Quantum chemical investigation on the mechanism and kinetics of OH radical-initiated atmospheric oxidation of PCB-47

• Oxidation mechanism for PCB-47 with OH radicals was investigated firstly.
• Water molecule plays an important role during the whole degradation process.
• The favorable products of the title reactions are indicated in detail.
• The calculated total rate constant is 1.27 × 10−12 cm3 molecule−1 s−1 at 298 K.

The OH radical-initiated atmospheric oxidation degradation of 2,2′,4,4′-tetrachlorobiphenyl (PCB-47) was investigated by using quantum chemical calculations. All possible pathways involved in the oxidation process were discussed. Potential barriers and reaction heats have been obtained to assess the energetically favorable reaction pathways and the relatively stable products. The study shows that the OH radicals are more likely to attack the C3 and C5 atom of the aromatic ring in the PCB-47 molecule to form PCB–OH adducts. Subsequent reactions are the addition of O2 or NO2 molecule to the PCB–OH adducts at the ortho position of the OH group. Water molecule plays an important role during the whole degradation process. The individual and overall rate constants were calculated by using the Rice–Ramsperger–Kassel–Marcus (RRKM) theory over the temperature range of 180–370 K. At 298 K, the atmospheric lifetime of PCB-47 determined by OH radicals is about 9.1 d. The computational results are crucial to risk assessment and pollution prevention of PCBs.