It is known that NO in the flue gas can be effectively converted to NO2 by O-3. The objective of this work is to investigate the feasibility of simultaneously abating NO2 and SO2 from flue gas by liquid-phase conversion. A suite of cost-effective additives for enhancing NO2 absorption through enriching the concentration of sulfite ion, S-IV, in the liquid phase has been evaluated under pH similar to traditional flue-gas desulfurization (FGD). Experiments were conducted in a lab-scale washing tower with CaSO3 slurry, including metal and non-metal additives: FeSO4, FeCl2, Fe-2(SO4)(3), MnSO4, MnCl2, MgSO4, MgCl2, (NH4)(2)SO4, and NH4Cl. All of these additives enhance the absorption efficiency of NO2. Ferrous sulfate, FeSO4, is the most effective additive, with absorption efficiency reaching 95%, but the loss of additive is high because of the oxidation of Fe-II into Fe-III. Ammonium sulfate, (NH4)(2)SO4, has similar absorption efficiency but shows lower loss during absorption. Its absorption efficiency improves with an increasing temperature and decreases with a decreasing pH, although NO2 absorption is still noticeable when pH varies between 5 and 7, which is within the operating range of a typical wet FGD. The presence of O-2 causes a 4% decrease in NO2 removal when MnSO4 and (NH4)(2)SO4 are used as additives.