Denis Bémer

Characterizing the effective density and primary particle diameter of airborne nanoparticles produced by spark discharge using mobility and mass measurements (tandem DMA/APM)

Nanoparticles are increasingly used in a wide variety of industries. As yet, their health effects are incompletely characterized. Effective density is among the key characteristics of airborne nanoparticles due to its role in particle deposition in the human respiratory tract and in the conversion of number distributions to mass distributions. Because it cannot be measured directly, different methods have been developed to accede to this parameter. The approach chosen in this study is based on the tandem measurement of airborne nanoparticles electrical mobility and mass (tandem differential mobility analyzer/aerosol particle mass analyzer), which major advantage lies in the absence of hypothesis contrary to the tandem differential mobility analyzer/electrical low pressure impactor (DMA/ELPI). The methodology was first applied to spherical model particles to validate the associated data treatment and protocol. In particular, the influence of APM rotational velocity and airflow rate were investigated with regards to the separation of multiply charged particles and electrometer signal. It emerged from experimental data that a compromise between separation efficiency and detection limit shall be found, depending on the nanoparticles to characterize. Accounting for their wide use in different domains, airborne nanoparticles of constantan®, copper, graphite, iron, silver and titanium, produced by spark discharge appear to be representative of ultrafine particles stemming from different industrial processes. In addition to their effective density, the mass-mobility exponents and primary particle diameters were determined for these particles, and found to agree well with published data.

Calculation of the theoretical response of an optical particle counter and its practical usefulness

Abstract The response of an optical particle counter (OPC) was modelled from the Mie theory of light scattering and the built-in parameters of the counter. The model allowed the calculation of the output signal for any spherical particle, of a given complex refractive index, on a microcomputer. It was applied to a Royco 225 instrument. The simulation required a calibration with a reference aerosol. This calibration was carried out with monodisperse spherical particles of oleic acid obtained by a vibrating orifice aerosol generator (VOAG). The experimental values of the counter response obtained with monodisperse aerosols of oleic acid and methylene blue were then compared with the results obtained from the model. It was shown that the choice of the material used for generating monodisperse particles in order to calibrate the counter was not important. Particle size distributions were measured by the OPC for two polydisperse aerosols (coal and aluminium oxide particles), by using the response curve predicted from the model and the refractive index of the material, and then compared with those measured using a Coulter counter, after aerosol sampling onto a Nuclepore membrane filter. The comparison shows that the combination of optical measurements with the calculation of the response curve of the OPC yields accurate results when particle shape is close to the sphere, and for nonspherical particles when light absorption is high.

Evaporation of Liquid Semi-Volatile Aerosols Collected on Fibrous Filters

Numerous sources of liquid aerosols are to be found in industrial environments. Such aerosols may, for instance, be cutting fluids, pesticides, etc., that are harmful or even toxic to humans. To control and reduce worker exposure to potentially toxic aerosols, these latter are usually filtered through fibrous filters. When non-saturated air traverses a clogged filter, however, the drops deposited on the fibers may evaporate. Consequently, workers are exposed to greater amounts of more concentrated vapors than the initial state of the filtered aerosol. Furthermore, exposure readings are distorted by an artifact that may be significant. This study offers an experimental approach to long-term monitoring of the evaporation of a semi-volatile n-hexadecane liquid aerosol deposited on filters of varying efficiency. Results were modeled using two semi-empirical models for identifying the basic parameters of liquid aerosol evaporation on fibers. For the first time ever it has been demonstrated that the Ficks first law, as previously suggested by models proposed in the literature, does not control evaporation kinetic.

On the Importance of Density in ELPI Data Post-Treatment

This study compared number and mass concentrations obtained using two reference devices, a scanning mobility particle sizer (SMPS) and a tapered element oscillating microbalance (TEOM), with those calculated from raw electrical low-pressure impactor (ELPI) data. ELPI data post-treatment was performed assuming a mobility-dependent effective density and three constant densities: an average effective density, the raw material density, and the standard density (i.e., 1 g/cm3). For the mass concentration, whatever the density considered, the ELPI-determined value was close to the reference. For the number concentration, results indicate good agreement between SMPS and ELPI number concentrations when considering effective density and, to a lesser extent, average effective density. In contrast, with the raw material density or standard density, large uncertainties in number concentration measurements were produced. A good estimation of number concentration was obtained based on ELPI data when assuming a standard density only when there was fortuitous agreement between the number tested aerosol size distribution and its mobility-dependent effective density. Thus, contrary to what some authors recommend, a standard density cannot be universally used. Copyright

Evolution of microbial aerosol behaviour in heating, ventilating and air-conditioning systems--quantification of Staphylococcus epidermidis and Penicillium oxalicum viability.

The aim of this study was to develop an experimental set-up and a methodology to uniformly contaminate several filter samples with high concentrations of cultivable bacteria and fungi. An experimental set-up allows contaminating simultaneously up to four filters for range of velocities representative of heating, ventilating and air-conditioning systems. The test aerosol was composed of a microbial consortium of one bacterium (Staphylococcus epidermidis) and one fungus (Penicillium oxalicum) and aerosol generation was performed in wet conditions. Firstly, the experimental set-up was validated in regards to homogeneity of the air flows. The bioaerosol was also characterized in terms of number and particle size distribution using two particle counters: optical particle counter Grimm® 1.109 (optical diameters) and TSI APS 3321 (aerodynamic diameters). Moreover, stabilities of the number of particles generated were measured. Finally, concentrations of cultivable microorganisms were measured with BioSamplers (SKC) downstream of the four filters.