This study validates the Hg emissions rates from NEA's MercuRator (TM) with field test data for 25 full-scale utility gas cleaning systems that emphasize SCR/ESP/FGD combinations and activated carbon injection (ACI). Validations of the extents of Hg(0) oxidation across SCRs and of Hg retention in wet FGDs gave correlation coefficients greater than 0.9 for both units. The validations for ACI applications yielded the first quantitative interpretations for different saturation levels of Hg capture for the highest ACI rates. When all the reaction mechanisms were combined to simulate Hg transformations along complete gas cleaning systems, the predicted Hg emissions rates were correctly rank ordered for nine of ten stations with SCR/CESP/FGD combinations, and for all six ACI test sites. (C) 2009 Elsevier Ltd. All rights reserved.