With rapid development, increasing sulfur dioxide (SO2) emission becomes a key environmental issue in China. To respond to this challenge, the Chinese government established a top-down scheme to reduce its SO2 emissions. However, regional disparity and the associated cost differences brought uncertainties to the policy effectiveness and efficiency. Few studies focus on this field. Therefore, this study tries to fill such a gap by investigating the differences of SO2 emissions, reduction potential, and cost-effectiveness through use of the GAINS-China model in five mega-cities in China, namely, Beijing, Shanghai, Tianjin, Chongqing, and Hong Kong. A scenario analysis approach is employed, focusing on two technologies named flue gas desulfurization (FGD) and limestone injection (LINJ). Results demonstrated that a large SO2 reduction potential exists, as well as a great disparity, among the five mega-cities. Chongqing had the largest reduction potential with lowest unit cost, while Beijng and Hong Kong showed the lowest reduction potential with higher unit cost. In Beijing and Shanghai, FGD and LINJ in the power generation sector had the larger reduction potential with the highest cost-effectiveness. However, in Chongqing, the industry sectors also had large reduction potentials. Finally, appropriate SO2 control strategies and policies are raised by considering the local realities. (C) 2013 Elsevier Ltd. All rights reserved.