Hydroxyl Radical Generation from Environmentally Persistent Free Radicals (EPFRs) in PM_2.5

Hydroxyl radicals were generated from an aqueous suspension of ambient PM_2.5 and detected utilizing 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap coupled with electron paramagnetic resonance (EPR) spectroscopy. Results from this study suggested the importance of environmentally persistent free radicals (EPFRs) in PM_2.5 to generate significant levels of ·OH without the addition of H₂O₂. Particles for which the EPFRs were allowed to decay over time induced less hydroxyl radical. Additionally, higher particle concentrations produced more hydroxyl radical. Some samples did not alter hydroxyl radical generation when the solution was purged by air. This is ascribed to internal, rather than external surface associated EPFRs.