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

  • Organosulfates
  • Thermal desorption

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-f7td-0p70

• License

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