Mechanism and kinetics study on the ozonolysis reaction of 2,3,7,8-TCDD in the atmosphere.

The ozonolysis of 2,3,7,8-tetra-chlorodibenzo-p-dioxin (2,3,7,8-TCDD) is an efficient degradation way in the atmosphere. The ozonolysis process and possible reactions path of Criegee Intermediates with NO and H2O are introduced in detail at the method of MPWB1K/6-31+G(d,p)//MPWB1K/6-311+G(3df,2p) level. In ozonolysis, H2O is an important source of OH radical formation and initiated the subsequent degradation reaction. The Rice-Ramsperger-Kassel-Marcus (RRKM) theory was applied to calculate rate constants with the temperature ranging from 200 to 600 K. The rate constant of reaction between 2,3,7,8-TCDD and O3 is 4.80 x 10(-20) cm3/(mole x sec) at 298 K and 760 Torr. The atmospheric lifetime of the reaction species was estimated according to rate constants, which is helpful for the atmospheric model study on the degradation and risk assessment of dioxin.