Abstract: In order to reduce the electrical resistance of entrained fine particles of fly ash resulting from the burning of low sulfur coal and to enhance the efficiency of their collection by an electrical precipitator means, there is a conditioning of the particles carried in the flue gas stream by having a very fine mist of H.sub.2 SO.sub.4 condensed and adsorbed on the particles themselves. Sulfuric acid is mixed with air in an acoustic nozzle to form a mist having a mean particle size of less than 10 microns which is injected uniformly into the flue gas stream at a zone ahead of the precipitator unit so that the acid can condense on the particles. The acid is preferably transported through the apparatus at ambient temperature and then heated just prior to injection to a temperature less than its vaporization temperature.