Abstract: A method for modelling engine emissions output is provided. The method includes determining a stoichiometric engine output emission value based on a dynamic data-based model and parameters associated with at least one engine operating state, wherein the at least one engine operating state is calculated at a substantially stoichiometric air-fuel ratio, selecting a target air-fuel ratio based on the at least one engine operating state and a desired engine performance, applying a predetermined static model to determine a correction factor to the stoichiometric engine output emission value, based on the target air-fuel ratio, and applying the correction factor to the determined stoichiometric engine output emission value to yield an air-fuel-ratio-corrected emission output value.