Deterioration of gasoline vehicle emissions and effectiveness of tune-up for high-polluted vehicles

This study investigates the emissions using a chassis dynamometer for three types of passenger vehicles, including new vehicles, in-use vehicles, and highly polluted vehicles, based on the US federal test procedure (FTP-75). In-use high emitters, emit about 5-12 times more CO, NOx and HC. Emission tests before and after repair and maintenance for high emitters indicated that tune-ups fail to reduce emissions because of deterioration of the three-way catalyst over time.