Investigation of mineral-mediated photochemical processes and the development of an automated TD-GC-FID/MS system coupled to an atmospheric reaction chamber

  • Author / Creator
    Schmidt, Mario
  • The atmospheric aqueous phase is an important reaction medium for the processing
    of both biogenic and anthropogenic organic compounds. Particularly,
    the formation of aqueous-phase secondary organic aerosol (aqSOA) and the
    influence on ambient air quality and regional climate are of increasing interest
    compared to data from comparable gas-phase processes contributing to SOA
    formation. A fundamental component for the investigation of atmospheric aqueous-phase
    reactions is the availability of a photochemical reactor. For this purpose, a multiposition
    photoreactor was designed and characterized with detailed comparisons
    of exchangeable sample adaptors regarding their stirring performance for the
    application in heterogeneous, aqueous-phase photochemistry.
    The developed photoreactor was applied for the investigation of a new, mineralmediated,
    photochemical formation mechanism of organosulfates (OS) in the
    aqueous phase using methacrolein, a major atmospheric oxidation product of
    isoprene, an abundant biogenic volatile organic compound, as precursor. Since
    organosulfates are known to make a significant contribution to particulate matter
    (PM) mass loadings and SOA, the OS formation was studied under several
    conditions, such as the illumination time, catalyst loading, sulfate concentration,
    counterion identity, and methacrolein concentration.
    SOA formation in the atmosphere also occurs from gas-phase precursors, the
    concentrations of which can be monitored with both optical spectroscopic techniques,
    such as differential optical absorption spectroscopy (DOAS) and via gas
    chromatographic (GC) separation and hyphenation techniques, such as flame
    ionization detection (FID) and mass spectrometry (MS). GC-MS is a powerful tool
    for the analysis and structural elucidation of gas-phase species. However, volatile
    organic compounds and related atmospheric oxidation products are usually detected
    at low concentration ranges, which require an analyte preconcentration
    and thermal desorption (TD) step prior to a gas chromatographic analysis. Consequently,
    a thermal desorption unit for GC-FID/MS coupling was designed,
    characterized and further developed to achieve an automated TD-GC-FID/MS
    system for a continuously operated analysis process of samples generated in
    smog chamber studies.

  • Subjects / Keywords
  • Graduation date
    Fall 2019
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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