CHEMICAL CHARACTERIZATION OF SOURCE-SPECIFIC ATMOSPHERIC ORGANIC AEROSOL VIA MASS SPECTROMETRY

Atmospheric fine aerosol (PM2.5) is important to Earth’s biogeochemical cycles and climate, and adversely impacts air quality and human health. Specifically, organic aerosol (OA) substantially contributes to PM2.5 mass but remains poorly characterized due to the diversity and complexity of its sources, formation mechanisms, and chemical composition. A suite of state-of-the-art mass spectrometry (MS) methods were deployed and optimized to analyze distinct sets of source-specific OA samples collected from field studies and laboratory experiments in order to chemically characterize OA constituents at the molecular level. First, over 200 archived marine aerosol samples collected from Cape Grim, Tasmania, Australia under remote background conditions from 1991-2015, were analyzed using ultra-performance liquid chromatography interfaced to a high-resolution quadrupole time-of-flight mass spectrometer equipped with an electrospray ionization source (UPLC/ESI-HR-QTOFMS) and gas chromatography interfaced to a quadrupole mass spectrometer equipped with electron ionization source (GC/EI-MS). Several ng m-3 of biogenic (e.g., isoprene- and monoterpene-derived) secondary organic aerosol (SOA) tracers were quantified from 29 summer and winter seasons. Biogenic SOA tracers were enhanced during summer seasons and had moderate-to-strong correlations with marine bioactivity indicators such as methanesulfonic acid and chlorophyll-a. In addition, UPLC/ESI-HR-QTOFMS coupled with inline diode array detection (DAD) were utilized to assess light-absorbing brown carbon (BrC) OA from over 100 systematically-performed laboratory-simulated primary and aged wildfire emissions during the 2016 Fire Influence on Regional and Global Environments Experiment (FIREX) at the US Forest Service Fire Science Lab in Missoula, Montana. 37 solvent-extractable BrC constituents were characterized in terms of their composition, contributions to PM2.5 mass, emission factors, light absorbance, and evolution due to photochemical aging. Furthermore, we developed and optimized a versatile hydrophilic interaction liquid chromatography (HILIC)/ESI-HR-QTOFMS method that can efficiently resolve and measure the major isoprene epoxydiols (IEPOX)-derived and several other water-soluble SOA constituents with enhanced resolution of separation, sensitivity of detection, and accuracy of measurements. These findings provide detailed chemical composition of the atmospheric OA constituents that originate from varying sources, and thus, can serve as inputs for future studies on atmospheric analytical chemistry, earth science modeling, environmental management, and health effects of PM2.5.Doctor of Philosoph