The impact of the coexistence of SO2 and NO in flue gas on Hg-0 removal over HNO3-modified activated carbon (HNO3-AC) was evaluated. In addition, the effect of adding HCl on Hg-0 removal was also investigated. Hg-0 removal strongly depends upon the composition of the acidic gas. The results indicated that physically adsorbed SO2 inhibited Hg-0 removal because of competitive adsorption, while chemically adsorbed SO2 slightly promoted He removal by generating HgSO4. The formation of N-containing active species, such as NO2, facilitates the removal of Hg-0 in the presence of NO to primarily produce Hg(NO3)(2) or HgO. In comparison to the study performed under NO, SO2 suppressed Hg-0 removal by weakening the amount of active NO2 species that were generated over the samples. The presence of HCl strongly affected Hg-0 removal, and HgCl2 and Hg2Cl2 were produced in all of the flue gases containing HCI. In addition, the binding abilities between mercury and the different groups that formed on the samples follow the order: Cl- > S- > N-containing groups.