MOLECULAR & STRUCTURAL CHARACTERIZATION OF COMPLEX ATMOSPHERIC AND ENVIRONMENTAL MIXTURES USING MULTI MODAL SEPARATIONS & HIGH RESOLUTION MASS SPECTROMETRY
Atmospheric aerosols formed through primary emissions, secondary gas-particle formations, and multi-phase chemical processes are composed of solid, semi-solid, or liquid-like particles suspended in the air that have direct implications towards the global radiative balance and human health as air pollutants. Direct emissions of primary organic aerosols (POA; e.g. soot, BrC) and multi-phase formation of secondary organic aerosols (SOA) from the oxidation of biogenic monoterpene isomers represent two important sources/classes of particulate matter in the atmosphere. Multi-phase chemical processes driving the atmospheric and environmental aging through the photochemistry of iron(III), FeIII in organic aerosol particles and aqueous media drives the multiphase chemistry leading to systematic aging of their chemical composition and modifications to resulting light-absorption properties. The molecular composition, organic structures, physical properties, and sources of emissions are complex requiring development of powerful multi-modal analytical metrology, such as high-resolution mass spectrometry (HRMS) hyphenated with liquid chromatography (LC), photodiode array optical detection, drift tube ion mobility (IM) spectrometry, and desorption and ambient ionization of multi-components mixtures in atmospheric particles using temperature programmed desorption Direct analysis in real time (TPD-DART). Disseminating the molecular-specific composition, chemical and physical properties of complex mixtures in atmospheric organic particles and mixed inorganic/organic systems will help improve our understanding of their formation mechanisms, transformative chemical ageing processes, as well as improved detection of individual components in complex mixtures.
Chapter 1 and 2 of dissertation introduces complexity of atmospheric organic, carbonaceous aerosols, and complex environmental mixtures and discusses analytical metrology, experiments, and data analysis procedures used for detailed molecular-level characterization of mixtures. Chapter 3 the development of a robust analytical method for untargeted screening and determination of the physical and chemical properties (e.g. vapor pressures, enthalpies of sublimation, and saturation mass concentrations) of single components out of complex SOA particles using temperature programmed desorption Direct analysis in real time ionization – high resolution mass spectrometry (TPD-DART-HRMS). Chapter 4 introduces the use of ion mobility - mass spectrometry (IM-MS) separation and multidimensional characterization of structural isomers in complex SOA mixtures. The chapter discusses the advanced usage of IM-MS to investigate the molecular and structural properties of isomers of alpha-pinene and limonene derived SOA, use of advanced data analysis procedures to resolved complex conformational and structural isomers, and investigate single-molecule structural changes from atmospheric-like ageing in SOA particles using IM-MS. Chapter 5 discusses the chemical characterization and analysis of individual brown carbon (BrC) chromophores out of mixture of colorless organic carbon constituents and insoluble soot particles generated from controlled flame combustion of ethane fuel, a surrogate system representing gasoline combustion of motor vehicles. The chapter focuses on the quantitative method development and use of state-of-the-art liquid chromatography coupled to photodiode array followed by dopant assisted atmospheric pressure photoionization and HRMS (LC-PDA-HRMS) analysis, followed by conversion to quantitative optical information for comparisons with retrieved literature reports. Chapter 6 examines the complex multiphase photochemical cycling of Fe(III)-citrate, a relevant proxy for [FeIII-carboxylate]2+ complexes in atmospheric water using complementary analytical metrology of optical spectroscopy, LC-PDA-HRMS, oil immersion flow microscopy. Multi-modal datasets from these complementary techniques provide a unique experimental description of various stages of FeIII-citrate photochemistry, elucidate individual components of this reacting system, determine mechanistic insights, and quantify environmental parameters affecting the photochemistry.
- Doctor of Philosophy
- West Lafayette