Improvement of on-line characterization of aerosol particles by means of laser based ionization techniques in a time-of-flight mass spectrometer

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Anthropogenic ambient aerosols exhibit negative health effects (particulate matter problem) and are relevant for the climate (condensation nucleus properties, light absorption etc.). Due to the highly dynamic character of aerosols the development of on-line real-time analytical techniques takes a prominent position for the detection of their physico-chemical properties. Single particle aerosol laser time-of-flight mass spectrometry (S-ATOFMS) allows for characterization of individual particles toward both, particle size and chemical composition. With a new S-ATOFMS technique, where particle resolved desorption of organic molecules (LD/TD) and soft photo-ionization methods (REMPI/SPI) are combined, for the first time mass spectrometric detection of organic compounds from single airborne aerosol particles became feasible. For example, an on-line detection of carcinogenic and toxic polycyclic aromatic hydrocarbons (PAH) could be realized. However, until now, individual particles could be investigated for either inorganic or organic components. In the framework of the proposed project a novel instrumental S-ATOFMS concept will be developed and tested. Thereby, an aerosol particle, after passing the size determination on its flight through the ion source, will first be laser-desorbed and investigated for organic molecules (PAH with REMPI) by mass spectrometry. A few micro seconds later, the inorganic matrix of the same particle core will be measured by another mass spectrometric technique (LDI). Besides the development of a new laser ionization and ionization chamber setup, the implementation of a very fast polarity reversal in the utilized bipolar time-of-flight mass spectrometer is necessary. The on-line acquisition of information about inorganic and organic components of single aerosol particles is of great importance, since only this approach permits a robust and comprehensive, single particle resolved source attribution of particle ensembles. First test applications of the novel technique comprise besides ambient measurements the particularly relevant emissions of ship diesel engines (especially when driven by heavy fuel oil). The latter measurements will be conducted in cooperation with the chair of piston machines and internal combustion engines at the university of Rostock.