NOVELTY - Purifying gaseous effluent containing pollutants comprising tars, non-methane volatile organic compounds (NMVOCs), halogenated compounds, hydrogen sulfide, ammonia, sulfur dioxide, nitrogen oxides or carbon dioxide, comprises analyzing gaseous effluent to identify pollutants and performing successive operations comprising (1) removing tars by cooling gaseous effluent, (2) removing NMVOC by bubbling gaseous effluent in liquid mixture of NMVOC, (3) removing halogenated compounds by bubbling gaseous effluent to salification solution, and (4) removing e.g. ammonia and nitrogen oxides.    USE - The process is useful for purifying a gaseous effluent containing pollutants consisting of tars, NMVOCs, halogenated compounds, hydrogen sulfide, ammonia, sulfur dioxide, nitrogen oxides and carbon dioxide, where the gaseous effluent is natural gas, gas associated with oil extraction, biogas, syngas or industrial waste gases (claimed).    ADVANTAGE - The process: does not release any harmful emissions into the atmosphere, does not cause water pollution as it is operated in closed circuit operation, does not cause soil pollution (as it disposes non-toxic products and does not require landfill), and thus facilitates the purification of gaseous effluent in an environmentally friendly, energy efficient, economical and uncomplicated manner; and is capable of treating all types of pollutants.    DETAILED DESCRIPTION - Purifying a gaseous effluent containing pollutants consisting of tars, non-methane volatile organic compounds (NMVOCs), halogenated compounds, hydrogen sulfide, ammonia, sulfur dioxide, nitrogen oxides and carbon dioxide, comprises analyzing the gaseous effluent to be purified to identify the pollutants contained in it, and performing by successive operations, according to the identified pollutants, comprising (1) removing at least partially, preferably fully, tars by cooling the gaseous effluent to pass tars from gaseous to liquid state and their physical separation to recover a treated gaseous effluent, (2) removing at least partially, preferably fully, NMVOC by bubbling the gaseous effluent in a liquid mixture of NMVOC the same composition as NMVOC present in the effluent to process gas so that the gas condenses and NMVOCs join the liquid mixture and recovering the treated gaseous effluent, (3) removing at least partially, preferably fully, the halogenated compounds by bubbling the gaseous effluent to a salification solution, where salifying allows simultaneous drying of the gaseous effluent, and recovering the treated gaseous effluent, (4) at least partial removal of at least one of hydrogen sulfide, ammonia, sulfur dioxide, carbon dioxide and nitrogen oxides by selecting from (4a) at least partial removal of at least one of hydrogen sulfide, ammonia, sulfur dioxide and carbon dioxide by passing the gaseous effluent in cooled water in which the hydrogen sulfide, ammonia, sulfur dioxide, carbon dioxide which are in a gaseous state are trapped in this state by physisorption, and process water which is saturated with the gaseous pollutants is separated to obtain a treated gaseous effluent, or (4b) at least partial removal of hydrogen sulfide in the case where carbon dioxide is co-present with it, by bubbling the gaseous effluent in a liquid to the chemical absorption of hydrogen sulfide with simultaneous removal of at least a portion of carbon dioxide, or at least partial removal of nitrogen oxides by bubbling the gaseous effluent in a liquid to the chemical absorption, and recovery of the chemical treated effluent, or (4c) removing, in any order, (4ca) only hydrogen sulfide or carbon dioxide by spraying into a stream of gaseous effluent of a suitable reagent to combine with hydrogen sulfide or carbon dioxide+hydrogen sulfide respectively to give a solid reaction product which gaseous effluent is removed to recover it to the clean state, (4cb) sulfur dioxide alone or carbon dioxide alone or sulfur dioxide+carbon dioxide by humidifying the gaseous effluent and then spraying the humidified flue gas to combine a suitable reagent with the reaction product of humidifying water and sulfur dioxide or carbon dioxide respectively or sulfur dioxide+carbon dioxide to give a final reaction product which is removed from the gaseous effluent to recover it to the clean state, and (4cc) only nitrogen oxide by reaction with the gaseous effluent and then spraying hydrogen peroxide into the thus treated gaseous effluent a reagent adapted to combine with the product of reaction between nitrogen oxide and hydrogen peroxide to give a final reaction product that the gaseous effluent is removed to recover it in the purified state.