HR: 0800h
AN: A41A-0009    [Abstracts]
TI: An Electrostatic Sampler to Collect Ultrafine Particles: Design, Calibration and Application.
AU: * Kaegi, R
EM: ralf.kaegi@empa.ch
AF: Swiss Federal Laboratories for Materials Testing and Research, Ueberlandstrasse 129, Duebendorf, 8600
AU: Fierz, M
EM: m.fierz@fh-aargau.ch
AF: Fachhochschule Aargau, University of Applied Sciences Aargau, Klosterzelgstrasse, Windisch, 5210
AU: Burtscher, H
EM: h.burtscher@fh-aargau.ch
AF: Fachhochschule Aargau, University of Applied Sciences Aargau, Klosterzelgstrasse, Windisch, 5210
AB: Ultrafine particles ($<$100 nm) are of increasing importance due to their adverse health effects and their impact on the global climate. However, there is still a lack of knowledge of the characteristics of ultrafine particles in ambient air. Single particle analysis using TEM (Transmission electron microscopy) allows to gather the most comprehensive data - such as morphology, chemistry and crystallinity - of ultrafine particles. Most measurement devices are designed to collect particles for bulk analytical methods, such as gravimetric or bulk chemical analysis. Thus, these devices are not well suited for collection of particles for single particle analysis. Due to their low mass ultrafine particles cannot be collected using inertial impaction at ambient conditions. It is possible to sample ultrafine particles using low pressure impactors, however, sampling with an impactor results in a heterogeneous grain size distribution on the substrate and thus a quantification of particle abundances based on single particle analysis is difficult. A possibility to overcome this problem is to use an electrostatic sampler, as presented in this study. Particles are positively charged using a corona charger and deposited in an electric field directly onto a TEM grid. Calibration runs using either monodisperse Au, W or NaCl particles (30 - 300 nm in diameter) have been performed. For that purpose, the aerosol was split into two parts, one part being directed to the electrostatic sampler, the other to a CPC (condensation particle counter). Particles deposited on the TEM grid were counted using an ESEM (environmental scanning electron microscope). The total amount of particles deposited on the TEM grid was estimated based on the ESEM measurements and compared to the results from the CPC. The calculated sampling efficiency was roughly 3%. Due the radialsymmetric electric field, the amount of deposited particles was highest in the center and lower towards the rim of the TEM grid. The sampler was additionally tested using oil combustion particles. In these experiments, 10 nm size particles were successfully sampled on TEM grids. Thus, the presented electrostatic sampler is well suited for the collection of ultrafine particles from ambient air as well as from test facilities. It will, thus, be of great benefit for applications related to single particle analysis of ultrafine particles.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting