PhD dissertation defense: Madison Rutherford

Madison Rutherford will be presenting her PhD dissertation defense, "Emissions and chemistry of volatile organic compounds in indoor and ambient environments," on Monday, March 13, at 2 pm in the CIRES auditorium.

Abstract: Volatile organic compounds (VOCs) play an important role in atmospheric chemistry and air quality in urban and indoor environments, and participate in reactions that can consume and produce pollutants such as ozone and secondary organic aerosol (SOA). Advancements in instrument technology have allowed for new measurement methods, resulting in larger, more complex datasets that have the potential to provide new insights into VOC chemistry. This thesis explores VOCs in environments relevant to human health and discusses data interpretation of new measurement methods across four projects. First, we discuss two series of mobile VOC measurements; next, we analyze the impact of 222 nm germicidal UV (GUV222) use on VOCs; and finally, we characterize a novel traveling-wave ion-mobility spectrometer (IMS) to better speciate VOCs.

The first mobile measurement study took place around the Elyria Swansea neighborhood in Commerce City, CO, which is within a mile of a major oil refinery, a wastewater treatment plant, and multiple major highways. A small proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) installed in the back of a passenger vehicle measured hundreds of VOCs around the neighborhood. Mobile measurements proved to be effective in identifying small, “hyperlocal” VOC sources, which can lead to high concentrations of VOCs at the ground level that are important for air quality. A second series of mobile measurements around landfills along the Colorado Front Range showed that landfills contain distinct sources of VOCs that could relate to different landfill processes and methane production.

Next, a suite of instruments including a new chemical ionization (CI) TOF-MS with an IMS was deployed to investigate the impact of GUV222 lamps on VOCs indoors, with a focus on the formation of SOA under GUV222 from limonene ozonolysis. GUV222 lamp use was shown to lead to the formation of secondary organic aerosol (SOA) in the presence of limonene, with similar SOA yields in a real room as in an environmental chamber. Additionally, these lamps led to elevated VOC concentrations, in part from increased surface emissions.

The final project characterizes the CI-IMS-TOF-MS and demonstrates how computational chemistry can assist us in interpreting IMS data. Adducts of monoterpene oxidation products with iodide or bromide are modeled, with modeled parameters shown to clearly relate to measured drift times. As a result, this modeling can help us identify potential structures of peaks observed in the drift spectrum.