Proof of Concept Investigation for the Physical Emission Rate Estimator(PERE) to be Used in MOVES (EPA-420-R-03-005, February 2003)

The new EPA mobile source inventory model, Multi-scale mOtor Vehicle & equipment Emission System or MOVES, is an ambitious effort to model emissions from the micro to the macro level. To maintain consistency across the scales, a road load based quantity known as Vehicle Specific Power, or VSP, has been chosen as the primary causal variable in emissions formation for modeling purposes. This work attempts to take the physical link between driving activity and emissions one step further by introducing the Physical Emission Rate Estimator (PERE). PERE is meant to supplement the data driven portion of MOVES and fill in gaps where necessary. The model is essentially an effort to simplify, improve and implement the Comprehensive Modal Emissions Model (CMEM) developed at University of California, Riverside. PERE is based on the premise that for a given vehicle, (engine out) running emissions formation is dependent on the amount of fuel consumed. As such, it models fuel rate as well as CO2 generation with some degree of accuracy, which is the first step in the MOVES development. Being a physically based model, it has the potential (with some modification) to model new technologies (vehicles meeting new emissions standards), deterioration, off-road sources, I/M programs, as well as being able to easily extrapolate to areas where data are sparse. It may even save in data taking costs in the long run. Before the concepts in PERE can be implemented however, it must be demonstrated to work in a limited case scenario. This paper is an attempt to demonstrate the feasibility of PERE on a sample of (hot running and non hiemitting) Tier 1 vehicles. It is shown that the fuel consumption and CO2 predictions were reasonably accurate for an independent driving sample, though uncertainty remains about a possible 'speed' effect. Fuel and CO2 is the first installment of MOVES and is discussed in some detail in this paper. The second part of this paper deals mainly with criteria pollutants. The engine out behavior is demonstrated to be relatively steady across engine families and for Tier 1 vehicles. This allows the model, which is calibrated to only a few samples of engine data, to be generalized to other data sets, where only tailpipe measurements are available. The engine out model is demonstrated to be reasonably accurate; both in estimating VSP based as well as total cumulative emissions. The catalyst (or tailpipe) portion of the model introduces some additional complexities, where it is demonstrated that VSP or fuel rate is not the only explanatory variable in emissions formation. A speed (or aggressivity) factor is encountered in the analysis, which needs to be investigated further. It is possible that the emissions will need to be further subdivided into modes of driving. This model is preliminary and will require more research, however, the initial validation looks promising.