Coupling of Photoionization Mass Spectrometry to Thermal Optical Carbon Analysis (EC/OC-Measurement) for Rapid PM-Characterization
Hendryk Czech, Patrick Martens, Paul Kösling, Marco Schmidt, Christopher Rüger, Thorsten Streibel, Sven Ehlert, Andreas Walte, Martin Rigler, Johannes Passig, RALF ZIMMERMANN, Mass Spectrometry Centre;Rostock University/Helmholtz Munich
Abstract Number: 275
Working Group: Instrumentation and Methods
Abstract
At several air monitoring station worldwide, PM is routine sampled on quartz fiber filters and analyzed by thermal-optical carbon analysis (TOCA) for organic and elemental carbon (OC and EC). Individual OC- and EC-fractions are analyzed in the TOCA-process by stepwise heating of a small PM-loaded filter-punch. With the coupling of different photoionization and electron ionization mass spectrometry setups to the TOCA, additional information on average carbon oxidation state (OSC), content of polyaromatic hydrocarbons (PAH) or source specific markers are gained.
A subset of material evaporating during a temperature protocol is transferred to a time-of-flight mass spectrometer (TOFMS) prior to catalytic conversion for TOCA and ionized by either Single Photon (SPI)- or Resonance-Enhanced Multiphoton Ionization (REMPI). While REMPI provides a selective and sensitive detection of polyaromatic compounds including PAH, SPI refers to a more universal ionization technique capable to special features of PM sources.
A new hyphenated TOCA-REMPI/EI-TOFMS approach enables the simultaneous determination of toxic PAH and the OSC in PM. Similar to the high-resolution Aerosol Mass Spectrometer (AMS), the TOCA-REMPI/EI-TOFMS-approach provides quantitative results on organic matter, nitrate and sulfate. Furthermore, key isobaric ions C3H7+ and C2H3O+ at m/z 43, necessary to distinguish between oxidized and hydrocarbon-like organic aerosol, are separated due to a mass resolution of ~2,800. Simultaneously, the selective REMPI detection of toxic PAH was realized by a KrF laser with 248 nm radiation.
In a high resolution approach, REMPI is conducted directly in the C-Trap of a modified Orbitrap-MS for hyphenation to TOCA. Stored ions subsequently are injected into the Orbitrap-MS for mass analysis by pulsing of the C-trap. A high-resolution analysis of the evolved gases is achieved, allowing the resolution of isobaric aromatic systems and a direct sum formula assignment. This is particular important for studying photochemical degradation of polyaromatics or the speciation of sulfur containing compounds in combustion emissions.