Atmospheric chemistry of 2,3,7,8-TCDD/F: Mechanism and kinetics study

• Atmospheric reactions of TCDD/F initiated by OH and HO2, O3, NO3, and Cl were investigated.
• TCDD/F will be mainly scavenged by OH during daytime, while NO3 is the primary oxidant at night.
• Reactions with Cl atoms are the dominant removal pathway of TCDD/F in coastal area after sunrise.

The reactions of gas-phase PCDD/Fs with oxidizing agents are believed to be the major atmospheric sink. In this study, the density functional theory (DFT) method is employed to investigate the reaction mechanisms of 2,3,7,8-tetrachlorinated dibenzo-p-dioxins (2,3,7,8-TCDD) and 2,3,7,8-tetra chlorinated dibenzofuran (2,3,7,8-TCDF) initiated by a series of atmospheric oxidants (e.g., OH, HO2, O3, NO3 radicals, and Cl atom). The rate constants obtained from the reactions of the 2,3,7,8-TCDD/F with the corresponding oxidants are 7.75 × 10−12/9.78 × 10−13, 2.53 × 10−25/3.61 × 10−25, 3.71 × 10−21/6.86 × 10−22, 3.96 × 10−14/6.46 × 10−15, and 1.23 × 10−9/1.37 × 10−10 cm3 molecule−1 s−1, respectively. The results show that 2,3,7,8-TCDD/F will be mainly scavenged by OH radical, while NO3 radical is the primary oxidant at night and Cl atom dominates after sunrise in coastal and marine areas.