1. A method comprising: providing an exhaust stream for an internal combustion engine, the exhaust stream fluidly coupled to an aftertreatment component; optically determining an amount of exhaust gas constituents in the exhaust stream during the operation of the internal combustion engine, the exhaust gas constituents comprising urea, NO, NO 2 and soot; diagnosing the aftertreatment component in response to the amount of the exhaust gas constituents; and wherein diagnosing the aftertreatment component comprises: determining that a soot filter has failed in response to the optically determined amount of soot; and determining a catalyst NO to NO 2 conversion effectiveness of an oxidation catalyst in response to the optically determined amount of NO and NO 2 .