In this study, CaSO3, the by-product of flue gas desulfurization (FGD) process, was used as an absorbent for NO2 absorption. As the CaSO3 content exceeded 0.1 mol L-1, the absorption efficiency of NO2 could reach more than 70%. Three types of additives, MgSO4, Na2SO4 and MgCl2. were also investigated for the enhancement of NO2 absorption, and it was found that MgSO4 was the most effective. When MgSO4 was added, the NO2 absorption efficiency could increase significantly from 70.8% to 86.0%. and the oxidation rate of CaSO3 became around 10 times higher than that of additive free condition. Furthermore, the addition of MgSO4 would also lead to the raise in the ratio of NO2- to the total NO2 absorption products. All these aspects could be ascribed to the increment of the capacity of dissolved sulfite species (CDSS) which resulted from the combined effects of SO42- and Mg2+. Firstly, SO42-would react with Ca2+ and promote the dissolution of CaSO3, resulting in the increase of CDSS. And then the neutral MgSO30 ion pair would form in the absorbent slurry, which could play the same role as dissociated SO32- in the NO2 absorption. (C) 2010 Elsevier B.V. All rights reserved.