Investigation of the photo-oxidation of benzaldehyde and hydroxylated aromatic compounds: application of laser ionization mass spectrometry

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It is well established that the gas phase photo-oxidation of aromatic hydrocarbons (AH), benzene, toluene and the xylene isomers (BTX), leads to formation of secondary organic aerosol (SOA). While the primary reaction steps have been intensively studied, secondary and subsequent reaction steps, which lead to compounds eventually producing SOA, remain obscure. There is evidence that further oxidation of primary ring-retaining products, e.g., aromatic aldehydes, phenols (mono- and dihydroxy substituted), and nitrophenols, could play an important role in the initiation of SOA formation. To date studies on the further oxidation of the primary products using the available analytical techniques have only been marginally successful in identifying i) the chemical nature of the main products and ii) the main aerosol precursors as well as the chemical composition of the aerosol. The main aim of this project is, therefore, a detailed investigation of the reaction products from the OH and NO3radical initiated photo-oxidation of selected primary ring-retaining compounds observed in the oxidation of AH. The investigations will be performed in large volume photoreactors. In addition to available in situ FTIR und GC-MS analytical methods the chemical evolution of selected systems will be monitored using new novel mass spectrometric techniques, which are based on the Atmospheric Pressure Laser Ionization (APLI) method, recently introduced by our group. The application of the laser based ionization methods will serve to identify products which are not easily amendable or not detectable with conventional analytical techniques. Such studies are of fundamental importance for obtaining a better Benter/Barnes POXSA general understanding of the overall photo-oxidation mechanism of aromatic hydrocarbons and assessing their ability to form secondary organic aerosol. The broader impact of the proposed work is expected to be high in several regards. First, the results from the smog-chamber studies will contribute significantly i) to our understanding of the secondary processes involved in the oxidation of aromatic hydrocarbons (BTX), ii) it will help to remove many of the uncertainties currently inherent in chemical models of atmospheric chemistry and iii) it will improve our general understanding of the potential of these processes to form aerosol in the atmosphere. Second, the work will provide and an important platform for demonstrating the laser based mass spectrometric techniques which will be applied. Third, the scientific training of the involved Ph.D. students as well as Diploma/Masters students will encompass a broad variety of interdisciplinary research work. After completion of their Ph.D. thesis they will be well prepared for either entering the work market, or continuing their research work at the university level.