Abstract: The present invention is related to a method for preventing the formation of NH.sub.4 HSO.sub.4 during the noncatalytic reduction of nitric oxide by ammonia or ammonia precursors in combustion effluents. The present invention is also related to a method for preventing the formation of H.sub.2 SO.sub.4 in the absence of ammonia or its precursors. The formation of these corrosive substances is extremely detrimental. NH.sub.4 HSO.sub.4 formation is a limitation upon the usefulness of nitric oxide reduction processes, particularly in boilers, furnaces, and other combustion devices. The formation of H.sub.2 SO.sub.4 limits effective heat recovery in combustion equipment.The present invention specifically teaches the use of methanol to reduce SO.sub.3 in the effluent stream to SO.sub.2. The noncatalytic reduction of SO.sub.3 by methanol is selective in that a large fraction of the SO.sub.3 is converted to SO.sub.2, while on a percentage basis very little oxygen is consumed.