Mobile Source Emissions Inventory

Background

The Motor Vehicle Emissions Inventory is an accounting of those pollutants to both on-road and off-road mobile sources. On-road motor vehicles include motorcycles to 18 wheel tractors, while off-road sources cover string trimmers to bulldozers. The Air Resources Board has maintained these inventories, which are the product of population, activity and emissions over 25 years.

The Planning and Technical Support Division has the primary responsibility for developing on-road and off-road mobile source emissions inventories in California and for maintaining those mathematical models, EMFAC and OFFROAD, used to project changes in future inventories of movile source emissions.

The on-road emission inventory data has two parts: emissions-related and activity-related. The emissions-related data reflects new vehicle testing information and the latest vehicle registration data from the California Department of Motor Vehicles. The activity-related data are updated by the regional transportation agencies which estimate of the daily vehicle miles of travel, the distribution of travel by speed, and the number of starts per vehicle per day by year.

The off-road emissions inventory is an estimate of the population, activity, and emissions estimate of the varied types of off-road equipment. The major categories of engines and vehicles include agricultural, construction, lawn and garden and off-road recreation, and includes equipment from hedge trimmers to cranes.

What's New

Model Clarification: Both EMFAC and OFFROAD Models develop CO2 and CH4 emissions estimates; however, they are not currently used as the basis for ARB's official GHG inventory which is based on fuel usage information. The ARB's official GHG inventory can be found in the following link: http://www.arb.ca.gov/cc/inventory/inventory.htm . However, ARB is working towards reconciling the emission estimates from the fuel usage approach and the models.
Review of Ocean-Going Vessel PM Emission Factors
New Version of OFFROAD released - OFFROAD2007
New Version of EMFAC released - EMFAC2007

Contact Information

For more information, please contact: Michael Benjamin at (916) 323-2915.