Pollutions atmosphérique et sonore en milieu urbain : le cas d'Abidjan (Côte d'Ivoire)

Les pollutions atmosphérique et sonore sont un enjeu environnemental et de santé publique dans de nombreuses villes tant des Nords que des Suds. Les sources de pollution de ces deux nuisances sont aujourd’hui bien connues, soit principalement le transport et les activités industrielles. D’autres sources, comme la poussière et la combustion de la biomasse, sont spécifiques aux villes des Suds. Durant les dernières décennies, de nombreuses études ont modélisé et cartographié différents polluants atmosphériques et sonores. Toutefois, ces études ont été très majoritairement réalisées dans les villes des Nords. Parmi les villes des Suds, celles d’Afrique de l’Ouest (ex. : Abidjan), ont été peu étudiées. Pourtant, les niveaux de pollution y sont souvent bien plus élevés et en augmentation en raison de changements majeurs qui s’y opèrent, notamment des démographies et urbanisations accélérées générant un étalement non maîtrisé et une croissance exponentielle du parc automobile. Fort du constat relatif au manque des connaissances sur les pollutions atmosphérique et sonore dans les villes d’Afrique de l’Ouest, cette thèse portant sur le cas d’Abidjan vise à modéliser et à cartographier une série de polluants atmosphériques (dioxyde d’azote, PM2,5 et PM10) et d’indicateurs de bruit (LAeq,30, LAmin, LA10, LA50, LA90 et LAmax). Cette thèse est composée de six chapitres. Le premier est une revue de la littérature sur les pollutions atmosphérique et sonore. Elle conclut à la nécessité de caractérisation des villes des Suds en prenant en compte les approches émergentes de recherche. Le second chapitre fait une présentation de la méthodologie déployée, celle-ci met l’accent sur l’utilisation des capteurs à faible coût qui est une opportunité dans des contextes africains marqués par une faible surveillance continue. Une collecte extensive visant à maximiser la couverture de la ville et les types d’environnements urbains traversés a été réalisée. Au total, 920 kilomètres ont été parcourus dans les rues d’Abidjan avec des vélos instrumentés de différents appareils à faible coût mesurant trois polluants de l’air, le bruit et la position géographique et enregistrant des vidéos. Les chapitres trois et quatre présentent les résultats de la modélisation sur le bruit et les polluants atmosphériques. Ces résultats indiquent que le type de route, la nature du revêtement (asphalte) et la présence de feu tricolore contribuent à augmenter le niveau des polluants. Des modèles généralisés additifs avec un terme autorégressif sont utilisés pour prédire les niveaux de pollution sur l’ensemble du réseau routier de la ville et produire ainsi des cartes. Le chapitre cinq fait une classification de la ville d’Abidjan en tenant compte des divers types de polluants étudiés. Celle-ci donne trois types d’environnement qui sont très-moyen-peu pollués, puis fait une analyse partielle de l’équite environnementale. Et enfin le dernier chapitre croise les résultats des modélisations et de la classification, fait une comparaison avec d’autres études avant d’émettre des perspectives tant pour la recherche que pour la planification tout en tenant compte des limites de la thèse. Air and noise pollution are major environmental and public health issues in many cities, both in the global North and South. Today, the sources of air and noise pollution are well known and derive mainly from transportation and industrial activities. Other sources, such as dust and biomass combustion, are specific to cities in the South. In recent decades, numerous studies have modeled and mapped various air and noise pollutants. However, most of these studies have been carried out in Northern cities. Among the Southern cities, West African cities (e.g., Abidjan) have been little studied. Yet pollution levels in these cities are often much higher, and on the rise, due to the major changes taking place. These changes are notably accelerated demographic and urbanization trends generating uncontrolled sprawl and exponential growth in the number of cars on the road. Given the limited knowledge of air and noise pollution in Abidjan, this thesis aims to model and map several air pollutants (nitrogen dioxide, PM2.5 and PM10) and noise indicators (LAeq,30, LAmin, LA10, LA50, LA90 and LAmax). This thesis is divided into six chapters. The first is a review of the literature on air and noise pollution. It concludes with the need to characterize cities in the South, taking into account new research paradigms. The second chapter takes stock of the methodology deployed, emphasizing the use of low-cost sensors as an opportunity in African contexts marked by low levels of continuous monitoring. Extensive data collection was carried out to maximize coverage of the city and the types of urban environments encountered. A total of 920 kilometers were covered in the streets of Abidjan with bicycles instrumented with various low-cost devices measuring three air pollutants, noise and geographical position, and recording video. Chapters three and four present the modelling results for noise and air pollutants. These results indicate that the type of road, the nature of the surface (asphalt) and the presence of traffic lights all contribute to increasing pollutant levels. Additive generalized models with an autoregressive term are used to predict pollution levels across the city's road network and produce maps. Chapter five classifies the city of Abidjan according to the various types of pollutants studied. This gives three types of environments that are either very, moderately, or little polluted, followed by a partial analysis of environmental equity. Finally, the last chapter cross-references the results of the modelling and classification, compares them with those of other studies and sets out prospects for both research and planning, bearing in mind the limits of the thesis

