Atmospheric chemical reactions of 2,3,7,8-tetrachlorinated dibenzofuran initiated by an OH radical: mechanism and kinetics study.

Reactions with the OH radical are expected to be the dominant removal processes for gas-phase polychlorinated dibenzo-p-dioxins and dibenzofuran (PCDD/Fs). The OH-initiated atmospheric chemical reaction mechanism and kinetics of 2,3,7,8-tetrachlorinated dibenzofuran (TCDF) are researched using the density functional theory and canonical variational transition state theory. The reaction mechanism of TCDF with the OH radical and ensuing reactions including bond cleavage of furan ring, O(2) addition or abstraction, dechlorination process, bimolecular reaction of TCDF-OH-O(2) peroxy radical with NO, and reaction of carbonyl free radicals TCDF-OH-O with H(2)O are investigated. In the subsequent reactions of TCDF-OH, O(2) abstraction and dechlorination are most likely to predominate the process. As the main products, the HO(2) radical and the Cl atom are active and may play important roles in the atmospheric oxidation processes. The rate constants of TCDF with the OH radical are calculated, which are consistent with the reported data.