Importance of size representation and morphology in modelling optical properties of black carbon: comparison between laboratory measurements and model simulations

Black carbon (BC) from incomplete combustion of biomass or fossil fuels is the strongest absorbing aerosol component in the atmosphere. Optical properties of BC are essential in climate models for quantification of their impact on radiative forcing. The global climate models, however, consider BC to be spherical particles, which causes uncertainties in their optical properties. Based on this, an increasing number of model-based studies provide databases and parameterization schemes for the optical properties of BC, using more realistic fractal aggregate morphologies. In this study, the reliability of the different modelling techniques of BC was investigated by comparing them to laboratory measurements. The modelling techniques were examined for bare BC particles in the first step and for BC particles with organic material in the second step. A total of six morphological representations of BC particles were compared, three each for spherical and fractal aggregate morphologies. In general, the aggregate representation performed well for modelling the particle light absorption coefficient σabs, single-scattering albedo SSA, and mass absorption cross-section MACBC for laboratory-generated BC particles with volume mean mobility diameters dp,V larger than 100nm. However, for modelling Ångström absorption exponent AAE, it was difficult to suggest a method due to size dependence, although the spherical assumption was in better agreement in some cases. The BC fractal aggregates are usually modelled using monodispersed particles, since their optical simulations are computationally expensive. In such studies, the modelled optical properties showed a 25% uncertainty in using the monodisperse size method. It is shown that using the polydisperse size distribution in combination with fractal aggregate morphology reduces the uncertainty in measured σabs to 10% for particles with dp,V between 60-160nm. Furthermore, the sensitivities of the BC optical properties to the various model input parameters such as the real and imaginary parts of the refractive index (mre and mim), the fractal dimension (Df), and the primary particle radius (app) of an aggregate were investigated. When the BC particle is small and rather fresh, the change in the Df had relatively little effect on the optical properties. There was, however, a significant relationship between app and the particle light scattering, which increased by a factor of up to 6 with increasing total particle size. The modelled optical properties of BC are well aligned with laboratory-measured values when the following assumptions are used in the fractal aggregate representation: mre between 1.6 and 2, mim between 0.50 and 1, Df from 1.7 to 1.9, and app between 10 and 14nm. Overall, this study provides experimental support for emphasizing the importance of an appropriate size representation (polydisperse size method) and an appropriate morphological representation for optical modelling and parameterization scheme development of BC

Metrological Characterization of an Aerosol Exposure Chamber to Explore the Inhalation Effects of the Combination of Paraquat and TiO2 Nano-objects

International audienceAgriculture emits a significant quantity of airborne contaminants, and the prospective environmental release of nanopesticides, a new type of agrochemical that employs engineered nanomaterials (ENMs) as either active substances or additives in a pesticide formulation, raises concerns about the risks of inhalation which are still unknown. Although the adverse effects of pesticides have been studied extensively, the potential synergistic toxicity between these substances and ENMs has rarely been investigated. To this end, toxicological models are essential to estimating the health consequences of such aerosols. Thus, to assess the respiratory hazards of titanium dioxide nano-objects (specifically, AEROXIDE (R) TiO2 P25 nanopowder [nTiO(2)]) in combination with paraquat (PQ), we developed a dynamic whole-body exposure chamber for rodents in compliance with guidelines for inhalation toxicity testing (Organization for Economic Cooperation and Development (OECD)) and animal welfare. First, we metrologically characterized the generated test aerosols by determining their mass and number concentrations, size distributions and atmospheric homogeneity at the laboratory. Then, we evaluated the reproducibility and proper functioning of the chamber during a preliminary field campaign, which validated the consistency of the aerosols' mass and number concentrations between the laboratory characterization and the rodent exposure sessions. Finally, we examined the inhalation effects on the rodents

Demande d’avis complémentaire (à l’avis du HCSP du 29 avril 2018) en lien avec des mesures de protection des populations potentiellement exposées autour des sites industriels manipulant du dioxyde de titane (TiO2) - Eléments relatifs à la surveillance métrologique dans l’environnement et à l’examen de la faisabilité

