Date of Award:

12-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Seth Lyman

Committee

Seth Lyman

Committee

Randal Martin

Committee

Kimberly Hageman

Abstract

Mercury (Hg) is a highly toxic metal found ubiquitously throughout the environment that has the potential to harm wildlife and human health. Human exposure to Hg can lead to symptoms such as blindness, loss of memory, ataxia, and death. Hg exposure to pregnant women and young children is of even greater concern, as high levels of Hg can hinder fetal and child development.

Hg is emitted into the atmosphere through natural and anthropogenic processes such as biomass burning and the incineration of coal, respectively. Hg exists in the atmosphere as elemental Hg (Hg0) or in an oxidized form (HgII). HgII is more reactive and is easily deposited to earth’s surface where it can be converted into highly toxic organic Hg. Once in an ecosystem, Hg is subject to biomagnification and bioaccumulation, leading to high levels of Hg in food such as fish and rice.

Most previous measurements of atmospheric HgII were biased low and uncalibrated. Utah State University has developed an unbiased dual channel HgII measurement system that avoids a low bias, as well the first HgII calibration system that has been shown to work in field conditions. Both systems were deployed at Storm Peak Laboratory (SPL).

Many uncertainties surround Hg redox chemistry in the atmosphere, and 3-D photochemical models (e.g. GEOS-Chem) are useful tools to help elucidate Hg chemistry in ambient air. In this study, GEOS-Chem was used to simulate Hg at SPL and model output was compared to measurements made by the dual channel system. The model underestimated HgII concentrations by up to 88 %.

This work provides the first NIST-traceable calibrated HgII measurements ever. GEOS-Chem modeling results indicate missing redox pathways in the model, an overestimation of HgII deposition, and possibly an underestimation of Hg emissions. Our work shows that routine calibration of HgII measurements is possible, and supports the need for kinetics, modeling, and measurement studies in the future.

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