Date of Award

12-2017

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry/Green Chemistry

First Advisor

Robyn Hannigan

Second Advisor

Timothy Dransfield

Third Advisor

Michelle Foster

Abstract

Climate change processes are complex and require an interdisciplinary approach to predict how anthropogenic activities may shape future climates and impact our environment. Research presented in this dissertation spans both organic geochemistry and atmospheric chemistry to focus on two systems, Étang Saumâtre (Haiti) and the gas-phase reaction of OH and acrolein. Projects are connected through the ultimate goal to better understand impacts of anthropogenically induced perturbations on environmental systems. First, a paleoenvironmental reconstruction of a tropical, closed-basin, brackish lake was conducted using fatty acid biomarkers extracted from age-constrained sediment cores. Results provide insight into how other larger, open systems and saline bodies may respond to climate change. Spatial and temporal changes in abundances of allochthonous and autochthonous organic matter suggest that historical lake productivity maintained a relatively constant mesotrophic state over the past century, but local, basin-specific productivity and processes were influenced by surrounding land use practices and fluctuating water levels. A subsequent analysis of individual fatty acid carbon isotope signatures refined the origin of organic matter deposited in lake sediments, and as such, also refined trophic status assessments. Correlations between allochthonous and autochthonous fatty acid concentrations and compositional changes in sedimentary organic carbon suggest that anthropogenic drivers influenced lake carbon cycling both spatially and temporally. These data provide insight into how other lacustrine systems may respond to anthropogenic perturbations, influencing the net role of lacustrine systems in the global cycling of carbon.

Lastly, a product study for the reaction of OH and acrolein in the presence of NOx was conducted over a range of pressures, using a flow system, to characterize the fate of acrolein in the upper troposphere. Formaldehyde, CO, CO2, and glycolaldehyde were identified as major products followed by ketene, glyoxal, and APAN. Fractional product yields suggest that acrolein oxidation may be a significant atmospheric source of molecules that impact both climate processes (e.g., glycolaldehyde) and human health (e.g., formaldehyde). Results provide insight into the atmospheric fate of other more complex molecules with respect to OH, and ultimately, provide data needed to more accurately model impacts of anthropogenic emissions on climate processes.

Comments

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