International audienceRésumé : Mesures de protection des populations potentiellement exposées autour des sites industriels manipulant du dioxyde de titane (TiO2) - Eléments relatifs à la surveillance métrologique dans l’environnement et à l’examen de la faisabilitéDans le cadre de la protection des travailleurs et des personnes au voisinage de sites de production ou de manipulation de nanoparticules de dioxyde de titane (TiO2), la faisabilité d’une surveillance métrologique dans l’environnement du TiO2 nanométrique doit être examinée.Pour le HCSP il est envisageable de réaliser des mesures de taux de concentrations de nanoparticules de TiO2 dans l’air autour des sites industriels. Il n’existe cependant pas actuellement de méthode unique opérationnelle permettant de mesurer simultanément le nombre/la masse des particules et de réaliser l’analyse chimique des du TiO2 nanoparticulaire. Le HCSP considère que la mise en œuvre des méthodes de mesures ainsi que des modélisations sont très fortement dépendantes des situations à considérer et nécessitent différentes approches dont dépendront les stratégies de mesures à mettre en place.Ce rapport fait suite à la demande, faite au HCSP par la Direction générale de la prévention des risques, la Direction générale de la santé et la Direction générale du travail, de compléter son avis et son rapport du 29 avril 2018 concernant la protection des travailleurs et des personnes au voisinage de sites de production ou de manipulation de nanoparticules de dioxyde de titane.Le sujet des valeurs de gestion pour la protection des populations potentiellement exposées devra faire l’objet par la suite d’un autre rapport.Pour la réalisation du présent rapport, le HCSP a auditionné notamment des experts des méthodes de mesures des concentrations de particules dans l’air ainsi que des experts de la modélisation de la dispersion des particules dans l’air. Le HCSP a pris en compte les dispositions d’un arrêté préfectoral relatif à un industriel qui a mis en place une surveillance environnementale de routine des incidences de ses émissions de particules de TiO2.Lire aussi :•Protéger les travailleurs et les personnes au voisinage de sites de production ou de manipulation de nanoparticules de dioxyde de titane du 29 avril 201

Extending traceability in airborne particle size distribution measurements beyond 10 µm : Counting efficiency and unit-to-unit variability of four aerodynamic particle size spectrometers

The aim of this study was to establish traceable number concentration measurements of airborne particles beyond 10 μm in particle size. To this end, the primary standards for particle number concentration at the National Metrology Institutes of Switzerland and Japan were further developed to extend their measurement capabilities. Details on the upgraded setup are provided. An inter-comparison of the two primary standards using an optical particle counter as transfer standard showed that these agree well within the stated uncertainties at polystyrene (PS) equivalent optical diameter of 15 µm. Subsequently, four Model 3321 (TSI Inc., USA) aerodynamic particle size spectrometers (APS) were calibrated against the primary standard of Switzerland using size-certified PS spheres with optical/aerodynamic diameter up to 20 µm as test aerosols. The counting efficiency profile and unit-to-unit variability of the APS units were determined. The results presented here can be useful for the analysis and interpretation of data collected by the different atmospheric aerosol networks worldwide. The outlined methodology can also be applied in the calibration of automated bio-aerosol monitors

Demande d’avis complémentaire (à l’avis du HCSP du 29 avril 2018) en lien avec des mesures de protection des populations potentiellement exposées autour des sites industriels manipulant du dioxyde de titane (TiO2) - Eléments relatifs à la surveillance métrologique dans l’environnement et à l’examen de la faisabilité

International audienceRésumé : Mesures de protection des populations potentiellement exposées autour des sites industriels manipulant du dioxyde de titane (TiO2) - Eléments relatifs à la surveillance métrologique dans l’environnement et à l’examen de la faisabilitéDans le cadre de la protection des travailleurs et des personnes au voisinage de sites de production ou de manipulation de nanoparticules de dioxyde de titane (TiO2), la faisabilité d’une surveillance métrologique dans l’environnement du TiO2 nanométrique doit être examinée.Pour le HCSP il est envisageable de réaliser des mesures de taux de concentrations de nanoparticules de TiO2 dans l’air autour des sites industriels. Il n’existe cependant pas actuellement de méthode unique opérationnelle permettant de mesurer simultanément le nombre/la masse des particules et de réaliser l’analyse chimique des du TiO2 nanoparticulaire. Le HCSP considère que la mise en œuvre des méthodes de mesures ainsi que des modélisations sont très fortement dépendantes des situations à considérer et nécessitent différentes approches dont dépendront les stratégies de mesures à mettre en place.Ce rapport fait suite à la demande, faite au HCSP par la Direction générale de la prévention des risques, la Direction générale de la santé et la Direction générale du travail, de compléter son avis et son rapport du 29 avril 2018 concernant la protection des travailleurs et des personnes au voisinage de sites de production ou de manipulation de nanoparticules de dioxyde de titane.Le sujet des valeurs de gestion pour la protection des populations potentiellement exposées devra faire l’objet par la suite d’un autre rapport.Pour la réalisation du présent rapport, le HCSP a auditionné notamment des experts des méthodes de mesures des concentrations de particules dans l’air ainsi que des experts de la modélisation de la dispersion des particules dans l’air. Le HCSP a pris en compte les dispositions d’un arrêté préfectoral relatif à un industriel qui a mis en place une surveillance environnementale de routine des incidences de ses émissions de particules de TiO2.Lire aussi :•Protéger les travailleurs et les personnes au voisinage de sites de production ou de manipulation de nanoparticules de dioxyde de titane du 29 avril 201

