One embodiment is a method including determining whether an ammonia storage device has a stored quantity of ammonia, predicting an impending ammonia release from the ammonia storage device, determining a NOx increase amount in response to the impending ammonia release, and increasing an amount of NOx provided by an engine based on the NOx increase amount. In certain embodiments, determining the NOx increase amount in response to the impending ammonia release comprises determining a NOx increase schedule based on the stored quantity of ammonia. In certain embodiments, the NOx increase schedule comprises a specified NOx increase time period, and in certain further embodiments, the method further includes decrementing the specified NOx increase time period based on an estimated catalyst degradation value.