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MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014 The baseline of uncertainty in aerosol radiative forcing is large and depends on aerosol characteristics (e.g. size and composition), which can vary significantly on a regional scale. Sources (natural and anthropogenic) can be directly linked to the aerosol characteristics of a region, making monitoring campaigns to determine aerosol composition in different regions very important. Limited data currently exists for atmospheric aerosol black carbon (BC) and organic carbon (OC) in South Africa. In this study, BC and OC concentrations were explored in terms of spatial and temporal patterns, mass fractions of BC and OC of the overall aerosol mass, as well as possible sources. Primary pollutants, of which BC is an example, are emitted directly from the source. Certain primary pollutants can react with other pollutants to form secondary pollutants. OC can either be a primary or secondary pollutant, e.g. formed by gas-to-particle conversion of volatile organic compounds (VOCs) in the atmosphere (nucleation and condensation of gaseous precursors). Greenhouse gases (GHG) and BC absorb terrestrial long wave radiation causing an increase of atmospheric temperature. In contrast, OC generally reflects incoming radiation, cooling the atmosphere. GHGs have a long residence time in the atmosphere (10 to 100 years), while the residence time of aerosols is usually only a week or more. The climatic effects of aerosols are therefore particularly important from a regional perspective. Aerosols are also important from an air quality perspective, especially since ultrafine particles (diameter smaller than 100nm) are small enough to go through the membranes of the respiratory tract and into the blood stream. They can then be transported to the brain. Up to 2005, DEBITS (Deposition of Biogeochemical Import Trace Species) activities in South Africa did not include aerosol measurements. In order to initiate aerosol monitoring, campaigns were launched during the 2005 to 2007 period. Additionally, OC and BC measurements for the PM10 and PM2.5 (particulate matter smaller than or equal to 10 and 2.5 μm, respectively) fractions were started in 2009. PM10 and PM2.5 samples were collected at five sampling sites in South Africa operated within the DEBITS network, i.e. Louis Trichardt, Skukuza, Vaal Triangle, Amersfoort and Botsalano, with MiniVol samplers. The selected sites are mostly located in rural areas, but with the surrounding atmosphere influenced by industries, transportation, biomass burning, etc. Winters are characterised by an increase in biomass burning (fires) and combustion for domestic use (cooking and space heating). Samples were analysed with a Thermal/Optical Carbon analyser (Desert Research Institute). OC and BC results showed that the total carbonaceous content decreased during the summer due to less biomass burning (fires). BC was the highest at the industrially influenced sites, while OC was highest at regional background sites. OC was higher than BC concentrations at all sites in both size fractions. Most OC and BC occurred in the PM2.5 fraction. OC/BC ratios reflected the setting of the different DEBITS sites, with sites in or close to anthropogenic source regions having the lowest OC/BC ratios, while background sites had the highest OC/BC ratios. The OC mass fraction percentage of the total aerosol weight varied up to 24% and the BC up to 12%. The highest OC mass fraction was found at Skukuza, which was attributed to both natural (lies within the savannah biome) and anthropogenic (dominant path of air mass movement from the anthropogenic industrial hub of South Africa) reasons. The highest mass fraction of BC was found in the Vaal Triangle, since it is situated within a well-known anthropogenic source region. Household combustion for space heating and cooking also seemed to make a significant contribution to BC at this site in the cold winter months. A relatively well-defined seasonal pattern was observed, with higher OC and BC concentrations measured from May to October, which coincides with the dry season in the interior of South Africa. Positive correlations between OC and BC concentrations with the distance back trajectories passed fires were observed, indicating that fires contribute significantly to both atmospheric OC and BC during the burning season. Masters

This study presents a total of four years of sub-micron aerosol particle size distribution measurements in the southern African savannah, an environment with few previous observations covering a full seasonal cycle and the size range below 100 nm. During the first 19 months, July 2006–January 2008, the measurements were carried out at Botsalano, a semi-clean location, whereas during the latter part, February 2008–May 2010, the measurements were carried out at Marikana (approximately 150 km east of Botsalano), which is a more polluted location with both pyrometallurgical industries and informal settlements nearby. The median total concentration of aerosol particles was more than four times as high at Marikana than at Botsalano. In the size ranges of 12–840 nm, 50–840 nm and 100–840 nm the median concentrations were 1856, 1278 and 698 particles cm−3 at Botsalano and 7805, 3843 and 1634 particles cm−3 at Marikana, respectively. The diurnal variation of the size distribution for Botsalano arose as a result of frequent regional new particle formation. However, for Marikana the diurnal variation was dominated by the morning and evening household burning in the informal settlements, although regional new particle formation was even more frequent than at Botsalano. The effect of the industrial emissions was not discernible in the size distribution at Marikana although it was clear in the sulphur dioxide diurnal pattern, indicating the emissions to be mostly gaseous. Seasonal variation was strongest in the concentration of particles larger than 100 nm, which was clearly elevated at both locations during the dry season from May to September. In the absence of wet removal during the dry season, the concentration of particles larger than 100 nm had a correlation above 0.7 with CO for both locations, which implies incomplete burning to be an important source of aerosol particles during the dry season. However, the sources of burning differ: at Botsalano the rise in concentration originates from regional wild fires, while at Marikana domestic heating in the informal settlements is the main source. Air mass history analysis for Botsalano identified four regional scale source areas in southern Africa and enabled the differentiation between fresh and aged rural background aerosol originating from the clean sector, i.e., western sector with very few large anthropogenic sources. Comparison to size distributions published for other comparable environments in Northern Hemisphere shows southern African savannah to have a unique combination of sources and meteorological parameters. The observed strong link between combustion and seasonal variation is comparable only to the Amazon basin; however, the lack of long-term observations in the Amazonas does not allow a quantitative comparison. All the data presented in the figures, as well as the time series of monthly mean and median size distributions are included in numeric form as a Supplement to provide a reference point for the aerosol modelling community.