Ionization photophysics and Rydberg spectroscopy of diacetylene

International audiencePhotoionization of diacetylene was studied using synchrotron radiation over the range 8-24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron-photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IEad = (10.17 ± 0.01) eV, and the appearance energy of the principal fragment ion C4H+ as AE = (16.15 ± 0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions ? , C3H+, ? and C2H+. Structured autoionization features observed in the PEPICO spectrum of diacetylene in the 11-13 eV region were assigned to vibrational components of three new Rydberg series, R1(nsσg, n = 4-11), R2(ndσg, n = 4-7) and R3(ndδg, n = 4-6) converging to the A2Πu state of the cation, and to a new series R‧1(nsσg, n = 3) converging to the ? state of the cation. The autoionization mechanisms and their consistence with specific selection rules are discussed

Prenatal exposure to paraquat and nanoscaled TiO2 aerosols alters the gene expression of the developing brain

International audienceNanopesticides are innovative pesticides involving engineered nanomaterials in their formulation to increase the efficiency of plant protection products, while mitigating their environmental impact. Despite the predicted growth of the nanopesticide use, no data is available on their inhalation toxicity and the potential cocktail effects between their components. In particular, the neurodevelopmental toxicity caused by prenatal exposures might have long lasting consequences. In the present study, we repeatedly exposed gestating mice in a whole-body exposure chamber to three aerosols, involving the paraquat herbicide, nanoscaled titanium dioxide particles (nTiO2), or a mixture of both. Particle number concentrations and total mass concentrations were followed to enable a metrological follow-up of the exposure sessions. Based on the aerosols characteristics, the alveolar deposited dose in mice was then estimated. RNA-seq was used to highlight dysregulations in the striatum of pups in response to the in utero exposure. Modifications in gene expression were identified at post-natal day 14, which might reflect neurodevelopmental alterations in this key brain area. The data suggest an alteration in the mitochondrial function following paraquat exposure, which is reminiscent of the pathological process leading to Parkinson disease. Markers of different cell lineages were dysregulated, showing effects, which were not limited to dopaminergic neurons. Exposure to the nTiO2 aerosol modulated the regulation of cytokines and neurotransmitters pathways, perhaps reflecting a minor neuroinflammation. No synergy was found between paraquat and nTiO2. Instead, the neurodevelopmental effects were surprisingly lower than the one measured for each substance separately

Ionization photophysics and spectroscopy of cyanoacetylene

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Ionization photophysics and spectroscopy of dicyanoacetylene.

International audiencePhotoionization of dicyanoacetylene was studied using synchrotron radiation over the excitation range 8-25 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and detailed spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of dicyanoacetylene was measured as 11.80 ± 0.01 eV. A detailed analysis of the cation spectroscopy involves new aspects and new assignments of the vibrational components to excitation of the quasi-degenerate A(2)Πg, B(2)Σg(+) states as well as the C(2)Σu(+) and D(2)Πu states of the cation. Some of the structured autoionization features observed in the 12.4-15 eV region of the total ion yield spectrum were assigned to vibrational components of valence shell transitions and to two previously unknown Rydberg series converging to the D(2)Πu state of C4N2(+). The appearance energies of the fragment ions C4N(+), C3N(+), C4(+), C2N(+), and C2(+) were measured and their heats of formation were determined and compared with existing literature values. Thermochemical calculations of the appearance potentials of these and other weaker ions were used to infer aspects of dissociative ionization pathways