Description
A main task in aerosol science is the measurement ofairborne particles. Especially the analysis of nanoparticles
in the range between 1nm to 50nm requires particular
attention, since they cannot be observed with visible light
anymore. To determine the size and number concentration
of aerosol nanoparticles Differential Mobility Particle
Sizer (DMPS) and Condensation Particle Counter (CPC)
are mostly used. A common drawback of these techniques
is that they extract the aerosol particles from their original
environment. 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 (Wang et al., 2002).
Hence, an in-situ measurement technique can
overcome these shortcomings of the conventional aerosol
instruments. Small-angle X-ray scattering (SAXS) is capable to measure in-situ particle size distribution in the nanometer range and has already been applied in
nucleation studies with extremely high nanoparticle concentrations of ~1012/cc and carrier gas pressures ~2kPa (Laksmono et al., 2011). In order to compare the insitu SAXS results to the DMPS and CPC measurements it is important to choose system settings as close to ambient conditions as possible.
Here we report experiments conducted at the SAXS beamline at the Elettra synchrotron near Trieste.
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 a flow tube operated under ambient pressure,
temperature and particle concentrations was used. Figure 1 shows a schematic of the flow tube setup at the ELETTRA synchrotron.
The scattered intensity depends on the electron density of the particles. Therefore tungsten particles with a high electron density were used and generated by a hotwire-generator. A critical issue for SAXS experiments is the background scattering signal originating from air. The background is almost as large as the signal from the tungsten particles. This was resolved by the use of helium
as carrier gas. The advantage of helium is the operation under ambient conditions (temperature, pressure), which allows the usage of modified state-of-the-art aerosol instruments like CPC and DMPS system.
Due to the low background of helium and the high electron density of tungsten particles we obtained defined signals from aerosol SAXS measurements. Thereby a
comparison between in-situ results to conventional measurement techniques can be achieved.
| Period | 1 Sept 2017 |
|---|---|
| Event title | European Aerosol Conference 2017 |
| Event type | Conference |
| Location | Zürich, SwitzerlandShow on map |