Abstract: A shroud (102) for an aftertreatment device (100) for treating exhaust gas from an internal combustion engine comprises a stepped conduit (126) configured to be disposed over an upper surface of the aftertreatment device (100) and extending over substantially the entire length of the aftertreatment device (100), wherein the stepped conduit (126) is configured to channel a flow of cleaning air longitudinally along the outer and upper surface of the aftertreatment device (100), wherein an inner surface of the stepped conduit (126) defines at least a first downwardly extending step (134, 136, 138) and a second downwardly extending step (134, 136, 138) that are spaced apart along the length of the aftertreatment device (100), to direct at least a portion of the flow of cleaning air downward.