Transformations of Gas-phase PCBs, PCDDs and PCDFs

To date, the kinetics of the gas-phase reactions of 03 with biphenyl, 2,2 -dichlorobiphenyl, dibenzo-p-dioxin, 1-chlorodibenzo-p-dioxin and diben-zofuran have been studied at room temperature.93-95 In all cases, no reactions were observed and the measured upper limits to the rate constants are given in Table 1. The observed lack of reaction of 03 with gas-phase PCBs, PCDDs and PCDFs is expected,77 based on literature data for other aromatic compounds,96,97 and it is anticipated that the room temperature rate constants for the gas-phase reactions of 03 with PCBs, PCDDs and PCDFs are all 2 x lCT20cm3 molecule s 1. 

The measured rate constant, kohs, is then given by 

The experimental data for dibenzo-p-dioxin, 1-chlorodibenzo-p-dioxin95,99 and polycyclic aromatic hydrocarbons92 show that under the experimental conditions employed, kc NOz kd[02] and that equation (13) simplifies to 

In addition, a direct reaction pathway (for example, involving H-atom abstraction) should be considered (although the experimental data do not show any evidence for this pathway, nor is it expected92)  

3Rate constant ratio cited in Kwok et al.95 was erroneously a factor of 10 low. bUncertain to a factor of 2. 

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