In this work satellite based observations were used to estimate the concentration of nucleation mode aerosols over South Africa. The nucleation mode aerosols can not be detected directly with satellite instruments since they are much smaller than the optically active aerosols, hence the concentrations were estimated using proxies introduced by Kulmala et al. (2011). Results showed enhanced values of both primary and regional scale nucleation proxies over the Mpumalanga Highveld industrial area, whereas over the Johannesburg-Pretoria megacity only the primary nucleation proxy showed elevated values. To estimate how well satellite based proxies work, the relation between satellite and in situ based quantities was studied in more detail. The correlation between aerosol optical depth (AOD) and condensation sink (CS) was 0.2-0.3 depending on the location. Boundary layer height affected the correlation somewhat, but there are other factors, such as the effect of dust on AOD, that are more likely to have a stronger impact.

The tropospheric ozone concentrations over southern Africa are relatively high due to large precursor emissions from biomass burning, vegetation and anthropogenic sources and the intensity of solar radiation. In this study, we summarize ozone concentration data from both literature and new measurements. Further, we present data on the accumulated vegetation exposure to ozone in terms of the AOT40 index, which is calculated for the sites with hourly ozone and radiation data, with an aim to assess the potential for adverse effects on vegetation. As the seasonal variation of ozone concentrations is large, we discuss the effect of growing season onset on the stomatal gas exchange and the related potential for vegetation impacts. Finally, future research needs are discussed.

Production of ferrochrome is an energy intensive process. Pelletised chromite pre-reduction is most likely the ferrochrome production process with the lowest specific electricity consumption, i.e. MWh/t ferrochrome produced. Higher chromite pre-reduction levels correspond to lower specific electricity corzsumptions. In this paper the effect of CaC03 addition and clay binder selection on pelletised chromite pre-reduction is presented. Results indicated that CaC03 addition significantly enhances the level of chromite pre-reduction achieved within a given time and temperature horizon. Hovvever, CaC03 addition caused severe decreases in both compressive and abrasion strengths of pre-reduced pellets, which is unlikely to be negated by mitigation measures. The addition of CaC03 in the pelletised chromite pre-reduction process will therefore most probably result in the formation of excessively fine feed materials. In practise, this reduces the usefulness of this technique for submerged arc furnace f errochrome production significantly, since excessive fines in the feed material are likely to result in increased operational instabilities, equipment damage and safety risks. TGA and thermochemical calculations also indicated that C02 released from the CaC03 will result in additional carbon consumption, which is an additional negative associated with its use as an additive during pre-reduction of composite chromite pellets. Although the research work covered in this paper was not specifically aimed at obtaining mechanistic information, thermo-mechanical analysis indicated that especially iron pre-reduction rates were enhanced by CaC03 addition. It was also proved that clay binder selection not only ilifluence the physical strength of the pre-reduced pellets, but also the level of achievable pre-reduction. Additionally, increased addition of clay binder to the composite pellet was found to result in progressive decline in the degree of chromite pre-reduction achieved within a specified timetemperature reference frame

Raman lidar data of one year was been analyzed to obtain information relating aerosol layers in the free troposphere over South Africa, Elandsfontein. In total, 375 layers were observed above the boundary layer during the period 30 th January 2010 – 31 st January 2011. The seasonal behavior of aerosol layer geometrical characteristics as well as intensive and extensive optical properties were studied. In general, layers were observed at higher altitudes during spring (2520 ± 970 m) while the geometrical layer depth did not show any significant seasonal dependence. The variations of most of the intensive and extensive optical properties analyzed were high during all seasons. Layers were observed at mean altitude of 2100 m ± 1000 m with lidar ratio at 355 nm of 67 ± 25 and extinction-related Angstrom exponent between 355 and 532 nm of 1.9 ± 0.8.

The Multi-Angle Absorption Photometer (MAAP) is a widely-used instrument for aerosol black carbon (BC) measurements. In this paper, we show correction methods for an artifact found to affect the instrument accuracy in environments characterized by high black carbon concentrations. The artifact occurs after a filter spot change – as BC mass is accumulated on a fresh filter spot, the attenuation of the light (raw signal) is weaker than anticipated. This causes a sudden decrease, followed by a gradual increase in measured BC concentration. The artifact is present in the data when the BC concentration exceeds ~3 μg m−3 at the typical MAAP flow rate of 16.7 L min−1 or 1 m3 h−1. The artifact is caused by erroneous dark counts in the photodetector measuring the transmitted light, in combination with an instrument internal averaging procedure of the photodetector raw signals. It was found that, in addition to the erroneous temporal response of the data, concentrations higher than 9 μg m−3 (at the flow rate of 16.7 L min−1) are underestimated by the MAAP. The underestimation increases with increasing BC accumulation rate. At a flow rate of 16.7 L min−1 and concentration of about 24 μg m−3 (BC accumulation rate ~0.4 μg min−1), the underestimation is about 30%. There are two ways of overcoming the MAAP artifact. One method is by logging the raw signal of the 165° photomultiplier measuring the reflected light from the filter spot. As this signal is not affected by the artifact, it can be converted to approximately correct absorption and BC values. However, as the typical print formats of the MAAP do not give the reflected signal as an output, a semi-empirical correction method was developed based on laboratory experiments to correct for the results in the post-processing phase. The correction function was applied to three MAAP datasets from Gual Pahari (India), Beijing (China), and Welgegund (South Africa). In Beijing, the results could also be compared against a photoacoustic spectrometer (PAS). The correction improved the quality of all three MAAP datasets substantially, even though the individual instruments operated at different flow rates and in different environments.

Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013 Volatile organic compounds (VOCs) are emitted into the atmosphere from biogenic and anthropogenic sources with atmospheric lifetimes ranging from minutes to months, depending on the specific VOC compound considered. It is estimated that biogenic VOCs (BVOCs) (e.g. isoprenes, terpenes) make up 90% of the global atmospheric VOC budget. However, in highly industrialised regions, anthropogenic VOCs (e.g. benzene, toluene, ethylbenzene and xylene, combined abbreviated as BTEX) might dominate. VOCs have various reversible and irreversible effects on human health. They also have environmental impacts that range from changes in the population of terrestrial and aquatic ecosystems to the extinction of vulnerable species. VOCs are precursors for the formation of ozone (O3) during solar radiation initiated reactions in the presence of NOx. Tropospheric O3 is considered a pollutant, with negative impacts on human health, ecosystems and food security. O3 is also a short-lived greenhouse gas. Through reactions with radical species, VOCs lead to the formation of higher molecular weight organic compounds, which produce carbon monoxide (CO), peroxyacytyl nitrate (PAN) and ultimately secondary organic aerosol (SOA) particles. SOA particles impact directly on air quality and visibility, as well as directly and indirectly on the radiation balance of the earth that contributes to the regulation of climate. Notwithstanding the importance of atmospheric VOCs, limited data is available for VOCs in South Africa. In this study, a comprehensive dataset of BVOC and anthropogenic VOC species was obtained at the Welgegund measurement station in the North West Province, South Africa. Measurements were conducted from 9 February 2011 to 4 February 2012. Samples were collected on Tenax-TA and Carbopack-B adsorption tubes twice a week for two hours during day time and two hours during night time. The first 1.25m of the stainless steel sampling inlet was heated to 120ºC to remove O3 that could lead to sample degradation. Analyses of the sampled adsorption tubes were conducted by thermal desorption, cryofocusing, re-desorption, followed by gas chromatography separation and analysis with a mass selective detector (GC-MS). The results indicated that toluene was the most abundant aromatic hydrocarbon and heptane the most abundant alkane. Benzene is currently the only VOC listed as a criteria pollutant in the South African Air Quality Act with an annual average standard of 1.6ppb. The annual median benzene concentration was 0.13 ppb, while the highest daily benzene concentration measured was 8.7 ppb. No distinct seasonal cycles were identified for anthropogenic VOC species measured, i.e. aromatic hydrocarbons and alkanes. However, air mass history analysis indicated that air masses that passed over the Mpumalanga Highveld, the Vaal Triangle and the Johannesburg-Pretoria conurbation (collectively referred to as Area I) had significantly higher concentrations of these anthropogenic VOCs compared to air masses that passed over the western and eastern Bushveld Igneous Complex, and a region over which air masses typically followed an anti-cyclonic movement pattern (collectively referred to as Area II). Anthropogenic VOC levels in air masses that passed over the regional background (areas with no large point sources) had levels similar to air masses that had passed over Area II. Relatively good interspecies correlations (r > 0.8) between most of the aromatic hydrocarbons in air masses that had passed over Area I, with the exception of benzene, indicated that these species had common sources. Benzene, however, correlated well with CO, indicating that sources associated with incomplete combustion were most likely the origin of benzene in air masses that had passed over Area I. The interspecies concentration ratios for plumes passing over Area I indicated that this source region is relatively close to the Welgegund monitoring station and air masses that passed over this source region were substantially influenced by anthropogenic activities. The concentration ratios for plumes that passed over Area II and the Regional Background indicated that these were aged air masses. Furthermore, the concentration ratios of toluene, ethylbenzene and o,m,p-xylene (TEX) to the total aromatic concentration for air masses that passed over the various source regions showed a greater contribution to the total VOC concentration during periods of higher temperature, i.e. summer. This proved that the evaporation of solvents contributes significantly to VOC levels during the months with higher temperatures. The relative contribution of aromatic hydrocarbons to photochemical O3 formation in air masses that passed over the various source regions indicated the highest contribution was observed for air masses that passed over Area I, with Area II and the Regional Background in the same order of magnitude. The annual temporal variations of the measured BVOCs indicated that 2-methyl-3-buten-2-ol (MBO) and isoprene exhibited distinct seasonal patterns, i.e. higher values in summer and lower values in winter. The monoterpenes (MT) and the sesquiterpenes (SQT) did not follow distinct seasonal patterns. BVOC concentrations correlated relatively well to seasonal variations in temperature, photosynthetically active radiation (PAR), rainfall, relative humidity (RH) and CO2 flux. This proved that biogenic activity is responsible for BVOCs emitted. The most abundant MT was 􀄮-pinene, while 􀈕-caryophyllene was the most abundant SQT with annual median concentrations of 0.468 ppb and 0.022 ppb, respectively. Pollution roses for isoprene showed a dominance of sources from the north-west to the north-east, as well as the south-east. These directions correlated to areas where pockets of the savannah biome are located. Masters

