A combustion product control system includes a first sensing device that measures a concentration of NOx in a fluid stream and a second sensing device that measures NH3 slip in the stream. The system also includes at least one combustion product control element. The system further includes at least one processor coupled to the sensing devices and the control element. The processor is programmed to generate predetermined parameters for NOx values in the stream at least partially as a function of transient stream conditions. The processor is also configured to use model predictive control (MPC) processing to generate predetermined values for a NH3 injection rate during stream transients. The predetermined values vary at least partially as a function of modeled stream characteristics. The processor is further configured to regulate the control element to facilitate simultaneous regulation of the NOx and NH3 slip in the stream within respective predetermined parameters.