Abstract: A method for injecting a reductant into an exhaust gas of a power system. The method includes oscillating injections of the reductant between a higher reductant injection rate and a lower reductant injection rate. The higher injection rate is high enough to result in storage of a decomposed form of the reductant on a selective catalytic reduction on-filter (“SCR+F”), and the lower injection rate being low enough to result in depletion of the decomposed form of the reductant on the SCR+F. The SCR+F includes a diesel particular filter and a selective catalytic reduction catalyst applied thereto.