Neste trabalho foi apresentado um sistema para decomposição de aerossóis partindo de soluções contendo naftaleno (C10H8) e tolueno (C7H8) diluídos em nitrogênio por meio da aplicação individual e combinada de plasma e micro-ondas. O naftaleno e o tolueno são chamados nesta tese como \"compostos modeladores de alcatrão\" como sugere a literatura. A disposição e geometria das câmaras de plasma e micro-ondas foram estabelecidas por meio do auxílio de simulações fluidodinâmicas empregando o FloEFD V.16 (Mentor Graphics) associado aos modelos sólidos desenhados no Solid Edge ST10 (SIEMENS). Os processos de coleta de resíduos dos compostos modeladores de alcatrão, seja das cinzas, sejam da fração não decomposta foram obtidos de acordo com um protocolo bem estabelecido baseado em estudos descritos na literatura. As concentrações de tolueno e naftaleno foram obtidas utilizando espectrometria de mobilidade iônica com ionização por electrospray (ESI-IMS). Não foram empregados materiais catalisadores. As densidades de energia empregadas ao longo deste trabalho foram 0,73, 1,22 e 1,98 kWh·m-3, sob uma vazão constante de 10 L·min-1 de N2 para concentrações de 3,0 e 5,0 g·m-3 de naftaleno e tolueno. As temperaturas empregadas na decomposição térmica assistida por micro-ondas foram de 845, 960 e 1.016 °C. Para cada uma das densidades de energia, considerando a concentração de 3,0 g·m-3 de naftaleno, as eficiências obtidas por meio do plasma foram de 48,3, 59,6 e 72,2%, enquanto que aplicando micro-ondas foram de 46,2, 57,9 e 68,2%. Por outro lado, considerando a concentração de 5,0 g·m-3, as eficiências foram 31,5, 45,9 e 64,8% para plasma e 26,6, 44,3 e 56,8% empregando a decomposição térmica assistida por micro-ondas, respectivamente. Analogamente, considerando a concentração de 3,0 g·m-3 de tolueno, as eficiências foram de 52,2, 69,9 e 84,5 % por meio de plasma e 49,3, 66,8 e 79,9% por meio de micro-ondas. Finalmente, considerando a concentração de 5,0 g·m-3, as eficiências foram 33,8, 60,7 e 80,7 % empregando plasma e 30,1, 54,1 e 72,9% empregando a decomposição térmica assistida por micro-ondas, respectivamente. Por meio do teste pareado de Wilcoxon, pôde ser afirmado com evidência estatística suficiente a 95% de certeza de que decomposição por plasma foi mais eficiente do que a decomposição térmica assistida por micro-ondas e SiC. / In this work a system for the aerosols decomposition from aerosols containing naphthalene (C10H8) and toluene (C7H8) diluted in nitrogen by means of the individual and combined application of plasma and microwaves was presented. Naphthalene and toluene are referred to in this thesis as \"modeling compounds of tar\" as suggested by the literature. The arrangement and geometry of the plasma and microwave chambers were established with the aid of fluid dynamics simulations using FloEFD V.16 (Mentor Graphics) associated to solid models drawn in Solid Edge ST10 (SIEMENS). The residues collection processes of the tar model compounds, whether from the ashes or from the non-decomposed fraction of the tar model compounds were constructed according to a protocol based on well-established studies presented in the literature. The toluene and naphthalene concentrations were obtained using ion mobility spectrometry with ionization by electrospray (ESI-IMS). No catalyst materials were used. The energy densities employed during this work were 0.73, 1.22 and 1.98 kWh·m-3, under a constant flow rate of 10 L·min-1 of N2 at concentrations of 3.0 and 5.0 g·m-3 of naphthalene and toluene. The temperatures obtained in microwave assisted thermal decomposition were 845, 960 and 1016 °C. For each of the energy densities, considering the concentration of 3.0 g·m-3 of naphthalene, the efficiencies obtained by means of plasma were 48.3, 59.6 and 72.2%, while applying microwave were 46.2, 57.9 and 68.2%. On the other hand, considering the concentration of 5.0 g·m-3, the efficiencies were 31.5, 45.9 and 64.8% for plasma and 26.6, 44.3 and 56.8% using decomposition microwave assisted thermal power, respectively. Similarly, considering the 3.0 g·m-3 concentration of toluene, the efficiencies were 52.2, 69.9 and 84.5% by means of plasma and 49.3, 66.8 and 79.9% by means of microwaves. Finally, considering the concentration of 5.0 g·m-3, efficiencies were 33.8, 60.7 and 80.7% using plasma and 30.1, 54.1 and 72.9% employing assisted thermal decomposition by microwave, respectively. The Wilcoxon paired test was applied and it was stated sufficient statistical evidence with a 95% level of certainty that plasma decomposition was more efficient than microwave and SiC assisted thermal decomposition.

La crise alimentaire de 2008 a suscité un regain d’intérêt pour les questions agricoles et de sécurité alimentaire dans les pays en développement. Partant du constat que près de 27% de la population d’Afrique Sub-saharienne souffre de malnutrition, cette thèse a pour objectif de contribuer à une meilleure compréhension des causes complexes de l’insécurité alimentaire. Le premier chapitre étudie les mécanismes de transmission des variations du prix mondial du riz aux prix domestiques dans trois pays ouest-africain: le Sénégal, le Tchad et le Mali. Les résultats indiquent que le prix du riz importé à Dakar et le prix du riz local à Bamakorépondent de façon asymétrique aux variations du prix mondial. Le chapitre 2 teste la présence d’obstacles aux échanges agricoles entre pays d’Afrique de l’Ouest et du Centre. Il ressort de l’analyse que le passage des frontières est coûteux. Toutefois, le coût associé au passage de la frontière est plus faible entre pays membre d’une même union économique et monétaire. Le chapitre 3 a pour objectif le renforcement des systèmes d’alertes précoces des crises alimentaires existants au Sahel. Il montre qu’il est possible d’anticiper les crises de prix avec six mois d’avance en analysant les mouvements passés des prix des céréales. Enfin, le chapitre 4 s’intéresse à la vulnérabilité des ménages face aux chocs pluviométriques. Il révèle que les ménages ruraux au Burkina Faso n’ont pas la capacité d’assurer ou d’absorber ces chocs climatiques. / This doctoral thesis is in line with the renewed interest in research on agriculture and food security, following the 2008 global food crisis. The aim of this thesis is to contribute to a better understanding of the complex issues surrounding food security. The first chapter investigates whether the changes in the international price of rice are transmitted to the domestic prices of rice in Senegal, Mali and Chad. Results indicate that the domestic prices of imported rice in Dakar and of local rice in Bamako react differently to changes in the world price depending on whether the world price is rising or falling. Chapter 2 analyses by how much trade barriers at the border and transport costs impede the integration of agricultural markets in West and Central Africa. Results highlight the role played by borders in explaining price deviations between markets. Additionally, belonging to an economic union and sharingthe same currency appear as major determinants of market integration. The third chapter aims at providing new early warning indicators based on food prices in Mali, Niger and Burkina Faso. Our analysis reveals that price crisis can be predicted about 6 months in advance through the observation of past price movements. Chapter 4 focuses on the analysis of children’s vulnerability to climate shocks in Burkina Faso. By combining health data originating from a 2008 household survey with meteorological data, we show the importance of weather conditions in prenatal period and in the first year of life on the future nutritional status of the children.