A first aspect of the present disclosure includes a method of controlling nitric oxides emissions. The method may include producing an exhaust gas stream containing NOx and supplying the exhaust gas stream to an exhaust passage. The method may further comprise supplying ammonia to the exhaust passage at a location upstream of a first selective catalytic reduction catalyst, wherein the amount of ammonia supplied at the first location is less than about 90% of the effective amount of ammonia needed for reduction of all NOx at the first location. Further, ammonia may be supplied to the exhaust passage at a second location downstream of the first selective catalytic reduction catalyst and upstream of a second selective catalytic reduction catalyst.