Un modèle d'autocorrélation de Paire pour une meilleur description morphologique des Aggrégats Fractals

National audienceDans de nombreux cas, les aérosols de nanoparticules prennent la forme d’agrégats de particules dites “primaires”. Quand l’agrégation est pilotée par le mouvement Brownien des particules, ce qui est le cas par exemple pour les particules de suie, la structure ramifiée des particules ainsi générées est qualifiée de fractale introduisant une dimension fractale qui quantifie la compacité de ces particules. Cependant, les objets réels sont quasi-fractals car limités spatialement aux petites et aux grandes échelles. Si la limite supérieure a déjà été considérée par le passé, beaucoup moins d’attention a été portée à l’impact de la prise en compte de la limite inférieure, pilotée par les sphérules primaires. Dans ce travail, on modélise la fonction d’autocorrélation de paire en tenant compte de ces deux limites. Il en découle une modélisation analytique du préfacteur fractal individuel ainsi que de la fonction de phase intervenant dans les mesures optiques des particules agrégées. Ceci ouvre la voie à une caractérisation morphologique plus fine des agrégats quasi-fractals

Un modèle d'autocorrélation de Paire pour une meilleur description morphologique des Aggrégats Fractals

National audienceDans de nombreux cas, les aérosols de nanoparticules prennent la forme d’agrégats de particules dites “primaires”. Quand l’agrégation est pilotée par le mouvement Brownien des particules, ce qui est le cas par exemple pour les particules de suie, la structure ramifiée des particules ainsi générées est qualifiée de fractale introduisant une dimension fractale qui quantifie la compacité de ces particules. Cependant, les objets réels sont quasi-fractals car limités spatialement aux petites et aux grandes échelles. Si la limite supérieure a déjà été considérée par le passé, beaucoup moins d’attention a été portée à l’impact de la prise en compte de la limite inférieure, pilotée par les sphérules primaires. Dans ce travail, on modélise la fonction d’autocorrélation de paire en tenant compte de ces deux limites. Il en découle une modélisation analytique du préfacteur fractal individuel ainsi que de la fonction de phase intervenant dans les mesures optiques des particules agrégées. Ceci ouvre la voie à une caractérisation morphologique plus fine des agrégats quasi-fractals

Un modèle d'autocorrélation de Paire pour une meilleur description morphologique des Aggrégats Fractals

National audienceDans de nombreux cas, les aérosols de nanoparticules prennent la forme d’agrégats de particules dites “primaires”. Quand l’agrégation est pilotée par le mouvement Brownien des particules, ce qui est le cas par exemple pour les particules de suie, la structure ramifiée des particules ainsi générées est qualifiée de fractale introduisant une dimension fractale qui quantifie la compacité de ces particules. Cependant, les objets réels sont quasi-fractals car limités spatialement aux petites et aux grandes échelles. Si la limite supérieure a déjà été considérée par le passé, beaucoup moins d’attention a été portée à l’impact de la prise en compte de la limite inférieure, pilotée par les sphérules primaires. Dans ce travail, on modélise la fonction d’autocorrélation de paire en tenant compte de ces deux limites. Il en découle une modélisation analytique du préfacteur fractal individuel ainsi que de la fonction de phase intervenant dans les mesures optiques des particules agrégées. Ceci ouvre la voie à une caractérisation morphologique plus fine des agrégats quasi-fractals

Airborne release of hazardous micron-sized metallic/metal oxide particles during thermal degradation of polycarbonate surfaces contaminated by particles: Towards a phenomenological description

International audienceExperimental results are reported on the resuspension of particles deposited on polycarbonate (PC) samples representative of glove boxes used in the nuclear industry, under thermal degradation. A parametric study on the influence of particles deposit properties, i.e. equivalent volume diameter, density, morphology and number of mono-layers, was carried out. Significant influence of equivalent volume diameter and density has been identified associated to a peak of release for diameter close to 6 µm and decreasing airborne release fraction (ARF) with increasing density. Furthermore, particle deposit structure has been identified as a major influencing parameter, ARF strongly decreasing for number of mono-layer increasing up to nearly 0.3 and remaining constant above this threshold. Finally, experimental results obtained in the present study have been compared with literature values for proposing a phenomenological description of the airborne release of particles from PC surfaces subjected to thermal degradation

Specific surface area of combustion generated soot particles determined by TEM image analysis: Effects of primary particle overlapping and necking

