Redox activity of atmospheric fine particulate matter in Hong Kong: characterization and source apportionment

Redox activity is an important factor of PM toxicity. It is suggested that many of the PM-associated adverse health effects are caused by the generation of reactive oxygen species (ROS) and the resulting oxidative stress within the affected cells. Some studies have been carried out to explore the relationships between PM composition and PM-induced redox activity. However, most of these studies only focused on the contributions of metals and polycyclic aromatic hydrocarbons (PAHs) to PM toxicity. Little information is available on how specific organic species other than PAHs, such as oxygenated multifunctional organic compounds, relate to ROS generation capacity of PM. In this project, we propose to characterize the redox activity of PM2.5 samples collected in Hong Kong during a one-year long period using three complementary methodologies, namely the cell-free dichlorodihydrofluorescien assay, the plasmid scission assay, and the lacate dehydrogenase assay. A series of advanced analytical techniques will be used to identify and quantify metals, ionic species, elemental carbon, organic carbon, and organic species, especially PAHs, nitrated PAHs, oxygenated PAHs, nitro-phenols and the derivatives, and primary and secondary organic aerosol (POA and SOA) markers in both whole and water-soluble fractions of PM2.5 samples. We plan to perform positive matrix factorization analysis of the measured redox activity in PM2.5 together with SOA, POA, PAHs and derivatives thereof, and major aerosol constitutes to apportion the primary and secondary sources of PM2.5-associated redox activity in Hong Kong and estimate the contributions of individual sources to PM toxicity. Correlation analysis of PM-associated redox activity with individual organic species and specific groups of compounds (e.g. individual SOA markers for monoterpenes and the sum of monoterpenes SOA markers) will be carried out. The seasonal variation of PM redox activity and factors influencing it, such as origin of air masses and aerosol acidity, will be investigated. Such a comprehensive study on the characterization and source apportionment of PM2.5-associated toxicity has not been carried out in the region before. Results from this project will provide a quantitative understanding of the redox activity of PM2.5 in Hong Kong and contributions of different primary and secondary sources to PM toxicity in the region. Such information is essential for the prediction of PM-associated adverse health effect and implementation of cost-effective and source specific air quality regulations for a better protection of human health.