Transit Bus Load-Based Modal Emission Rate Model Development (EPA/600/R-07/106) July 2007
Heavy-duty diesel vehicle (HDDV) operations are a major source of oxides of nitrogen (NOx) and particulate matter (PM) emissions in metropolitan areas nationwide. Although HDDVs constitute a small portion of the on-road fleet, they typically contribute more than 45 percent of NOx and 75 percent of PM on-road mobile source emissions. HDDV emissions are a large source of global greenhouse gas and toxic air containment emissions. Over the last several decades, both government and private industry have made extensive efforts to regulate and control mobile source emissions. The relative importance of emissions from HDDVs has increased significantly; today’s gasoline-powered vehicles are more than 95 percent cleaner than vehicles in 1968.
In current regional and micro-scale modeling conducted in every state except California, HDDV emission rates are taken from EPA’s MOBILE 6.2 model. EPA is currently developing a new set of modeling tools for the estimation of emissions produced by on-road and off-road mobile sources. The new Multi-scale mOtor Vehicle and equipment Emission System, known as MOVES, is a modeling system designed to better predict emissions from on-road operations.
The focus of this research is to develop a new heavy-duty vehicle, load-based modal, emission rate model that overcomes some of the limitations of existing models and emission rates prediction methods. This model is part of the proposed Heavy-Duty Diesel Vehicle Modal Emission Modeling (HDDV-MEM), which was developed by Georgia Institute of Technology. HDDV-MEM differs from other proposed HDDV modal models in that the modeling framework first predicts second-by-second engine power demand as a function of vehicle operating conditions and then applies brake-specific emission rates to these activity predictions.
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