AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
First Field Application of a Thermal Desorption Resonance-Enhanced Multiphoton-Ionisation Single Particle Time-of-Flight Mass Spectrometer for On-line Measurements of Particle Bound Polycyclic Aromatic Hydrocarbons and Source Identification
MARKUS OSTER, Michael Elsasser, Jürgen Schnelle-Kreis, Ralf Zimmermann, Helmholtz Zentrum München
Abstract Number: 61 Working Group: Instrumentation and Methods
Abstract Laser based mass spectrometry is an important tool for the on-line detection of individual single aerosol particles. The detection of organic molecules, that are often responsible for adverse health effects, is often complicated due to a high degree of fragmentation in single particle laser mass spectrometry. Therefore, an analytical tool that uses soft ionisation techniques would be desirable.
The results of a first field application of a single particle laser mass spectrometry setup combining single particle (SP) analysis with soft ionisation during a measurement campaign are presented. This setup consists of a differentially pumped inlet system to generate a particle beam, a sizing unit for laser velocimetry of individual particles, an ion source and a reflectron time-of-flight mass spectrometer (TOFMS) for ion production and detection. The ion source consists of a heated metal surface (T=550 degrees C) for thermal desorption (TD) of particle bound components and a KrF-excimer laser (lambda=248 nm) for resonance-enhanced multiphoton-ionisation (REMPI) that is triggered according to the particle velocity to selectively ionise polycyclic aromatic hydrocarbons (PAH). The two-step desorption/ionisation allows the detection of organic molecules with reduced fragmentation.
The TD-REMPI-SP-TOFMS setup was successfully tested for the first time in the field during a measurement campaign in Augsburg, Germany in winter 2010 with the aim to analyse the impact of wood combustion on ambient aerosol with an urban background. About 360.000 particle events were detected with this setup during the campaign. Data analysis of the acquired mass spectra showed, that PAH could be found on 15.7 % of the observed particles. 2.1 % of the spectra showed besides peaks typical for PAH a peak at m/z=234, that is dedicated to retene, a marker for coniferous wood combustion. It could be shown, that there are differences in the time series, diurnal variation of occurrence and size distributions of PAH-containing and PAH-free particles, that indicate that mainly agglomerated and re-suspended particles were detected.