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Last Updated: Tuesday, July 22, 2008 8:24 AM

EMFAC Software

Emission factors that represent the vehicle fleet, speeds, and environmental conditions associated with a project are needed to perform project-level air quality modeling. In California, the EMFAC model issued by the California Air Resources Board is used for this process. For more details regarding project-level CO modeling, please refer to the CO Protocol, Appendix B.

The California Air Resources Board (ARB) released EMFAC 2007, in November 2006, and confirmed that this is the final version in February 2007. This version is required for new project-level conformity studies starting after July 31, 2007 (6 months after ARB final release; see FHWA letter, second page). Projects where air quality studies started prior to August 1, 2007 may continue to use the prior version (EMFAC 2002) to complete those studies. Non-conformity (CEQA and NEPA) air Quality studies should be using EMFAC 2007 for any studies started since February 2007. U.S. EPA made EMFAC 2007 available for conformity use through a notice of availability in the Federal Register on January 18, 2008 (PDF or HTML file at EPA) .

The EMFAC software is available from the ARB web site at: http://www.arb.ca.gov/msei/onroad/latest_version.htm.

The EMFAC model and all supporting data, are provided and supported by the California Air Resources Board.

Procedure For Using EMFAC with CO Modeling

UC Davis has prepared a procedure to assist with using the EMFAC (2002 or later) model in project-level CO analysis, using a simplified approach based on regional default fleet mixes. The procedure is intended primarily for guidance of Caltrans staff, has no regulatory status, and is provided here for information only.

Analyses requiring substantial changes to the county- or air basin-level default vehicle fleet characteristics contained in EMFAC, due to site-specific vehicle fleet information, should be discussed with the appropriate regional Conformity Interagency Consultation group. Post-processing, or more complex procedures to provide the necessary inputs to the EMFAC model, may be needed in such cases.

DOWNLOAD Procedure for Using EMFAC 2002 with CO Protocol Appendix B (PDF file)

CT-EMFAC

Caltrans and UC Davis have interpreted the EMFAC 2007 model to provide a user interface for project-level emission analysis, including emission factors and emissions of Mobile Source Air Toxics (based on ARB's speciation factors for Total Organic Gases - TOG). For more information and to download the software package, see the CT-EMFAC page, or go to the UCD/Caltrans Air Quality Project web site.

EMFAC 2007 Notes (10 March 2008)

ARB's latest EMFAC model should be used for CEQA and NEPA project-level air quality analysis as soon as it becomes available. For conformity analysis, when a new version of the model is released, it must be reviewed and made available by U.S. EPA before it can be used. The January 18, 2008 Federal Register notice made EMFAC 2007 available for conformity use. However, the Federal Highway Administration, for "latest planning assumptions" reasons, does not accept conformity analyses prepared with the older EMFAC (2002) version if they were started after August 1, 2007. Older analyses based on EMFAC 2002 can be completed with that version as long as the final action based on it occurs within 3 years of when the work started.

When using EMFAC 2007, beware of the year 2005. There are known issues with that year; emission estimates are anomalously high especially for heavy duty trucks. ARB recommends that 2005 not be used as an analysis year. Other years seem to work properly. Where 2005 must be used for SIP and emission budget reasons, ARB can supply an off-model adjustment - contact ARB (Dennis Wade, (916) 327-2963) for details if needed. If possible, however, simply avoid 2005 as an analysis year.

Be sure you are using the latest version of the EMFAC model. The current release according to ARB's web site is November 2006. However, if you downloaded and installed it before May 2007 you should download it again and replace the original installation. Minor changes were made, and the current version has a main .exe file date of April 2007 or later.

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