Novel optical approaches for studying biogenic nanoparticles

Paulus Bauer, Heinz Amenitsch, Herwig Peterlik, Christian Rentenberger, Paul Winkler

Gas-to-particle conversion is known to dominate the aerosol number concentration in the global atmosphere (Kulmala et al., 2004). The rigorous study of airborne particles in the size range from 1 nm to 50 nm is hence crucial for a better understanding of the underlying nanoparticle formation mechanisms. Conventional techniques are able to retrieve size information from electrical mobility analysis or use mass spectrometers to determine the chemical composition of nanoparticles. However, most techniques don’t gain direct information on geometric size and structure and suffer from insufficient time resolution (Winkler et al., 2012).
Non-invasive optical approaches can provide size and structure information at time scales as low as milliseconds. To this end, wavelengths close to the size of the particles are needed. For the study of nanoparticles this implies radiation at wavelengths close to or below 1nm. Accordingly, hard x-rays (ca. 0.1 – 0.2 nm) or accelerated electrons can be considered appropriate for optical nanoparticle characterization.
Transmission electron microscopy (TEM) is a well-known technique for investigating structures at the nanometer and sub-nanometer scale. TEM allows the examination of deposited aerosol particles which reveals information about a static selection of particles located in the area of interest. Thereby gathered structural and size information is of importance for integral techniques like Small Angle X-ray Scattering (SAXS) or Dynamic Light Scattering (DLS).
SAXS is commonly used in material science or in biochemical process analysis in order to acquire structural information from 1 nm to 50 nm. In aerosol science this approach promises in situ information on nucleation mode particles (Laksmono et al., 2011). Here we report experiments conducted recently at the SAXS beamline at the Elettra synchrotron Triest. We have chosen this beamline due to high beam intensity and the available experience on aerosol studies in flow tubes (Jungnikl et al., 2011). To provide a representative environment for aerosols a flow tube with a movable inlet for variable residence time was used. Figure 1 shows a picture of the flow tube setup at the Elettra synchrotron. A tungsten oxide aerosol distribution was generated in the flow tube to achieve a better understanding of the behavior of the system. For validation purposes measurements of deposited aerosols with TEM and laboratory SAXS (University of Vienna) were performed. Figure 2 displays a TEM image of tungsten oxide nanoparticles. Furthermore we extended this approach to the study of newly formed biogenic particles from the ozonolysis of α-pinene.
Figure 1. Setup of the flow tube with moveable inlet at the SAXS beamline at the Elettra synchrotron.
Figure 2. TEM image of tungsten oxide aerosol deposit.
This work was supported by the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement No. 616075.

Aerosolphysik und Umweltphysik, Dynamik Kondensierter Systeme, Physik Nanostrukturierter Materialien
Externe Organisation(en)
Technische Universität Graz
ÖFOS 2012
103008 Experimentalphysik, 105904 Umweltforschung, 103039 Aerosolphysik
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