Thesis (PhD (Environmental Sciences))--North-West University, Potchefstroom Campus, 2013 A megacity is generally defined as a city that, together with its suburbs or recognised metropolitan area, has a total population of more than 10 million people. Air pollution in megacities is a major concern due to large increases of populations over the past decades. Increases of air pollution result from more anthropogenic emission sources in megacities, which include energy production, transportation, industrial activities and domestic fuel burning. In the developing parts of Africa, urbanisation is increasing rapidly, with growth rates of populations in cities of up to 5% per annum. The major driving forces for these population increases in African countries can be attributed to population growth, natural disasters and armed ethnic conflicts. In South Africa, 62% of the total population lived in cities in 2010. The rate of urbanisation growth is predicted to be 1.2% per annum. The largest urbanised city in South Africa is the Johannesburg-Pretoria conurbation (referred to as Jhb-Pta megacity) that has more than 10 million inhabitants. Johannesburg is considered to be the central hub of economic activities and -growth in South Africa. The larger conurbation includes all the suburbs of Johannesburg and Pretoria. In South Africa, household combustion and traffic emissions are major sources of pollutants in urbanised areas. The major pollutants emitted from these activities include nitrogen oxide (NO), nitrogen dioxide (NO 2), sulphur dioxide (SO2), carbon monoxide (CO), particular matter (PM) and various organic compounds. The Jhb-Pta megacity is also located relatively close to large industrialised regions in South Africa, i.e. the Mpumalanga Highveld and the Vaal Triangle. Very few air quality modelling studies have been conducted for the Jhb-Pta megacity. According to the knowledge of the author, no literature existed in peer-reviewed publications at the time of the study. An in-depth modelling study was therefore conducted to assess the current state of air quality within the Jhb-Pta megacity. The main objectives were to optimise an existing photochemical box model for the Jhb-Pta megacity and to utilise the model to investigate the photochemical processes in the Jhb-Pta megacity and surrounding areas. In this investigation, ground-based measurements of criteria atmospheric pollutant species representative of the Jhb- Pta megacity were obtained to utilise as input data in the model, as well as to compare to results determined with the model. From the ground-based measurements, the possible contribution of the Jhb-Pta megacity to the NO2 hotspot observed over the South African Highveld from satellite retrievals was also contextualised. Five ground-based monitoring sites were situated strategically within the boundaries of the Jhb- Pta megacity to measure the direct influences of urban air pollution, e.g. traffic emissions, biomass burning and residential pollution. One measurement site was situated outside the modelling domain in order to collect rural background data in close proximity to the Jhb-Pta megacity. All the air quality stations continuously measured the criteria pollutants NOx, SO2 and O3. In addition, benzene, toluene, ethylbenzene and xylene (BTEX) were measured at four sites. Passive sampling of NOx, SO2 , O3 and BTEX was also conducted in March and April 2010. Active data was obtained for March to May 2009, since no active measurements were available for the same year that passive sampling was performed due to logistical reasons. Meteorological parameters that included temperature, pressure and relative humidity were also measured at the monitoring stations Ground-based measurements provided a good indication of the state of the air quality in the Jhb-Pta megacity. The air quality levels of NO2 , SO2 , O3 and BTEX could be compared to other cities in the world. A distinct diurnal cycle was observed for NO2 at most of the stations. An early morning peak between 6:00 and 9:00 coincided with the time that commuters travel to work, whereas an evening peak between 18:00 and 21:00 could be attributed to traffic emissions and household combustion. Levels of O3, which is a secondary pollutant, peaked between 13:00 and 15:00. This diurnal pattern could be attributed to the photochemical formation of O3 from precursor species NO and VOCs. Toluene was predominantly higher than the other BTEX species. Benzene and xylene concentrations were in the same order, while the lowest levels were measured for ethyl benzene Ground-based measurements also indicated that the NO2 Highveld hotspot, which is well known in the international science community due to its prominence in satellite images, is accompanied by a second hotspot over the Jhb-Pta megacity. Peak NO2 pollution levels in the Jhb-Pta megacity exceeded the maximum daily Highveld values during the morning and evening rush hours. This result is significant for the more than 10 million people living in the Jhb-Pta megacity. Although satellite instruments have been extremely valuable in pointing out global hotspots, a limitation of satellite retrievals due to their specific overpass times has been presented. Chemical processes in the Jhb-Pta megacity were investigated by utilising an existing photochemical box model, i.e. MECCA-MCM. This model was further developed in this study and was termed the MECCA-MCM-UPWIND model. This model included horizontal and vertical mixing processes in the atmosphere. These processes were included to simulate the advection of upwind air masses into the modelling domain, as well as the entrainment from the troposphere resulting from the diurnal mixing layer (ML) height variation. Three processes, i.e. horizontal mixing, vertical mixing and ML height variation, were built into the MECCA-MCM- UPWIND model. The model was tested and evaluated to determine the efficiency of the model to represent atmospheric mixing processes. MECCA-MCM-UPWIND simulated horizontal mixing, vertical entrainment and ML height variations as expected. The input data for the model runs for the Jhb-Pta megacity modelling runs were either obtained from ground-based measurements or literature. Input data included meteorology, emission inventory, ML height and mixing ratios of the atmospheric chemical species. The chemical composition of the air mass entering the Jhb-Pta megacity was determined with MECCA-MCM- UPWIND. The concentrations and diurnal variability of criteria pollutant species were well predicted with the MECCA-MCM-UPWIND model. The day-time chemistry, especially, compared well, while slight under-predictions were observed for the night-time chemistry for most of the species. The differences observed between modeled and measured data could partially be ascribed to uncertainties associated with some of the input data obtained from literature used. The MECCA-MCM-UPWIND model was used to perform sensitivity studies on the influence of different parameters on O3 levels in the Jhb-Pta megacity. Possible scenarios to alter or mitigate pollution were also investigated. The results from the sensitivity analyses showed that O3 mixing ratios decreased within the Jhb-Pta megacity with increasing wind speeds. The contribution of local emissions to the change in the concentration of pollutants is reduced at higher wind speeds. It also indicated that the Mpumalanga Highveld can potentially be a source of NOx in the Jhb-Pta megacity that can lead to the titration of O3 . This also implies that if the air quality of the surrounding area improves, the concentration of the secondary pollutant O 3 will increase in the Jhb-Pta megacity due to the decrease in the titration of O3 . Sensitivity analyses also indicated that the Jhb-Pta megacity is a VOC-limited (or NOx-saturated) regime. Therefore, O3 reduction in the Jhb-Pta megacity will mostly be effective if VOC emissions are reduced. The same effect was observed in various cities world-wide where O3 increased when NOx emissions the Jhb-Pta megacity on the instantaneous production of O3 was also investigated. A significant increase of approximately 23ppb O3 production was observed when changing from Euro-0 to Euro-3 vehicles with lower emissions of VOCs, NOx and CO. This compares with other modelled sensitivity studies of traffic emissions that also predict that future urban O3 concentrations will increase in many cities by 2050 due to the reduction in the NOx titration of O3 despite the implementation of O3 control regulations. Doctoral

Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2011. The presence of trace transition metal species in the atmosphere can be attributed to the emission of particulate matter into the atmosphere by anthropogenic activities, as well as from natural sources. Trace metals emitted into the atmosphere can cause adverse health–related and environmental problems. At present, limited data exists for trace metal concentrations in South Africa. In this investigation, the general aim was to determine the concentrations of trace metals in atmospheric aerosols in the industrialised western Bushveld Igneous Complex, as well as to link the presence of these species in the atmosphere to possible sources in the region. The measurement site was placed in Marikana, a small rural town situated 35 km east from Rustenburg in the North West Province of South Africa. It is surrounded by numerous industrial and metallurgical operations. MiniVolumeTM samplers and Teflon® filters (2 ;m pores) were utilised to collect PM2.5 and PM10 particulate samples. The MiniVolumeTM samplers were programmed to filter 5 litres of air per minute for 12 hours per day, over a six–day period. The starting time for sampling was altered every six days, in order to obtain both day and night samples. Sampling was performed for a period of one year. The collected samples were chemically analysed with inductively coupled plasma mass spectroscopy (ICP–MS). Surface analysis of the sampled filters was performed with a scanning electron microscope (SEM) in conjunction with energy–dispersive spectroscopy (EDS). The dataset was also subjected to factor analysis in an attempt to identify possible sources of trace metal species in the atmosphere. The concentrations of 27 trace metals (Be, B, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Pd, Cd, Ba, Pt, Au, Hg, Tl, Pb, U) were determined. Pd, Hg, Tl, U, Ca, Co, As, Cd, Ba and Au were above the detection limit 25% or less of the time during the sampling period. With the exception of Ni, none of the trace metals measured at Marikana during the sampling period exceeded local and international standards. Higher Ni levels were possibly due to base metal refining in the region. Pb, which is the only metal species that has a standard prescribed by the South African Department of Environmental Affairs (DEA), did not exceed any of the standards. It is also significant to refer to Hg that was below the detection limit of the analytical instrument for the entire sampling period. The impact of meteorological conditions revealed that wet removal of atmospheric PM10 trace metals was more significant than the wind generation thereof. During the dry months, the total trace metal concentrations in the PM10 fraction peaked, while PM10 particles were mostly washed out during the wet season. Wind speed showed an unexpected inverse pattern compared to wet deposition. A less significant seasonal trend was observed for the trace metal concentrations in the PM2.5 fraction, which was attributed to a faster replenishment of smaller particles into the atmosphere after rain events. Separation of trace metal concentrations into PM10–2.5 and PM2.5 fractions indicated that 79% of the total trace metal levels that were measured were in the PM2.5 fraction, which indicated a strong influence of industrial and/or combustion sources. Fractionalisation of each of the trace metal species detected showed that for each metal species, 40% and more of a specific metal was in the PM2.5 fraction, with Cr, V, Ni, Zn and Mn occurring almost completely in the PM2.5 fraction. Surface analysis with SEM supported results from the chemical analysis, which indicated that a large fraction of the particles was likely to originate from anthropogenic activities and from wind–blown dust. SEM–EDS also detected nonmetallic S that is usually associated with the Pt pyrometallurgical industry that is present in the western Bushveld Igneous Complex. Correlations between Cr, V, Ni, Zn and Mn revealed that the main sources of these species were pyrometallurgical industries. Explorative factor analysis of the unprocessed and Box–Cox transformed data for all 27 metals detected, resolved four meaningful emission sources, i.e. crustal, vanadium related, base metal related and chromium related. Comparison of trace metal species to other parameters measured (e.g. CO, BC) also indicated pyrometallurgical activities and wind–blown dust to be the main sources of trace metals in this region. Masters

Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012. As a result of increasing cost, efficiency and environmental pressures ferrochrome producers strive towards lower overall energy consumption. Increases in local electricity prices have placed particular pressure on South African ferrochrome producers. Pelletised chromite pre–reduction is likely the currently applied ferrochrome production process option with the lowest specific electricity consumption. In this process fine chromite, together with a carbonaceous reductant and a clay binder is milled, pelletised and pre–reduced. In this dissertation it is demonstrated that the functioning of the clay binder in this process is not as straightforward as in conventional metallurgical pelletisation processes, since the cured pre–reduced pellets are characterised by an oxidised outer layer and a pre–reduced core. Conventional performance characteristics of clay binders (e.g. compressive strength and abrasion resistance) therefore have to be evaluated in both oxidative sintering and reducing environments. Two clay samples, i.e. attapulgite and bentonite, were obtained from a local ferrochrome producer and investigated within the context of this study. Results indicated that the compressive and abrasion resistance strengths of oxidative sintered pellets for both clays were substantially better than that of pre–reduced pellets. Thus, although the objective of the chromite pre–reduced process is to achieve maximum pre–reduction, the strength of pre–reduced chromite pellets is significantly enhanced by the thin oxidised outer layer. The strength of the bentonite–containing pellets was found to be superior in both pre–reducing and oxidative sintering environments. This is significant, since the attapulgite clay is currently the preferred option at both South African ferrochrome smelting plants applying the pelletised chromite pre–reduction process. Although not quantitatively investigated, thermo–mechanical analysis indicated that the hot strength of the attapulgite pellets could be weaker than the bentonite–containing pellets. The possible effects of clay binder selection on the level of pre–reduction were also investigated, since it could have substantial efficiency and economic implications. For both case study clays investigated, higher clay contents resulted in lower pre–reduction levels. This has relevance within the industrial process, since higher clay contents are on occasion utilised to achieve improved green strength. The average pre–reduction of the bentonite–containing pellets were also consistently higher than that of the attapulgite–containing pellets. Again, this is significant, since the attapulgite clay is currently the preferred option. In general the case study results presented in this dissertation indicated that it is unlikely that the performance of a specific clay binder in this relatively complex process can be predicted; based only on the chemical, surface chemical and mineralogical characterisation of the clay. Masters

