, may be primarily responsible for extraordinarily high perchlorate levels between 1908 and 1914. The breakup of the Tunguska meteor could have directly released perchlorate, or the increased aerosol/dust from the explosion could have enhanced chlorine activation in the stratosphere leading to elevated perchlorate concentrations.

Library of Congress Subject Headings

Perchlorates -- Environmental aspects

Ice cores -- Analysis

Atmospheric chlorine compounds

Chlorofluorocarbons

High performance liquid chromatography

Tandem mass spectrometry

Description

Includes bibliographical references (page 111-129)

Format

application/pdf

Number of Pages

144

Publisher

South Dakota State University

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Rights Statement

In Copyright