Il est probable qu'à terme les émissions de nanoparticules soient réglementées et ce sont donc les concentrations en nombre qui seront considérées. Il convient donc d'adapter les modèles afin de pouvoir simuler correctement les concentrations en nombre, dans les ambiances confinées comme dans l'atmosphère. Un modèle de dynamique des particules capable de suivre avec autant de précision la concentration en nombre que la concentration en masse, avec un temps de calcul optimal, a été développé. La dynamique des particules dépend de divers processus, les plus importants étant la condensation/évaporation, suivie par la nucléation, la coagulation, et les phénomènes de dépôts. Ces processus sont bien connus pour les particules fines et grossières, mais dans le cas des nanoparticules, certains phénomènes additionnels doivent être pris en compte, notamment l'effet Kelvin pour la condensation/ évaporation et les forces de van der Waals pour la coagulation. Le travail a tout d'abord porté sur le processus de condensation/évaporation, qui s'avère être le plus compliqué numériquement. Les particules sont présumées sphériques. L'effet Kelvin est pris en compte car il devient considérable pour les particules de diamètre inférieur à 50 nm. Les schémas numériques utilisés reposent sur une approche sectionnelle : l'échelle granulométrique des particules est discrétisée en sections, caractérisées par un diamètre représentatif. Un algorithme de répartition des particules est utilisé, après condensation/évaporation, afin de conserver les diamètres représentatifs à l'intérieur de leurs sections respectives. Cette redistribution peut se faire en terme de masse ou de nombre. Un des points clé de l'algorithme est de savoir quelle quantité, de la masse ou du nombre, doit être redistribuée. Une approche hybride consistant à répartir la quantité dominante dans la section de taille considérée (le nombre pour les nanoparticules et la masse pour les particules fines et grossières) a été mise en place et a permis d'obtenir une amélioration de la précision du modèle par rapport aux algorithmes existants, pour un large choix de conditions. Le processus de coagulation pour les nanoparticules a aussi été résolu avec une approche sectionnelle. La coagulation est régie par le mouvement brownien des nanoparticules. Pour cette approche, il a été constaté qu'il est plus efficace de calculer le noyau de coagulation en utilisant le diamètre représentatif de la section plutôt que de l'intégrer sur la section entière. Les simulations ont aussi pu montrer que les interactions de van der Waals amplifient fortement le taux de coagulation pour les nanoparticules. La nucléation a été intégrée au modèle nouvellement développé en incorporant un terme source de nanoparticules dans la première section, commençant à un nanomètre. La formulation de ce taux de nucléation correspond à celle de l'acide sulfurique mais le traitement des interactions numériques entre nucléation, coagulation et condensation/évaporation est générique. Différentes stratégies de couplage visant à résoudre séparément ou en même temps les trois processus sont discutées. Afin de pouvoir proposer des recommandations, différentes méthodes numériques de couplage ont été développées puis évaluées par rapport au temps de calcul et à la précision obtenue en terme de concentration massique et numérique / It is necessary to adapt existing models in order to simulate the number concentration, and correctly account for nanoparticles, in both free and confined atmospheres. A model of particle dynamics capable of following accurately the number as well as the mass concentration of particles, with an optimal calculation time, has been developed. The dynamics of particles depends on various processes, the most important ones being condensation/evaporation, followed by nucleation, coagulation, and deposition phenomena. These processes are well-known for fine and coarse particles, but some additional phenomena must be taken into account when applied to nanoparticles, such as the Kelvin effect for condensation/evaporation and the van der Waals forces for coagulation. This work focused first on condensation/evaporation, which is the most numerically challenging process. Particles were assumed to be of spherical shape. The Kelvin effect has been taken into account as it becomes significant for particles with diameter below 50 nm. The numerical schemes are based on a sectional approach : the particle size range is discretized in sections characterized by a representative diameter. A redistribution algorithm is used, after condensation/ evaporation occurred, in order to keep the representative diameter between the boundaries of the section. The redistribution can be conducted in terms of mass or number. The key point in such algorithms is to choose which quantity has to be redistributed over the fixed sections. We have developed a hybrid algorithm that redistributes the relevant quantity for each section. This new approach has been tested and shows significant improvements with respect to most existing models over a wide range of conditions. The process of coagulation for nanoparticles has also been solved with a sectional approach. Coagulation is monitored by the brownian motion of nanoparticles. This approach is shown to be more efficient if the coagulation rate is evaluated using the representative diameter of the section, rather than being integrated over the whole section. Simulations also reveal that the van derWaals interactions greatly enhance coagulation of nanoparticles. Nucleation has been incorporated into the newly developed model through a direct source of nanoparticles in the first size section, beginning at one nanometer. The formulation of this rate of nucleation corresponds to that of sulfuric acid but the treatment of the numerical interactions between nucleation, coagulation and condensation/evaporation is generic. Various strategies aiming to solve separately or jointly these three processes are discussed. In order to provide recommendations, several numerical splitting methods have been implemented and evaluated regarding their CPU times and their accuracy in terms of number and mass concentrations

This thesis is focused on nanoparticles produced by internal combustion engines utilized in vehicles. It deals with spatial distribution of nanoparticles within urban areas, impact of alternative fuels usage on particle production and toxicity, and a particle toxicological testing methodology. Monitoring of airborne nanoparticles identified traffic as the main source of airborne nanoparticles in places with heavy traffic load (Prague), as well as in a small city with only local traffic (Čelákovice). Most particles were likely emitted during short episodes of high emissions (e.g. uphill acceleration). During the measurements, high-emission vehicles responsible for a large fraction of the air pollution were also identified. On the other hand, small non-road internal combustion engines, which are not subject to any limit on particle emissions, such as a lawn mower, were operated during the measurement and generated a large number of nanoparticles. The amount and characteristics of the particles produced by combustion depend on the combustion technology and the fuel composition. A large part of the thesis deals with alternative fuels and their effects on the quantity of produced particles and toxicity of organic matter adsorbed on the particles. Hydrotreated vegetable oil (HVO) exhibited the lowest...

