Abstract: The present invention concerns a method and an apparatus for removing substances from gases discharged from gas phase reactors. In particular, the invention provides a method for removing substances contained in gases discharged from an ALD reaction process, comprising contacting the gases with a “sacrificial” material having a high surface area kept at essentially the same conditions as those prevailing during the gas phase reaction process. The sacrificial material is thus subjected to surface reactions with the substances contained in the gases to form a reaction product on the surface of the sacrificial material and to remove the substances from the gases. The present invention diminishes the amount of waste produced in the gas phase process and reduces wear on the equipment.