Date of Award
Doctor of Philosophy (PhD)
Organic aerosols are ubiquitous to the lower atmosphere and there is growing concern about their impact on climate and human health. These aerosols typically have multicomponent compositions that change over time in part due to oxidation by reactive trace gases, such as ozone. A current challenge to the atmospheric research community is to develop better methods of analysis of these particles. Photoelectron resonance capture ionization aerosol mass spectrometry (PERCI-AMS) is an online mass spectrometric method that has been applied to the analysis of organic aerosols. One of its key advantages is that it employs low energy (~ 0 eV) photoelectrons in the ion forming process, which has been shown to minimize fragmentation in the organic analytes, thus simplifying mass spectral interpretation. This dissertation focuses on the application of PERCI-AMS to the analysis of organic particles. Initial emphasis is placed on the heterogeneous reaction of gas phase ozone with liquid oleic acid particles. Products identified included carboxylic acids, aldehydes, and peroxides including alpha-acyloxyalkyl hydroperoxides polymers. The evidence of peroxidic products suggested the stabilization of carbonyl oxide intermediates (i.e. Criegee intermediates) that are formed during ozonolysis. Subsequent PERCI-AMS experiments investigated the reactivity of the stabilized Criegee intermediates. This included investigating the reaction of Criegee intermediates with unsaturated fatty acids and methyl esters. A novel ketone-forming reaction is described in these systems, suggesting the Criegee intermediates can react at a carbon-carbon double bond. Further PERCI-AMS experiments investigated the oxidative processing of particulate amines including octadecylamine and hexadecylamine. Ozonolysis of these amines resulted in strong NO2 - and NO3 - ion signals that increased with the ozone exposure and suggested a mechanism of progressive oxidation. Additionally, a strong ion signal was detected for NO3 -(HNO3), which is the ion core of the most important ion cluster series in the troposphere, NO3 -(HNO3)n(H2O)m. PERCI-AMS was applied to the analysis of ozonized mixed particles of amines with oleic acid or dioctyl sebacate. In the ozonolysis of the amines with oleic acid, products included imines and amides. The routes to the amides were shown to most likely arise from the reactivity of stabilized Criegee intermediates and/or secondary ozonides with the amines. There was also direct evidence of the formation of a surface barrier in the octadecylamine and oleic acid reaction system, which resulted in the retention of oleic acid at high ozone exposures. These experiments have fostered a better understanding of the analytical capacity of PERCI-AMS in assaying the reactivity of organic aerosols as well as giving a more accurate description of the heterogeneous chemistry of these challenging reaction systems. Suggestions for adaptations to PERCI-AMS and future experiments on
Zahardis, James, "Photoelectron Resonance Capture Ionization Aerosol Mass Spectrometry of Organic Particulate Matter" (2008). Graduate College Dissertations and Theses. 243.