Mobile Source Emissions Inventory -- Categories

This page last updated on May 15, 2015

Category specific emissions estimates have been developed over the past several years in support of specific agency regulatory objectives. Documentation and emissions estimates are available through the regulatory process. This site provides links to available information for each rulemaking.

On-Road Motor Vehicles:

The EMFAC emissions model is developed and used by ARB to assess emissions from on-road vehicles including cars, trucks, and buses in California, and to support ARB's regulatory and air quality planning efforts to meet the Federal Highway Administration's transportation planning requirements. USEPA approves EMFAC for use in State Implementation Plan and transportation conformity analyses. The most recent approved version is EMFAC2011. ARB has recently submitted EMFAC2014 to USEPA for its review. USEPA approval is expected by the end of 2015. USEPA will provide a transition period during which either version may be used. Therefore, in anticipation of USEPA approval, use of EMFAC2014 before the end of the year is appropriate.

Recommended Tools to Use for On-Road Emissions Analyses
Analysis Recommended Tool
Criteria Pollutant Emissions EMFAC, EMFAC Web Database
Greenhouse Gas Emissions Greenhouse Gas Inventory
State Implementation Plans EMFAC with MPO Activity
Conformity Analyses EMFAC with MPO Activity
SB375 Analyses EMFAC with MPO Activity and SB375
CEQA with Localized Data EMFAC Emission Rates Mode (PL)

EMFAC2011 (USEPA Approved Model)

EMFAC2014 (Pending USEPA Approval)

ARB has submitted EMFAC2014 to USEPA for approval. It is currently being reviewed by USEPA staff. As the latest version of the model, EMFAC2014 represents ARB's current understanding of motor vehicle travel activities and their associated emission levels. Compared to previous versions of EMFAC, there has been a variety of changes to the Graphical User Interface and to the overall flow of using EMFAC. As a result, it is strongly recommended that users thoroughly read the User's Guide before installing and running the model. In addition, ARB will be scheduling training webinars that will provide tutorials on how to use EMFAC2014. Please join the MSEI mailing list if you would like to be informed of the dates and times of future training webinars as well as general developments related to EMFAC2014. For EMFAC2014 related questions please email us at


Over the past 8 years ARB has also developed emissions inventories for regulatory purposes. Historical documentation and methods are posted below.

On-Road Passenger Cars and Light Trucks:


On-Road Heavy Duty Diesel Trucks:


Off-Road Motor Vehicles:

In the past ARB released the OFFROAD model which calculated emissions from off-road sources.  The OFFROAD model is now being replaced by category specific methods and inventory models that are being developed for specific regulatory support projects.  The categories listed below have been or are being updated with new methods and data.  Where available, new inventories and models are provided.  If a category is not listed below, OFFROAD2007 is the current tool for estimating emissions.  It is available here.


Off-Road Diesel Equipment:

  • Ocean Going Vessels

Off-Road Gasoline-Fueled Equipment: