A study on the oxidative potential and chemical characteristics of fine particulate matter

Abstract

Air pollution has played a major environmental issue globally. Several health studies have associated fine particulate matter (PM2.5) to various adverse health effects. PM2.5 has gained most concern due to its capacity to reach deeper in the respiratory system causing wide range of acute and chronic health diseases. Most health studies have used the mass concentration of particles as the exposure metric. But, evidence indicates that the chemical composition, surface area, and other characteristics of PM are potentially more closely linked to the induction of toxic responses. Hence, even with the same mass concentration, the health effects might be different. Since PM2.5 is composed of complex mixture of different components, a clear identification of components of PM2.5 that are toxic can be a challenging task. There has been growing interest in the capability of oxidative potential (OP) of PM2.5 as a more appropriate health-based measure. The OP is the capacity of PM2.5 to oxidize target molecules causing oxidative stress in the cell through the formation of reactive oxygen species (ROS). The OP properties of PM2.5 allow a more direct assessment of the mechanism behind PM2.5 and its adverse health effects making it a particular interest in the field. In this research, OP and its association to chemical characteristics of ambient PM2.5 was elucidated to support the mechanism of oxidative stress as a complementary health-based measure for ambient PM2.5 monitoring. The OP and chemical characteristics of ambient PM2.5 collected from various site types (urban, roadside, rural, and industrial sites) in Korea and an urban site in Philippines were measured to grasp the toxicity of the aerosols to which humans are exposed to. The OP was determined by using two different assays (dithiothreitol (OP-DTT) and electron spin resonance (OP-ESR)), and chemical components (ions, elements, organic carbon (OC), and elemental carbon (EC)) were measured for the ambient PM2.5. Both OP and chemical data were used to compare their spatial characteristics among site types having different PM2.5 sources, and to determine their seasonal variations. Further, the strength of association between OP and chemical components of PM2.5 were investigated by using the Principal Component Analysis (PCA) and a stepwise Multiple Linear Regression (MLR) analysis. After determining the toxicity levels of aerosols in different ambient environments, the toxicity of specific sources was investigated to better grasp how each source in the ambient atmosphere affects the ambient OP. The OP and chemical characteristics from laboratory-generated source-specific PM2.5 collected from developed aerosol-generating chambers. This chapter aimed to quantify the OP from 12 | P a g e specific sources that are common in ambient PM2.5 including biomass burning, coal burning, engine exhausts, road dust, and secondary inorganic aerosols (SIA) in order to assess the potential toxicological impacts of source-specific PM2.5 and to identify which sources have relatively higher health impacts. Additionally, the OP and chemical characteristics of source-specific PM2.5 were integrated to derive a source-specific OP metric for ambient PM2.5. A new OP metric was derived to serve as a potentially useful indicator to estimate the adverse health effects caused by oxidative stress and to provide practical management of PM2.5 beyond what can be achieved using PM2.5 mass concentration which is the current regulation standard. After establishing the usefulness of OP as a health-based air quality metric, it was imperative to develop an online system that will be able to determine the OP on a higher time resolution and faster operation time. An automated OP monitor was for ambient PM2.5 using OP-DTT assay was developed to provide online and time-resolved assessment of the capacity of ambient particles to generate ROS. The automated OP monitor consists of three combined systems: 1) a particle collector 2) a chemical module, and 3) a detector. In summary, this study successfully conducted the first comprehensive OP measurements of ambient PM2.5 in Korea and Philippines significantly bridging air quality research gaps. Highest ROS-generating capability was measured in an industrial site. Consistent association between OP and chemical components (OC, and transition metals) were found. Frequent dust events (increased metals) and strong photochemical activity (increased OC) possibly facilitated elevated OP measurements during spring and summer season, respectively. Laboratory-generated PM2.5 from combustion sources (biomass burning, vehicle exhaust, and coal combustion) yielded higher OP activity than non-combustion sources (road dust, sea spray, secondary inorganics). The source apportioned profile of PM2.5 in each site and source-specific OP was proved to be helpful in deriving a more accurate heath metric. The derived OP-based metric in this study can be used as complementary information to current health standards of PM2.5. An automated OP monitor was constructed for better accessibility of semi-real time measurements of OP. The OP monitor provided time-resolved OP measurements allowing the determination of OP activity hourly peaks that is essential in air quality monitoring. The collection of knowledge on OP of PM2.5 in this dissertation showed promise as a vital tool for further field studies on toxicological characterization of PM2.5 and may lead to a better understanding of how PM can affect human and environmental health.