AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
In-Situ Characterization of Aerosol Nanoparticles at Close-to-Ambient Concentrations by Small Angle X-Ray Scattering (SAXS)
PAULUS S. BAUER, Heinz Amenitsch, Paul M. Winkler, Universitaet Wien, Vienna, Austria
Abstract Number: 15 Working Group: Instrumentation and Methods
Abstract In-situ characterization of aerosol nanoparticles is a challenging task in aerosol science. Common aerosol analyzers such as differential mobility analyzers usually extract the particles from their original environment for analysis. Thereby, nanoparticles can get modified or get lost e.g. by wall collisions inside the instrument, which can affect the measured size distribution and concentration Thus, there is an essential demand for an in-situ measurement technique. Small-angle X-ray scattering (SAXS), commonly used in material science or in biochemical process analysis, can fill this gap. It is capable of measuring in-situ particle size distribution in the nanometer range if the scattering contrast between nanoparticles and gas molecules is sufficiently large. SAXS has already been applied in nucleation studies with extremely high nanoparticle concentrations of ~10$^(12) /cc and carrier gas pressures ~2 kPa. (Laksmono et al. (2011), Phys. Chem. Chem. Phys., 13, 5855)
Here we report first experiments on nanoparticle characterization by SAXS at concentrations of about 10$^6 /cc. To provide a representative environment for aerosols a flow tube was operated at ambient pressure. The experiments were conducted at the Elettra synchrotron near Trieste, Italy, due to the available high beam intensity and the experience on aerosol studies in flow tubes (Jungnikl et al. (2011), Aerosol Sci. Technol., 45, 805). We analyzed high molecular weight tungsten oxide particles having a high scattering contrast compared to the air background. For direct comparison of the SAXS data to conventional aerosol measurements a Differential Mobility Particle Sizer (DMPS) and a Condensation Particle Counter (CPC) were run in parallel. Results show that SAXS can be used to obtain in-situ size information of nanoparticles at close-to-ambient concentrations.