10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

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Gas-to-Particle Partitioning of Major Oxidation Products from Monoterpenes and Real Plant Emissions as Measured by Three Novel Aerosol Chemical Characterization Techniques

Georgios Gkatzelis, THORSTEN HOHAUS, Ralf Tillmann, Iulia Gensch, Markus Mueller, Philipp Eichler, Xu Kang-Ming, Patrick Schlag, Sebastian H. Schmitt, Yu Zhujun, Rupert Holzinger, Armin Wisthaler, Astrid Kiendler-Scharr, Forschungszentrum Juelich GmbH, Germany

     Abstract Number: 963
     Working Group: Aerosol Chemistry

Abstract
Secondary organic aerosol (SOA), formed through the oxidation of volatile organic compounds in the atmosphere, play a key role in climate change and air quality. Due to thousands of individual compounds involved in SOA formation, the chemical characterization of organic aerosols (OA) remains a huge analytical challenge. In this framework, a comparison of three different aerosol chemical characterization techniques has been performed. The aerosol collection module (ACM) (Hohaus et al., 2010), the chemical analysis of aerosol online (CHARON) (Eichler et al., 2015) and the collection thermal desorption unit (TD) (Holzinger et al., 2010) are different inlets connected to a Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS). These techniques were deployed in a set of chamber experiments at the atmosphere simulation chamber SAPHIR to investigate the composition of fresh and aged biogenic SOA from monoterpenes and real plant emissions. Furthermore, the partitioning of major biogenic oxidation products between the gas- and particle-phase was investigated.

Despite significant differences in the aerosol collection and desorption methods of the PTR-based techniques, the determined chemical composition was comparable, with the same major contributing ions found by all instruments. These ions could be attributed to known products expected from the oxidation of the examined monoterpenes. Differences in total mass recovery between the instruments were found to result predominately from differences in the electric field strength (V cm-1) to buffer gas density (molecules cm-3) (E/N) ratio in the drift-tube reaction ionization chambers of the chemical ionization instruments and from dissimilarities in the collection/desorption of aerosols.

Gas-to-particle partitioning values were determined based on the saturation mass concentration (C*) of the individual ions. Theoretical calculations based on the molecular structure of the compounds showed, within the uncertainties ranges, good agreement with the experimental C* for most semi-volatile organic compounds, while intermediate-volatility organic compounds deviated up to a factor of 300. These major differences point towards (i) possible interferences by thermal and ionic fragmentation of higher molecular weight compounds, produced by accretion and oligomerization reactions that show up at m/z’s detected by the instruments, as well as (ii) kinetic influences in the distribution between gas- and particle-phase with condensation to the particle-phase and irreversible uptake.

References
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