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- Gaita, Samuel Mwaniki, 1976
(författare)
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Airborne particulate matter in a Sub-Saharan Africa city: Nairobi, Kenya, and at an Equatorial high altitude site: Mount Kenya
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In Sub-Saharan Africa (SSA), air quality is gravely understudied despite the existing influential factors such a rapid urbanization and population growth that negatively affect the environment. Majority of urban areas in SSA face challenges that include lack of social services, poor infrastructure development, exponential increase of second-hand vehicles and extensive use of biomass-based fuel for energy needs. There is a systemic lack of continuous monitoring of air pollution in most SSA cities and hence it is yet to be seen if SSA will meet the set air quality targets of the sustainable development goals (SDGs) by the year 2030. Although the focus of air quality is on the urban areas, there is a need to monitor atmospheric composition at remote areas in SSA in order to build a baseline level and understand the influence of anthropogenic and natural aerosol sources on regional/global scale. This thesis work sought to study physical and chemical properties of airborne particulate matter (PM) in a typical SSA urban area, Nairobi city, and a high altitude site, Mount Kenya. Results from spatial distribution of black carbon (BC) and PM2.5 (particulate matter less than 2.5 aerodynamic diameter) showed that air quality on the road to the city and within the city is deteriorating. Factor analysis of the PM2.5 results showed that pollution sources were traffic, mineral dust, industrial, combustion, biomass burning, secondary aerosol and aged sea salt. Traffic and mineral dust contributed about 74% of the PM2.5 in Nairobi. Exposure to particulate pollutants was expressed in terms of deposition fractions from the size segregated PM data. The head airways region was found to receive the highest dose (about 86%) compared to the tracheobronchial and pulmonary regions. The reported high PM2.5 and BC concentrations measured along the main street of Nairobi city, indicated the urban population is frequently exposed to elevated pollutants concentrations and thus have high risk factor to respiratory illnesses and lung cancer. Aerosol study from Mount Kenya showed air pollutants are transported from the surrounding and far away sources by local and regional meteorology dynamics. The results from this study provides insight into the air quality issues from pollution sources, exposure to the population and dispersal to remote regions.
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| 2. |
- Mburu, Caroline W., et al.
(författare)
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Influence of Yttrium Concentration on Local Structure in BaZr(1-x)Y(x)O(3-δ) Based Proton Conductors
- 2017
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:30, s. 16174-16181
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 American Chemical Society. The evolution of local structure, coordination of protons, and proton conductivity in yttrium-doped barium zirconate, BaZr 1-x Y x O 3-δ (x = 0-0.5), has been investigated using thermal-gravimetric analysis, impedance spectroscopy, and infrared spectroscopy. Low-frequency (50-1000 cm -1 ) infrared absorbance spectra provide evidence of increasing local structural distortions as a function of yttrium concentration as well as subtle differences, mainly linked to the oxygen sublattice, between the dry and hydrated samples. High-frequency (1700-4500 cm -1 ) spectra of the hydrated samples, distinguished by a broad O-H stretch continuum, manifest a varying degree of hydrogen bond interactions between the protons and nearest neighbor oxygens due to the disordered crystal structure with a general weakening in particular of the strongest hydrogen bonding interactions with increasing dopant levels. It is argued that compositions within the range 0.15 ≤ x ≤ 0.3 possess a favorable level of local structural distortions to facilitate high proton conductivity, and this, coupled with a significant proton concentration, may be a factor in explaining the high proton conductivity these phases display.
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| 3. |
- Mburu, C. W., et al.
(författare)
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Influence of Yttrium Concentration on Local Structure in BaZr1-xYxO3-delta Based Proton Conductors
- 2017
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:30, s. 16174-16181
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of local structure, coordination of protons, and proton conductivity in yttrium-doped barium zirconate, BaZr1-xYxO3-delta (x = 0-0.5), has been investigated using thermal-gravimetric analysis, impedance spectroscopy, and infrared spectroscopy. Low-frequency (50-1000 cm(-1)) infrared absorbance spectra provide evidence of increasing local structural distortions as a function of yttrium concentration as well as subtle differences, mainly linked to the oxygen sublattice, between the dry and hydrated samples. High-frequency (1700-4500 cm(-1)) spectra of the hydrated samples, distinguished by a broad O-H stretch continuum, manifest a varying degree of hydrogen bond interactions between the protons and nearest neighbor oxygens due to the disordered crystal structure with a general weakening in. particular of the strongest hydrogen bonding interactions with increasing dopant levels. It is argued that compositions within the range 0.15
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