AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Heterogeneous Reaction of SOA-Coated Ammonium Bisulfate Aerosol with Gas-phase Ammonia: Impact of SOA Diffusivity
SHOUMING ZHOU, Alex Tevlin, Jennifer Murphy, Jonathan Abbatt, University of Toronto
Abstract Number: 511 Working Group: Aerosol Chemistry
Abstract Recent studies have displayed evidence that both laboratory generated and ambient secondary organic aerosols (SOA) behave as highly viscous solid or semi-solid particles rather than well mixed, low viscosity liquids. Since aerosol physical properties, such as phase, morphology and viscosity/diffusivity affect their atmospheric behavior in a number of ways, such as particle formation, evaporation, hygroscopic growth and oxidative aging, there is the need to investigate fundamental properties of SOA.
In this work we will report a study on the diffusivity of SOA formed from reaction of α-pinene with ozone. In particular, we investigate the effect on the rate of the heterogeneous reaction of particulate-phase ammonium bisulfate (ABS) with excess gas-phase ammonia when the particles are coated with SOA. ABS particles are coated with α-pinene SOA in a 1 m3 Teflon chamber and introduced into an aerosol flow tube where the kinetics studies are performed. An Aerodyne Aerosol Mass Spectrometer (AMS) and a quantum cascade tunable infrared laser differential absorption spectroscopy (QC-TILDAS) are used to measure particulate-phase ammonium mass loading and gas-phase ammonia mixing ratios, respectively. Reactive uptake coefficients of ammonia on SOA-coated and uncoated ABS particles under room temperature (296±3K) will be measured. Indications of the SOA bulk diffusivity can be estimated by the constraints of the SOA coating on the heterogeneous reactivity of ABS towards gas-phase ammonia. In addition, the effect of temperature and relative humidity (RH) on the SOA diffusivity will also be presented.