Air quality assessment and pollution measurements in a typical Sub-Sahara African city: Nairobi, Kenya
Sammanfattning: Exposure to air pollution is detrimental to human health and is reported to cause about 7 million premature deaths in 2012 according to the World Health Organization. In sub-Sahara Africa (SSA) cities, air quality issue is complex due to challenges resulting from the rapid growth of urban population, poor infrastructure development and an exponential increase in number of vehicles. The problem is compounded by lack of continuous monitoring of air pollution in most SSA cities. In this work, sources of particulate matter (PM) were identified as traffic, mineral dust, industrial, combustion, biomass burning, secondary aerosol and aged sea salt using positive matrix factorization analysis. Traffic and mineral dust factors were found to contribute about 74% of PM2.5 mass (aerodynamic particle diameter less than 2.5 µm). Analysis of size-segregated PM showed the crustal elements (Si and Fe) dominated in all the measured PM size fractions. K, Cu, Zn and Pb displayed a bimodal mass-size distribution pattern emphasizing the multiplicity of their sources. Statistics from size-segregated data was utilized in calculating the deposition fractions of PM in human respiratory system. The head airways region had the highest percentage for both coarse (87%) and fine particles (84%) compared to the tracheobronchial and pulmonary regions. Given the high average PM2.5 concentration (98 µg m-3) measured in the main street of Nairobi city, the urban population is regularly exposed to elevated pollutants concentrations with potentially health risks implications. The information resulting from this study provides a foundation for policy formulation and mitigation strategies with regard to air pollution and quality in SSA cities.
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