Marine aerosols have attracted increasing attention over the past 15 years because of their potential significance for global climate modelling. The size distribution of these aerosols extends from super-micrometer sea salt mode particles down through 150 nm accumulation mode particles, 40 nm Aitken mode particles and nucleation mode particles which extend from 25 nm right down to clusters of a few molecules. The process by which the submicrometer modes form and grow and their composition have remained topics of debate throughout this time in large part because of the difficulties associated with determining their composition and relating it to proposed models of the formation process. The work compared the modality of marine aerosol influencing the South-east-Queensland region with that of other environmental aerosols in the region. The aerosol was found to be consistent with marine aerosols observed elsewhere with concentrations below 1000 cm-3 and frequently exhibiting the distinct bimodal structure associated with cloud processing, consisting of an Aitken mode at approximately 40 nm, an accumulation mode in the range 100-200 nm and a coarse mode attributed to sea salt between 600 and 1200 nm. This work included the development of two new techniques for aerosol research. The first technique measures aerosol density using a combination of aerosol size distribution and gravimetric mass concentration measurements. This technique was used to measure the density of a number of submicrometer aerosols including laboratory generated NaCl aerosol and ambient aerosol. The densities for the laboratory generated aerosols were found to be similar to those for the bulk materials used to produce them. The technique, extended to super-micrometer particle size range may find application in ambient aerosol research where it could be used to discriminate between periods when the aerosol is dominated by NaCl and periods when the density is more representative of crustal material or sulfates. The technique may also prove useful in laboratory or industrial settings for investigating particle density or in case where the composition is known, morphology and porosity. The second technique developed, integrates the existing physicochemical techniques of volatilisation and hygroscopic growth analysis to investigate particle composition in terms of both the volatilisation temperatures of the chemical constituents and their contribution to particle hygroscopic behaviour. The resulting volatilisation and humidification tandem differential mobility analyser or VH-TDMA, has proven to be a valuable research tool which is being used in ongoing research. Findings of investigations relating the composition of the submicrometer marine aerosol modes to candidate models for their formation are presented. Sea salt was not found in the numerically dominant particle type in coastal nucleation mode or marine Aitken and accumulation modes examined on the Southeast Queensland coast during periods where back trajectories indicated marine origin. The work suggests that all three submicrometer modes contain the same four volatile chemical species and an insoluble non-volatile residue. The volatility and hygroscopic behaviours of the particles are consistent with a composition consisting of a core composed of sulfuric acid, ammonium sulfate and an iodine oxide coated with a volatile organic compound. The volume fraction of the sulfuric acid like species in the particles shows a strong dependence on particle size.

Nano-particle aerosols are one of the major types of air pollutants in the urban indoor and outdoor environments. Therefore, determination of mechanisms of formation, dispersion, evolution, and transformation of combustion aerosols near the major source of this type of air pollution - busy roads and road networks - is one of the most essential and urgent goals. This Thesis addresses this particular direction of research by filling in gaps in the existing physical understanding of aerosol behaviour and evolution. The applicability of the Gaussian plume model to combustion aerosols near busy roads is discussed and used for the numerical analysis of aerosol dispersion. New methods of determination of emission factors from the average fleet on a road and from different types of vehicles are developed. Strong and fast evolution processes in combustion aerosols near busy roads are discovered experimentally, interpreted, modelled, and statistically analysed. A new major mechanism of aerosol evolution based on the intensive thermal fragmentation of nano-particles is proposed, discussed and modelled. A comprehensive interpretation of mutual transformations of particle modes, a strong maximum of the total number concentration at an optimal distance from the road, increase of the proportion of small nano-particles far from the road is suggested. Modelling of the new mechanism is developed on the basis of the theory of turbulent diffusion, kinetic equations, and theory of stochastic evaporation/degradation processes. Several new powerful statistical methods of analysis are developed for comprehensive data analysis in the presence of strong turbulent mixing and stochastic fluctuations of environmental factors and parameters. These methods are based upon the moving average approach, multi-variate and canonical correlation analyses. As a result, an important new physical insight into the relationships/interactions between particle modes, atmospheric parameters and traffic conditions is presented. In particular, a new definition of particle modes as groups of particles with similar diameters, characterised by strong mutual correlations, is introduced. Likely sources of different particle modes near a busy road are identified and investigated. Strong anti-correlations between some of the particle modes are discovered and interpreted using the derived fragmentation theorem. The results obtained in this thesis will be important for accurate prediction of aerosol pollution levels in the outdoor and indoor environments, for the reliable determination of human exposure and impact of transport emissions on the environment on local and possibly global scales. This work will also be important for the development of reliable and scientifically-based national and international standards for nano-particle emissions.