Oxidation products of alpha-pinene and their electrical mobilities

OXIDATION PRODUCTS OF ALPHA-PINENE AND THEIR ELECTRICAL MOBILITIES
A. SKYTTÄ 1 , L. AHONEN 1 , R. CAI 1 and J. KANGASLUOMA 1
1 Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of
Helsinki, Helsinki, 00140, Finland

α-pinene C10H16 is a monoterpene emitted by vegetation and its low volatile oxidation products are important source for secondary organic aerosols (SOA) in the atmosphere (Ehn et al., 2014). Because of the significant amount of α-pinene in the atmosphere, we investigated the oxidation
products of α-pinene.

In our setup we used parallel plate DMA (SEADM; (de la Mora et al., 2006)) at mobility resolution of about 80 coupled with APITOF-MS (Tofwerk AG; (Junninen et al., 2010)) and a flow tube system. A DMA can be used to measure the electrical mobility of the molecule or cluster and mass
spectrometer to measure the mass of those clusters. Based on the mass the chemical composition of the cluster can be determined.

The electrospray solution is sprayed through a thin capillary into the chamber through which neutral
sample is passed through. As a solute we used NaNO3 , NaI, LiCl and CH3CO2K dissolved in
methanol all charged in positive and negative mode. Particles that are charged by reagent ions are
led into the DMA via narrow inlet slit.

α-pinene was evaporated into a carrier gas flow and then oxidized using ozone produced from synthetic air with UV-light. The oxidation products are detected by charging them with ions sprayed from the electrospray solution and then directed into the DMA chamber. α-pinene oxidation products of oxidation state C10H16O2−7 were detected with almost all charger ions. Also, other products with different amounts of carbon and hydrogen were detected. Measurements made in negative mode were much more clear and because of this concentrated to examine them.

Mobility provides information on the structure of the compound. One cluster can have multiple peaks in the mobility spectrum if it has multiple different structures. In the mobility spectrum of C10H16O3 charged with NO3− we observe two peaks clearly separate mobility peaks that likely
correspond to two different structural isomers of the compound. We will present analysis of the mobility-mass measurements of α-pinene oxidation products, from where structural information will be obtained when combined to chemical reaction pathways and modeling of the electrical mobilities from the calculated structures.

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Junninen, H. et al, (2010). A high-resolution mass spectrometer
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