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Development and Evaluation of a Thermophoretic Personal Sampler for Nanoparticle Exposure Studies

Azong-Wara, Nkwenti

Some Nanoparticles have been shown to cause adverse health effects. Assessment of personal exposure to these nanoparticles is a major step towards evaluating this potential risk. Assessment measurements of fine and coarse particles have been carried out mainly with samplers consisting of a miniaturized impactor with a defined cut off size followed by a filter for off-line weighing. This approach is unsuitable for nanoparticles due to their low mass. One applicable way of sampling nanoparticles is by employing the principle of thermophoresis. In this thesis, a personal sampler (Thermal Precipitator, TP) which thermophoretically samples particles, was developed based on CFD-modelling. The objective was to uniformly deposit a representative sample of nanoparticles on a substrate to simplify the subsequent off-line Scanning Electron Microscopy (SEM) analysis by minimising the analysis time. Numerical simulations provided information about the deposition characteristics and this was used as the basis to develop the sampler. Laboratory tests were carried out with the TP using monodisperse PSL particles of 95,6 nm and 305 nm in diameters as well as polydisperse soot particles in the size range of about 14 – 98 nm. The particles were sampled with the TP on substrates and later analysed by SEM. Different locations along the entire length of the substrate were investigated. A more detailed analysis was made of the evaluation region on the substrate, where a uniform deposition of particles is expected according to the prior modelling. Experimental results show a homogeneous deposition of particles up to a size range of 300 nm in the evaluation region independent of particle material type as well as the orientation of the device during sampling. Independence of deposition is important since the worker is mobile in all directions Unlike with an older version of the TP where up to 32 SEM images of its non-uniform particle deposition had to be evaluated to obtain an average particle size distribution, an evaluation of the uniform deposition with the new TP is much more simplified, remarkably reducing the time and cost of the evaluation, while improving the statistics of the results.

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Azong-Wara, Nkwenti: Development and Evaluation of a Thermophoretic Personal Sampler for Nanoparticle Exposure Studies. 2013.

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