Spatial assessment of nighttime anthropization in the Comoé National Park in Côte d’Ivoira (West Africa)

Protected areas play a crucial role in preserving biological diversity, providing ecosystem services, and regulating hydroclimatic processes. However, the environmental balance of these areas is increasingly under threat due to rapid population growth, high demand for natural resources, and the effects of global warming. To address this, sustainable management of protected areas is essential. This study aims to develop a methodology for monitoring and assessing levels of nocturnal anthropogenic aggression in the Comoé National Park (CNP) in Côte d’Ivoire. By using geospatial data from the Day/Night Band of the Visible Infrared Imaging Radiometer Suite (VIIRS/DNB), the study characterizes the nocturnal anthropization of CNP through the use of several indices. First, light reflectance density is used to identify nighttime light emission foci. Second, the lighted area density index (LADI) is employed to understand the nature of nocturnal activities taking place within CNP, as indicated by artificial light at night (ALAN). Finally, the light intensity index (LII) is used to evaluate the degree of influence of nocturnal anthropogenic activities on biodiversity. The study also found important activities through LADI and observed a high level of light pollution in CNP. Ultimately, the findings of this study indicate that there is a significant level of nocturnal anthropization within CNP, highlighting the need for effective management and conservation efforts in the area

Communicable and non-communicable disease risks at the Grand Magal of Touba: The largest mass gathering in Senegal

International audienceBackground: An estimated 4-5 million individuals gather each year in the holy city of Touba, Senegal during the Grand Magal religious pilgrimage. Pilgrims come from across Senegal and the surrounding countries, as well as from countries outside Africa. It is the largest mass gathering (MG) of the Mouride community and the largest Muslim religious MG in West Africa. Method: A cross-sectional study was conducted on all patients who attended a public healthcare structure during the November 2015 Grand Magal. Result: Data were collected on a total of 32,229 healthcare contacts. The most frequent reasons for consultation were trauma, followed by fatigue and heatstroke. Infectious diseases were also prevalent with, notably, a high rate of febrile systemic illnesses and malaria, diarrheal diseases, and respiratory tract infections. Such results are likely to be linked to overcrowding and climatic conditions, the relative lack of sanitary facilities, and limited medical resources available during the event. Conclusion: The context of the Grand Magal MG is unique, given its location in a tropical developing country and its international component which may favor the globalization of locally endemic diseases. As such, it warrants investment in modern methods for public health surveillance and planning of the event. (C) 2017 Elsevier Ltd. All rights reserved

Urban expansion of Korhogo City (Côte d’Ivoire) using gis and nocturnal remote sensing

Abstract Temporal data series of stable Artificial Lights At Night (ALAN) obtained from sources such as DMSP/OLS and VIIRS/DNB provide valuable insights into the dynamics of urban expansion. This study introduces a novel methodology for characterizing urban boundaries, which combines textural analysis utilizing the Co-occurrence matrix and urban surface delineation employing the Wombling contour detection algorithm. Applying this method to the city of Korhogo in northern Côte d'Ivoire, the findings reveal an irregular and gradual evolution of urban surfaces between 1992 and 2012, with a rate of change of 35 km2. However, starting from 2012, a rapid urbanization process is observed, continuing until 2020, characterized by an evolution rate of approximately 45 km2. Considering the significant urban expansion witnessed in the city of Korhogo, it is imperative to implement appropriate urban management strategies and measures for ecosystem protection