Due to the prevalence of coal combustion technologies utilizing calcium-based materials, it is important to understand the varied reactions between the flue gas species and these calcium-based materials. Of particular importance is the reaction between sulfur oxides (SO2 or SO3) and calcium oxide (CaO), which plays an important role in sulfur retention on fly ash during oxy-coal combustion or carbon capture with calcium looping. To better understand these reactions, density functional theory (DFT) calculations were performed investigating SOx binding to CaO surfaces functionalized by other flue gas components. Analyses of the energetic, geometric and electronic nature of the modeled systems were conducted. Generally, the most stable conformation on the surface is in the form of either a sulfite-or sulfate-like structure. Water can have an effect on sulfur binding by introducing other favorable intermediate conformations, while carbon dioxide could negatively impact adsorption by weakening sulfur-surface bonds. (C) 2017 Elsevier Ltd. All rights reserved.