In order to effectively reduce the total vehicle emissions, identifying and understanding the effects of high-emitting vehicles plays an important role. While several studies have documented the environmental impacts of high-emitting vehicles, these studies have not looked at the operational impacts of high-emitting vehicles. This paper uses field-collected and simulated data 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 using on-road emission measurement data. The study demonstrates that catalytic converter malfunctions produce significant increases in HC, CO, and NOx 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 malfunctions 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 in the case of NOx emissions. Simulation analysis of various driving cycles demonstrates that catalytic converter malfunctions produce overall increases in HC, CO, and NOx emissions in the range of 251%, 225%, and 336%, respectively. The study demonstrates that high emitters can be significant contributors to air pollution, implying that eliminating high emitters can significantly improve air quality in many metropolitan areas.
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