An investigation of vehicle operating mode profiles for use in preparing a high-resolution emission inventory

The purpose of this investigation was to determine operating mode profiles for vehicles in the cold-start, hot-start and stablized modes on five roadway types, 24 hours of the day, for rural and urban fringe areas. The results are referred to as the New Jersey/California (NJCA) profile. The NJCA profile was developed from available data and engineering judgement. The NJCA profile was designed for the preparation of a high-resolution gridded mobile source emission inventory in Tennessee. The EPA MOBILE4 model was used to calculate vehicle emissions based on the NJCA profile versus the Federal Test Procedure (FTP) operating mode mix for hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NO_x) . Differences in emissions for three levels of resolution were determined: 1) daily, county-wide emissions, 2) hourly emissions for 5 by 5 kilometer grids, and 3) hourly emissions for individual facilities. An example case run for Rutherford County, Tennessee showed daily, county-wide emissions ranged from 2% lower to 3% higher using the NJCA operating mode profile versus the FTP operating modes. Comparing emissions for each of approximately 100, 5 by 5 kilometer grids for Rutherford County showed variations from 9% lower to 19% higher emissions during the morning peak hour using the NJCA versus the FTP operating modes. Peak hour emissions based on the NJCA profile were from 14% lower to 32% higher than emissions based on the FTP operating mode mix. At lower temperatures emission differences are much greater. The NJCA profile provided the spatial and temporal resolution required for a high-resolution emission inventory used in photochemical modeling studies.