The chemical interactions responsible for sintering in a coal mineral mixture were investigated in air and in N2. A mineral mixture was made up by mixing kaolin, pyrite, quartz, calcite, hydromagnesite, FeCO3 and anatase in a fixed ratio. The mineral mixture was pelletized and heat-treated up to 1100 °C in order to evaluate sintering by recording the compressive strength values and visual assessment with scanning electron microscopy (SEM). Chemical interactions responsible for the trends in the compressive strength results were investigated with simultaneous thermogravimetric and differential thermal analysis (TG/DTA), as well as X-ray diffraction. The results indicated that the formation of anhydrite (CaSO4) was responsible for increased mechanical strength in the mineral mixture pellets heated in air at temperatures higher that 400 °C. CaSO4 formed from the reaction of the decomposition products of pyrite and calcite (SOx and CaO). The TG/DTA results also indicated that the reaction with pyrite in air caused the decomposition of calcite in the mixture at a lower temperature than was observed for calcite only. The pellets heated in N2 did not increase in mechanical strength during heat-treatment due to the lack of CaSO4 formation in the inert atmosphere. However, SEM analysis indicated that sintering did occur at the higher temperatures in N2. A decrease was observed in the compressive strength values obtained in air at temperatures from 900 °C to 1100 °C. Reasons for the decreased compressive strengths may include increased porosity, decomposition of CaSO4, and changes in the characteristics of the aluminosilicate phases. http://dx.doi.org/10.1016/j.fuproc.2010.12.030

Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012 South Africa has the largest economy in Africa, with significant mining and metallurgical activities. A large fraction of the mineral assets is concentrated in the Bushveld Igneous Complex (BIC), with the western limb being the most exploited. Although the western BIC is considered to be an air pollution hotspot, inadequate air quality data currently exists for this area. To partially address this knowledge gap, a comprehensive air quality monitoring station was operated for more than two years at Marikana in the western BIC. Basic meteorological parameters, precipitation, Photosynthetic Photon Flux Density (PPFD), trace gas concentrations (SO2, NO, NOx, O3, and CO), physical aerosol parameters (particle number and air ion size distributions, as well as aerosol light absorption) and total PM10 mass concentration were measured. Compared with South African and European ambient air quality standards, SO2, NO2 and CO concentrations were generally below the air quality standards, with average concentrations for the sampling period of 3.8ppb (9.9μg/m³), 8.5ppb (15.9μg/m³) and 230ppb (270μg/m³), respectively. The major source of SO2 was identified as high-stack industry emissions, while household combustion was identified as the predominant source of NO2 and CO. In contrast, O3 exceeded the eight-hour moving average standard (61ppb / 120μg/m³) 322 times per year. The main contributing factor was identified to be the influx of regional air masses, with high O3 precursor concentrations. PM10 exceeded the current South African 24-hour standard (120μg/m³) on average 6.6 times per year, the future 2015 standard (75μg/m³) 42.3 times per year and the European standard (50μg/m³) 120.2 times per year. The PM10 average concentration for the sampling period was 44μg/m³, which exceeded the current European and future (2015) South African annual average standard (40μg/m³), emphasising the PM pollution problem in the western BIC. The main source of PM10 was identified as household combustion. Masters

Thesis (MSc (Chemistry))--North-West University, Potchefstroom Campus, 2012 Ozonation, or advanced oxidation processes (utilising ozone decomposition products as oxidants) are widely used in industrial waste water and drinking water treatment plants. In these applications the use of ozone is based on ozone and its decomposition by-products being strong oxidants. A case study revealed that several waterworks in South Africa successfully utilise ozone as a pre-oxidant for the treatment of raw waters. South Africa holds more than three quarters of the world’s viable chromium ore (chromite) reserves. Subsequently the Cr-related industry-within is considerable in size and a major producer of large volumes of waste materials. Chromium also occurs commonly in other industrial waste materials (e.g. fly ash and clinkers originating from coal combustion) and is a natural occurring element in natural sediments, since chromium is the 21st most abundant element in the earth’s crust with an average concentration of approximately 100 ppm. Considering the abundance of natural and anthropogenic Cr-containing materials in South Africa the possibility exists that some of these materials might be suspended in raw water entering water treatment facilities. In this dissertation, the possible oxidation of non-Cr(VI) Cr-containing materials suspended in water during ozonation, is presented within the context of water treatment applications (Chapter 4). The results indicate that in situ formation of hazardous Cr(VI) is possible during aqueous ozonation. pH had a significant influence, since the decomposition products of aqueous O3, i.e. hydroxyl radicals that form at higher pH levels, were found to be predominantly responsible for Cr(VI) formation. Increased ozonation contact time, water temperature and solid loading also resulted in elevated Cr(VI) concentrations being formed. Occasionally these values exceeded the drinking water standard 50 ppb Cr(VI). The results therefore indicate the importance of removing suspended particulates from water prior to ozonation. Additionally, pH-control could be used to mitigate the possible formation of Cr(VI) during ozonation. In Chapter 5, exploratory work is presented on the possibility of utilising Cr(VI) formation via ozonation as a means of recovering chromium from Cr-containing waste materials. Such a study is of particular interest within the local context, considering the large volumes of waste produced by the Cr-related industry in South Africa. This exploratory work is based on the fact that unlike Cr(0) and Cr(III), most Cr(VI) compounds are relatively soluble in water. Cr(VI) is a carcinogen if inhaled, however the probability of negative health effects are substantially reduced if it occurs in solution. Thus a hydrometallurgical route of recovering Cr-units via Cr(VI) generation represents the safest route with regard to Cr(VI) exposure. Such a hydrometallurgical route could also addresses the limitations of the physical separation methods currently applied, which fails to recover fine Cr-containing solids. The degree of Cr2O3-liberation achieved in this exploratory work was relatively low. However, the Cr2O3-liberation achieved for the ferrochromium slag (15%) indicated some promise, considering the limitations of this exploratory work. Several steps can be considered in future studies, which would in all likelihood improve the Cr2O3-liberation further. Masters

Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2010. The industrial importance of the chromium industry to South Africa is emphasised by the fact that it is considered the largest chromite (chromium ore) and ferrochrome (chrome-iron alloy) producing country in the world. Although South Africa holds three quarters of the world's chromite ore reserves, the chrome-to-iron (Cr-to-Fe) ratio of the local chromite ores is relatively low (1.47 to 1.55), compared to other deposits in the world (2.6 to 3.5). Additionally, iron is more readily reduced than chromium. The combination of these two factors implies that ferrochrome produced from South African chromite ore contains 47-53% chromium. Current pricing practises in the world ferrochrome industry dictate that ferrochrome producers are only paid for the chromium content in the ferrochrome, which implies that South African ferrochrome producers export a large percentage of their product without any financial benefit. Research to improve the Cr-to-Fe ratio is therefore essential to support sustainability of the local ferrochrome industry. Conventional beneficiation methods such as gravity concentration, magnetic separation and floatation are unlikely to increase the Cr-to-Fe ratio, since both iron and chromium are part of the same mineral phase, i.e. the spinel, which requires structural dissociation. It has been proven on laboratory scale that high temperature carbochlorination (CO and Clz atmosphere) can be used to selectively remove iron from chromite. However, such methods are unlikely to be implemented on an industrial scale due to health, environmental and cost considerations. In light of this, an alternative approach to chromite chlorination, avoiding the use of chlorine and other toxic gasses, was investigated during this study. Since it was found that NaCI addition significantly improved the effectiveness of carbochlorination of chromite, the effect of adding only NaCI during high temperature treatment of chromite was investigated. The material utilised during this investigation consisted of local chromite, anthracite (source of carbon) and attapulgite clay (serving as a binder). These materials were mixed in a ratio and subsequently milled toD90 = 75µm to represent materials and specifications similar to those used during pelletisation of the chromite in the pre-reduction ferrochrome production process. This mixture could also be used to generate a partially reducing atmosphere (CO rich) during high temperature treatment, which was similar to the reaction conditions utilised during carbo-chlorination. The above mentioned milled mixture was pelletised into cylindrical pellets with a die set and a hydraulic press. This experimental investigation was based on a mono-variance procedure, in that the four different variables investigated, i.e. maximum pellet treatment temperature, exposure time, wt% NaCI addition to the pellets and the atmosphere the pellets were exposed to, were varied one at a time during experimentation. After each alteration of the afore-mentioned variables, the Cr-to-Fe ratios, together with other parameters, were measured. Analyses undertaken included Scanning Electron Microscopy, with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and cured breaking strength. Although this investigation did not focus on the cured breaking strength of the pellets, it is a very important industrial parameter and was therefore measured. Results indicated that the addition of NaCI had a definite effect. In both oxidising and partially reducing atmospheres the cured breaking strength of the cured pellets increased up to 800°C exposure, where after it decreased. This was attributed to melting of NaCI at 801 °C. In the oxidising atmosphere, the cured breaking strength increased again at temperatures higher than 1 000°C, due to the formation of a thin oxldised layer on the outside of the pellets, which could be confirmed by SEM analysis. Fine, metallic-like crystals were noticed inside and on the lids of crucibles in which pellets containing NaCI as an additive were cured at temperatures of 900°C or higher. SEM-EDS analysis and weight-ratio calculations revealed that these crystals were pure FeO. This indicated that some iron might have been liberated from the chromite spinel matrix. However, ICP-OES analyses revealed that Cr-to-Fe ratios did not change significantly under any of the experimental conditions (NaCI addition 5wt% to 15wt%, curing between 500'C and 1200'C, and oxidative/partially reducing atmospheres). The observed FeO crystals did not make any meaningful difference to the Crto-Fe ratio of the chromite, but was of great academic interest as iron was extracted from the chromite spinel. This indicated that it is not only the formation of low melting point species, such as those proposed in previous mechanistic studies of carbochlorination of chromite, but that molten NaCI alone could also initiate the extraction of iron out of chromite. According to the knowledge of the author, this is the first report of its nature in open literature. SEM and SEM-EDS analyses also proved that the addition of NaCI to the chromite/carbon/clay mixtures enhanced the rate of chromite pre-reduction. This finding was in agreement with earlier literature reports. In conclusion, it can be stated that the addition of NaCI alone cannot alter the Cr-to-Fe ratio of chromite during high temperature treatment. NaCI addition did, however, have an effect on other important parameters i.e. initiation of iron removal, cured breaking strength and the rate of chromite pre-reduction. From the results and experience gained in this study, certain recommendations with regard to possible future studies could also be made. This included investigating i) other single component additives to possibly alter the Cr-to-Fe ratio during high temperature treatment, ii) the effect of industrially relevant additives such as CaO/CaC03, Mg03 and SiOz on the rate of chromite pre-reduction and iii) the effect of different clays (e.g. attapulgite, bentonite, etc.) on the rate of chromite pre-reduction. Masters

