NEAR SOURCE MEASUREMENTS OF ORGANIC CARBON IN THE GAS- AND AEROSOL-PHASES USING MASS SPECTROMETRY

Abstract

Atmospheric organic carbon includes diverse classes of compounds that play a key role in a variety of atmospheric processes affecting air quality and human health. Gas-phase organic carbon emissions fuel atmospheric oxidation, ozone production, and can contribute to aerosol loading via secondary organic aerosol formation. This complex mixture of organic molecules has a wide range of sources, both anthropogenic and biogenic. Primary gas-phase emissions have an atmospheric lifetime dependent on the individual molecule’s reactivity to atmospheric oxidants. These reactions will eventually lower the chemical’s volatility via a series of functionalization reactions or convert it to CO2 through fracturing of its carbon backbone. Once organic carbon is sufficiently low in volatility, it will partition into the aerosol-phase and be later removed from the atmosphere via dry or wet deposition. Due to atmospheric organic carbon’s complexity and tendency to evolve, it is crucial to characterize its emission near their source. Detecting and characterizing this mixture of atmospheric chemicals, which contains hundreds of thousands of unique compounds, is challenging due to the sheer size and overall chemical complexity, which is compounded by its ability to move between the gas- and aerosol-phases. While no single instrument can measure organic carbon its entirety, a suite of different mass spectrometers (including aerosol-, proton transfer reaction-, and iodide chemical ionization-) can be utilized to detect the bulk of atmospheric organic carbon in both the aerosol- and gas-phases. When coupled with specialized inlets (e.g., thermal-denuder or filter inlet for gas and aerosol – FIGAERO), these mass spectrometers can also characterize organic carbon as a function of their volatility, allowing us to understand the interplay between the two phases. In this dissertation, we use a range of state-of-the-art mass spectrometers to perform near-source measurements of atmospheric organic carbon in the gas- and aerosol-phases, in both indoor and outdoor environments. In Chapter 3, we show that cooking emissions are the dominant source of aerosol-phase organic carbon indoors, and due to their semi-volatile nature, undergo dilution-driven evaporation as they transport outdoors. In Chapter 4, we explore the biosphere-atmosphere exchange of gas-phase organic carbon from a ponderosa pine forest. We show the forest has a diel emissions trend, acting as a stronger source of organic carbon during the daytime compared to nighttime. Using chemical family analysis to bin >800 organic species, we show that exchange velocities can be parameterized simply based on a compound’s oxygen number. As a unifying theme, this dissertation highlights the necessity of pairing instrumentation with complementary analytical techniques to explore the dynamic nature of atmospheric organic carbon close to its emissions.