Characterization and Laboratory Testing of an Oxidation Flow Reactor (DOFR) to Study Secondary Organic Aerosol Formation
ANSSI ARFFMAN, Stephen Robertson, Miikka Dal Maso, Markus Nikka, Pauli Simonen, Anette Karppinen, Gordon McFiggans, Dekati Ltd.
Abstract Number: 395
Working Group: Carbonaceous Aerosols
Abstract
The atmospheric ageing of gases released by different sources can form low vapor pressure compounds that condense to aerosol particles called secondary aerosols. The oxidation flow reactors (OFR) are used for simulating atmospheric ageing in a short time scale for studying the potential of different sources to form secondary aerosols but also for producing secondary organic test aerosols for different applications. Especially, OFR’s are useful tools in studying the aging of transient emissions sources owing to their high time resolution compared to environmental chambers and compact size. Despite the limitations of accelerated photochemistry of OFRs, they provide properly used a joint metrics that can be used to compare the potential of different precursor sources to produce secondary aerosols.
In this study, we present characterization results and secondary organic aerosol (SOA) ageing experiments with a new commercially available OFR called Dekati Oxidation Flow Reactor (DOFR) and its associated sampling unit. The DOFR design is similar to the previously introduced Tampere University Secondary Aerosol Reactor (TSAR). The characterizations performed for the DOFR include the photochemical ageing range, the gas and the particle residence time distributions, and particle losses of reactor and sampling unit. The DOFR was then used for ageing toluene and a-pinene precursor vapors and the SOA yields were determined using the Electrical Low Pressure Impactor (ELPI) and a simplified chemical kinetics model. In addition, the effect of seed particle morphology and concentration on SOA production was measured with soot and ammonium sulfate seed particles.
The ageing range was found to span 1 – 35 days with the CO tracer oxidation experiment. The toluene precursor oxidation experiments showed comparable results to previous studies showing 10% – 30% yields for tested toluene concentrations. The different seeds were found to have significant effect on nucleation and could practically inhibit the nucleation entirely.