Isomer Separation of Multifunctional Atmospheric Compounds Using Gas Chromatography and Chemical Ionization Mass Spectrometry

Author: Vasquez, Krystal TonyBeth

Year: 2022

Degree: Dissertation (Ph.D.)

Advisor: Wennberg, Paul O.

Committee Members: Seinfeld, John H.; Okumura, Mitchio; Blake, Geoffrey A.; Wennberg, Paul O.

Option: Chemistry

DOI: 10.7907/yaz8-qr39

Abstract

Oxygenated volatile organic compounds are a group of carbon-containing species that include one or more functional groups. They are formed during oxidation of hydrocarbons in the atmosphere. Afterwards, they readily undergo atmospheric processing, which—depending on their chemical properties—can lead to the formation of harmful pollutants, such as ozone or secondary organic aerosols (SOA). Prolonged exposure to either compound can negatively impact human health.

Unfortunately, most existing analytical techniques struggle to quantify the concentrations of the majority of OVOCs due to their characteristic low abundances and high reactivities. In addition, most of these compounds are also made up of a complex mixture of isomers that few instruments are able to resolve. Since even slight changes in structure can impact an OVOC’s atmospheric fate, this can lead to uncertainties when elucidating their chemical mechanisms. As a result, despite decades of research, there are still many outstanding questions pertaining to atmospheric processing of OVOCs and, by extension, their impact on air quality.

To combat this issue, novel instrumentation was developed that can provide accurate, isomer-resolved measurements of a wide variety of OVOCs, which it achieves by combining the sensitive, specific nature of gas chromatography (GC) with the equally sensitive, yet non-invasive aspects of chemical ionization mass spectrometry (CIMS). To showcase its capabilities, these new instrumental methods are applied to the study of isoprene oxidation. More specifically, we report new insights into the isomer-specific loss processes of isoprene-derived hydroxy nitrates. Inclusion of our findings into atmospheric models can greatly improve our simulations of NOₓ, ozone, and nitric acid.

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