Measuring axial exhaust species concentration distributions within a wall-flow aftertreatment device provides unique and significant insights regarding the performance of complex devices like the SCR-on-filter. In this particular study, a less complex aftertreatment configuration which includes a DOC followed by two uncoated partial flow filters (PFF) was used to demonstrate the potential and challenges. The PFF design in this study was a particulate filter with both through and plugged (or wall-flow) channels. A SpaciMS instrument was used to measure the axial NO2 profiles within adjacent through and plugged channels of each filter element during an extended passive regeneration event using a full-scale engine and catalyst system. By estimating the mass flow through the plugged and through channels, the axial soot load profile history could be assessed. The paper will describe the catalyst system, measurement and analysis, and give insights regarding the spatiotemporal evolution of a passive regeneration event within the PFF system.