Gas-to-particle partitioning of major biogenic oxidation products
from monoterpenes and real plant emissions
Authors: Gkatzelis Georgios I. , Hohaus Thorsten , Tillmann Ralf , Gensch Iulia , Müller Markus , Eichler Philipp , Xu Kang-Ming , Schlag Patrick , Schmitt Sebastian H. , Yu Zhujun , Wegener Robert , Kaminski Martin , Holzinger Rupert , Wisthaler Armin , Kiendler-Scharr Astrid 
Published: February 2018

Abstract. Secondary organic aerosols (SOA) play a key role in climate change and air quality. Determining the fundamental parameters that distribute organic compounds between the phases is essential, as atmospheric lifetime and impacts change drastically between gas- and particle-phase. In this work, gas-to-particle partitioning of major biogenic oxidation products was investigated using three different aerosol chemical characterization techniques. The aerosol collection module (ACM), the collection thermal desorption unit (TD) and the chemical analysis of aerosol on-line (CHARON) are different aerosol sampling inlets connected to a Proton Transfer Reaction-Time-of-Flight-Mass Spectrometer (PTR-ToF-MS). These techniques were deployed at the atmosphere simulation chamber SAPHIR to perform experiments on the SOA formation and aging from different monoterpenes (β-pinene, limonene) and real plant emissions (Pinus sylvestris L.). The saturation mass concentration C* and thus the volatility of the individual ions was determined based on the simultaneous measurement of their signal in the gas- and particle-phase. A method to identify and exclude ions affected by thermal dissociation during desorption and ionic dissociation in the ionization chamber of the PTR-MS was developed and tested for each technique. Narrow volatility distributions with organic compounds in the semi-volatile (SVOCs) to intermediate volatility (IVOCs) regime were found for all systems studied. Despite significant differences in the aerosol collection and desorption methods of the PTR based techniques, comparison of the C* values obtained with different techniques were found to be in good agreement (within 1 order of magnitude) with deviations explained by the different operating conditions of the PTRMS. The C* of the identified organic compounds were mapped onto the 2-dimensional volatility basis set (2D-VBS) and results showed a decrease of the C* with increasing oxidation state. For all experiments conducted in this study, identified partitioning organic compounds accounted for 20–30 % of the total organic mass measured from an AMS. Further comparison between observations and theoretical calculations was performed for species found in our experiments that were also identified in previous publications. Theoretical calculations based on the molecular structure of the compounds showed, within the uncertainties ranges, good agreement with the experimental C* for most SVOCs, while IVOCs deviated up to a factor of 300. These latter differences are discussed in relation to two main processes affecting these systems: (i) possible interferences by thermal and ionic fragmentation of higher molecular weight compounds, produced by accretion and oligomerization reactions, that fragment in the m / z range detected by the PTRMS and (ii) kinetic influences in the distribution between gas- and particle-phase with gas-phase condensation, diffusion in the particle-phase and irreversible uptake.