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Monitoring and analysis of semi-volatile organic compounds in ambient air
Ketsise, Marina Nkhalong
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The growing concern for environmental pollution indicates the importance of correctly predicting the fate of pollutants in ambient air. This study was conducted to predict the ambient levels of polycyclic aromatic hydrocarbons (PAH's) in the greater Sasolburg area and to better understand the distribution and the sources of PAH's in ambient air. PAH's are chemical compounds which consist of two or more fused benzene rings and made entirely from carbon and hydrogen. PAH's are widespread environmental pollutants which are mainly emitted from combustion sources, which includes automobiles, industrial processes and domestic heating systems. As a result of the ubiquitous presence of these combustion sources, PAH's are distributed throughout the atmosphere in both the gas and particulate phases. There is an international concern about human exposure to a number of PAH's, mainly benzo[a]pyrene and their associated health effects (carcinogenic and mutagenic). Human exposure to PAH's may occur via food, water, air and direct contact with materials containing PAH's. In the case of PAH's, monitoring is difficult as these species have a very low ambient concentration. Advanced sampling techniques are necessary to collect adequate volumes of air samples. A high volume sampler equipped with polyurethane foam (PUF) and quartz filters were used to collect the air samples in the greater Sasolburg area. The polyurethane is used to collect gas-phase samples while the filter is used to collect the particle-phase samples. Ambient air quality measurements for PAH's were conducted during the period of November to December 2005 at two sites in Sasolburg region (industrial and hospital area). Sixteen PAH species were targeted for this study and of the sixteen species; seven of them were identified as priority PAH's by US EPA; on basis of concern that they might cause cancer in animals and humans. The measured results obtained showed anthracene to be one of the most predominant PAH species obtained in both the gas and particle phase. The total PAH emissions produced in the Sasolburg area were determined by using emission factors from the United State Environmental Protection Agency  for residential area and the emission factors from environmental Protection Agency 42  were used to determine the total emission produced for the industrial area. The measured results were modelled using an Atmospheric Dispersion Modelling System developed by Cambridge Environmental Research Consultants to predict the ambient levels of PAH's. The results showed naphthalene, phenanthrene and fluoranthene to be the dominant PAH species at the industrial area. The accuracy of the model predicted concentrations performed best for the following PAH species: fluorene; fluoranthene and pyrene at both the Sasolburg hospital and industrial receptors. Conversely the accuracy of the model predicted concentrations consistently performed worst for the following PAH species: acenaphthene; acenaphthylene; naphthalene and phenanthrene at both the Sasolburg hospital and industrial receptors. The model predicted that the concentrations were significant overestimates of the actual measured concentrations, resulting in huge model deviations. From the results obtained in this study, it is deduced that most of the PAH's were obtained in the gas-phase than in the particle phase. The highest PAH concentration in particle-phase was obtained at Sasolburg industrial area while the highest PAH concentration in gas-phase was observed at Sasolburg hospital area