Development of a new online method for compound specific measurements of organic aerosols

Atmospheric aerosols play an important role in many environmental processes, affecting human health and global climate. In many environments organic matter significantly contributes to the composition of atmospheric aerosols influencing its properties. Due to the huge variety of organic compounds present in atmospheric aerosol detailed chemical characterization of ambient aerosols is critical in order to understand the formation process, composition, and properties of aerosols in the atmosphere. However, current analytical methods are far from full speciation of organic aerosols and often require long sampling times. Offline methods are also subjected to artifacts during aerosol collection and storage. In the present work a new technique for online compound specific measurements with a high time resolution was developed. The Aerosol Collection Module (ACM) is a new scientific instrument designed to sample and transfer atmospheric aerosols. The system consists of an aerodynamic lens system which focuses particles into a beam. The beam is directed to a cooled sampling surface. After collection the aerosol sample is evaporated from the collection surface through heating and transferred to a detector. For laboratory characterization the ACM was interfaced with a Gas Chromatograph Mass Spectrometer system (GC-MS). The particle collection efficiency, gas phase transfer efficiency, and linearity of the ACM-GC-MS was determined using laboratory generated octadecane aerosols. It could be proven that the ACM-GCMS is linear over a mass range of 2 to 100 ng and that the ACM-GC-MS had a recovery rate of 100% for octadecane aerosols. An experiment carried out at the Jüulich aerosol chamber focused on the characterization of secondary organic aerosols (SOA) formed from $\beta$-pinene oxidation. SOA formed by the ozone oxidation of $\beta$-pinene was successfully measured with the ACM-GC-MS. Nopinone, myrtanal, myrtenol, 1-hydroxynopinone, 3- oxonopinone, 3,7-dihydroxynopinone, and bicyclo[3,1,1]hept-3-ene-2-one could be identified as products of the $\beta$-pinene ozonolysis. For nopinone, one of the major oxidation products, the partitioning coefficient was determined. It was found to be on average 7.75×10$^{−5}$ ± 1.9×10$^{−5}$ m$^{3} \mu$g$^{−1}$ which is between model estimates of 2.4 × 10$^{−7}$ m$^{3}$ $\mu$g$^{−1}$ and 7.6 × 10$^{−4}$ m$^{3} \mu$g$^{−1}$. In future studies the ACM should be applied to measure ambient aerosol and to further explore the analytical potential of the ACM by coupling it6 to different gas phase detectors.