Emission inventories for on-road mobile sources are compiled across the country in support of State Implementation Plans (SIPs) and Conformity Demonstrations as mandated by the Federal Clean Air Act. Each local agency responsible for developing these inventories has created its own approach for combining vehicle activity, area specific fleet information, local regulations, and EPA's MOBILE6 emissions modeling software. All of these approaches will soon have to be redesigned in order to work with EPA's replacement for MOBILE6, entitled the Motor Vehicle Emission Simulator (MOVES) model. The primary goal of this study is to ease the transition to the MOVES model by providing both a road map for developing updated emissions inventories, as well as an analysis of the likely impacts of the transition on the emissions inventories themselves.
The adoption of EPA's new MOVES model represents a fundamental change in the on-road vehicle emission inventory process. MOVES uses real world driving cycle data and the measured emissions from associated drive cycles to model a wide range of possible driving patterns and their resultant emissions. With this approach, emissions due to any particular driving cycle may be estimated. The resulting estimates are based on real world driving and are well-suited for integration with transportation models. Effective utilization of the new MOVES model within the existing inventory development framework may require extensive modification to on-road data collection and processing requirements. However, successful integration of the MOVES model into this process offers the potential for significant improvements in both the accuracy and precision of the resulting emissions estimates. With this in mind, another goal of this study was to evaluate the effects of using alternative drive cycles within the MOVES model upon vehicle emissions.
This study was designed specifically to answer the following questions:
We hope that the findings of this study will help agencies responsible for developing on-road emission inventories to effectively use data processing tools provided by EPA to convert existing MOBILE6-based vehicle characteristic and activity data to be compatible with MOVES, and to develop additional such tools where necessary. We have also set out to help identify those factors responsible for the largest changes in emission estimates when migrating from MOBILE6 to MOVES, using real world data and case studies. In this way, agencies will be informed as to which types of on-road activity data may be most important to develop and refine for use within MOVES.
In addition to the key questions above, we also kept the following questions in mind:
The version of MOVES used in this study was MOVES2010, originally released in December of 2009. Although we have attempted in this report to cover as much ground as possible in comparison of MOBILE6 to MOVES, the reader should understand that the information provided here is not all-encompassing. For example, this study only examines a specific ozone season day, for a single year, in the eight-county Houston non-attainment area, and its results should not be assumed to be applicable to other regions of the country. Similarly, the data used for the calculation of alternate drive cycles input to the model is derived from data collected in Kansas City, and should be considered specific to that area. In addition, the study only examines impacts from CO, NOx, and VOC emissions; other outputs from MOVES (such as PM10, CO2, or total energy consumption) were not modeled.
Section 2 discusses methodologies for preparation of the inputs necessary to perform a MOVES model run, and details the inputs used in the model runs we developed for this project. Section 3 focuses on the successful execution of MOVES, and processing of output from the model. Section 4 discusses the development of drive cycles based upon the Kansas City Emissions Study previously performed for EPA by ERG, and the steps necessary for integration of those drive cycles into MOVES. Section 5 presents summaries of the emissions inventories for CO, NOx, and VOC emissions calculated using MOVES for all modeled scenarios, and compares those outputs both to the TTI MOBILE6-based inventory, and in the case of alternate drive cycles, to each other. Finally, Section 6 summarizes our conclusions from this study, and attempts to answer the study questions set forth here.