In a method of controlling air pollution, a combustion gas is passed through a slurry of an alkaline-earth metal sulfide and a redox buffer (e.g., a phosphate), preferably in combination with an alkaline-earth metal carbonate and/or hydroxide. A composition for removing a heavy metal from a combustion gas is also provided, as an aerosolized, aqueous dispersion or slurry of an alkaline-earth metal sulfide and a buffering agent. A solid residue of the air pollution control process is also described.