Photocatalytic reduction of oxidative potential of particulate matter 2.5 (PM2.5)

Oxidative stress induced by fine particulate matter 2.5 (PM2.5) is a potential cause of adverse health effects due to production of reactive oxygen species (ROS). This study aimed to investigate effect of photocatalytic reaction on the oxidative potential (OP) of PM2.5 collected on TiO2 supporting quartz fibre filter. The OP of PM2.5 was measured by dithiothreitol assay coupled with a flow injection analysis. The results showed OP of PM2.5 collected in Kanagawa, Japan ranged from 0.18 to 0.31 nmol min-1 m-3 with a median of 0.21 nmol min-1 m-3 (n=9). After irradiating ultraviolet ray (UV) onto the surface of PM2.5 on the TiO2 filter for 3 days, the OP significantly reduced to 0.088 - 0.19 nmol min-1 m-3 with a median of 0.15 nmol min-1 m-3 (p＝0.008). However, the reduction in OP was not monotonous; temporally increased at 5 days and then decreased with duration of UV irradiation. This suggests the ROS producing substances can be removed by the photocatalytic reaction, whilst OH radicals generated during UV-irradiation may produce the ROS producing substances, such as quinones from polycyclic aromatic hydrocarbons co-exiting in PM2.5 particles.