Method of operating an exhaust-emission control system with a nitrogen oxide adsorber and a loading sensor

This application claims the priority of German patent document DE 199 54 549.9, filed on Nov. 12, 1999, the disclosure of which is expressly incorporated by reference herein. A method of operating an exhaust-emission control system with a nitrogen oxide adsorber and a loading sensor includes alternately operating the nitrogen oxide adsorber in adsorption phases with an at least stoichiometric exhaust air ratio and in regeneration phases with an at most stoichiometric exhaust air ratio. The loading sensor is able to ascertain continuously the nitrogen oxide loading of the adsorber even during the regeneration phases. By suitable evaluation of the loading sensor signal, the time for a changeover from an adsorption phase to a desorption phase and vice versa is determined. In addition, the storage capacity of the adsorber at a given time, when desulphating of the adsorber should take place, and whether the desulphating effect achieved was adequate, are determined.