The effect of the presence of HCl and SO2 in the simulated coal combustion flue gas on the Hg-0 removal by a commercial activated carbon (coconut shell AC) was investigated in a laboratory-scale fixed-bed reactor in a temperature range of 80-200 degrees C. The characteristics (thermal stability) of the mercury species formed on the sorbents under various adsorption conditions were investigated by the temperature-programmed decomposition desorption (TPDD) technique. It was found that the presence of HCl and SO2 in the flue gas affected the mercury removal efficiency of the sorbents as well as the characteristics of the mercury adsorption species. The mercury removal rate of AC increased with the HCl concentration in the flue gas. In the presence of HCl and the absence of SO2 during Hg-0 adsorption by AC, a single Hg-0 desorption peak at around 300 degrees C was observed in the TPDD spectra and intensity of this peak increased with the HCl concentration during mercury adsorption. The peak at around 300 degrees C may be derived from the decomposition and desorption of mercury chloride species. The presence of SO2 during mercury adsorption had an adverse effect on the mercury removal by AC in the presence of HCl. In the presence of both HCl and SO2 during Hg-0 adsorption by AC, the major TPDD peak temperatures changed drastically depending upon the concentration of HCl and SO2 in flue gas during Hg-0 adsorption.