Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

Veronica Vaida

Second Advisor

Joel Eaves

Third Advisor

Barbara Ervens

Fourth Advisor

Eleanor Browne

Fifth Advisor

Margaret Tolbert

Abstract

Atmospheric aerosols play a vital role in influencing Earth’s energy budget and overall atmospheric chemistry. Secondary organic aerosols (SOA) are a current focus of climate science, as they are not yet well constrained in global models and contribute large uncertainties to radiative forcing calculations. Oxidation of isoprene, an abundant unsaturated organic compound, leads to a series of multigenerational products that have been collectively identified as a major source of SOA. Some of these species also partition to the condensed aerosol phase where further processing generates additional SOA precursors.

Pyruvic acid is a key intermediate within these oxidation pathways and a prime model for keto-acid chemistry in the atmosphere. Here, the kinetics of pyruvic acid photolysis in the gas and aqueous phases were derived from laboratory and chamber experiments. Results demonstrate that product branching ratios and reaction rates in each phase are determined by a number of factors, including the initial pyruvic acid concentration, the presence of oxygen, and the total pressure of the system.

The thesis culminates with a discussion of the multiphase photochemistry of pyruvic acid, performed in an atmospheric simulation chamber. The results are consistent with my previous bulk-phase studies, and the identification of high molecular weight compounds confirms that aqueous radical chemistry can form some polymers and oligomers in particles, even with oxygen present. Furthermore, a new high molecular weight product was characterized that is specific to the multiphase chemistry. The results from this experiment also show significant changes in particle properties, with implications for aerosol hygroscopicity and scattering efficiency.

Overall, the work contained in this thesis reveals a complex pyruvic acid system that is heavily dependent on the environment, and indicates that the multiphase photolysis of pyruvic acid may contribute to SOA mass in the atmosphere. The thesis also comments on further directions for aerosol research, as it illustrates the importance of investigations under realistic atmospheric conditions in order to improve climate-forecasting calculations.

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