The creation of new atmospheric particles via nucleation is an important source of particles, and may influence climate by altering the aerosol size distribution. The objectives of my dissertation research were to better understand the process by which new particles are created (homogeneous nucleation), and how these particles are modified throughout their lifetime in the atmosphere. The approach combined field-measurements and observations with advanced instrumentation development and extensive data analysis. In the laboratory, a Dry-Ambient Aerosol Size Spectrometer (DAASS) was constructed. The DAASS is an automated combination of aerosol sizing instruments and supporting equipment that measures aerosol size distributions from 10.9 nm to 10 µm at both ambient and dry relative humidities and was deployed during the MILAGRO field campaign. The design and construction of a Differential Mobility Analyzer from parts was also completed in order to provide the capability to perform Tandem DMA (or TDMA) measurements. New particle formation events, occurring in both rural (Midwest United States) and urban (Mexico City) locations were analyzed. In the Midwest, the temporal pattern, frequency, associated meteorology and contributing factors were quantified for the first time in this location. The urban observations were conducted in Mexico City, Mexico, as part of an international field campaign known as MILAGRO (Megacity Initiative: Local and Global Research Observations 2006). It was determined that new particle formation in Mexico City occurs following periods of decreased pre-existing aerosol surface area. These sharp decreases in pre-existing aerosol surface area are tied to the rapid ventilation of the Mexico City basin that occurs in the early afternoon as a result of its unique geographical setting in a mountain basin. Number-based emission factors representative of Mexico City were determined using a method of signal peak identification in collocated SMPS and CO2 measurements. The emission factor as a function of time of day, day of week, and wind direction were examined. The overall emission factor is size resolved, and comparisons to other size resolved emission factors determined in other locations (such as Los Angeles) were performed.

1 ABSTRACT: This study is dedicated to the study of nucleation of sulphuric acid and water, which presents the key process associated with secondary aerosol formation via gas to particle conversion. We investigated the nucleation rates, new aerosol particles formation and growth dynamics of newly nucleated particles. These processes were explored in both laboratory and field experiments. In the laboratory measurements, we explored the H2SO4 - H2O nucleation rates and growth rates of newly formed particles under well-defined conditions and we also investigated the effect of experimental conditions on particle growth dynamics. Furthermore, we proposed a model, which predicts the particle growth and accounts for condensation of H2SO4, H2O and NH3. The comparison of experimental growth rates with atmospheric ones was made and resulting implications of the chemical nature of compounds involved in the early growth of nucleated particles is also presented. To investigate the atmospheric H2SO4 - H2O nucleation and new particle formation, we analysed a two-year long dataset of particle number size distributions, obtained from a urban background station in Prague Suchdol. A special attention was given to a recently reported special feature of particle growth dynamics - a particle shrinkage following previous new...

L’objectif de ce travail de thèse est d’améliorer l’état de nos connaissances sur les processus de formation et du devenir de l’AOS, en lien avec la réactivité des COVB avec les oxydants de l’atmosphère et en particulier l’ozone, en utilisant le potentiel de l’écosystème landais en tant que source d'AOS biogénique. Pour cela, des campagnes de terrain ont été menées sur un site de mesure en forêt landaise, écosystème particulièrement approprié pour l’étude de la formation et du devenir des AOS. Au cours de ces campagnes, différents paramètres physico-chimiques complémentaires ont été mesurés, tels que les concentrations et les flux de particules, d’oxydants et de COVB. Des épisodes nocturnes de formation de nouvelles particules ont été mis en évidence, ce qui constitue un résultat original car les évènements rapportés jusqu’ici dans la littérature étaient principalement diurnes. La contribution importante de l’ozonolyse des monoterpènes émis par les pins maritimes, dominés par l’α- et le β-pinène, à la formation nocturne de nouvelles particules a également été démontrée. Les mesures de flux de particules réalisées suggèrent que les particules formées au cours de la nuit sont transférées depuis la canopée vers les plus hautes couches de l’atmosphère. Une production d’ozone a également été démontrée par la comparaison des mesures de flux d’ozone à un modèle physique de dépôt. Cette source d’ozone pourrait être liée à la photooxidation des COVB / Forest ecosystems affect air quality and climate, especially through the emissions and the reactions of biogenic volatile organic compounds (BVOCs) with the atmospheric oxidants, known to generate Secondary Organic Aerosols (SOAs). This work aims to improve our knowledge on the processes involved in biogenic SOA formation and fate. Two field campaigns have been conducted in the Landes forest. In a first step, the measurement site was characterized by a statistical study of local meteorological conditions. During these campaigns, complementary physical and chemical measurements have been carried out, implying measurements of fluxes and concentrations of particles, BVOCs and oxidants. The results evidenced nocturnal new particle formation, which is an original result as this process was usually only reported during daytime. The strong contribution of BVOCs (dominated by α- and β-pinene) ozonolysis to nocturnal new particle formation has been demonstated. Particle flux measurements suggested that particles are transfered from the canopy to the higher atmospheric surface layer. The comparison between ozone fluxes and a physical ozone deposition model also highlighted an ozone production source. This ozone production might be related to BVOC photooxidation.