Environmental Impacts of Catalytic Converter Malfunctions

For effective reduction of total vehicle emissions, identifying and understanding the effects of high-emitting vehicles play an important role. Although several studies have documented the environmental impacts of high-emitting vehicles, these studies have not looked at the operational impacts of these vehicles on the environment. In this study, field-collected and simulated data are used to explain the operational effects associated with catalytic converter malfunctions on vehicle emissions. In addition, the study develops microscopic emission models for vehicles with catalytic converter malfunctions by using on-road emission measurement data. The study demonstrates that catalytic converter malfunctions produce significant increases in hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NO_x) emissions of 297%, 211%, and 378%, respectively, during cruising operations. Furthermore, increases of 63.4%, 26.9%, and 76.1% are observed during acceleration maneuvers. The study also found that under extremely aggressive driving conditions, both normal and high-emitting vehicles produce very high emission rates. The simulation results demonstrate that the highest impact of catalytic converter malfunction occurs in the 45- to 85-km/h speed range at mild acceleration levels for HC and CO emissions and between 20 and 55 km/h at high acceleration levels for NO_x emissions. Simulation analysis of various driving cycles demonstrates that catalytic converter malfunctions produce overall increases in HC, CO, and NO_x emissions in the range of 251%, 225%, and 336%, respectively. The study demonstrates that high-emitting vehicles can be significant contributors to air pollution, implying that eliminating high-emitting vehicles could significantly improve air quality in many metropolitan areas.