International audienceThe specific surface area of ultrafine particles is an important parameter affecting their physical and chemical properties. For example, the specific surface area of combustion-generated black carbon (BC) particles has been linked to their toxicity and identified to be a more relevant metric to assess their biological response than particle size or mass (Schmid and Stoeger, 2016). Several methods have been developed to measure or determine the specific surface area of aerosol particles, such as the Brunauer-Emmett-Teller (BET) method based on nitrogen adsorption, the diffusion charging (DC) method, scanning Mobility Particle Sizing (SMPS), and the laser-induced incandescence (LII). BET is used as a reference method; however, it is an off-line method and requires a large quantity of sample (several hundreds of milligrams). DC, SMPS, and LII are on-line and faster methods, however, they are indirect methods and rely on various assumptions. Although DC and LII hold a good potential for online determination of the specific surface area of irregular particles, they require further development and evaluation. Recently, it has been demonstrated that the specific surface area of combustion generated black carbon particles can also be determined based on transmission electron microscope (TEM) image analysis; fairly good agreement between the results of BET and TEM was shown in several recent studies (Bau et al., 2010; Bourrous et al., 2018; Ouf et al., 2019). The fairly good agreement between the specific surface areas determined by BET and TEM image analysis of various BC and carbon black (CB) aerosols is an indication that there are negligible internal voids in BC and CB particles. Although TEM image analysis is an off-line method, its main advantage is that it requires only a small amount of sample to be collected on the grid for TEM analysis. Combustion generated BC particles appear as fractal aggregates formed by primary particles that display certain degrees of polydispersity, overlapping, and necking, which in general vary with fuel and flame conditions. Although the specific surface area of BC particles is mainly related to the mean primary particle diameter, other parameters, such as the aggregate size, fractal parameters (pre-factor and fractal dimension), the distribution of primary particles, and the degrees of primary particle overlapping and necking are also relevant. It is important to point out that whereas primary particle overlap reduces both the particle surface area and volume, primary particle necking reduces the particle surface area but increases the particle volume. Figure 1 shows two typical TEM images of flame generated soot particles. Figure 1. Two typical TEM images of flame generated soot particles showing primary particle overlapping, a, and primary particle necking, b (Yon et al., 2015). The effect of primary particle overlapping on the specific surface area of BC particles inferred from TEM image analysis has been investigated recently by Bourrous et al. (2018) and Ouf et al. (2019). However, the potential importance of primary particle necking to BC particle specific surface area determined by TEM image analysis has not been previously investigated. In this study, the TEM images of BC particles produced in laboratory soot generators and from literature were analysed to obtain the primary particle size distribution, primary particle overlapping, and necking. Based on these parameters, the particle specific surface area was inferred, and the results are compared with those obtained from BET or reported previously in the literature. Bau, S., Witschger, O., Gensdarmes, F., Rastoix, O., and Thomas, D. (2010) Powder Technol. 200, 190-201.Bourrous, S., Ribeyre, Q., Lintis, L., Yon, Y., Bau, S., Thomas, D., Vallières, C., and Ouf, F.-X. (2018) J. Aerosol Sci. 126, 122-132. Ouf, F.-X., Bourrous, S., Vallières, C., Yon, J., and Lintis, L. (2019) J. Aerosol Sci. 137, 105436.Schmid, O., and Stoeger, T. (2016) J. Aerosol Sci. 99, 133-143.Yon, J., Bescond, A., Liu, F. (2015) J. Quantitative Spectroscopy & Radiative Transfer 162, 197-206

Specific surface area of combustion generated soot particles determined by TEM image analysis: Effects of primary particle overlapping and necking

