A process of using solutions containing thiosulfate and/or chloride salt reagents to remove SO3 and H2SO4 acid gases from a flue gas. The solution is injected into a moving volume of flue gas to achieve a droplet size that enables the solution to dry on contact with the flue gas, generating dried particles of the reagent that react with the SO3 and H2SO4 acid gases yielding a salt precipitate. SO2 present in the flue gas may also be absorbed with the solution, with a subsequent reaction yielding bisulfite species that, upon drying of the droplet, react with the SO3 and H2SO4 acid gases to form salts that are removed from the gas. The removal of these acid gases from a flue gas reduce corrosion of equipment used in coal or oil fired power plants downstream of the injection cite.