Emissions emerge during the combustion of various fuel types which contain harmless and harmful components. It is necessary to reduce these harmful emissions, a task which is assumed by the catalytic converter. The limit values for the discharge of harmful emissions are defined in the so-called Euro standards.
In order to ensure optimal operating conditions of the catalytic converter, vehicles have at least one lambda sensor. This regulates the ideal mixture ratio of air and fuel. Only with the ideal mixture ("stoichiometric range") can the catalytic converter convert nearly all harmful emissions.