Abstract: A method of controlling air pollution arising from sulphur trioxide and or sulphuric acid in coal combustion gases, combustion gases passing through the demister region of a wet flue gas desulphurization unit are exposed to a sulphide based reducing agent such as hydrogen sulphide, such that metal catalysts promoting the oxidation of ammonia leading to the formation of nitrosylsulfuric acid are poisoned and so prevented from catalysing the formation and discharge of sulphuric acid in aerosol emissions in stack gases.

Abstract: 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.