An improved method of controlling air pollution, a combustion gas is passed through a solution of an alkaline-earth metal sulfide and a redox buffer (e.g., a mono alkaline-earth metal phosphate salt), preferably but not essentially in combination with an alkaline-earth metal carbonate FGD system. The reagents are provided in a fully soluble form enabling low cost application and retrofitting of existing facilities whilst also including alkaline-earth bases salts, which advantageously afford stability to the process product. The reagents co-precipitate when the solution achieves a pH of 4.5 to 6.5 such as is encountered in the acidic environment in conduits that carry combustion flue gases.