UVM Theses and Dissertations
Format:
Print
Author:
Geddes, Scott Robertson
Title:
Dept./Program:
Chemistry
Year:
2011
Degree:
PhD
Abstract:
Atmospheric Chemistry is primarily driven by low concentrations of highly reactive oxidants acting upon a large variety of species emitted into the atmosphere both via natural and anthropogenic processes. Condensed phase materials that are small enough to remain suspended in the atmosphere are known as aerosols and these are highly varied in temporal, chemical and spatial properties. Aerosol particles have important consequences to atmospheric chemistry via oxidative reaction processes which continuously modify their chemical properties. Subsequently they can also affect physical processes such as the absorption and scattering of solar radiation (affecting the earth's albedo). Additionally, by acting as water or ice condensation nuclei, aerosol particles play a key role in cloud formation processes and therefore have numerous indirect effects upon the global climate via alterations in cloud-based physical processes.
Aerosol Mass Spectrometry (AMS) has emerged as the principal tool for aerosol analysis and soft ionization techniques are an important subset particularly suited for chemical speciation investigations. This dissertation presents the use of soft ionization AMS for the analysis of complex organic aerosols in laboratory studies, both as models for Primary Organic Aerosol (POA) and for Secondary Organic Aerosol (SOA).
An established technique (Photo-Electron Resonance Capture Ionization AMS) is used to identify the resonance capture mechanisms for cysteine containing peptide residues which generate tractable fragmentation patterns following electron capture at the C-S o* orbital. This technique is then applied to investigate the ozonolysis of mixed particles representative of biogenic rich organic aerosol as is common for marine aerosols. Particle phase' processing of peptide molecules into imines, enamines and amides, whilst in the presence of an unsaturated particle matrix, was directly observed and postulated as a potential HULlS inclusion mechanism.
In order to apply soft ionization AMS to lower concentrations of particle mass more representative of ambient aerosol loadings and thus allow SOA investigations, an entirely new AMS technique was developed and is presented utilizing Near-Infrared LaserDesorption-Ionization (NIR-LDI-AMS). This technique is characterized utilizing a model POA system of oleic acid, whereby a limit of detection (LOD) of 1.7 ng m⁻³ per minute sampling time was measured for pure oleic acid. Subsequent analysis of an [Greek alpha]-pinene SOA formation reaction resulted in high quality mass spectra with a two minute time resolution for total aerosol mass loadings ranging from 1.5 to 8.7 [Greek mu]g m⁻³.
The advantages of soft ionization AMS techniques of high sensitivity such as NIR-LDI-AMS are exemplified by an analysis of limonene ozonolysis SOA whereby first generation homogeneous oxidation products are delineated from second generation heterogeneous oxidation products. Future development of NIR-LDI-AMS and potential applications of high sensitivity soft ionization AMS systems are also discussed.
Aerosol Mass Spectrometry (AMS) has emerged as the principal tool for aerosol analysis and soft ionization techniques are an important subset particularly suited for chemical speciation investigations. This dissertation presents the use of soft ionization AMS for the analysis of complex organic aerosols in laboratory studies, both as models for Primary Organic Aerosol (POA) and for Secondary Organic Aerosol (SOA).
An established technique (Photo-Electron Resonance Capture Ionization AMS) is used to identify the resonance capture mechanisms for cysteine containing peptide residues which generate tractable fragmentation patterns following electron capture at the C-S o* orbital. This technique is then applied to investigate the ozonolysis of mixed particles representative of biogenic rich organic aerosol as is common for marine aerosols. Particle phase' processing of peptide molecules into imines, enamines and amides, whilst in the presence of an unsaturated particle matrix, was directly observed and postulated as a potential HULlS inclusion mechanism.
In order to apply soft ionization AMS to lower concentrations of particle mass more representative of ambient aerosol loadings and thus allow SOA investigations, an entirely new AMS technique was developed and is presented utilizing Near-Infrared LaserDesorption-Ionization (NIR-LDI-AMS). This technique is characterized utilizing a model POA system of oleic acid, whereby a limit of detection (LOD) of 1.7 ng m⁻³ per minute sampling time was measured for pure oleic acid. Subsequent analysis of an [Greek alpha]-pinene SOA formation reaction resulted in high quality mass spectra with a two minute time resolution for total aerosol mass loadings ranging from 1.5 to 8.7 [Greek mu]g m⁻³.
The advantages of soft ionization AMS techniques of high sensitivity such as NIR-LDI-AMS are exemplified by an analysis of limonene ozonolysis SOA whereby first generation homogeneous oxidation products are delineated from second generation heterogeneous oxidation products. Future development of NIR-LDI-AMS and potential applications of high sensitivity soft ionization AMS systems are also discussed.