Oxidative potential of particulate matter as a health-relevant exposure metric

Though numerous epidemiological studies have observed consistent associations between exposure to ambient air pollution and adverse health effects, the underlying mechanisms of these effects have not yet been fully established. Ambient particulate matter (PM) is currently regulated on a mass basis, but not every component in the PM mixture is equally important. As PM toxicity is most likely to reflect exposure to the sum of multiple toxic components, oxidative potential (OP), which measures the inherent capacity of PM to oxidize target molecules, has been proposed as an additional exposure metric alongside PM mass concentrations. Whilst OP is considered a promising metric, actual application in epidemiological studies is limited. This thesis evaluates the value of oxidative potential (OP) of particulate matter (PM) as a health-related exposure metric for air quality assessment, with these specific aims: 1) 1) To compare OP assays and evaluate the impact of extraction solvent and filter type on these OP assays 2) 2) To assess the spatial and temporal variation of OP in ambient air 3) 3) To evaluate the relationships of ambient OP with indoor and personal exposure 4) 4) To evaluate the relationship of long-term exposure to OP of PM with respiratory health in children. Our findings suggest that the choice of filter type has a stronger influence on measured OP than extraction solvent; however, the relative OP reactivity is not influenced by filter type or extraction solvent. OP has high spatial and temporal variations, with road traffic being a major source of OP. Measurements of OP at a central monitoring site were found to represent wider surroundings. Furthermore, central site OP measurements were a reasonable surrogate for personal exposure in assessing short-term health effects of OP. Land use regression model could well predict the spatial variation of OP. These models were used to investigate the relationship between the OP and the respiratory health effects of children. The OP of particulate matter was significantly correlated with respiratory symptoms and reduced lung function in children.