Photocatalytic reduction of oxidative potential of particulate matter 2.5 (PM_2.5)

Abstract

Oxidative stress induced by fine particulate matter 2.5 (PM_2.5) 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 PM_2.5 collected on TiO₂ supporting quartz fibre filter. The OP of PM_2.5 was measured by dithiothreitol assay coupled with a flow injection analysis. The results showed OP of PM_2.5 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 PM_2.5 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 PM_2.5 particles.