An isomer prediction model for PCNs, PCDD/Fs, and PCBs from municipal waste incinerators

Isomer patterns of polychlorinated naphthalenes (PCNs), polychlorinated dib enzo-p-dioxins (PCDDs), polychlorinated biphenyls (PCBs), and polychlorinat ed dibenzofurans (PCDFs) from municipal waste incinerators (MWIs) were pred icted by a model based on symmetry numbers and preferential chlorination po sitions. Fly ash isomer patterns from five stoker and seven fluidized bed i ncinerators were compared to validate the prediction model. The isomer patt erns of the highly chlorinated PCN homologues from stoker type incinerators were successfully predicted. The relative equilibrium concentrations of te trachloronaphthalenes (TeCNs), calculated by an ab initio method, cannot ex plain the field isomer patterns. Formation pathways involving chlorophenol precursor condensation reactions should be examined to see whether these is omer patterns provide a better fit to the field PCDD data. The PCB isomer p atterns were fit reasonably well, but this finding could merely be an artif act of the limited data and the large number of isomers. The prediction equ ations of PCDFs, revised from prior work to include a symmetry number for e ach isomer, represented the field data patterns for the higher chlorinated isomers very well. Successful prediction of isomer patterns for partial hom ologue ranges suggests that these patterns are determined by a mechanism go verned by Cl-position-specific preferences.