Doctoral Degrees (Physics)

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Browsing Doctoral Degrees (Physics) by Subject "Air pollution"

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    Elemental Analysis of Mosses and Lichens from the Western Cape (South Africa) using INAA and ICP-MS
    (Stellenbosch : Stellenbosch University, 2016-12) Ndlovu, Ntombizikhona Beaulah; Newman, Richard T.; Frontasyeva, Marina V.; Maleka, Peane P.; Stellenbosch University. Faculty of Science. Dept. of Physics
    ENGLISH ABSTRACT : Mosses and lichens, analyzed by nuclear and related techniques, have been extensively used as biomonitors in the European countries to provide information about air quality, but not in South Africa. The aim of this project was to infer air pollution levels in the Western Cape, South Africa by collecting and analysing mosses and lichens for chemical content using nuclear and related techniques. Since they lack a root system, which causes them to trap chemicals from air only through wet and dry deposition, mosses and lichens serve as good biomonitors of air pollution. These plants possess efficient accumulation capacity for many air pollutants (heavy metals and other trace elements). Three major causes of atmospheric pollution are industrialisation, urban growth and the wide-spread use of vehicles. Studying air pollution with plants, instead of the commercial air filters is a simple but effective method to estimate levels of air pollutants. Biomonitoring can be performed using naturally growing (indigenous) biomonitors collected in the area under investigation. This is known as passive biomonitoring. The steady global increase in the use of active biomonitoring, whereby biomonitors are collected from relatively pristine habitats and transplanted to different environments, is due to the scarcity or total absence of native biomonitors in certain environments e.g. large cities with heavy technogenic load and industrial regions as well as in arid areas. Hence active biomonitoring was also used in this study to assess elemental content of atmospheric pollution due to urbanisation, industrialisation and vehicle use, in selected areas of the Western Cape, South Africa. In this study, the collected samples were analysed by the multi-elemental nondestructive technique called instrumental neutron activation analysis (INAA) as well as the ion-coupled mass spectrometry (ICP-MS), thus facilitating an intercomparison of the results obtained by both techniques. From both passive and active biomonitoring techniques, the intercomparison of INAA and ICPMS results showed major and essential elements (i.e. Na, Ca, Mg, K, Mn, Sr, Al, V, Ba, Zn) to have good linear correlations, R ≥ 80%. In order to facilitate the identification and characterization of different pollution sources from the collected sample element content, descriptive statistics were generated and correlation analyses were done using the StatisticaTM package. Our passive biomonitoring results showed the concentration levels for halogens (Cl, I, Br) to be elevated in areas closest to the ocean. The moss-sampling areas closest to the ocean, in relation to Stellenbosch, were False Bay and Betty’s Bay. Signal Hill was the lichen-sampling area closest to the ocean, in relation to Stellenbosch, Coetzenburg Mountain and Franschoek. High concentrations of elements associated with vehicular emission (i.e. Pb, V, Zn, Cd, Cr, Cu, Ni, As, Ba, Sn) were observed for Stellenbosch samples that were collected adjacent to roads (Marais Road and Victoria Street). The active biomonitoring results showed Stellenbosch to have higher concentration levels of Al, V, Ba, Cr, Cu, Ti and Zn. These indicate emissions from soil and vehicles. The fingerprints for a combination of potential air pollution sources (oil rig facility, steel plant, heavy mineral plant, galvanising plant and the oil storage facility as well as sea-salt emissions) were identified in the Vredenburg results. The elements associated with these fingerprints are Fe, Al, Hg, As, Cd, Pb, Ba and Na. The Huguenot tunnel results revealed high concentrations of elements associated with the fingerprints for vehicle emissions. These are Zn, V, Ba, Cr, Pb, Ni, Cu, Al and Sb. In general, mosses showed the highest bioaccumulation capacity for metals and presented a more linear element accumulation trend than lichens. Due to their differences in metal uptake and retention, it is advisable to use mosses and lichens concurrently, since the respective results will be complementary.