A l'échelle locale et dans les zones habitées, une part importante de la pollution particulaire est imputable au trafic automobile. Plus précisément, il contribue fortement à l'augmentation des concentrations en nombre. Principalement deux sources de particules sont reliées au trafic. L'émission primaire de particules de suies et la formation de nanoparticules secondaires par nucléation. Les émissions et les mécanismes menant à la formation de cette distribution bimodale sont encore mal connus de nos jours. Dans cette thèse, on propose de tenter de répondre à cette problématique par la modélisation numérique. Le modèle modal d'aérosols MAM est utilisé, couplé à deux codes 3D : un CFD (Mercure Saturne) et un CTM (Polair3D). La méthode consiste à effectuer des tests de sensibilité, à l'échelle d'un bord de route mais aussi dans les premiers mètres du panache d'échappement, afin d'identifier les rôles respectifs des divers processus ainsi que les paramètres sensibles de la modélisation.

Exposure to aerosol particles can cause health issues such as respiratory and cardiovascular diseases. Nevertheless, aerosol particle exposure with size-resolved information was seldom investigated in real-life European houses in the long term, especially for the ultrafine size range. In this work, indoor and outdoor measurements were conducted from December 2016 to March 2019. A standard of high-quality indoor and outdoor particle measurements in multi-homes was established for the first time. For more than 500 days, measurement data were collected in 40 German homes, including particle mass concentrations (PMC) of PM10, PM2.5, and PM1, particle number concentration (PNC) and size distribution, equivalent black carbon (eBC) mass concentration, CO2 concentration, and the residents’ activity log. With such novel dataset, representative patterns of diurnal and seasonal variation of particle concentration and size distribution as well as eBC mass concentration have been captured. In the warm season, diurnal cycles of indoor PMC and PNC showed weaker variation and less intense peaks (around the time of breakfast, lunch and dinner) than in the cold season, due to ventilation reducing the effect of indoor sources. To better understand the key dynamic processes of indoor particles (i.e. ventilation, building shell penetration, particle losses and emission), two commonly used quantitation methods, single parameter approach (SPA) and Indoor Aerosol Model approach (IAM), were compared and evaluated for the first time. Correction factors were derived to adjust the emission rates calculated from the simplified SPA approach, making emission rates derived from different levels of analysis mutually comparable. Results show that indoor source was the major contributor (56%) to indoor particle number exposure in investigated German residences. For the contribution of outdoors, penetration through the building envelope (26%) was higher than infiltration through open windows (15%). Burning candles and opening of window(s) led to seasonal differences in the contributions of indoor sources to residential exposure (70% and 40% in the cold and warm season, respectively). Indoor sources should be taken into consideration in future epidemiological studies and risk assessment of exposure to particle air pollution. / Aerosolpartikel können gesundheitliche Probleme wie Atemwegs- und Herz-Kreislauf-Erkrankungen verursachen. Jedoch wurde die Aerosolpartikelexposition, insbesondere für ultrafeine Partikel, in realen Europäischen Haushalten bisher nicht langfristig untersucht. Für diese Arbeit wurden Messungen im Innen- und Außenbereich von Dezember 2016 bis März 2019 durchgeführt. Erstmals wurde ein Standard für qualitativ hochwertige Innen- und Außenmessungen von Aerosolpartikeln in Wohnhäusern etabliert. An mehr als 500 Tagen wurden Messdaten verteilt über 40 deutsche Haushalte gesammelt, darunter die Partikelmassekonzentration (PMC) von PM10, PM2,5 und PM1, die Partikelanzahlkonzentration (PNC) und deren Größenverteilung, die Massekonzentration des äquivalenter schwarzer Kohlenstoff (eBC – equivalent Black Carbon) und ein Aktivitätsprotokoll der Bewohner. Mit diesem neuartigen Datensatz wurden repräsentative Muster der tages- und jahreszeitlichen Variation der Partikelkonzentration und Partikelgrößenverteilung sowie der eBC-Konzentration erstellt. Im Sommerhalbjahr zeigen sich schwächere Variationen und weniger intensive Spitzen (während der Frühstücks-, Mittags- und Abendessenszeit) in den Tageszyklen von PMC und PNC als im Winterhalbjahr. Dies ist auf die die Belüftung zurückzuführen, die den Effekt von Innenraumquellen reduziert. Zwei häufig verwendete Quantifizierungsmethoden der Schlüsselprozesse, der Single-Parameter-Ansatz (SPA) und der Indoor-Aerosol-Modellansatz (IAM), wurden zum ersten Mal quantitativ verglichen und bewertet. Es wurden Korrekturfaktoren abgeleitet, um die mit dem vereinfachten SPA-Ansatz berechneten Emissionsraten anzupassen, so dass die aus verschiedenen Analyseebenen abgeleiteten Emissionsraten miteinander vergleichbar sind. Die Ergebnisse zeigen, dass Quellen in Innenräumen den größten Beitrag (56%) zur Partikelanzahlexposition der Bewohner der untersuchten deutschen Haushalte leisten. Der Beitrag des Außenbereichs durch das Eindringen durch die Gebäudehülle (26%) ist höher als der durch offene Fenster (15%). Brennende Kerzen und das Öffnen von Fenster(n) hatten den größten Einfluss auf die saisonalen Unterschiede in der Partikelexposition. Innenraumquellen sollten in zukünftigen epidemiologischen Studien und bei der Risikobewertung Aerosolpartikelexposition berücksichtigt werden.

