Mercury emission field measurements based on the Ontario Hydro Method (OHM) were conducted for six coal-fired power plants in China. The mercury mass balances for the six power plants varied from 100.3% to 139.5% of the input coal mercury for the whole system. About 0.02%-1.2% of the mercury remained in the bottom ash. In the first five power plants equipped with pulverized coal boiler, most of the mercury was emitted from the stack to the atmosphere. The plants with Electrostatic Precipitator (ESP) system emitted more He than He2+, while the plants with the Fabric Filter (FF) emitted less He than Hg2+. Virtually all of the Hg-P enter the ESP or the FF was removed. The FF systems had better He and He2+ removal efficiencies than the ESP systems. The flue gas desulfurization (FGD) system removed up to 78.0% of He2+ and only 3.14% of He-0 in the flue gas, while 8.94% of the original mercury in the coal was removed by the FGD system. The average mercury removal efficiencies of the ESP systems was 11.5%, that of the FF systems was 52.3% and that of the combined ESP+FGD system was 13.7%, much lower than the average removal efficiencies of pollution control device systems in US plants which have been used in previous studies of Chinese mercury emission inventory. He, rather than Hg2+ as assumed in previous estimates, has been found to be the dominant species emitted in the atmosphere. The average emission factor was found to be 4.70 g/TJ (10.92 bl/Tbtu), which is much higher than for US plants burning bituminous coals due to the high mercury content in the Chinese coal and the low mercury removal efficiency of air pollution control devices of power plants. (C) 2008 Elsevier B.V. All rights reserved.