A method includes providing an exhaust stream for an internal combustion engine, where the exhaust stream is fluidly coupled to an aftertreatment component. The method includes optically determining an amount of an exhaust gas constituent in the exhaust stream. The method further includes modifying a model stored on a computer readable medium in response to the amount of the exhaust gas constituent. The model is an engine NOx generation model, a catalyst NOx storage model, a catalyst NOx conversion model, a catalyst NO to NO2 conversion model, a catalyst conversion efficiency model, an engine soot generation model, and/or a urea hydrolysis model.