Chemical and Biological Characterization of Air Particulate Matter in Japan, New Zealand and Rwanda As Case Studies
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Particulate matter in the air is recognized as the largest environmental cause of premature human mortality worldwide. Their health risk arises largely from carcinogenic chemical components (polycyclic aromatic hydrocarbons (PAHs) and their nitro-derivatives (NPAHs)), and the allergenic and pathogenic effects of the biological components that are bound to inhalable particulate matter (PM), all of which can affect the human respiratory system. The synergistic effects that both of these components have to one another and to human health are currently poorly understood. Given the potential health effects of PM and the scarcity of information about atmospheric levels and components of PM in some parts of the world, monitoring is necessary to evaluate mitigation strategies. The aim of this thesis was to characterize chemical and biological composition of PM in Japan, New Zealand and Rwanda. PM with aerodynamic diameters of ≤ 2.5 μm and ≤ 10 μm (PM2.5 and PM10, respectively) was collected using high volume air samplers at three locations (urban roadside, urban background and rural sites) in Rwanda and PM2.5 samples were also collected in two cities and rural locations in Japan and New Zealand. PAHs and NPAHs in these three countries were characterized using high-performance liquid chromatography. Microbial community structure (estimated using bacterial and fungal rRNA gene sequences) were characterized, and relationships were investigated using multivariate statistics. The mean concentrations of ΣPAHs and ΣNPAHs followed similar distribution profiles in all three countries, with higher concentrations in urban than in rural sites. Source identification using diagnostic ratio analysis and principal component analysis revealed diesel and gasoline-powered vehicles in the urban locations and wood/coal burning in rural locations were the major sources of PAHs and NPAHs in all three countries. Back trajectory analyses showed that high levels of PAHs detected in Japan and Rwanda were the result of long-range transport from neighbouring countries in close proximity, which was not observed in New Zealand due to its isolation from other countries. The analyses demonstrated that PM concentrations and lifetime cancer risks resulting from inhalation exposure to PM-bound PAHs and NPAHs exceeded the World Health Organization safe limits in Rwanda. Microbial analysis revealed that the diversity and composition of the airborne bacterial and fungal communities in Rwanda varied by site, PM size fraction, and season. The majority of the biological material originated from dust and plants. Redundancy analysis indicated that PAH and NPAH species were significantly negatively correlated with microbial communities. Overall, this study provides insights into aerosol PM, PAHs and NPAHs in African, Japanese and New Zealand cities and rural areas with added microbial insight in Rwanda, and their possible threats to respiratory health. Exposure to toxic PAHs and NPAHs and to pathogenic microorganisms associated with PM air pollution is a global problem, and the research presented in this thesis has produced findings that may be relevant world-wide.