The gaseous pollutants can be controlled through the techniques of combustion, absorption adsorption and cold trapping.
(a) Combustion: Though combustion is a major cause of is pollution but it helps in controlling pollution by converting hazardous pollutants like volatile organic compounds (VOC) and other gaseous hydrocarbons to CO2 and H2O. If pollutants are organic in nature flame combustion is employed. Catalytic combustion is employed where low operating temperature is required.
(b) Absorption/adsorption: Gaseous effluents are allowed to pass through scrubbers. This technique can be wet or dry. Some of solvents used for wet scrubbing are NaOH, Na2SO3, Ca (OH)2
For dry Scrubbing activated carbon is used which attracts gases and vapour to its surface.
(c) Cold trapping: All pollutants from air stream may be removed by cold trapping i.e. freezing them (gases or vapors) in collectors maintained at a low temperature. Fractionation is achieved by using bath (00C) and last collector at a liquid nitrogen.