International audienceThe specific surface area of ultrafine particles is an important parameter affecting their physical and chemical properties. For example, the specific surface area of combustion-generated black carbon (BC) particles has been linked to their toxicity and identified to be a more relevant metric to assess their biological response than particle size or mass (Schmid and Stoeger, 2016). Several methods have been developed to measure or determine the specific surface area of aerosol particles, such as the Brunauer-Emmett-Teller (BET) method based on nitrogen adsorption, the diffusion charging (DC) method, scanning Mobility Particle Sizing (SMPS), and the laser-induced incandescence (LII). BET is used as a reference method; however, it is an off-line method and requires a large quantity of sample (several hundreds of milligrams). DC, SMPS, and LII are on-line and faster methods, however, they are indirect methods and rely on various assumptions. Although DC and LII hold a good potential for online determination of the specific surface area of irregular particles, they require further development and evaluation. Recently, it has been demonstrated that the specific surface area of combustion generated black carbon particles can also be determined based on transmission electron microscope (TEM) image analysis; fairly good agreement between the results of BET and TEM was shown in several recent studies (Bau et al., 2010; Bourrous et al., 2018; Ouf et al., 2019). The fairly good agreement between the specific surface areas determined by BET and TEM image analysis of various BC and carbon black (CB) aerosols is an indication that there are negligible internal voids in BC and CB particles. Although TEM image analysis is an off-line method, its main advantage is that it requires only a small amount of sample to be collected on the grid for TEM analysis. Combustion generated BC particles appear as fractal aggregates formed by primary particles that display certain degrees of polydispersity, overlapping, and necking, which in general vary with fuel and flame conditions. Although the specific surface area of BC particles is mainly related to the mean primary particle diameter, other parameters, such as the aggregate size, fractal parameters (pre-factor and fractal dimension), the distribution of primary particles, and the degrees of primary particle overlapping and necking are also relevant. It is important to point out that whereas primary particle overlap reduces both the particle surface area and volume, primary particle necking reduces the particle surface area but increases the particle volume. Figure 1 shows two typical TEM images of flame generated soot particles. Figure 1. Two typical TEM images of flame generated soot particles showing primary particle overlapping, a, and primary particle necking, b (Yon et al., 2015). The effect of primary particle overlapping on the specific surface area of BC particles inferred from TEM image analysis has been investigated recently by Bourrous et al. (2018) and Ouf et al. (2019). However, the potential importance of primary particle necking to BC particle specific surface area determined by TEM image analysis has not been previously investigated. In this study, the TEM images of BC particles produced in laboratory soot generators and from literature were analysed to obtain the primary particle size distribution, primary particle overlapping, and necking. Based on these parameters, the particle specific surface area was inferred, and the results are compared with those obtained from BET or reported previously in the literature. Bau, S., Witschger, O., Gensdarmes, F., Rastoix, O., and Thomas, D. (2010) Powder Technol. 200, 190-201.Bourrous, S., Ribeyre, Q., Lintis, L., Yon, Y., Bau, S., Thomas, D., Vallières, C., and Ouf, F.-X. (2018) J. Aerosol Sci. 126, 122-132. Ouf, F.-X., Bourrous, S., Vallières, C., Yon, J., and Lintis, L. (2019) J. Aerosol Sci. 137, 105436.Schmid, O., and Stoeger, T. (2016) J. Aerosol Sci. 99, 133-143.Yon, J., Bescond, A., Liu, F. (2015) J. Quantitative Spectroscopy & Radiative Transfer 162, 197-206

Specific surface area of combustion generated soot particles determined by TEM image analysis: Effects of primary particle overlapping and necking

International audienceThe specific surface area of ultrafine particles is an important parameter affecting their physical and chemical properties. For example, the specific surface area of combustion-generated black carbon (BC) particles has been linked to their toxicity and identified to be a more relevant metric to assess their biological response than particle size or mass (Schmid and Stoeger, 2016). Several methods have been developed to measure or determine the specific surface area of aerosol particles, such as the Brunauer-Emmett-Teller (BET) method based on nitrogen adsorption, the diffusion charging (DC) method, scanning Mobility Particle Sizing (SMPS), and the laser-induced incandescence (LII). BET is used as a reference method; however, it is an off-line method and requires a large quantity of sample (several hundreds of milligrams). DC, SMPS, and LII are on-line and faster methods, however, they are indirect methods and rely on various assumptions. Although DC and LII hold a good potential for online determination of the specific surface area of irregular particles, they require further development and evaluation. Recently, it has been demonstrated that the specific surface area of combustion generated black carbon particles can also be determined based on transmission electron microscope (TEM) image analysis; fairly good agreement between the results of BET and TEM was shown in several recent studies (Bau et al., 2010; Bourrous et al., 2018; Ouf et al., 2019). The fairly good agreement between the specific surface areas determined by BET and TEM image analysis of various BC and carbon black (CB) aerosols is an indication that there are negligible internal voids in BC and CB particles. Although TEM image analysis is an off-line method, its main advantage is that it requires only a small amount of sample to be collected on the grid for TEM analysis. Combustion generated BC particles appear as fractal aggregates formed by primary particles that display certain degrees of polydispersity, overlapping, and necking, which in general vary with fuel and flame conditions. Although the specific surface area of BC particles is mainly related to the mean primary particle diameter, other parameters, such as the aggregate size, fractal parameters (pre-factor and fractal dimension), the distribution of primary particles, and the degrees of primary particle overlapping and necking are also relevant. It is important to point out that whereas primary particle overlap reduces both the particle surface area and volume, primary particle necking reduces the particle surface area but increases the particle volume. Figure 1 shows two typical TEM images of flame generated soot particles. Figure 1. Two typical TEM images of flame generated soot particles showing primary particle overlapping, a, and primary particle necking, b (Yon et al., 2015). The effect of primary particle overlapping on the specific surface area of BC particles inferred from TEM image analysis has been investigated recently by Bourrous et al. (2018) and Ouf et al. (2019). However, the potential importance of primary particle necking to BC particle specific surface area determined by TEM image analysis has not been previously investigated. In this study, the TEM images of BC particles produced in laboratory soot generators and from literature were analysed to obtain the primary particle size distribution, primary particle overlapping, and necking. Based on these parameters, the particle specific surface area was inferred, and the results are compared with those obtained from BET or reported previously in the literature. Bau, S., Witschger, O., Gensdarmes, F., Rastoix, O., and Thomas, D. (2010) Powder Technol. 200, 190-201.Bourrous, S., Ribeyre, Q., Lintis, L., Yon, Y., Bau, S., Thomas, D., Vallières, C., and Ouf, F.-X. (2018) J. Aerosol Sci. 126, 122-132. Ouf, F.-X., Bourrous, S., Vallières, C., Yon, J., and Lintis, L. (2019) J. Aerosol Sci. 137, 105436.Schmid, O., and Stoeger, T. (2016) J. Aerosol Sci. 99, 133-143.Yon, J., Bescond, A., Liu, F. (2015) J. Quantitative Spectroscopy & Radiative Transfer 162, 197-206

