A method of treating exhaust gas from an internal combustion engine includes sensing a temperature of the exhaust gas with a temperature sensor, comparing the sensed temperature with a threshold temperature, injecting a first reductant into the exhaust gas at a first location if the sensed temperature is less than the threshold temperature, and injecting a second reductant having a different composition than the first reductant into the exhaust gas at a second location if the sensed temperature is greater than the threshold temperature.