Insights on the Importance of Intermediate and Semi-volatile Organic Precursor Compounds in the Formation of Ambient SOA
MARKUS MUELLER, Tobias Reinecke, Markus Leiminger, Todd Rogers, Martin Graus, IONICON Analytik GmbH., Innsbruck, Austria
Abstract Number: 156
Working Group: Aerosol Chemistry
Abstract
Quantifying the influence of intermediate (IVOC) and semi-volatile organic compounds (SVOC) on the formation of SOA is challenging because of the difficulties in detecting such low-volatile gas-phase compounds. Recently, a novel approach was introduced for studying the contribution of these compounds to ambient SOA formation. This method utilizes the well studied absorption processes of low volatiles onto polymer tubing to separate volatility classes prior to injection into an oxidation flow reactor for rapid oxidation of ambient air. Hence, via automated addition and removal of absorbing polymer tubing, the SOA formation potential of the sample can be studied with and without IVOCs and SVOCs. However, although clear effects are reported, the identification of specific compounds of IVOCs or SVOCs, that drive the additional SOA formation, remains challenging.
To fill this gap, we apply the novel IONICON Laminar-flow Oxidation reactor (ILOx) for rapid photochemical aging of ambient air in Innsbruck, Austria. Importantly, the ILOx reactor’s CFD-optimized sheath air design allows for transmitting IVOCs and even SVOCs with lowermost losses. The aged ambient air is then analyzed by a FUSION PTR-TOF 10k equipped with a CHARON particle inlet to measure gas-phase and condensed particulate organics. The instrument is operated in fast reagent ion switching mode. Proton transfer reaction of organic analytes with H3O+ primary reagent ions provides highly quantitative results while soft adduct ionization with ammonium (A.NH4+) produces almost fragmentation free mass spectra of oxidized organics. Hence, gas-phase and condensed organics are analyzed at highest analytical precision and lowermost limits of detection (~100 ppqV and ~20 pg/m³, respectively).
By periodically switching inlet ports from ambient air to the ILOx reactor, with and without absorbing conductive PTFE tubing, compounds that contribute to the oxidation potential and SOA formation can be directly identified. Herein we present first insights gained with this optimized method.