Oxidative Potential by PM2.5 in the North China Plain: Generation of Hydroxyl Radical

Adverse health effects of ambient PM2.5 (d(p) < 2.5 mu m) can be associated with the production of reactive oxygen species (ROS), among which hydroxyl radical (center dot OH) is the most reactive. However, center dot OH generated by PM2.5 has not been quantified and studied in the North China Plain (NCP), which has suffered from heavy air pollution in recent years. In this study, PM2.5 samples were collected at an urban site (Beijing) and a suburban site (Wangdu), extracted in a cell-free surrogate lung fluid (SLF), and center dot OH generated in the extracts were quantified. The results show that more center dot OH is produced on heavily polluted days than that on clean days (2.0 and 1.6 times higher in Beijing and Wangdu, respectively). The production of center dot OH per unit mass (ng/mu g center dot PM2.5) decreases with the increase of ambient PM2.5 concentration because SO42-, NO3-, and NH4+ dominate the increased PM2.5, while these secondary inorganic components do not contribute to the generation of center dot OH. Trace metals (e.g., Fe, Cu, Se) and carbonaceous species (organic carbon and elemental carbon) correlate well with the center dot OH production, indicating that particles from combustion sources including coal combustion, vehicle exhaust, and industry contribute more to center dot OH generation.