Aerosols contribute the largest uncertainty to estimates of radiative forcing of the Earth’s atmosphere, which are thought to exert a net negative radiative forcing, offsetting a potentially significant but poorly constrained fraction of the positive radiative forcing associated with greenhouse gases. Aerosols perturb the Earth’s radiative balance directly by absorbing and scattering radiation and indirectly by acting as cloud condensation nuclei, altering cloud albedo and potentially cloud lifetime. One of the major factors governing the uncertainty in estimates of aerosol direct radiative forcing is the poorly constrained aerosol single scattering albedo, which is the ratio of the aerosol scattering to extinction. In this thesis, I describe a new instrument for the measurement of aerosol optical properties using photoacoustic and cavity ring-down spectroscopy. Characterisation is performed by assessing the instrument minimum sensitivity and accuracy as well as verifying the accuracy of its calibration procedure. The instrument and calibration accuracies are assessed by comparing modelled to measured optical properties of well-characterised laboratory-generated aerosol. I then examine biases in traditional, filter-based absorption measurements by comparing to photoacoustic spectrometer absorption measurements for a range of aerosol sources at multiple wavelengths. Filter-based measurements consistently overestimate absorption although the bias magnitude is strongly source-dependent. Biases are consistently lowest when an advanced correction scheme is applied, irrespective of wavelength or aerosol source. Lastly, I assess the sensitivity of the direct radiative effect of biomass burning aerosols to aerosol and cloud optical properties over the Southeast Atlantic Ocean using a combination of offline radiative transfer modelling, satellite observations and global climate model simulations. Although the direct radiative effect depends on aerosol and cloud optical properties in a non-linear way, it appears to be only weakly dependent on sub-grid variability.

Aerosol properties are highly variable in space and time which makes the aerosol study more complex. The sources and production mechanism of aerosols decide the properties of the aerosols. Aerosol radiative forcing is defined as the perturbation to the radiative fluxes of the earth atmosphere system caused by the aerosols. High uncertainty in the aerosol radiative forcing values exists today due to the lack of the exact chemical composition data of the aerosols everywhere. There are previous studies which have introduced methods to estimate ‘optical equivalent’ composition of aerosols using spectral aerosol optical depth measurements at the surface. The impact of aerosols on the solar radiative flux depends on its size distribution and composition. Hence, measurements of downward solar spectral fluxes at the surface can be used to infer ‘optically equivalent’ composition of aerosols. Measurements of downward solar spectral flux at Bangalore were made on clear days using a spectroradiometer. This data has been used to infer the aerosol composition following an iterative method with the help of the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART). Aerosols have been classified as water soluble, black carbon and three types of dust. Influence of the different aerosol types on spectral down welling irradiance at the surface have been simulated using Optical Properties of Aerosols and Clouds (OPAC) and SBDART models. The strong spectral dependence influence of water soluble aerosols and the dust aerosols on the spectral irradiance is shown. Aerosol composition was inferred following least square error minimization principle. This method can be used to estimate near-surface aerosol concentration if the vertical profile of aerosols is known a priori. This method also enables derivation of spectral single scattering albedo. The aerosol spectral radiative forcing has been estimated using downward spectral flux at the surface and compared with modeled fluxes. The contribution to the total forcing by the wavelength band 360 – 528 nm is around 60% of the total forcing. The wavelength band of 453-518 nm contributes maximum to the total forcing and it is seen that the shape of the spectral forcing is a major function of shape of the incoming solar spectrum. Aerosol spectral radiative forcing from observations of radiative fluxes agreed with modeled values when derived aerosol chemical composition was used as input. This study demonstrates that spectral flux measurements at the surface are useful to infer aerosol composition (which is optically equivalent) when and where the conventional chemical analysis is unavailable.

Des modèles de chimie transport permettent le suivi réaliste des polluants en phase gazeuse dans l'atmosphère. Cependant, lapollution atmosphérique se trouve aussi sous forme de fines particules en suspension, les aérosols, qui interagissent avec la phase gazeuse, le rayonnement solaire, et possèdent une dynamique propre. Cette thèse a pour objet la modélisation et la simulation numérique de l'Equation Générale de la Dynamique des aérosols (GDE). La partie I traite de quelques points théoriques de la modélisation des aérosols. La partie II est consacrée à l'élaboration du module d'aérosols résolu en taille (SIREAM). dans la partie III, on effectue la réduction du modèle en vue de son utilisation dans un modèle de dispersion tel que POLAIR3D. Plusieurs points de modélisation restent encore largement ouverts: la partie organique des aérosols, le mélange externe, le couplage à la turbulence, et les nano-particules.