Assessing the Relative Importance of Saharan Dust, Biomass Burning, and Urban Emissions on PM2.5 in West African Cities PDF Download

Author: Aara L. Yarber
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Languages : en
Pages : 0

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Book Description
West Africa is an intense emitter of both anthropogenic and natural particulate pollution, both of which have been shown to have adverse health effects on human populations. Hosting some of the world's largest pollutant sources, such as Saharan dust and biomass burning, coupled with rapid urbanization, exploding population growth, and extreme poverty, West African pollution is complex. Despite its nuances, particulate pollution is not well characterized throughout the region, partially due to a lack of air quality monitoring networks. The recent emergence of PM2.5 measurements provided by the Environmental Protection Agency presents a unique opportunity to increase our understanding of particulate pollution in West African cities. The first part of this dissertation uses a series of ground based aerosol measures and satellite derived aerosol products to examine spatiotemporal aerosol patterns. The objective was to ascertain the comparative impact of Saharan dust, biomass burning, and urban emission on PM2.5 concentrations in West African cities. The main findings indicate that background emissions, particularly Saharan dust, was the dominant emission source during the dry season, with dust events causing unhealthy to hazardous air quality regionally. Biomass burning and urban PM2.5 signals were less distinct throughout the year, suggesting their relative contributions were generally lower than dust. However, urban emission appeared to be the dominant source during the wet season, particularly in Nigerian cities and cities along the southern Gulf of Guinea coast. The second part of this dissertation involves evaluating aerosol levels and composition with WRFChem to assess the model's reliability for source characterization in West Africa. The results indicate that the model showed skill in reproducing the seasonality of daily PM2.5 and AOD averages throughout the year. However, the model's performance in replicating observed PM2.5 and AOD varied by location. PM2.5 and AOD were largely overestimated during the dry season, especially in Northwest Africa. The evaluation of PM2.5 speciation in Ilorin revealed that dust was largely overestimated. However, black carbon in Ilorin was underestimated by the model, likely in part due to an underestimation of biomass burning and urban emissions. The last part of this dissertation uses WRF-Chem to examine the relative importance of dust, biomass burning, and urban emission on total PM2.5. The main findings suggest that dust was the dominant emission source during the dry season across all cities. However, dust was significantly overestimated across West Africa, often exceeding total observed PM2.5 and AOD. During the wet season, dust was the dominant source across cities in Northwest Africa. However, urban emission became the predominant emission source in Nigerian cities as well as cities along the southern Gulf of Guinea coast. West African biomass burning and biomass burning advection from Central Africa had a significant effect on air quality in West African cities during the dry and wet season. Furthermore, emissions from each source repeatedly exceeded the WHO 24-hour limit throughout the year. Thus, single sources alone are likely problematic for public health in the region. Though dominant emission sources inferred from observational and modeled data were aligned, significant model biases in aerosol composition were revealed. The degree to which PM2.5 and AOD biases are attributed to inaccuracies in emission fluxes versus meteorology, however, remains unclear. To fully refine models, enhance inventories, evaluate pollution sources, and thus create efficient control strategies, extensive meteorological and air quality observational networks are required.