A density functional theory calculation for revealing environmentally persistent free radicals generated on PbO particulate

In particulate matter, organic precursors generate environmentally persistent free radicals (EPFRs) on metal oxides and attract worldwide attentions in health risk assessment and environmental protection. For the first time, we determined characteristics and formation processes of EPFRs evolved from different organic precursors on PbO particulate. As a result, phenol resulted in phenoxyl radical at 230 °C by releasing one H atom. One Cl atom was eliminated from monochlorobenzene and 1,2-dichlorobenzene, producing phenyl and chlorobenzene radicals, respectively. The decays of these radicals had an order of chlorobenzene radical (4 d) > phenyl radical (3 d) > phenoxyl radical (2 d). Density functional theory calculations indicated that the long decay of chlorobenzene radical was contributed to the high adsorption energy of 1,2-dichlorobenzene on PbO particulate. Furthermore, chlorobenzene radical produced more reactive oxygen species than the other two radicals in oxidative-stress investigations. Therefore, 1,2-dichlorobenzene creates more persistent EPFR, which will cause more dangerous health impact. The main results of this article provide a new insight into the health risk assessment of organic and oxide-containing particulate matter.