NOVELTY - Regeneration of lean nitrogen oxide adsorber used to remove nitrogen oxide from exhaust gases by combustion of a fuel in a combustion chamber of an operating internal combustion engine, comprises determining a target regeneration flow of the exhaust gas; and directing a regeneration flow of the exhaust gas through the adsorber, the regeneration flow being established by bypassing a bypass flow of the exhaust gas around the adsorber.    USE - For regenerating a lean NOx adsorber.    ADVANTAGE - The method provides an easily recognizable marker indicating the completion of a regeneration cycle. This allows for real time monitoring of regeneration or a closed-loop regeneration method.    DETAILED DESCRIPTION - Regeneration of lean nitrogen oxide (NOx) adsorber used to remove nitrogen oxide from exhaust gases by combustion of a fuel in a combustion chamber of an operating internal combustion engine, comprises determining a target regeneration flow of the exhaust gas through the adsorber; directing a regeneration flow of the exhaust gas through the adsorber, the regeneration flow being established by bypassing a bypass flow of the exhaust gas around the adsorber when the target regeneration flow is less than exhaust gas flow from the engine, resulting in the regeneration flow being the same as the target regeneration flow, or directing all of the exhaust gas through the adsorber when the target regeneration flow is greater than the exhaust gas flow from the engine, the exhaust gas flow from the engine and the bypass flow established by reference to engine speed, engine load, intake manifold temperature of the engine, intake air mass flow, fuel flow into the engine, intake manifold pressure of the engine, a measured flow of the exhaust gas out of the engine, exhaust gas temperature, and exhaust gas pressure; and reacting within the exhaust gas and upstream of the lean adsorber, a reductant to maintain a lambda of the regeneration flow of less than one across the adsorber.    An INDEPENDENT CLAIM is also included for an after treatment system for removing NOx from exhaust gas produced during combustion of a fuel within a combustion chamber of an operating internal combustion engine, comprising exhaust line (22) for directing the exhaust gas from the engine; lean NOx adsorber (46) in the exhaust line for removing the NOx; regeneration catalyst (42) in the exhaust line upstream of the adsorber, and capable of promoting oxidizing or reforming of reductant; reductant line for delivering the reductant from a reductant store to the exhaust line upstream of the catalyst; reductant flow control in the reductant line for controlling flow of the reductant into the exhaust line; bypass line (12) for directing the exhaust gas around the lean NOx adsorber; at least one bypass control capable of controlling flow of the exhaust gas through the bypass line; controller (70); and at least one sensor (71) providing control information to the controller, the controller capable of adjusting the valve in response to the control information.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic of NOx management system.    Bypass line (12)    Exhaust line (22)    Regeneration catalyst (42)    Adsorber (46)    Controller (70)    Sensor (71)