Method and appts. for electron beam irradiation treatment of flue gas in which active seeds, e.g. O or OH radicals, are produced by electron beam irradiation of external air or a portion of gas that is to be treated, the irradiated air or gas is injected into a main flue gas duct and uniformly mixed with the gas to be treated to convert harmful components, e.g. SO2, NOx, etc into mist or dust and the mist or dust is subsequently captured by a collector.