An intercomparison exercise of good laboratory practices for nano-aerosols sizemeasurements by mobility spectrometers

International audienceAn intercomparison campaign on nanoparticle size measurement was organized in the frame of the French nanoMetrology club. The aim of this study is to make an inventory of the metrological capabilities of all measurement techniques in France involved in the “nano” size range, including the SMPS (Scanning Mobility Particle Sizer) concerning aerosol metrology. For this study, four samples have been proposed, namely (1) - a SiO2 colloidal suspension (FD304) consisting of a monomodal population, (2) - two samples consisting of two nanoparticle populations of SiO2 having proportions to be determined and (3) - a TiO2 colloidal suspension. Ten SMPS associated to five participants around a common experimental setup were performed in link with a control SMPS to have simultaneous measurements with a same instrument in each laboratory in parallel with the SMPS used by each partner. This article presents SMPS results of this study associated with the description of the experimental set-up and the sample preparation protocol with an identified schedule and comparison with SEM measurements. The present paper does not focus on the actual capability of the tested mobility spectrometers, but aims to highlights the good laboratory practices using their own but common resources in terms of aerosol generation and measurement set-ups

A performance evaluation and inter-laboratory comparison of community face coverings media in the context of covid-19 pandemic

International audienceDuring the recent pandemic of SARS-CoV-2, and as a reaction to the worldwide shortage of surgical masks, several countries have introduced new types of masks named “community face covering” (CoFC). To ensure the quality of such devices and their relevance to slow down the virus spreading, a quick reaction of the certification organisms was necessary to fix the minimal acceptable performances requirements. Moreover, many laboratories involved in the aerosol research field have been asked to perform tests in a quick time according to (CEN, 2020) proposed by the European committee for standardization. This specification imposes a minimal air permeability of 96 L.m-2.s-1 and a minimal filtration efficiency of 70% for 3 µm diameter particles. In the present article, an intercomparison of efficiency and permeability measured by 3 testing laboratories has been performed. Results are in good agreement considering the heterogeneity of the considered material samples (within 27 % in terms of filtration efficiency and less than 20 % in terms of permeability). On this basis, an analysis of 233 materials made of woven, non-woven and mixed fibrous material has been done in terms of filtration efficiency and air permeability. For some of them, measurements have been performed for 0.2 µm, 1 µm and 3 µm particle diameters. As expected, no deterministic correlation could be determinated to link these efficiencies to the permeability of the considered samples; however, a trend could be identified. The same exercise has been conducted to link the filtration efficiency measured at 3 µm to the filtration for lower diameters. Finally, a discussion on the kind of material that is the most relevant to manufacture “community face covering” (CoFC) supported by spectral filtration efficiency (from 0.02 µm to 3 µm) is proposed

The MERMOSE project: Characterization of particulate matter emissions of a commercial aircraft engine

WOS:000394199200005International audienceThe French national project MERMOSE gathers the capabilities of seven organizations to better characterize commercial aircraft engine emissions and to better understand their impact on nucleation processes in the atmosphere. In this frame, a measurement campaign has been performed on a Snecma/NPO Saturn SaM146-1S17 turbofan. During this work, we used a complete set of on-line and off-line techniques to measure radial and angular profiles of particulate matter (PM) properties in the engine exhaust hot flow. We studied different engine thrust settings, selected to match the aircraft main operating conditions (idle, climb, take-off, approach and "ground" cruise). The mode of the emitted particles size distribution ranged from 17 nm to 55 nm and was sensitive to the thrust. The sampled PM showed a complex morphology and were formed by primary nanoparticles of about 15 rim in diameter. They were mainly composed of carbon (with traces of oxygen, sulfur and calcium) and their organic carbon to total carbon ratio (OC/TC) ratio showed a decrease as a function of the maximum thrust from similar to 80% for 30% thrust setting to similar to 12% for 100%