Thesis (Ph.D. (Chemistry))--North-West University, Potchefstroom Campus, 2010. A series of experiments was conducted to investigate the potential influence of selected inorganic compounds on sintering and agglomeration of a model mineral mixture. The minerals and inorganic compounds were chosen based on the constituents found in coal. The study simulated ash formation processes in the temperature range of 500 °C to 1000 DC. The mineral mixture consisted of kaolinite, quartz, pyrite, siderite, calcite, Ti02 and magnesite in a fIxed ratio. The mixture was doped with 4% (by weight) of each trace or minor element species. Different analytical methods were employed to investigate the extent of sintering and agglomeration and to identify the possible interactions between the species. Compressive strength measurements, TG/DTA, SEMIEDS and XRD analysis were used to evaluate the interactions in oxidizing and inert atmospheres. The influence of the compounds on the reducing-atmosphere ash fusion temperatures of the mineral mixture was also investigated. The results indicated that NaCl, Na2C03, Ge02, Mn20 3, NbS2, srCo3 and PbS increased sintering in the mineral mixture in the oxidizing atmosphere. Sintering was increased by enhancing sulfation of limestone, and/or by affecting the characteristics of the aluminosilicate phases. Na2C03, Ge02 and Mn2O3 increased sintering of the mineral mixture in the inert atmosphere by affecting the characteristics of the alurninosilicate phases. MOS2 and PbMo04 decreased sintering of the mineral mixture in the oxidizing atmosphere, while CU2S, CuS, PbS and NaCI decreased sintering in the inert atmosphere. The results obtained in oxidizing and inert atmospheres indicated that the oxidation numbers of the cations and the anions associated with the different compounds affected the potential of the additives to influence sintering and agglomeration of the mineral mixture. The influence of the inorganic compounds on the mineral mixture at different ashing temperatures was investigated with the ash fusion temperature test. The results indicated that the ash fusion temperatures were decreased by the addition of GeS and PbC03 at an ashing temperature of 500°C, decreased by SrC03 at an ashing temperature of 815°C, and increased by cr03 at an ashing temperature of 500°C. The results confirm that the addition of trace element compounds can result in the formation of species with lower melting points, and that the ashing temperature has an influence on the ash fusion temperatures. Doctoral

Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2009. One of the major concerns that has been facing South Africa in recent years is the amount of gaseous pollutants emitted into the atmosphere. The Mpumalanga province is largely an industrialised area, which contributes approximately 83% to the country's total coal production. Eastern Gauteng and western Mpumalanga were identified as an air pollution hotspot and therefore declared the Mpumalanga Highveld Priority Area (HPA) on 4 May 2007. Diverse anthropogenic activities in this region result in high levels of organic aromates, such as benzene, toluene, ethylbenzene, and xylene (BTEX), as well as nitrogen dioxide (N02), sulphur dioxide (S02) and ozone (03). The monitoring of inorganic gases with active and passive samplers is well established in South Africa. In contrast, very little data exists for volatile organic compounds (VOCs), which necessitates the measurement of these gases. Therefore, the primary aim of this research project is to determine the spatial and temporal distribution of BTEX, N02, S02, and 03 in the HPA. A vertical assessment of BTEX was also conducted, in order to compare the upper atmospheric concentrations with the ground-level measurements. Lastly, all data were compared to the current legislation, in order to establish compliance. Eight sites, within a grid of 600 km2, were selected for the sampling. Passive sampling for the selected criteria pollutants was conducted on a monthly basis for a period of one year. The ground-level concentrations of BTEX were measured with Tenax TA adsorbent tubes, while N02, S02 and 03 were measured with passive samplers developed and used by the Atmospheric Chemistry Research Group of the North-West University. Vertical BTEX profiles were obtained with a Cessna 182 during a two-day winter and a two-day summer field campaign utilising 6L TO-14 canisters and absorbent tubes. Flights were undertaken at two altitudes, 500 ft and 1 500 ft above ground level (AGL), and on three flight paths. VOC samples were analysed, by using a gas chromatograph attached to a mass spectrometer for detection. Adsorbent tube samples were introduced into the system by a thermo desorber, while the canister had a slight modified inlet. Sulphurdioxide and 03 analyses were done on an Ion Chromatograph, while a UV-visible Spectrophotometer was used for N02 analysis. The spatial distribution of N02, S02, and BTEX indicated an increase towards the western parts of the HPA. This can be attributed to the prevailing north-easterly winds, as well as the increased industrial activity in the western parts. The rural areas such as Balfour and Delmas were influenced by the industrial activities in the surrounding areas. The temporal distribution of the inorganic gaseous species N02, S02, and 03 indicated seasonal trends. The N02 and S02 peaked during winter because of meteorological conditions that trap and recirculate the air mass, as well as increased household and biomass combustion. The 03 peak during spring could be explain by the CO peak, which is probably the most important 03 precursor species in South African conditions. The CO peak occurred due to increased veldt fires during the dry season. No seasonal trend was observed for BTEX. From the vertical BTEX assessment, it was clear that no significant difference exists between the upper atmospheric concentrations and the ground-level measurement. A good comparison between the canisters and adsorbent tubes was found. All the measured species were below their national- and proposed standards. However, the higher levels of S02, N02, and BTEX, measured in the western parts of the HPA, require attention. Witbank was the most polluted municipal area that was monitored. Masters